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AMER., ZOOL., 17:261-270 (1977). Species Recognition, Dewlap Function and Faunal Size ERNEST E. WILLIAMS Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138 AND A. STANLEY RAND Smithsonian Tropical Research Institute, Balboa, Canal Zone SYNOPSIS Although having a number of functions in reproductive, territorial and aggressive behavior, Anolis dewlaps are only one means of intraspecific signaling and they are always present in small anole faunas (e.g., those of one or two species islands) but here, in contrast to the situation in large faunas, their color and pattern appear usually very similar and appear to be unimportant for species (or population) recognition. The latter function is then performed by such characteristics as adult size and body color and pattern. Where, however, numerous species abut or overlap, dewlap color and pattern tend to be diverse and diagnostic (particularly between overlapping forms). Even here, however, adult size, body shape and body color often redundantly reinforce the species and population recognition function of even marked dewlap difference. In certain cases in complex faunas, size and/or body pattern substitute for the species recognition function of reduced or absent dewlaps. In Rand and Williams (1970) we argued that species recognition in anoline lizards is not based on a single sign stimulus or releaser but on a complex of stimuli, redundant to each other, which separately and in various combinations identify the display animal. Because natural selection insists that mates be recognizable under a variety of conditions, we have argued that selection must favor a system in which species identity is encoded redundantly. In the specific case analyzed by us in 1970—species recognition in the eight species sympatric at a single locality, La Paltna, on the Greater Antillean island of Hispaniola—we found that each of the eight species differed from the rest in several (average 2-54) characteristics of the dewlap. Thus the dewlap alone sufficed to separate these eight species. This redundant use of dewlap characteristics in species recognition is also largely true in complex anole faunas of Cuba, such as the Camaguey fauna studied by Ruibal (1961a) and by Ruibal and Williams (1961a, b). Species identity in anoles, however, can be encoded redundantly in more ways than by dewlap color and size. Even in the Cuban fauna dewlap color and size by themselves will not adequately distinguish the eleven species of Camaguey (Table 1). In three species, A. equestris, A. allisoni and A porcatus, dewlaps are similar in size (large relative to body size) and color (pink or pale pink), while in two others, A. angusticeps and A. isolepis, the dewlaps differ only slightly in color ("apricot" and "peach"). In these Cuban examples adult male size or body color and pattern or both are very different. These then are two additional ways in which species identity is encoded in anoles. Climatic niche and perch site are also important, since these provide part of the context in which species recognition occurs. (Body shape is adapted to perch site and thus correlates with the latter.) Thanks are due to David Crews, Neil Greenberg The important empirical observation is and William Haas for constructive comment. This research was supported by NSF grant GB 3773IX that species similar in dewlaps differ in some or all of these other characteristics. and previous grants to E. E. Williams. 261 NO NO TABLE 1. Dewlaps m local faunas (Greater Antilles)." CAMAGUEY, CUBA Species equestris allisoni porcatus angusticeps isolepis argillaceus loysiana lucius hovwlechis allogus sagrei a Dewlap color very pale pink to almost white reddish or mauve reddish or mauve peach apricot yellow yellow, orange-yellow or red tan to pink tan to pale orange red yellowish at base with white margin and 2-3 gray stripes grey or while yellow to apricot with 3-4 reddish stripes and white margin bright red, dark red or brownish yellow Body color bottle green with skin between scales white green with head and thorax blue grey with light and dark reticulation greyish bright green greyish with reticular and longitudinal markings greyish with reticular markings greenish blue with nuchal chevrons light tan with horizontal stripes and 4 dark chevrons reddish brown with yellow reticulations tan brown Size (maximum snout-vent length) Ecomorphb Microclimate 181 crown giant shade 91 66 trunk crown trunk crown sun 52 46 shade 48 twig twig trunk 42 trunk sun > 6 > shade W 73 X E »j w sun sun r > 70 crevice shade 58 trunk ground half shade 62 trunk ground shade r X 60 trunk ground sun JO > > Data from Ruibal and Williams (1961a and*), Ruibal (1964) and Schwartz and Garrido (1972). b Ecomorphs (Williams, 1972) differ characteristically in body shape, size, microhabitat and often in color. They are convergent phenotypes adapted to the specific stations in the vegetation (trunk-crown, trunk-ground, bush-grass) that they usually inhabit. o 263 SPECIES RECOGNITION, DEWLAPS AND FALNAL SIZE In faunas smaller and simpler than those of Cuba and Hispaniola, dewlaps quite often are of similar size and color. A comparison of dewlap colors and sizes at Mona on the Liguanea Plain in Jamaica shows that A. garmani, A. grahami and A. opalinus, all occurring in tree crowns, all have bright orange dewlaps (Table 2). (These differ radically in size.) At El Verde Luquillo Mt., Puerto Rico,/4. evermanni (an anole of the tree crowns) and krugi (an anole living in bushes or grasses) have orange dewlaps and the dewlap of A. gundlachi (a trunk-ground anole living in deep shade below A. evermanni) is dull orange (Table 3). (These are separated by perch site and correlated body shape.) In the still smaller faunas of the Lesser Antilles (only one or two anole species per island), the similarity in dewlaps within and between islands is still more striking. One set of colors—yellow to yellow-orange, darker or lighter—occurs almost throughout both on the one and two species islands (Tables 4 and 5). Extreme variants are whitish or grey or with some hint of green. The minor variations, however, only emphasize the general regularity of dewlap color in the Lesser Antilles, which contrasts markedly with the very striking body color and pattern differences between and within Lesser Antillean species. Thus A. marmoratus on Guadeloupe has a series of races all with very similar dewlaps, in one of which males have an apple green body and a blue-grey head with brilliant orange marbling, while in another males are plain green in ground color but anteriorly and dorsally have dark blotches tending to run together and set off by pale cream borders. In yet another race males are pale grey-green with brown heads, and there are still other remarkably different patterns within this one species on a complex island (see Figure 5, Crews and Williams, 1977). Similar differences in body pattern occur within A. roquet (Martinique) and A. oculatus (Dominica). (See Lazell, 1972, for more complete data on these and other species and color plates.) Yellow to yellow-orange are common dewlap colors also on other small (one to two species) islands in the Caribbean. Red -a ^ c c c .30 p I p "J b b So 5 Jt A A 3 c c c O 3 3 £ Z 3 bo c 2 1 2 Q 5 j£ •3 S ,. bo c 3 v >. S « u j, o a bo bo^J •a w re §| So bo bo bo= -^ c c c c T ; ft- 5 o S S s. lltl 1 264 ERNEST E. WILLIAMS AND A. STANLEY RAND x -c -o re re c re .£ J= 3 — c E .£ 3 •a -a c c c CSS re o 0 'boh h ss bo bo 0 3 3 2 3 bo 11 re c E.S c/5 11 -'I •= Q s •; « o .9-tfS 1 O 'c • o u -^ O 2 S S _re c " o £ 1's C -O « S O.-TJ u u ^ ^ ^ u 3 ? "u ? re Q. ' 3 C I -o c £! i U'r O " O C ^ c >^ ^ >^ re bO ! _o o O a. — bo a bo c ;2 >-£ -a c 1= 1 c _ jj bo JJ o b p ! : bo re re s- * o 'la ill to red-orange may be the darker extreme of this spectrum (A. concolor—orange to red-orange in San Andres; A. pinchoti — red to dusky red in Providencia; Corn and Dalby, 1973). It is to be remembered that the anoles of these small faunally depauperate islands all had ancestors that lived in the complex faunas of the Greater Antilles or in the equally or even more complex faunas of the continental mainland. The dewlaps of the small island anoles are clearly not a random sample of the wide diversity of dewlaps found in the anoles of complex faunas. The small island anoles come from several phyletic stocks, and the islands they inhabit include both low arid islands and high wet ones and a diversity of types in between. Clearly there is not a simple phyletic explanation for the relative uniformity of dewlaps in small island anoles nor a direct ecological correlation. It seems probable that some of this near uniformity in dewlap color has been evolved after arrival on the small islands. It is true that the orange dewlaps of sagrei (Little Cayman, Roatan) are derived from the ancestral populations of this species on Cuba, and the pink to red dewlaps of the carolinensis complex on the Bay Islands, Half Moon Cay off Belize and the Bahamas are to be regarded as directly derived from their Cuban ancestors (Williams, 1969). But the dewlaps of the distinctive long-headed species of the carolinensis complex, A. longiceps (Navassa) and A. maynardi (Little Cayman) are modified toward orange rather than pink or red (Thomas, 1966) and the sagrei relatives on Swan Island and on Cayman Brae (A. nelsoni and A. luteogularis) have changed toward yellow. In these cases convergence toward the yellow or orange of the Lesser Antilles may reflect longer periods of residence on these islands. If we consider only the small oceanic islands, the only truly anomalous cases are A. conspersus on Grand Cayman and A. lineatus on the arid island of Curacao, both "solitary" anoles. A. lineatus has no close mainland relatives and has a bicolor (black and orange) dewlap quite unlike anything anywhere on the mainland. A. conspersus, SPECIES RECOGNITION, DEWLAPS AND FAUNAL SIZE E E E E E E E E E E E E E E E E E E E E E E o o — ' C M d c o c o — co»n»n c c {- i - u -a ° fc C O be £»: J= c o re 1-8 ~J= •3 s J= .H ^ E S h o c •? c c oj £ o> SJ o ^ c o o % ,5 S S B3 5 ra 1- re re D- 1 ) > .0 > > re I c S E •0 O 0 D. oli' s 0 0 dul bo C a; 0 qj QJ lT2 0 0 Oj 0 O — — — — — - 0 2 n> _c 0 c3 >-, — a QJ Q- >L >L >* 0 C O —' rt "™ 1c So 0 ^ 3 : HI | < wz Q 265 on the other hand, is an obvious derivative of the Jamaican A. grahami, close enough to have been considered a subspecies of the latter, but it differs radically in its blue rather than orange dewlap. It is possible that these species have evolved their aberrant dewlaps as the result of "failed invasions" (Baskin and Williams, 1966; Williams, 1969). A. lineatus occurs on Aruba, which is on the continental shelf, as well as on Curacao, and both populations are close to mainland South American faunas. The species most likely to have made contact with lineatus are A. (Tropidodactylus) onca (red-orange dewlap)— but this is ordinarily a solitary anole wherever it occurs (Collins, 1971; Williams, 1974)—and A. auratus (black or blackish dewlap). A. lineatus is amply distinguished from these (even beyond any evident need; perhaps still other species were in contact in the past). A. conspersus is on an island in the direct line of drift from Jamaica. A critical frequency of failed invasions may provide the threshold for evolution of character displacement in these cases. In the two species islands of the Lesser Antilles, the species differ greatly in size as well as body shape, color and pattern (Schoener, 1970; Williams, 1972). The two species on a two species island do not differ in these respects as much as do the two most different species living together on a large multispecies island, but they do differ very much more in these characters than do the most similar species on such an island. The Lesser Antillean species pairs differ in at least the three ways mentioned above and we are suggesting that such differences in simple faunas permit species recognition with an adequate level of redundancy without dewlap differences. The long ignored experimental results of Greenberg and Noble (1944) are relevant here. They report that female A. carolinensis (an anole without sympatric congeners over most of its range within the United States) respond equally readily to males with normally pink or with green painted dewlaps. These results have been confirmed and extended recently by Crews (1975). (There are in fact green dewlap 266 ERNEST E. WILLIAMS AND A. STANLEY RAND ESE EEE EE EE£E SE EEES C^O^f d CO 00 <O "^" ^ E E £~- -o c o > bo r^" c a; O « bo O bo E c £ a. ra ^ "= cc _^ -> -n ra o 5b o O c a. 8 £ o h ; o P9 S- X * bo bo ; b0"O i o bo bo T3 bo I XI E J2 ; bo c I 3 T3 O u bo bo C c J bo •p ra O •= o ""* ? bo S c o u IS S =5 bo o c o. = ra = • aj 5 .SP — aj I •I ~ I.. - 3 '•§ "§ O(Si H Z O -o C -it ra c 3.2 o H Z o z z O 4) u bo populations of A. carolinensis in Florida [Duellman and Schwartz, 1958].) These many examples make clear that while, as at La Palma, the dewlap may in complex faunas be the major signal, or at least a signal, for species recognition, this is often not true and is in fact very unlikely to be true in simple faunas. Clearly, dewlaps in simple faunas must be serving some other function than species recognition, since species on one species islands or alone on the mainland characteristically not only retain but actively use their dewlaps. It is on Cuba, in a very complex fauna (more than 25 species), that two species {A. bartschi and A. vermiculatus) have totally lost their dewlaps (i.e., in a very complex fauna where there are many differences in one kind of signal—dewlap color—it is one additional kind of signal to omit the dewlap entirely). Other species in which dewlaps are greatly reduced are A. poncensis on Puerto Rico in a fauna of 10 species and the A. hendersoni complex, and to a lesser degree A. aliniger and A. singularis, on Hispaniola in a fauna of more than 20 species. The single very striking exception—the sole instance of reduction of the dewlap on a one anole island — is Anolis agassizi on the bare and very isolated Malpelo Id in the Pacific, a highly special case which is discussed below. Gorman (1968) and Rand (in preparation) have analyzed the use of the dewlap in the single species islands of the Lesser Antilles. Here dewlaps are used in stereotyped displays in both aggressive encounters and in courtship. Dewlaps serve in these situations (1) to identify the sex of the displaying animal; (2) to distinguish between juveniles and adults; (3) to indicate the size of the displaying animal; (4) to discriminate territory holders from wandering or subordinate animals; (5) to signal the mood (aggressive, sexual, etc.) of an animal; (6) to call attention to an animal by increasing its conspicuousness. In such single species islands we suggest that it is the change in shape of the displaying animal which dewlap extension produces rather than the color displayed that is the social signal (see also Crews, 1975). The color of the dewlap in this situation SPECIES RECOGNITION, DEWLAPS AND FAUNAL SIZE , ¥ would primarily be affected by selection pressures enhancing visibility. From the prevalence of yellow-orange in the dewlaps in single species faunas, it would seem probable that this is the most visible dewlap color against most backgrounds. It is a color that, as mentioned above, also occurs regularly in the complex faunas of the large West Indian islands and it is also common on the mainlands of Central and South America. The social uses of dewlap displays are, of course, not confined to Lesser Antillean anoles. They are retained in most anoles of complex faunas, both on islands and on the continental mainlands. Wherever dewlap remains a distance signal, color should also be retained. Echelle, Echelle and Fitch (1971), for example, remark on the conspicuousness provided by the flashing of the red dewlap in A. pentaprion in Costa Rica. Here the flashing of a conspicuously colored dewlap appears to permit A. pentaprion to signal its presence to conspecific and congeners without revealing itself to predators more than momentarily. In contrast, in another environment Ecuadorian A. gemmosus has a large but greenish dewlap (Williams, personal observation). Since this species lives in relatively dense wet forest vegetation, it is hard to believe that the dewlap can be a distance signal. The dewlap is more likely to be useful in increasing apparent size in close agonistic contacts between males. Quite another situation is seen in the case of A. agassizi on Malpelo Id. Because this bare rock provides an extraordinarily rigorous environment (Rand et al., 1975) A. agassizi has not adopted (most probably has lost) the strategy of territoriality, and instead social facilitation is an important phenomenon. The reduction of the dewlap is understandable in such a situation. In general it would appear that as long as species are sufficiently different in general appearance to preclude confusion, dewlaps, particularly dewlap colors, are not important in species recognition but are important in social signaling. However, in more complex faunas the coexisting species include many that are similar in size and general appearance—much more 267 similar than the species pairs on two species islands (Schoener, 1970; Williams, 1972). (See especially the colors of the dewlaps in the trunk-ground series in Cuba [Table 6].) The grass-bush series in Puerto Rico contains only three species, but the differences in dewlap are extremely sharp: A. krugi, orange; A. pulchellus, crimson; A. poncensis, white; (Schmidt, 1926). Although size difference in adults is a ready species recognition character, because of the species-packing on the large islands, ecological constraints reduce the possibility of marked size differences ("the crowded middle"—Williams, 1972). In the absence of size differences other characters must be used. Some species have evolved elaborate body color patterns (Lazell, 1972) but, except in the giant species of the two largest islands, this is not common on the large islands. Instead, dewlap differences are the rule. One of the exceptions, the A. hendersoni complex, comprises small species with striking body patterns and colors and very reduced dewlaps. This is concordant with the reciprocal relationship we are suggesting between body pattern and dewlap. Similarly consistent with this relationship is the situation in A. poncensis in which the male dewlap is reduced. Here there is much stronger sexual dimorphism in body color than in its relatives {A. pulchellus and A. krugi) in which there is a strong sexual dimorphism in dewlap size. Probably the emphasis on dewlaps rather than body patterns when it occurs is the result of predation pressures. The Greater Antilles have unquestionably greater number of kinds of visually hunting predators, both snakes and birds, than do the smaller islands of the Lesser Antilles (Bond, 1971; Underwood, 1962; Maglio, 1970). Where visual predators are common, there may be a strong advantage in being cryptic and therefore in a dewlap that is usually kept retracted and inconspicuous and will be displayed conspicuously only when needed. In contrast, when predators are fewer or less important, there is obvious social advantage in keeping display characteristics continuously in evidence. A lizard that is 268 ERNEST E. WILLIAMS AND A. STANLEY RAND TABLE 6. Dewlap within ecomorph series.* Cuba— The trunkground series Dewlap color Body color homolechis white or grey jubar yellow to orange with a variable white margin yellow with red stripes or light tan with a white-margined orange-yellow dark ocellus above shoulder" dark red basal spot with two light grey usually with a greenish orange-yellow stripes and wide cast white margin yellow to apricot with 3-4 reddish reddish brown with yellow stripes and a white margin reticulations large red spot surrounded by a tan with a greenish cast and broad yellow white area "salt and pepper" speckling 4-5 thin red lines on deep pale grey with "salt and pepper" yellow ground and a white margin speckling or vertical black bands brown [indistinct crossbandsp variable but with orange or tan with sometimes yellow vertical reddish tints stripes and dots brownish yellow with maroon tan with yellow markings markings quadriocelhfer meslrei allogus ahli rubribarbus tmias sagrei bremeri light tan with 4 dark chevrons on dorsum and horizontal stripes on flanks light tan Size (maximum 6 snout-vent length) 70 mm 62 mm 55 mm 56 mm 62 mm 58 mm 62 mm 64 mm 60 mm 71 mm a Data from Ruibal (1964). Note that species which are closest in dewlap color (jubar, quadriocelhfer and allogus, rubribarbus) differ in body color. c Only known from the type and paratype. The collector, P. J. Darlington, noted dewlap color in life but not body color. b are otherwise similar in size and general appearance which differ strikingly in dewlap color. When West Indian anoles have similar ecological adaptations, they usually have the same size and body form and even color, i.e., they are ecomorphs in the sense of Williams, 1972. They usually have differently colored dewlaps, particularly if they are not allopatric. (Again see the trunk-ground ecomorphs in Cuba, Table 6.) We predict that the exceptions will be found to differ in display much more strikingly than do species that are more different in appearance. Our contention that complexly colored dewlaps and striking body patterns may be alternative and equivalent solutions to the problem of species recognition is supported by an examination of intraspecific mentioned, A. equestris, A. porcatus, A. alli- variation—both inter- and intrapopulasoni, A. angusticeps and A. isolepis in the tional—in these characters. Camaguey local fauna are similar in dewIn the Lesser Antilles, as we have seen, lap color but sharply different in color or the variation between populations on the pattern or size or all three. same island or bank tends to be striking In the large faunas it is the species which only in body color and pattern (see spe- boldly and conspicuously marked is in a very real sense displaying much of the time without the energetic cost of dewlap display. Thus bold body patterns are utilized both by species in the Lesser Antilles where there are few predators and by giants such as those of the A. equestris complex of Cuba, which as adults must be invulnerable to most island predators. The apparent counterexamples—e.g., such a species or species complex as A hendersoni, which in the complex fauna of Hispaniola can show a male body pattern of startling beauty and brilliance—have also very dull cryptic color phases. Size and shape, in addition to body color, can, we emphasize, substitute for dewlap color in species recognition even in the largest of the Greater Antilles. As already SPECIES RECOGNITION, DEWLAPS AND FAUNAL SIZE 269 Most anoles also show variability within populations in dewlap colors and in body colors and patterns. Such variability certainly contradicts any hypothesis that a single character is a simple sign stimulus acting as a releaser. However, this variability fits rather well with our suggestion that a lizard encodes its species identification in several different ways and that redundancy itself is selected for because it is important in allowing species recognition under a variety of circumstances. If no one character is by itself necessary in recognition, then variation in display characA. equestris, A. ricordii and A. hendersoni, ters— and even individual recognition interpretation has recently shifted from (Rand, in preparation) — is possible withthat of geographic races of single species to out destroying the system. Note that such allopatric species. In at least the A. equestris individual difference in dewlap characcomplex in Cuba, instances of sympatry teristics is the indispensable prerequisite have been discovered (Schwartz and Gar- for evolution of geographic and interspecific evolution of dewlap differences. rido, 1972; Garrido, 1975). There do exist, however, in the Greater Thus while throughout the genus Anolis Antilles very remarkable examples of cor- the dewlap functions in intraspecific sigrelated geographic variation of dewlaps naling, encoding information about size, and body color within species {A. distichus sex, and in association with characteristic in Hispaniola and the Bahamas [Schwartz, display behavior, reproductive condition 1968, see the color plates], A. lineatopus in and motivational state (see also Crews, Jamaica [Underwood and Williams, 1959; 1975), in simple faunas species recognition see the diagrams of pattern difference is achieved by characteristics of size, color between populations; there is more varia- and pattern with little involvement of dewbility than the color plates or diagrams lap color. It is only in more complex and indicate, but the vivid nature of the differ- larger anole faunas that the color and ences is still very real].)Such variation in a pattern of the dewlap are important in characteristic presumed important in species recognition. In these cases, the use species recognition and mate selection of the dewlap as a distinguishing character could be the result of such factors as 1) environmental differences that result in between otherwise similar anoles may be different colors or patterns having differ- one significant factor explaining the ent visibilities; 2) sympatry with different coexistence of so many sympatric species. species thus requiring changes to facilitate REFERENCES recognition (this explanation, very improbable or impossible for A. lineatopus, has been documented for the contact Baskin, J. N. and E. E. Williams. 1966. The Lesser Antillean Ameiva (Sauria, Teiidae). 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