Amphibians

Most of the recent literature pertaining to communication and related biology in amphibians has been reviewed by Salthe and Mecham (1974). This review is quite thorough, and the reader is referred to it for a more complete survey of the literature. Yet, as Williams (1973) remarked, one must still turn to the classic work of Noble (1931) for the best overview of the biology of the amphibians.

CAECILIANS: APODA

Caecilians remain the least known of the eight orders of amphibians and reptiles, and are still resistant to further study. Taylor (1968) has provided a review of the species of the world. Caecilians possess eyes that are sometimes rudimentary and possibly without function. Presumably they are dependent on olfaction; they have a curious tentacle that may function as a chemoreceptive organ (Cochran, 1961). Taylor (1970) discusses the lateral line system of some caecilians, and Wake (1968) has given some evidence for seasonal cycles in breeding, but essentially nothing is known about communication in this group. This lack is not surprising in view of the habits of caecilians, which are primarily nocturnal burrowers. Even in captivity, if one is to keep them alive and well, they are almost impossible to observe.

FROGS AND TOADS: SALIENTIA

The vast majority of studies of communication behavior in amphibians have dealt with frogs and toads. Despite the fact that many species are nocturnal or cryptic or both, frogs are generally obvious creatures in the environment because of their striking vocalizations. With the advent of tape recorders and sound spectrographs, these vocalizations have become the subject of much study. Indeed, it is now commonplace to find sound spectrograms of mating calls as part of the conventional basic data of systematic studies including the description of new species (e.g., Pace, 1974). Much of the biology of calling in frogs has been reviewed by Bogert (1960). He provides a classification of frog calls that is still useful, despite the great amount of work in the field that has appeared since its publication. More recently SchiØtz (1973) has reviewed some of the ecological aspects of frog calls, Straughn (1973) has reviewed the broad-scale evolution of frog calls, and Martin (1972) has reviewed aspects of the evolution of calls in the toads (Bufo). In addition, Gans (1973) has reviewed the mechanisms of sound production in amphibians, and Schmidt (1973) has summarized his work on the nervous system control of calling.

Frogs are mostly visually oriented predators, and so one expects their vision to be rather acute. This is the case, but in a special way. Maturana et al. (1960) found that the visual system of the leopard frog (Rana pipiens) responds to rather specific stimuli. Certain units in the retina respond only to small moving objects ("bug detectors") or only to large moving objects ("predator detectors"). Thus the frog's view of the world may be rather limited. It would be interesting to continue this kind of study on some of the small, highly territorial species, such as some of the dendrobatids. Here one might expect that detection of a moving object the same size as the frog (namely, another frog) would be important, and that the neurophysiology might have developed accordingly.

In a similar way, hearing in frogs is very specifically tuned. The classic work of Capranica (1965) on the territorial call of the bullfrog (Rana catesbeiana) showed that the auditory system possesses a frequency response narrowly tuned to the frequency of the call. This work has been extended to mating calls in other species, and even further to the geographic variation of calls within a single species. Capranica, Frishkopf, and Nevo (1973) found that geographic variation in the tuning of the frequency response of the auditory system of cricket frogs (Acris crepitans) exactly matches the variation in the frequency of the mating call. Recently Lombard and Straughn (1974) have reported on other species and have discussed aspects of the tuning of the ear in detail. Olfaction appears to play some role in orienting frogs toward breeding areas. The possible specificity of the responses has not been studied directly, although Savage (1961) argues that the smell of algae is the attracting factor.

Most frogs are true jumpers and therefore move through their environment in a more or less discontinuous fashion. Some, especially toads, might be better described as waddlers, and others such as the Surinam toad (Pipa pipa)_}are aquatic. Frogs tend to be nocturnal, although there are many diurnal species as well. Many species aggregate seasonally to breed at particular localities, but again there are exceptions to this. Species such as the dendrobatid toads remain territorial and breed within their territories. The temporal pattern of aggregation can vary also. Salthe and Mecham (1974) review the various cases of the pattern of movement and aggregation for breeding, distinguishing cyclic and noncyclic patterns.

Some general patterns of frog life histories and environmental sampling methods seem to emerge. One pattern is shown by those frogs that are nocturnal, nonterritorial, aggregate breeders. Another pattern is apparent among diurnal, territorial, nonaggregate breeders. Examples of the first pattern are the classic frogs, such as the common European frog (Rana temporaria) or the American toad (Bufo americanus). The second type would be represented by the dendrobatids, such as Dendrobates pumilio. However, many species, such as the green frog (Rana clamitans), show elements of both. Male green frogs aggregate to breed but then set up territories along the edges of the breeding ponds and call frequently during the day.

Most species of frogs are not visually conspicuous. However, certain diurnal frogs, such as Dendrobates auratus and many of its relatives, are brightly colored. The brilliant coloration is often associated with extreme toxicity of the skin secretions (as in the poison-arrow frogs), and thus the coloration is believed to have an aposematic function (Daly and Myers, 1967). However, an aposematic function for a bright coloration does not prevent its use in species perception by other frogs. Here experimental analyses of the reactions of frogs and further neurophysiological studies would prove useful. At present there does not appear to be any evidence that frogs use chemical secretions or pheromones to affect species perceptibility, although this must be the case for at least some species.

It is, of course, the vocalizations of frogs that are their most striking form of communication. As mentioned above, these calls have been the subject of much analysis. Such analyses have certain technical difficulties associated with them that were not always appreciated in earlier studies; foremost among the biological problems is the influence of temperature on call rate. All studies, especially if they are to be comparative, must correct for this factor (Zweifel, 1968). Other factors that affect the call are body size and whether the animal is immersed in water. On the purely technical side, there are the usual difficulties associated with the interpretation of sound spectrographs (see Martin, 1972).

That frog calls contain an important genetic component is demonstrated by the analysis of the calls of hybrid species (e.g., Gerhardt, 1974). However, studies on the ontogeny of calling are lacking.

Mates or potential mates appear to be the most important resource about which frogs communicate. Indeed, it is now generally recognized that the dominant vocalization in the repertoire of almost all species is the mating call. Despite that, the exact functions and mechanisms involved in their use are the subjects of much ongoing research: the scales of space and time over which mating calls function as identifiers of potential mates have not been completely worked out. Much of the problem in working out the details stems from the difficulty of determining the specific behavioral responses needed to demonstrate the function of the call at a particular point in the life history of the animal.

In most cases it is not known at what distance and how long before the actual act of mating frog calls can affect the behavior of frogs. Experimental evidence that in some species frog calls can attract males as well as females to the actual breeding site (in the case of aggregate breeders) has been provided by Bogert (1960) and others. On the other hand, as mentioned by Salthe and Mecham (1974) in their review of this subject, many species orient and move toward breeding sites by using other cues. In view of the importance of breeding-site location to the reproductive success of frogs, it is not surprising that frogs would use all available cues and not be dependent on any one cue. Some of the problems of experimental analysis of this question are due to the limited responsiveness of the animals outside of a particular stage of their reproductive cycle, as mentioned above.

Once a female frog has arrived in the general vicinity of a breeding site, she must identify and orient on a particular male frog as a potential mate. It is at this stage that the mating call plays its most conspicuous role. From an evolutionary point of view, this is when the mating call functions as an isolating mechanism, and much of the research has been concerned with analyzing the calls as such. Beginning with the work of A. P. Blair (1941, 1942) and W. F. Blair (1956, 1958, 1964), a whole school of study has arisen around this topic. Few workers today would dispute that frog mating calls function as isolating mechanisms. But it has taken a good deal of effort to unravel the exact mechanisms underlying this function, and especially to demonstrate that female frogs do in fact respond to the specific calls of the males of their own species. Through the use of tape-recorded playback experiments, female choice has now been demonstrated in a number of cases (see reviews in Martin, 1972; Schiøtz, 1973; Salthe and Mecham, 1974). As Schiøtz (1973) explains in his review, the female is responsive to the call of the male for only a short period. For example, Heusser (1968) found that female Bufo bufo were responsive for six to fourteen days. Other cases are even more striking. In a series of experiments on female choice in the frog Physalaemus pustulosis, Rand (pers. comm.) found that only females collected in amplexus the same night would respond consistently. Thus, negative experimental results require cautious interpretation.

At the closest range actual courtship takes over, and here the mating call does not seem to play a dominant role. Once a female is in the immediate vicinity of the male, he usually attempts amplexus directly. From the initial approach through ovulation and fertilization, there appears to be a series of tactile stimuli that organize the overall pattern of behavior. For example, Rabb and Rabb (1963) have detailed the courtship, amplexus, and ovipositional behavior of the pipid Hymenochirus boettgeri. They describe eleven kinds of behavior other than the calls used in the process of egg laying and fertilization in pipids. A complete review of this aspect of frog behavior may be found in Salthe and Mecham (1974).

Another important call related to courtship is the male release call, given by male frogs with which other male frogs have attempted amplexus. These calls are common, but not universal, in aggregate breeders (Salthe and Mecham, 1974). Brown and Littlejohn (1972), in a study of the male release call of the Bufo americanus species group, found that while variation between species did exist in certain components of the call, on the whole the release calls seemed more conservative in their evolution than the mating calls. They postulate that this conservatism may be related to the fact that the male release call serves a purpose in interspecific as well as intraspecific communication. Obviously, both parties benefit from the appreciation of a mistake, regardless of species.

Bogert (1960) lists in his classification of frog calls the female release call, and the ambisexual release vibration (which is not really a call) as two other kinds of behavior that serve a function similar to that of the male release call. The female release call is apparently used by females of some species that are not receptive to mating. The ambisexual release vibration is used by both sexes. In addition, Bogert (1960) lists the postovipositional call of Phyllomedusa guttata reported by Lutz (1947) as a separate call type associated with mating.

From the perspective of the evolutionist and evolutionary ecologist, frog mating calls are of great interest in ways other than their relation to female orientation and mate recognition. Some of these can only be sketched here. Since mating calls are important as isolating mechanisms, the patterns of variation in mating calls within a single species are of interest. Geographic variation in mating calls has been described for a number of species (Blair, 1974). Studies of geographic variation must be undertaken with care because of the effects of temperature on call rates and structure. Sometimes this variation is correlated with variation in other characters that are related to the quality of the call, such as body size. The function of whatever variation in mating calls that is not due strictly to other factors is related to the problems of species identification and character displacement. Another as yet uninvestigated possibility is that dialects, together with female choice, constitute a mechanism for controlling genetic variation within the population. This problem needs to be investigated both theoretically and empirically. Character displacement in mating calls has been reported for several species (Salthe and Mecham, 1974; Blair, 1974) although in some cases problems in interpretation have arisen because of variation in several characters at once.

The extension of the concept of character displacement between any two species to consideration of whole communities of frogs leads to the problem of species packing. This is a very real problem in some communities, where as many as fourteen species of frogs may be calling at one time (Bogert, 1960). In such situations the problems of acoustical interference and signal detection are considerable. Straughn (1973) argues that as more species are added to a community, the frequency band-width available to each species decreases. Thus in order to convey ample species-identification information, the individual species calls must then take on longer and more complex temporal patterns. Straughn bases his argument on a well-known theorem of communications engineering (Shannon, 1949). There are some subtleties in interpreting this theorem (Dym and McKean, 1972), but it does seem that this idea might be developed into a theory of frog species packing.

The necessity of adapting a call to the acoustical interference created by the calls of other species is only one of many constraints on the morphology of the call. Localizability and transmissability of calls in particular environments are questions that have as yet received little attention. Schiøtz (1973) discusses these constraints and mentions some possible patterns, among which is the apparent correlation of quiet calls with a generally quiet habitat in western Africa.

Many frogs are now known to be territorial, but the nature of the territoriality varies considerably. Perhaps the most strictly territorial species are some of the dendrobatids, such as Dendrobates pumilio, studied by Bunnell (1973). Males of this species appear more or less permanently territorial and breed within their territories. In addition, males care for the young tadpoles once they have hatched out. These males emit a distinct call, which serves to maintain the spacing pattern. The calling of individual males can be adjusted to the calls of other males by changing the rate and temporal pattern of the call. Thus, territories are maintained by a combination of call adjustment and attack and fighting. In addition, the calls apparently serve to attract females. So at least for males for periods of time, this species gives a more or less typical picture of a vertebrate territorial system.

However, the frogs that give the territorial call as listed in Bogert's (1960) review of call types show a rather different pattern. In some aggregating breeders of the genus Rana, males at the breeding sites show a form of territoriality and have a specific call associated with the advertisement and defense of the territory. Both green frogs (Rana clamitans) and bullfrogs (Rana catesbeiana) are good examples of this. The call of the bullfrog and the way in which it provokes the calling by another male has been the subject of a classic study by Capranica (1965). That the calls also elicit aggressive behavior has been demonstrated by tape-recorder playback experiments (e.g., Wiewandt, 1969; Emlen, 1968). Several other cases of frog territoriality have been recorded and are reviewed in Bunnell (1973) and Salthe and Mecham (1974). There appears to be a great variety of calls used by territorial males with some species having a territorial call in addition to a mating call and others not.

More complete studies on the life histories and vocalizations of territorial frogs are needed to understand the relationship between territoriality and call type diversity. It is important in such studies that the entire repertoire of call types be studied, otherwise the interpretation of a territorial call may be somewhat difficult.

Perhaps related to territorial calling is the phenomenon of chorus structure in frog calls. The existence of duetting and more complex chorus structures is now known in many frog families and has recently been reviewed by Wickler and Seibt (1974). Chorusing occurs when the calling of one individual affects the pattern of calling in another. Wickler and Seibt list some nineteen genera in which chorusing of some sort has beenreported. As mentioned above, that chorusing exists in the territorial calls of Dendrobates pumilio (Bunnell, 1973). Wickler and Seibt (1974) found that in Kassina senegalensis (Rhaco-phoridae) males form groups of two or more in which one animal consistently sets the pace by calling once every two to eight seconds, thus eliciting replies from the other members of the chorus. On the other hand, these workers found that with Bufo regularis (Bufonidae) two males would alternate regularly. Duellman (1967) and Wickler and Seibt (1974) review other patterns in other species. Wickler and Seibt conclude that the biological function of chorusing is unknown. Brattstrom (1962) indicates that the dominant (first-calling) male in a chorus of Physalaemus pustulosus enjoyed a comparative mating advantage, but this point needs more investigation.

When artificially penned together, some frogs do show feeding hierarchies (Boice and Witter, 1969; Boice and Williams, 1971), but whether hierarchies of this sort occur in nature is not known.

The last type of call listed in Bogert's (1960) classification are "rain calls." These are calls given by males away from the breeding site and often either before or after the breeding season. They have been recognized in some species of Hyla and possibly in other genera as well. There is no clear characterization of "rain calls," other than their time and place of occurrence. Bogert describes them as being "a chirping sound, a feeble rendition of sounds resembling the mating call, or a vigourous but recognizable modification of the mating call" (1960:198). Bogert recognizes and discusses the difficulty of adequately characterizing these calls and identifying them in any particular case. Often they may be simply described as premature renditions of the mating calls. Bogert does not feel that there is a clear biological function associated with these calls.

Finally, no account of communication in frogs would be complete without mention of the possibility of social behavior and communication in tadpoles. Wassersug (1973) presents some evidence that tadpoles do respond to each other when aggregating rather than just responding in some common fashion to a physical factor. He concludes that more investigation is needed to establish the existence of socially based schooling in tadpoles. As yet, nothing concrete is known about their potential mechanisms for communication.

SALAMANDERS: CAUDATA

Most salamanders possess the normal range of sensory modalities for a vertebrate. Vision generally appears well developed, although details of the functioning of the visual system are not known, especially with regard to form perception. Some cave-dwelling species have extremely reduced eyes, e.g., the blind salamanders Typhlomolge and Hadieotriton, and many aquatic forms have rather small eyes, e.g., hellbenders (Cryptobranchus). There is evidence that salamanders use extra-optic photoreception in orientation (Adler, 1970; Landreth and Ferguson, 1967). Twitty (1959) found that blinding Taricha, a terrestrial newt, had little effect on their ability to home. This leads one to wonder what the role of vision is in the overall life of salamanders. Studies on the auditory abilities of salamanders are rare. Ferhat-Akat (1939) presents some evidence that salamanders can hear, but the role of hearing seems quite small in the lives of most. On the other hand, olfaction seems to be very important. In plethodontid salamanders special nasolabial grooves appear to act as conduits by which samples of the substrate are carried into the nasal cavity (Brown, 1968). Good behavioral evidence for the importance of olfaction in homing by the newt Taricha is given by Grant, Anderson, and Twitty (1968). They found that anosmic animals were unable to home.

Salamanders are best described as crawlers. The major exceptions are some of the permanently aquatic forms, such as the congo eels (Amphiuma) and the sirens (Siren). Many other aquatic forms, such as mudpuppies (Necturus) and hellbenders (Cryptobranchus), however, crawl along the bottoms of the bodies of water in which they live. Crawling tends to keep salamanders in more or less continuous contact with their substrate, which is generally rather damp.

The vast majority of salamanders are nocturnal. The outstanding exceptions are the aposematically colored terrestrial newts, such as the red eft (Notophthalmus) and the various species of Taricha. Of course, many of the cave species are not nocturnal. Otherwise the only other generalization that can be made about salamander activity is that it is strongly related to humidity, with most species being more active on wet or rainy nights.

The most striking seasonal activity patterns are the aggregations formed for breeding by those terrestrial species that return to bodies of water. These include such well-known species as the spotted and tiger salamanders (Ambystoma) and the various species of newts. Some permanently terrestrial species may do a significant amount of moving about on a seasonal basis. Often this takes the form of moving away from streams, up the sides of small canyons in the wet season and back again as drier conditions prevail, e.g., Ensatina (Stebbins, 1954). Others seem to restrict seasonal movement to vertical migration within the soil, e.g., slender salamanders (Batrachoseps), or movement in and out of caves, e.g., the Shasta salamander (Hydromantes shastae), in accordance with seasonal rainfall patterns.

Many salamanders are always either cryptic or aposematic, but others develop special coloration at breeding time. Some newts, such as the European Triturus, develop crests during the breeding season. Males of the plethodontid Aneides lugubris develop large front teeth and masseter muscles as secondary sexual characters. Many salamanders can produce sound of some sort, and there are several reports in the literature of vocalizations by salamanders (Maslin, 1950). S.J. Arnold (pers. comm.) has reported that Pacific giant salamanders (Dicamptodon ensatus) regularly emit a characteristic "bark" when attacked by snakes. But vocalizations do not appear to be used for communication. The production of particular chemical signals appears to be common in salamanders, but the lack of precise behavioral responses to most stimuli makes their study difficult. Good circumstantial evidence comes from consideration of the many glands and skin secretions found on most salamanders. A complete review of the evidence for chemical signals can be found in Salthe and Mecham (1974). Cedrini and Fasolo (1971) demonstrated by electrophysiological studies that newts (Triturus) could detect odors given off into water by conspecifics.

Most communication in salamanders appears to be related to mating, although its role in locating potential mates in both aggregate and nonaggregate breeding species is unknown. This lack of knowledge is not surprising, for if communication of this type does in fact occur, it is almost certainly by chemical means.

Courtship, on the other hand, is much better known. A summary of reviews on this subject may be found in Salthe and Mecham (1974:365— 79). As with frogs, salamander courtship involves a series of stimuli on the part of both males and females. But salamanders appear to use chemical signals as well as tactile and visual stimuli. This is especially true in aquatic breeding species, such as the newts of the genus Triturus.

Studies of salamander courtship have included work on the description of stimulus chains (Halliday, 1974) and phylogenetic analysis of the courtship patterns (Salthe, 1967). Arnold (1972) has examined some of the strategic aspects of courtship in certain salamanders. He distinguishes slow and fast courters and relates these two strategies to the competitive environment. Aggregate breeders, such as spotted salamanders (Ambystoma maculatum), court in groups, and competition among males for females is severe. In these species courtship is rapid (and in addition males have a series of behavioral tricks to induce other males to waste spermatheca). On the other hand, dispersed breeders, such as slimy salamanders (Plethodon jordani), usually court in single pairs and court more slowly and carefully.

Territoriality is known in some few species of salamanders, including the plethodontids Hemidactylium scutatum and Eurycea bislineata (Grant, 1955), several other plethodontids (Salthe and Mecham, 1974), and apparently the hellbender Cryptobranchus: Hillis and Bellis, 1971). Aggression has been observed in the field between males of some species, such as the plethodontid Aneides lugubris, in which the males possess enlarged teeth during the breeding season and may inflict injury on each other (Stebbins, 1951). However, the mechanisms of communication used in maintaining territoriality are little known. There is good reason to believe that many species possess no form of behavior similar to territoriality. Studies of artificially confined animals (which often show unexpected social behavior in frogs, turtles, and lizards) are few. Evans and Abramson (1958) report that a complex hierarchy is formed when individuals of Notophthalmus (=Triturus)viridescens are housed together. Such studies do not necessarily reflect any real behavior that may occur in the field, but they do indicate that further research may be warranted.

Reptiles

Brattstrom (1974) has reviewed social systems and much communication biology in reptiles. Mertens (1960) and Schmidt and Inger (1957) give good general accounts of the group. A more technical review of reptile biology may be found in Bellairs (1970). The multivolume series The Biology of the Reptilia will cover behavior and ecology in the near future.

TUATARAS: RHYNCHOCEPHALIA

Knowledge of the behavioral biology of this relict creature was reviewed by Wojtusiak (1973). Tuataras (Sphenodon punctatus) are primarily nocturnal, with good vision, are solitary, and live in burrows. Wojtusiak and Majlert (1973) report at least two distinct vocalizations given by a captive tuatara, but nothing appears known of the possible communicatory significance of these sounds. In general, the natural history of these animals in the wild, particularly their individual interactions, is little known.

LIZARDS: SAURIA

Lizards are usually credited with excellent vision. A complex radiation in the structure of the eye has occurred. Thus, the nocturnal geckos that have evolved from diurnal ancestors have developed highly specialized eyes, which allow them to remain largely dependent on vision even though they are normally active at low levels of illumination. Some other groups, such as the amphisbaenids and some species of fossorial skinks, have lost the emphasis on vision. Even within a group of species of the genus Anolis, Jenssen and Swenson (1974) found considerable variation in the function of the visual system. They studied the flicker-fusion frequency of seven species and found that the frequency varied from 26 to 42 cycles per sec. They were able to correlate the variation in frequency with the amount of light normally available in the habitats of the lizards. Those lizards that lived in more open, and hence more illuminated, habitats had higher frequencies. Thus, even at the generic level, a considerable amount of variation can occur. Benes (1969) gives behavioral evidence that whiptailed lizards (Cnemidophorus) can discriminate colors, and color vision probably occurs in other species as well. Extraoptic photoreception may occur in some lizards by way of the parietal eye (Stebbins and Eakin, 1958), but much remains to be learned about this system, and it is doubtful that it is ever used in communication.

Hearing also appears to be good in many species of lizard. Wever, Crowley, and Peterson (1963) have studied the auditory sensitivity of several species, and Campbell (1969) found definite temperature effects on auditory sensitivity. He found that the temperature of maximum sensitivity coincided with the preferred body temperature. This brings up the general question of temperature dependence of sensory functions in lizards. It is probable that most sensory systems function best at certain temperatures. Thus any interspecies comparison must be corrected for variation in preferred temperature. Olfaction and taste are not well known in lizards, but there is some anatomical and anecdotal behavioral evidence that it is important in many species (Bellairs, 1970). Kroll and Dixon (1972) have given evidence that the preanal patches of some geckos (Phyllodactylus) may function as a sense organ receptive to heat.

Daily activity patterns are extremely variable in lizards, ranging through all degrees of nocturnality and diurnality. The main requirement appears to be a certain amount of heat; consequently, few species are active in the late night or very early morning, while many are active during the day or early evening and night. Annual and seasonal cycles, especially in reproductive activity, may be very complex. Fitch (1970) reviews much of the literature on this question. As an example, Licht and Gorman (1970) and Gorman and Licht (1974) have found great variation and complexity in the reproductive cycles of several species of tropical and subtropical Anolis. Here different patterns of reproductive activity relative to weather may be found among rather closely related species, and within a single species great variation may be found over short distances.

Appearance in lizards is often extremely complicated. Complex color patterns and bizarre ornamental structures are common. Of course, many forms, especially those that are fossorial, are dull and cryptic. The well-known, brightly colored lizards are the diurnal iguanids and agamids, but certain species in many other groups are also brilliantly colored. For example, skinks are often thought to be predominantly dull and cryptically colored, but such species as Lamprolepis smaragdinum (Greer, 1970) and Oelofsea laevis, of which Steyn and Mitchell (1965) give a color photograph, are very bright. Ornamental structures include nuchal, dorsal, and caudal crests; cephalic spines, knobs, and horns; various enlarged scales; and gular dewlaps.

Mechanisms to modify appearance include the remarkable color change of many species, the most famous being the chameleons (e.g., Parcher, 1974; Burrage, 1973), but geckos and many iguanids, such as Anolis, have this ability also. Many species can alter the appearance of the whole body by flattening either laterally or dorso-ventrally, and by inflating themselves with air, as in the chuckwalla (Sauromalus: Berry, 1974). In many ways the most-developed case of modifiable appearance occurs in the dewlap of anoline lizards, a highly modified structure of skin and cartilage that hangs below the throat. It can be retracted until it is almost invisible or extended until it is larger than the head of the lizard (Fig. 1). These dewlaps are often brilliantly colored and in strong contrast to the colors of the body.

Fig. 1. An adult male Anolis cybotes with its dewlap extended.

In addition to varying the appearance of the body, lizards also often possess a series of postures and stereotyped movement patterns that are used in communication. They include the "nods," "bobs," and "pushups" of iguanids and agamids. These curious movements have been studied by herpetologists for many years. C. C. Carpenter and his students (for reviews see Carpenter, 1967; Brattstrom, 1974; Stamps, 1975) have brought the study of these motions into the realm of quantitative description. They film the lizards and then use frame-by-frame analysis to graph the vertical displacement of the head as a function of time. When working with Anolis, the extension of the dewlap is graphed in parallel as well. The resulting graphs, called DAP (=display action pattern) graphs, provide a description of several important aspects of the pattern. Using this technique, Carpenter (1962, 1966) and others (e.g., Clarke, 1963; Carpenter, Badham, and Kimble, 1970) have attempted to work out the phylogeny of several groups of lizards and of the displays themselves. For example, Gorman (1968) traced the evolution of the roquet species group of Anolis, using the male display as one important character. Other studies have examined the role of these display patterns in the organization of social systems in these lizards (see below).

These display patterns appear to have an important genetic component and are highly stereotyped. Gorman (1968) showed that the display of a natural hybrid of Anolis aeneus x trinitatis was intermediate between the two parental types. Although most of these displays are highly stereotyped, recent studies have begun to document individual variation within a species. Jenssen (1971), working with Anolis nebulosus, and Stamps and Barlow (1973), with Anolis aeneus, have analyzed variation in several components of the displays and have discussed the origin and function of the variation. According to Cooper (1971), hatchling Anolis carolinensis show components of the display almost immediately upon emergence from the egg. However, no detailed studies have been performed on the ontogeny of the displays. Such studies will probably be needed to unravel the source as well as the function of the variation in these display patterns.

Vocalizations among lizards occur most frequently among the geckos and are associated with their nocturnal habits (Evans, 1936). A well known case is that of the barking gecko (Ptenopw garrulus) of the Kalahari Desert, whose din can keep travelers from sleeping at night. These lizards live in individual burrows and call from the entrances (Haacke, 1969). Another recently studied case is that of the genus Ptyodactylus in Israel (Frankenberg, 1974). Many species of several other families of lizards are listed in the literature as producing vocalizations or sounds of one sort or another, but most of these are very poorly known and appear to be little used.

Chemical communication of some sort almost certainly occurs in some species of lizards. A well-known problem in lizard biology concerns the role of the femoral pore secretions found in such iguanids as Sceloporus. The femoral pores of males of many species of iguanids become enlarged during the breeding season and exude a waxy substance that apparently gets deposited on the rocks and other surfaces where the lizards are active. Lizards are sometimes seen to tongue or lick these areas, e.g., the chuckwalla (Sauromalus obesus: Berry, 1974), but no one, to my knowledge, has been able to demonstrate a specific behavioral response to these secretions. The situation may be even more complex in species of lizards like the skink Tribolonotus, in which several other skin glands are prominent (Greer and Parker, 1968).

Lizards rarely aggregate for the specific purpose of mating. Thus males and females tend to find each other either by individual attraction or by similarities in habitat selection. Male-female association in nature does occur as in the rusty lizard (Sceloporus olivaceous: Blair, 1960). Laboratory studies by Pyburn (1955) showed that individuals of S. olivaceous tend to associate more frequently with other individuals of the same species than with individuals of the related S. poinsetti. Kiester (ms.) showed that individuals of Anolis auratus would initially move toward other members of the species, regardless of sex, in an experimental choice apparatus. Since conspecific association occurred without regard to sex, it may have an adaptive value in habitat selection, rather than just mate selection. But certainly the two resources of habitat and mates are correlated. Long-term pair bonds may occur in some lizards, but this has yet to be demonstrated.

Recent investigations have demonstrated several effects of behavior, including communication behavior, on the hormonal and reproductive cycles of lizards. Crews (1974) and Crews, Rosenblatt, and Lehrman (1974) have analyzed the effect of various social behaviors on ovarian recrudescence in female Anolis carolinensis. During winter months ovarian activity is normally shut down; however, ovarian recrudescence can be induced by the application of gonadotropin or by providing the appropriate unseasonal environment. This environmentally induced recrudescence can be influenced by the behavior of a group of conspecifics. Crews (1974) found that a stable dominance hierarchy of adult males facilitates recrudescence, while an unstable hierarchy inhibits it. Courtship and male-male aggression are specifically responsible for this effect. In addition, ovarian development was graded in accordance with the amount of male courtship to which the female was exposed.

Courtship in lizards varies from direct attempts at copulation by the male to elaborate display action patterns Used only in the context of courtship. These patterns often bear some resemblance to the male aggressive patterns, but are usually quite distinguishable. Ferguson (1966, 1970) has given a detailed analysis of the courtship display of the iguanid Uta stansburiana. Crews (1975) showed that the ability of a male Anolis carolinensis to extend its dewlap was important in facilitating ovarian recrudescence in winter-dormant females, while the bobbing and strutting patterns were not.

Hunsaker (1962) showed that females of various species of the Sceloporus torquatus species group could recognize males of their own species partly by their display action pattern. He used mechanical models to simulate the various patterns of movement and then observed female response. Jenssen (1970), testing the response of female Anolis nebulosus to filmed displays of the males, found that the females would approach a film of a male displaying, and further that they could discriminate between the normal male display and one that was artificially altered. Thus female choice may be based on the display. On the other hand, Kiester (ms.) found that female Anolis auratus would choose live individuals of their own species over individuals of the similar-appearing Anolis tropidogaster in the absence of displays.

Another aspect of female choice is certain nonreceptivity signals given while a female is gravid. These appear after a female has copulated and seem to indicate nonreceptivity to courting males. In species such as Crotaphytus collaris (Cooper and Ferguson, 1971) and Sceloporus virgatus (Vinegar, 1972) females take on a distinct coloration during the time that they are gravid. On the other hand, Crews (1973) found that female Anolis carolinensis exhibited nonreceptivity by attempting to hide from males, and by not assuming a particular arched-neck stance that usually indicates receptivity to copulation. He was also able to demonstrate that this nonreceptivity was coition-induced. The causes of the variation among species in the mechanisms of demonstrating nonreceptivity are not clear, but appear worthy of future study.

In addition to the review by Brattstrom (1974), social systems in lizards have recently been reviewed by Stamps (1975), who gives a complete survey of the literature and proposes a model of the evolution of social systems in relation to phylogeny and sensory modalities. Many lizard species, especially iguanids and agamids, are normally territorial, while many others do not seem to show much social behavior at all. However, within a single normally territorial species a great deal of variation can often be seen. For example, Stamps (1973) found female Anolis aeneus in both territorial and hierarchical situations. She further found that particular display action patterns were associated with one or the other type of social system. Such variation between territorial and hierarchical systems appears common in iguanids (Kiester and Slatkin, 1974). Hunsaker and Burrage (1969) have argued that there is a continuum of social system types from territoriality to hierarchy in iguanids. However, evidence such as Stamps's (1973) seems to indicate that there are qualitative changes in behavior associated with the transition from territoriality to hierarchy. However this variation does occur, it appears to be a complicated phenomenon.

Colnaghi (1971) found that dominant males in an artificial hierarchy of Anolis carolinensis had greater access to food than subordinates. Kiester and Slatkin (1974) proposed a model of iguanid behavior in which all conspecific interactions are used as part of a strategy to estimate patterns of environmental variability and to structure daily movement patterns. Thus, interactions between individual lizards may have direct and indirect ecological effects as well as being acts of communication.

As with the mating calls of frogs, the display action patterns of lizards, especially the male territorial display, seem to function, in part, as isolating mechanisms. Thus the patterns of variation in these displays are of interest to evolutionists. Geographic variation in the display has been most thoroughly analyzed for Uta stans-buriana, a wide-ranging iguanid of central and western United States (Ferguson, 1966, 1971; McKinney, 1971a, 1971b). Here a great deal of variation in the display has been demonstrated although its biological function is unknown. As with frogs, the possibility that the variation functions together with differential female choice to control variation and to permit local adaptation, needs investigation. Character displacement in displays has been demonstrated for Sceloporus un-dulatus and S. graciosus by Ferguson (1973). An interesting failure of species recognition has been reported by Gorman (1969) for Anolis aeneus and A. trinitatis. These two species are very closely related, and both have recently been introduced by man to the island of Trinidad. A. trinitatis originally comes from the island of St. Vincent, while A. aeneus comes from Grenada. Despite the fact that the lizards differ somewhat in color and in the form of the male territorial display, a large hybrid population has developed where the two species have been artificially brought into contact, although the hybrids are completely sterile. Thus, difference in the male display alone may not be sufficient to insure premating reproductive isolation.

The role of species-recognition mechanisms in the problem of species packing has been considered for a community of eight Anolis species by Rand and Williams (1970). They attempt an analysis of the information content and redundancy of coding of species identification in the dewlaps. They conclude that species indentification is encoded in many ways, that is, redundantly. They conjecture that in habitats of poor visibility, such as forests, redundancy will have to be high to permit the same level of species packing as in open habitats. They also conjecture that the problems of encoding species identification may be one of the factors that limit the number of coexisting species. These are interesting research projects, but the data will be difficult to analyze quantitatively because of the problem of assessing the amount of information in a pattern as perceived by a lizard.

A further analysis by Williams and Rand (ms.) of both large and small communities of Anolis has revealed that species recognition in species that live in communities with few or no congeners is not encoded in the dewlap. Rather, in these simple fauna recognition is achieved through characteristics such as size, shape, color, and pattern. They argue that it is thus only in larger communities (six or seven species) that the dewlap functions in species recognition. Therefore only when the presence of many species makes encoding species identification difficult is the dewlap incorporated as an additional signal for species recognition.

SNAKES: SERPENTES

In terms of number of species, snakes constitute the largest order of amphibians and reptiles. They have undergone an extensive ecological radiation, occurring in a remarkable variety of habitat from below leaf litter to the tops of trees and from sand deserts to the open ocean. Coincident with this radiation is a considerable variation in sensory abilities. However, despite their diversity, abundance, and human interest, snakes are poorly known. Most herpetologists probably have an interest in the biology of snakes, and yet very few work on them. They are simply too difficult. Thus any generalizations about sensory or species-perceptibility systems in snakes are bound to be suspect.

Vision often appears to be the dominant sensory modality in snakes. Nocturnal or crepuscular species, such as the cat-eyed snakes (Leptodeira), frequently have distinctively developed eyes with vertically elliptical pupils. Many of the predominantly subterranean forms, such as the blind snakes (Leptotyphlops), have small or vestigial eyes. Snakes are capable of hearing, but only over certain frequency bands, and in general do not appear to depend on hearing (Wever and Vernon, 1960). They are, in addition, sensitive to low-frequency ground vibrations. On the basis of anatomical features the senses of taste and smell appear well developed and include such specialized organs as that of Jacobson (Bellairs, 1970). The constant use of the tongue in many species of snakes, of course, is well known. Bogert (1941) demonstrated experimentally that rattlesnakes (Crotalus) could recognize king snakes (Lampropeltis), which prey on them, by odors given off by the kingsnakes. Gehlbach, Watkins, and Kroll (1971) have shown that several species of snakes are capable of following pheromone trails. For example, blind snakes (Leptotyphlops dulcis) are able to follow the pheromone trails laid down by army ants (Neivamyrmex nigrescens), on which they prey. The pits of the pit vipers form a special sense organ used for the detection of infrared radiation and the tracking of warm-blooded prey. But there is no indication that this modality is used in communication.

The daily activity patterns of different species of snakes are as variable as those of lizards. Snakes appear to tolerate a greater range of environmental temperatures in their activity than do lizards. Annual activity patterns are generally poorly known. Some species of temperate zone snakes aggregate at "dens" for hibernation, and mating may take place near these dens (Evans, 1961). Information on the reproductive cycles of snakes has been summarized by Fitch (1970).

The visual appearance of snakes is as varied as their habits and habitats (see Schmidt and Inger, 1957; Mertens, 1960), ranging from cryptic to aposematic. Many species of snakes can inflate themselves or flatten the neck region. Sometimes this action causes the appearance of a particular pattern, as in the cobras and the African bird snake (Theletornis: Blair, 1968). In general, modifiable appearance mechanisms are not as well developed or common as in lizards. Vocalizations are restricted to hissing, which does not appear to serve a communicatory function. Other sounds produced by snakes, such as the rattle of the rattlesnake, also appear not to function in communication (Gans and Mader son, 1973).

Snakes produce a variety of smells and secretions, many of which are powerful and disagreeable to human beings and serve a defensive function (Mertens, 1946). The best-known case of chemical communication in snakes is that of the blind snake Leptotyphlops dulcis, studied by Watkins, Gehlbach, and Kroll (1969). These workers have demonstrated that blind snakes show a complex set of behavioral responses to their cloacal sac secretions. They are attracted to the secretion, which may cue both food sources and potential mates. On the other hand, several genera of snakes, which are sympatric with blind snakes (Sonora, Tantilla, Virginia, Diadophis, and Lampropeltis) and which include both potential competitors with and predators of blind snakes, are repelled by the secretion. In addition, army ants Neivamyrmex nigrescens, on which the blind snakes prey, as well as other species of ants are repelled by the secretion. The secretion itself is a mucuslike glycoprotein suspended in free fatty acids (Blum et al., 1971). It is quite likely that these studies represent only the tiniest tip of the iceberg of chemical communication in snakes.

The meager information available on social systems and intraspecific interactions and communication is summarized by Evans (1961) and Brattstrom (1974). One of the few obvious intraspecific interactions of snakes is the male combat dance, which usually takes the form of a ritualistic pushing match between males, although entwining may occur in some cases. Bogert and Roth (1966) list twenty six species in four families (Colubridae, Elapidae, Viperidae, and Crotalidae) for which male combat has been reported. They also give a detailed description of the combat of male gopher snakes (Pituophis melanoleucus). Several interpretations have been given to this behavior by various authors, including the idea that these combats represent attempts at homosexual matings. These interpretations have been reviewed by Brattstrom (1974), who concludes that more information is needed before the problem can be solved. Lowe and Norris (1950) review the known cases in which aggressive behavior in snakes is known to be associated with defense of a particular area, most notably in the cobras and their allies (Elapidae). They conclude that one of the functions of aggressive behavior in snakes may be the maintenance of territories. However, they too caution that insufficient information is available to determine the function or functions of aggressive behavior in snakes. Clearly, the relationships of aggressive behavior and movement and spacing patterns represent an outstanding problem in snake biology.

TURTLES: TESTUDINES

Virtually all turtles possess well-developed eyes and visual acuity. Hearing in turtles has been found to be fairly good in some species (Wever and Vernon, 1956). Many species of chelids possess large inner-ear structures, which may indicate the importance of hearing. As with snakes, turtles appear sensitive to low-frequency ground-transmitted vibrations. Olfaction also seems important in turtles. Eglis (1962) has described the motor patterns associated with sniffing behavior in several species of tortoise. This behavior may be quite stereotyped and is associated with the habit of sniffing at many objects in the environment. Some species, such as mud turtles (Kinosternon) and their relations and many side-necked turtles (Chelidae and Pelomedusidae), possess barbels—papillae on the chin or throat—which may serve a chemore ceptive function.

Most turtles' shells are basically cryptic in appearance. Even the brightly colored black and yellow shells of species like the star tortoise of India (Geochelone elegans) are cryptic in the habitats in which they live. On the other hand, the head and limbs of many species are quite distinctively and obviously colored. Thus turtles have the opportunity of controlling their appearance by withdrawing into or coming out of their shells. In addition, many possess stereotyped movement patterns consisting of head-nods and particular movements of the forelimbs, which are used in communicatory situations such as courtship and agonistic behavior. The iris of the eyes of male box turtles (Terrapene Carolina) develops a bright red color during the breeding season. Evans (1952, 1953) found that this coloration is controlled by the hormone testosterone and functions as a releaser in courtship. Many turtles can produce vocalizations of some sort, and these cases have been reviewed by Gans and Maderson (1973). Social vocalizations have been found in groups of aggregated Geochelone travan corica, a tortoise of India (Campbell and Evans, 1972), in situations other than courtship. But the biological function of the sounds remains unknown. Several turtles produce distinctive odors and have special glands to do so. The best known examples are the musk turtles or stinkpots (Sternotherus: Carr, 1952). But whether these odors are used other than in defense is unknown.

Most turtles are diurnal, and many water turtles commonly aggregate to bask. Annual cycles of movement are poorly known except in the sea turtles, such as the green turtle (Chelonia my das) and the ridley (Lepidochelys kempi), which migrate to particular beaches and form great aggregations for breeding (Carr, 1962, 1963). Many species of water turtles show seasonal movements overland (Gibbons, 1970), but the reasons for these movements are not well known.

Courtship behavior in turtles has been described for several species (Ernst and Barbour, 1972). More detailed studies of several species of tortoise (Gopherus and Geochelone) have been provided by Auffenberg (1964, 1965, 1966) and of members of the freshwater genus Pseudemys by Davis and Jackson (1970, 1973) and Jackson and Davis (1972). In most cases the male display consists of patterns of head movement ("nods") and attempts to bite or bump the female. Male water turtles also use the feet and claws to stimulate the female. Auffenberg (1966) suggests that glands on the chin of male Gopherus may produce a pheromone involved in courtship. Auffenberg (1965) found that individuals of two sympatric South American tortoises (Geochelone carbonaria and G. denticulata) could discriminate sex and species, in part, on the basis of the courtship display. Male tortoises, such as the Galapagos tortoise (Geochelone elephantopus) sometimes vocalize ("roar") while mating (Campbell and Evans, 1967; Gans and Maderson, 1973). Otherwise, few studies of species recognition for mating have been carried out on turtles. Some male sea turtles are notoriously nondiscriminatory during the breeding season. Male green turtles (Chelonia mydas) will often attempt to mate with almost any object of the appropriate size, including wooden decoys placed by fishermen (Carr, 1952).

Social organization and spacing mechanisms are not obviously well developed in turtles or tortoises. It is sometimes claimed that turtles possess no social spacing mechanisms, a characteristic Legier (1960) attributes to ornate box turtles (Terrapene ornata) on the basis of field observations. Yet in a laboratory situation under conditions of artificial crowding Harless and Lambiotte (1971) found evidence for a social hierarchy in this species. Hierarchical behavior has also been reported for captive eastern box turtles (TerrapeneCarolina: Boice, 1970), and Galapagos tortoises (Geochelone elephantopus: Evans and Quaranta, 1951). Combat between males in the field has been reported for the Texas tortoise (Gopherus berlandieri: Weaver, 1970) and desert tortoise (Gopherus agassizi: Patterson, 1971). In addition, Patterson (1971) found evidence for genuine territoriality in the desert tortoise, which marks out territories with the use of urine and feces.

CROCODILES AND ALLIGATORS: CROCODILIA

The biology of crocodilians has been reviewed by Neill (1971) and Guggisberg (1972), but only little progress has been made in recent years in understanding communication among these animals. These rather generalized reptiles possess the usual range of vertebrate sensory modalities. They do not seem to have any ability to change their appearance. Males of many species, including the American alligator (Alligator mississipiensis), produce striking vocalizations ("bellows" and "roars"), which appear to be used in part as spacing mechanisms (Beach, 1944; Campbell, 1973). Lee (1968) advances the hypothesis that the noises made by unhatched alligators serve a communicatory purpose. In some preliminary experiments he found that individual eggs within an artificially composed clutch would hatch out synchronously, although the eggs came from different clutches laid at different times. He suggests that the noises and possibly the movements made by the unhatched alligators may be the mechanisms by which synchronization is achieved, and that synchronous hatching helps to avoid predators. This line of investigation bears following up. Crocodilians of both sexes also produce strong distinctive odors by means of special musk glands.

The existence of maternal behavior in alligators has been the subject of some debate (Neill, 1971). Kushlan (1973) reports a case of a female American alligator's retrieving young and suggests that maternal behavior definitely exists in this species. Female alligators are also reported to guard their nests and to uncover the eggs at the time of hatching. Although there is good evidence that some kind of maternal behavior does occur in this species, the mechanisms by which the mothers recognize the young and the role of communication between mother and young remain unknown.

Discussion

Two points seem to stand out. First, I would agree with and generalize from Brattstrom's (1974:45) remarks that "there is more to snake social behavior than has been assumed." It is probably the case that except for certain well known lizards there is more to the social behavior and hence communication of amphibians and reptiles than has been assumed. Even in iguanid lizards, whose social and communication systems are probably better known than those of any other amphibians and reptiles, there are still questions about the existence of social organization in some genera. For example, Lynn (1965) reported that territoriality did not exist in horned lizards (Phrynosoma) and that displays were "weak" by iguanid standards. On the other hand, Whitford and Whitford (1973) report on actual combat in horned lizards. If combat is at all frequent, it is difficult to imagine that some sort of organization does not exist among populations of these lizards. In general, most amphibians and reptiles have been so poorly studied that the extent of social and communication behavior is in most species only dimly appreciated. Leyhausen (1965) has emphasized that many solitary species of mammals whose members encounter each other only infrequently have, nonetheless, rather complex social organizations. Thus communication between members of these species, no matter how fleeting or subtle, may have significant social and hence ecological consequences. I would expect that similar considerations may apply to many amphibians and reptiles.

Second, I would agree with and generalize from the remarks of Gans and Maderson (1973:1201), who conclude that the "sound-producing mechanisms [of reptiles] here described represent a random assemblage, with no central evolutionary tendency." In general, the communication mechanisms and responses of amphibians and reptiles also appear as a random assemblage. Stated more precisely, there is no clear phylogenetic model of communication behavior in these groups, partly because they do not constitute a natural phylogenetic assemblage (herpetology as a discipline thus sometimes seems to be a bit ill conceived). In addition, both groups have undergone extensive ecological and adaptive radiation.

The attempt to analyze communication behavior in amphibians and reptiles from an ecological point of view has not made great progress, because of the reasons discussed above. However, such an attempt does emphasize a class of questions and problems to which future research may profitably be devoted. I suggest that communication behavior should be studied in connection with the entire life history and life-history strategy of the species in question. Below are a number of areas of interest in the communication biology of amphibians and reptiles that are best studied in this fashion.

LONG-TERM AND STATISTICAL RESPONSES

A central problem in the communication behavior of amphibians and reptiles is that in many cases no immediate response is evidenced on the part of the supposed recipient, or there may be no obvious recipient at all. Frogs, geckos, and alligators all call, lizards give signature bobs, and so forth, without necessarily provoking any immediate response in a particular conspecific. However, there are examples of long-term responses to short-term communicatory acts: female Anolis carolinensis are induced to undergo ovarian recrudescence, in part, by viewing communicatory behavior by the male. I would expect that a similar phenomenon may occur as a result of calling by some species of frogs; that is, frog calls may affect hormonal and reproductive cycles in some species. If this hypothesis is true, it would help to explain the existence of some frog calls that are not given at the exact time or site of breeding (Bogert, 1960). Further, it would provide a mechanism for the synchronization of breeding cycles. Cunningham and Mullally (1956) have hypothesized that male Pacific tree frogs (Hyla regilla) are synchronized and that calls are, in part, responsible. These ideas need to be tested experimentally, and hypotheses of long-term response to communication need more attention generally.

Also, one can easily imagine that many territorial signals are given on the statistical expectation that a conspecific may be nearby and will perceive it. It may well be the case that much of the communication behavior of amphibians and reptiles may be of this statistical nature and not necessarily adapted only for direct, one-to-one encounters with individuals of their own species. If so, then the communication behavior can be understood only in the context of the statistical structure of the environment, in particular, in the context of the statistical expectation of the presence of conspecifics and their expected correlation with the resources in the environment.

DISPLAY CATALOGS

Unless communication behavior of amphibians and reptiles is studied in its ecological context, any attempt to compare displays between species or to compile a complete catalog of displays may lead to error. For example, there is some confusion in the literature in listing different types of calls emitted by frogs. Whether a certain species of frog possesses a call type previously described for another species or whether a given call is a mating call, a variation on the mating call, a territorial call, or a rain call can only be determined by studying the use of the call in the life history of the frog. Further, as Atz (1970) has emphasized, the homologies of behavior are difficult to determine, and comparisons of displays and their ecological contexts may help us understand the extent of this problem. Finally, only if the catalogs of the displays of any one species are compiled in reference to a complete knowledge of the life history of the species can the catalog be complete. It is only when complete catalogs are available that such information can be used to attack problems such as those posed by Moynihan's (1970) analysis of the evolution of display repertoires.

EFFECTS OF ENVIRONMENTAL VARIATION

Such a study of communication in an ecological context could also reveal the effects of environmental variation. Temperature variation is undoubtedly the best example of such effects. It is well known that temperature affects both sensory and species-perceptibility mechanisms. Even the frequency of the rattlesnake's rattle is temperature-dependent (Martin and Bagby, 1972). To understand these effects, both the temperature dependence of the physiological systems and the distribution of temperatures normally encountered in the environment must be determined. In addition, there is evidence that temperature variation affects more general behavior, such as learning ability (Krekorian, Vance, and Richardson, 1968). It is possible that other physical factors may affect communication systems as well.

INDIVIDUAL AND SPECIES RECOGNITION

The study of the mechanisms of species recognition has been a goal of many analyses of communication behavior in amphibians and reptiles. This has been true of studies of both frog calls and lizard display action patterns. However, it seems that species recognition is a complex of phenomena rather than single phenomenon for each species. The functions of species recognition are to find mates, select mates, synchronize breeding cycles, estimate patterns of environmental variability, and structure daily movement patterns (Kiester and Slatkin, 1974), select habitats (Kiester, ms.), and allow for maternal behavior.

Connected with the multiplicity of functions of species recognition is the fact, emphasized to me by Stanley Rand, that species recognition does not work with the same precision at all times. For instance, an individual may sometimes react to a member of another species as if it were a conspecific. Thus we may expect that the precision may vary from species to species and depend on both the ecological context and the strategic use to which the information gained by recognition is put. The ecological context includes the other species in the environment that may be confused with conspecifics or whose presence may sometimes impart the same information as a conspecific. The strategic considerations may include the degree to which conspecifics influence such activities as daily movement patterns and habitat selection.

Although no unequivocal evidence exists to show that individual recognition does occur in amphibians or reptiles, it is a possibility. Evans (1951) reported that subordinant individuals in a hierarchy of Mexican black iguanas (Ctenosaura pectinata) would react in a characteristic fashion to the approach of the dominant "tyrant" male. It is possible that they were responding simply to his size rather than to him per se. However, if individual recognition does occur, many of the complexities described for species recognition will have to be investigated.

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