UNIVERSITY OF KANSAS MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY U: NO. 70 ^. A f^\/A c? r-> Herp L 69 F553 981 Sexual Size Differences in Reptiles By Henry S. Fitch UNIVERSITY OF KANSAS LAWRENCE 1981 \Aerp. UNIVERSITY OF KANSAS PUBLICATIONS MUSEUM OF NATURAL HISTORY The University of Kansas Publications, Museum of Natural History, beginning with volume 1 in 1946, was discontinued with volume 20 in 1971. Shorter research papers formerly published in the above series are now published as Occasional Papers, Museum of Natural History. The Miscellaneous PubHcations, Museum of Natural History, began with number 1 in 1946. Longer research papers are pub- lished in that series. Monographs of the Museum of Natural History were initiated in 1970. All manuscripts are subjected to critical review by intra- and extramural specialists; final acceptance is at the discretion of the Director. 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Collins Miscellaneous Publication No. 70 pp. 1-72; 9 figures Published February 27, 1981 Museum of Natural History University of Kansas Lawrence, Kansas 66045 U.S.A. Printed by University of Kansas Printing Service Lawrence, Kansas CONTENTS INTRODUCTION 1 ACKNOWLEDGEMENTS 2 METHODS AND MATERIALS 2 RESULTS 5 Ontogenetic Change 6 Geographic Variation 7 Annotated Systematic List 11 Testudines 11 Squamata : Sauria 13 Squamata : Serpentes 21 Crocodyha 31 DISCUSSION 32 LITERATURE CITED 42 APPENDIX I 53 APPENDIX II 67 ) INTRODUCTION The kinds of vertebrates that have Mammalian groups that consistently males and females of just the same aver- have females larger include vespertilio- age size are a minority. More often one nid bats, rabbits (leporids), three families sex or the other is larger. There are of baleen whales, lobodontine seals, and varying degrees of size difference, with cephalophine and neotragine antelopes. a relatively large number of kinds hav- These diverse groups seem to have no ing only slight sexual differences and common traits such as polyandry, relatively few kinds having major differ- strongly developed female aggression, ences between the sexes. The present development of female weapons, or fe- study was undertaken to clarify these male dominance or matriarchy, that relationships in reptiles. would account for the larger size of Sexual size differences are better females. known in other groups of vertebrates Presumably the mean adult size of than in reptiles. In fishes and amphib- each species and the size relationships ians females are usually larger than of its sexes are the products of a com- males, but there are noteworthy excep- plex of selective pressures that change tions. In both birds and mammals males through time. Optimum adjustment to are usually larger than females. In birds available food, shelter, and other en- the most outstanding exceptions are the vironmental factors is involved. Some raptors, both Falconiformes and Strigi- selective factors that might cause one formes, in which females are larger in sex or both sexes to deviate from modal varying degrees (Hill, 1944; Amadon, adult size are: 1) need for the male to 1959). However, those raptorial birds dominate potential mates and/or rivals; that are mainly carrion-eaters or insecti- 2) need for the female to alter her re- vores tend to have similar sized sexes, productive strategy; 3) need for the spe- and the size difference is greatest in those cies to reduce intraspecific (intersexual) kinds that take relatively large prey. In competition for food and perhaps for these predators the female takes larger other resources. Each species, in its kinds of prey, on the average and as unique ecological niche, has presumably a result the pair jointly occupying a been influenced by its own peculiar set territory, utilizes a wider range of prey of selective pressures. which facilitates the securing of suffi- The present study is a preliminary cient food, particularly during the critical attempt to show general trends of sexual period when nestlings are being fed. size differences in living species of the In accipitrine hawks Reynolds ( 1972 class Reptilia, and to determine causes showed that the small male provides and correlations for them. Most previous prey for the female during incubation studies (e.g., Klauber, 1943; Shine, and for the nestlings during the early 1978b) have not undertaken to show the stages of their growth, allowing the fe- amount of sexual size difference, but male to spend her time at the nest, pro- have merely stated that one sex or the tecting the brood against extremes of other was the larger. No survey for the weather and predators; in the late stages group as a whole has been made hereto- of nestling growth, when the nestlings' fore, but a number of authors have in- need for food is maximal, the female is dicated sexual size differences in indi- active in hunting, and provides relatively vidual species. In the iguanid lizard large prey items. genera Ariolis and Sceloporus I deter- In mammals 84 species of 12 orders mined sexual size differences for a large and about 30 families are known to have number of species (Fitch, 1976, 1978) females larger than males (Ralls, 1976). and indicated various ecological factors MISCELLANEOUS PUBLICATION MUSEUM OF NATURAL HISTORY that affected them; Schoener (1970) and Hidalgo, Tsutomu Hikida, John B. Iver- Schoener and Schoener (1971a, 1971b) son, D. R. Jackson and R. Franz, Michael Hkewise determined sexual size relation- V. Plummer and D. B. Farrar. Alan E. ships in many species of Antillean Anolis. Leviton kindly advised me concerning However, my present study is a prelimi- the correct names of various Asiatic nary one because all figures obtained species. W. E. Duellman kindly made are in need of revision and/or refine- available his measurements of Ecua- ment. Some data are based on inade- dorian snakes and lizards, including sub- quately small samples. Literature rec- stantial series of many species from ords are sometimes based upon different Santa Cecilia and other localities in kinds of data, hence widely disparate the Amazon Basin. These are indi- figures have been obtained for the same cated in Appendix I by the abbrevia- kind of animal in a few instances. As tion "WED ms." data have accumulated, it has become evident that the sexual size difference of METHODS AND MATERIALS a species is subject to variation in time Data pertaining to sexual size differ- and space, and perhaps cannot be rep- ences collected during the resented adequately by a single figure. were course of field studies of several dozen local ACKNOWLEDGMENTS populations, in Kansas, Mexico and Costa Rica, and by examining museum The data that are the basis for this specimens in the University of Kansas report were accumulated in the course Museum of Natural History, the Univer- of field work and museum studies over sity of California Museum of Vertebrate a 30-year period. W. Frank Blair (Uni- Zoology, the American Museum of Nat- versity of Texas, Texas Natural History ural History and the University of Texas Collection), Charles M. Bogert (Ameri- Natural History Museum. Also, figures can Museum of Natural History), W. E. for many species were obtained from Duellman (University of Kansas, Mu- published literature. Most publications seum of Natural History), and Robert C. contained pertinent information on only Stebbins (University of California, Mu- one or a few species but some had rela- seum of Vertebrate Zoology) kindly per- ti\'ely large amounts of information. mitted examination of specimens in the Much information about African snakes collections under their care. Many per- was obtained from Laurent (1956, mostly sons assisted me in capturing the animals maxima), FitzSimons (1962, maxima measured alive in the field, and in other only), and Pitman (1974, maxima only). ways; special thanks are due to Anthony Likewise M. Smith (1943) presented A. Echelle, Alice Fitch Echelle, Chester much information about Indian snakes W. Fitch, David C Fitch, Virginia R. (maxima only) as did Wright and Wright Fitch, Robert R. Fleet and Robert W. (1957) for North American species (max- Henderson. My wife, Virginia R. Fitch, ima and minima). Useful papers on en- also helped me in various stages of gath- tire herpetofaunas were those of Fuhn ering and analyzing the data and prepar- and Vancea (1961) for Romania (means), ing the manuscript. Richard Shine shared Dixon and Soini (1975 and 1977) for with me the early planning of the study. Amazonian Peru (maxima and minima), Richard A. Seigel kindly contributed Duellman (1978) for Amazonian Ecuador unpublished data concerning sizes in and Hoogmoed (1973) for Surinam Malaclemys, Lawrence E. Hunt likewise (means for some). Two exceptionally contributed measurements for two kinds useful papers were those of Kopstein of Anniella. The following authors gen- (1941) on Malayan snakes and Schwaner erously made available material from ( 1980 ) on Samoan skinks and geckos, their unpublished manuscripts: Hugo both providing large series of individual SEXUAL SIZE DIFFERENCES IN REPTILES measurements for many species. Ernst Differences between the sexes in specific and Barbour (1972) provided the source gravity and in bodily proportions, which of much information on turtles.