Triploid Karyotype of Leposoma Percarinatum (Squamata, Gymnophthalmidae)

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Triploid Karyotype of Leposoma percarinatum (Squamata, Gymnophthalmidae)

KATIA C. M. PELLEGRINO,1,2 MIGUEL T. R ODRIGUES,3 AND YATIYO YONENAGA-YASSUDA1

1Departamento de Biologia, Instituto de Biocieˆncias, Universidade de Saõ Paulo, C.P. 11.461 CEP: 05422-970, Saõ Paulo, Brasil 3Departamento de Zoologia, Instituto de Biocieˆncias, and Museu de Zoologia, Universidade de Saõ Paulo, Saõ Paulo, Brasil

(30M ؉ 36m) 66 ؍ 10M ؉ 12m) comprise the 3n ;22 ؍ ABSTRACT.—Three ‘‘identical’’ haploid genomes (N karyotype in the parthenogenetic gymnophthalmid lizard Leposoma percarinatum from Brazil. A hybridization event between a bisexual and a diploid unisexual species might explain the origin of L. percarinatum.

Lizards of the genus Leposoma are restricted to low- somes (m); at least seven microchromosomes (pairs land tropical forests from Costa Rica throughout 11–16 and 19) are biarmed (Fig. 1). Further, the mor- Amazonia to the Atlantic slopes of eastern Brazil. Two phology of all presumed homologs (to the extent these species groups (parietale and scincoides) are recognized can be inferred from conventionally stained karyo- (Ruibal, 1952; Rodrigues, 1997), but there are not types) is ‘‘identical’’ for each member of the 3n set, enough data to properly elucidate phylogenetic rela- suggesting that three identical haploid genomes (N ϭ tionships within the genus. The parietale group ranges 22, 10M ϩ 12m) comprise the 3n ϭ 66 (30M ϩ 36) from Amazonia to Costa Rica and contains eight bi- karyotype. sexual species, and the parthenogenetic Leposoma per- Our present knowledge of species diversity in the carinatum (Hoogmoed, 1973; Uzzell and Barry, 1971). genus is far from complete (Rodrigues, 1997; Ro- The scincoides group contains five species: four are re- drigues and Borges, 1997; Rodrigues et al., in press), stricted to the Atlantic forest of eastern Brazil, and the and we lack a phylogenetic framework for the group. fifth is confined to an isolated forested mountain When cytogenetic data for other species of Leposoma range in the semiarid Caatingas of the state of Ceara´, are considered (Pellegrino et al., 1999), the 3n ϭ 66 northeastern Brazil (Rodrigues, 1997; Rodrigues and karyotype in L. percarinatum could result from hybrid- Borges, 1997; Rodrigues et al., in press). ization between a bisexual and a diploid unisexual Pellegrino et al. (1999) examined the karyotypes of species. One possibility is that the event occurred be- Leposoma guianense, Leposoma oswaldoi,andLeposoma tween a species with L. guianense/L. oswaldoi-like kar- scincoides and identified a 2n ϭ 44 karyotype with dis- yotype (N ϭ 22, 10M ϩ 12m) and a unisexual diploid tinction between macrochromosomes (20) and micro- cryptic form of L. percarinatum (2n ϭ 44, 20Mϩ24m). chromosomes (24) in L. guianense and L. oswaldoi,and This hypothesis assumes that the parthenogenetic L. a2nϭ 52 karyotype with gradual decrease in chro- percarinatum includes an as-yet undiscovered diploid mosome size in L. scincoides. Karyotypic differentia- clone. tion was inferred as resulting from Robertsonian re- This is the second cytogenetic study involving a arrangement and pericentric inversion (Pellegrino et unisexual species in the family Gymnophthalmidae. al., 1999). We here report a triploid karyotype in three In the genus Gymnophthalmus both hypotheses, hy- females of the parthenogenetic L. percarinatum from Vila Rica (09Њ54Ј32ЉS, 51dg12Ј58ЉW), Mato Grosso, bridization or spontaneous origin, are presently ad- Brazil. vanced to explain the origin of parthenogens (Mar- tins, 1991; Cole et al., 1993; Yonenaga-Yassuda et al., MATERIALS AND METHODS 1995; Benozzatti and Rodrigues, in press). Mitochon- Chromosome spreads were obtained from intes- drial DNA sequence analysis, coupled with additional tines prepared in the field following the squash tech- data on karyotypes from specimens at other localities, nique described by Bogart (1973). Only metaphase will help us address several questions about the origin preparations that allowed counting chromosomes of this unisexual clone of Leposoma percarinatum:isthe with confidence were considered, and specimens (field origin spontaneous or based on a hybridization mech- numbers MRT 978306, MRT 978110, MRT 978212) anism? If hybridization, was it the result of single or were deposited in the Museu de Zoologia, Universi- multiple events? Which bisexual populations provided dade de Saõ Paulo, Brazil. parental stock to the triploid clone?

RESULTS AND DISCUSSION Acknowledgments.—We thank M. J. J. Silva for pre- Our cytogenetic survey of L. percarinatum revealed paring specimens in the field; D. Pavan, G. Skuk, V. X. 66 chromosomes in 15 of 31 metaphase preparations Silva, and A. P. Carmignotto for help collecting; and analyzed after routine Giemsa staining. The karyo- J. Sites for valuable comments on early drafts of this type is comprised of 30 metacentric and submetacen- communication. We are also grateful to L. a´vila for his tric macrochromosomes (M) and 36 microchromo- suggestions. This research was supported by the Fun- daçaõ de Amparo a` Pesquisa do Estado de Sa˜ o Paulo (FAPESP), Conselho Nacional de Pesquisa e Desen- 2 Corresponding Author. E-mail address: kpelleg@ volvimento (CNPq), and the Conso´rcio Nacional de usp.br Engenheiros Consultores. 198 SHORTER COMMUNICATIONS m. ␮ 10 ϭ 36m), from Vila Rica, Mato Grosso, Brazil, after Giemsa-staining. Bar ϩ 66 (30M ϭ female, 3n Leposoma percarinatum . 1. Triploid karyotype of IG F SHORTER COMMUNICATIONS 199

LITERATURE CITED RODRIGUES, M. T. 1997. fbA new species of Leposoma (Squamata: Gymnophthalmidae) from the Atlantic BENOZZATI,M.L.,AND M. T. RODRIGUES. In Press. forest of Brazil. Herpetologica 53:383–389. Mitochrondrial DNA phylogeny of a Brazilian RODRIGUES,M.T.,AND D. M. BORGES. 1997. A new group of eyelid-less gymnophthalmid lizards, and species of Leposoma (Squamata: Gymnophthalmi- the origin of the unisexual Gymnophthalmus under- dae) from a relictual forest in semiarid northeast- woodi from Roraima (Brazil). Journal of Herpetol- ern Brazil. Herpetologica 53:1–6. ogy. RODRIGUES,M.T.,M.DIXO, AND G. M. D. ACCACIO. BOGART, J. P. 1973. Method for obtaining chromo- In Press. A large sample of Leposoma (Squamata, somes. Caldasia XI:29–40. Gymnophthalmidae) from the Atlantic forests of COLE, C. J., H. C. DESSAUER, AND A. L.MARKEZICH. Bahia, the status of Leposoma annectans Ruibal, 1993. Missing link found: the second ancestor of 1952, and notes on conservation. Papeís Avulsos de Gymnophthalmus (Reptilia: Teiidae), a South Amer- Zoologia, Saõ Paulo, Brazil. ican unisexual lizard of hybrid origin. American RUIBAL, R. 1952. Revisionary studies of some South Museum Novitates 3055:1–13. American Teiidae. Bulletin of the Museum of Com- HOOGMOED, M. S. 1973. Notes on the Herpetofauna parative Zoology 106:477–529. of Surinam. IV. The Lizards and Amphisbaenians UZZELL T., AND J. C. BARRY. 1971. Leposoma percari- of Surinam. Biogeographica, 4. W. Junk, The natum, a unisexual species related to L. guianense; Hague, The Netherlands. and Leposoma ioanna, a new species from Pacific MARTINS, J. M. 1991. An electrophoretic study of two coastal Colombia (Sauria, Teiidae). Postilla, Pea- sibling species of the genus Gymnophthalmus and body Museum 154:1–39. its bearing on the origin of the parthenogenetic G. YONENAGA-YASSUDA Y., P. E . V ANZOLINI,M.T.RO- underwoodi (Sauria: Teiidae). Revista Brasileira de DRIGUES, AND C. M. CARVALHO. 1995. Chromo- Gene´tica 14:691–703. some banding patterns in the unisexual microteiid PELLEGRINO K. C. M., M. T. RODRIGUES, AND Y. Gymnophthalmus underwoodi and in two related sib- YONENAGA-YASSUDA. 1999. Chromosomal evolu- ling species (Gymnophthalmidae, Sauria). Cyto- tion in Brazilian lizards of genus Leposoma (Squa- genetics and Cell Genetics 70:29–34. mata, Gymnophthlamidae) from Amazon and At- lantic forests: banding patterns and FISH of telo- meric sequences. Hereditas 131:15–21. Accepted: 8 May 2002.

Effect of Incubation Temperature on Incubation Period, Sex Ratio, Hatching Success, and Survivorship in Caiman latirostris (Crocodylia, Alligatoridae)

CARLOS I. PIN˜ A,1,2 ALEJANDRO LARRIERA,1,3 AND MARIO R. CABRERA4

1Proyecto Yacare´, Bv. Pellegrini 3100, (3000) Santa Fe, Argentina 4Departamento Diversidad Biolo´gica y Ecologı´a, Universidad Nacional de Co´rdoba, Ve´lez Sarsﬁeld 299, (5000) Co´rdoba, Argentina; E-mail: [email protected]

ABSTRACT.—Temperature-dependent sex-determination has been reported for all extant crocodilians. We present information about incubation temperature effects on incubation period, sex ratio, hatching success, and hatchling survivorship during the ﬁrst year of life for Caiman latirostris. Incubation period was negatively related to temperature. Sex of hatchlings were related to incubation temperature. Only females were .produced at 29؇Cand31؇C, only males were produced at 33؇C, and both males and females hatched at 34.5؇C Hatching success and survivorship were unaffected by incubation temperature.

Reptiles have a wide range of sex-determination (Ewert et al., 1994) and lizards (Rhen and Crews, systems, including genotypic sex determination (GSD) 1999), but all crocodiles studied to date (11 of 22 ex- and environmental sex determination (ESD; Wibbles tant species, Lang and Andrews, 1994) show only et al., 1994). Temperature-dependent sex determina- TSD. It is relevant to know whether temperature is tion (TSD), a form of ESD, is present in some turtles involved in sex determination of all crocodile taxa because, if all the extant species have TSD, it contrasts with the diversity found in other reptile groups. More- 2 Corresponding Author. Present address: Centro de over, the species studied showed different responses Investigaciones Cientı´ficas y Transferencia a la Prod- to incubation temperature, for example; Crocodylus uccioń-CONICET, Dr. Matteri y Espanã, (3105) Dia- johnstoni never produced more than 40% males under mante, Entre Rıós, Argentina; E-mail: cidcarlos@ constant temperature incubation, whereas Alligator infoshopdte.com.ar mississippiensis produced 100% males at certain tem- 3 E-mail: [email protected] peratures (Lang and Andrews, 1994). 200 SHORTER COMMUNICATIONS

Currently there are ranching programs under way in Argentina in which eggs of Caiman latirostris are collected and subjected to artificial incubation, and a percentage of hatchlings are reintroduced into the wild. Consequently, inappropriate management could be detrimental to wild populations. For example, the 30% rate of infertile eggs of the turtle Dermochelys cor- iacea (a TSD species) in Malaysia is attributed to lack of males in the population because of reintroduction of an inadequate number of males (Mrosovsky, 1994). There are no published data on sex determination in C. latirostris under laboratory conditions, and the pattern of TSD is unknown. The purposes of this study were to determine for C. latirostris if constant incubation temperature: influences incubation period, sex ratio, hatching success, or hatchling survivorship during the first year of life. FIG. 1. Days of incubation period in laboratory at four constant incubation temperatures. The All series MATERIALS AND METHODS represents the mean of all nests used in the experi- Eggs of C. latirostris came from two different sourc- ment (12), exception of nest A (other series) because es. Nine nests from Proyecto Yacare´ breeding stock this was the only one that produced hatchlings at (Santa Fe province, Argentina) were collected within 34.5ЊC. Analysis of nest A alone showed no significant 12 h of egg-laying during 1996 to 1998, and the other differences in incubation period between 33ЊCand four nests used were harvested within seven days af- 34.5ЊC(N are 29ЊC ϭ 5; 31ЊC ϭ 6; 33ЊC ϭ 9; 34.5ЊC ter laying from natural areas during 1998 and 1999. ϭ 6). For the experiment, we used 401 eggs from 13 clutch- es. Incubators consisted of a plastic container with water and one aquarium heater. Inside the container, above water, there was a grid containing nest material ANOVA using clutch and temperature treatment as where eggs and a Hobo Data Logger were placed. factors. Each incubator was covered with a styrofoam lid. In- cubators were set at selected temperature Ϯ 0.5ЊC. Hu- RESULTS midity at all treatments was high but was not mea- Incubation Period.—Time required to complete de- sured. velopment was 80.9 Ϯ 3.7 (mean Ϯ SD) days at 29ЊC, We incubated eggs at four constant temperature 73.4 Ϯ 3.5 days at 31ЊC, 69.9 Ϯ 5.1 days at 33ЊC, and treatments (29ЊC, 31ЊC, 33ЊC, and 34.5ЊC). Every clutch 69 days at 34.5ЊC. Incubation period differed among was randomly divided across treatments, to control temperature treatments (Fig. 1). Increasing tempera- for clutch effects. Animals were marked on both hind ture from 29ЊCto33ЊC reduced the incubation period feet using Monel tags (#001; Natl. Band and Tag Co., (F ϭ 414.3, P Ͻ 0.001), but no differences were ob- Newport, KY) after hatching, and the day of hatching served between 33ЊC and 34.5ЊC. Only one clutch in- was noted. Hatching success was measured as number cubated at 34.5ЊC produced hatchlings (shown in Fig. of hatchlings/number of eggs for each treatment. In- 1). Clutch was a significant source of variation (F ϭ cubation period was the number of days from the be- 373.5, P Ͻ 0.001). ginning of incubation to hatching, plus the estimated Sex Ratios.—Temperature during incubation had a ‘‘age’’ of the nest derived from the opaque band (if significant effect on sex determination of Caiman lati- the oviposition date was unknown). First-year survi- rostris (␹2 ϭ 163.68, df ϭ 3, P Ͻ 0.001). Eggs incubated vorship was recorded. at 29ЊC(N ϭ 52) and 31ЊC(N ϭ 54) produced 100% Sex was assessed by observing secondary sexual females. Incubation at 33ЊC produced 100% males (N characters (Webb et al., 1984; Allsteadt and Lang, ϭ 58). Highest temperature treatment (34.5ЊC) pro- 1995). We dissected at least one animal from each of duced both sexes, in a ratio of 6 males : 4 females (N the 13 nests, at the three lower incubation tempera- ϭ 10). Similar results were obtained in other experi- tures. We determined gonadal sex macroscopically by ments, incubating eggs at 29ЊCand33ЊC, carried out shape, texture, and color of the gonads, and by the in the same laboratory (results not reported here). presence/absence of Mu¨ llerian ducts of randomly se- There were twins in one egg incubated at 34.5ЊC, and lected newborn caimans from different treatments, both were males. No variation was found in sex ratios and sexing (whenever possible) embryos that failed to between nests or among years at the incubation tem- hatch (N ϭ 30). peratures studied in these experiments. The sex of an- Hatchlings were maintained as described in Larri- imals that failed to hatch was the same as hatchlings era (1993). Animals hatched in 1996 and 1999 were produced at same temperatures, indicating that tem- not included in survivorship to one year results. In perature does determine sex and does not act via dif- 1996, we used only one tag per animal, and some tags ferential mortality of males or females at different were lost. Survivorship could not be calculated for the temperatures. 1999 cohort because the study was completed before Hatching Success.—No differences in hatching suc- the caimans attained one year of age. Hatching success were found among treatments at 29ЊC, 31ЊC, and cess, survivorship, and sex ratio were analyzed using 33ЊC(␹2 ϭ 3.90, df ϭ 2, P ϭ 0.143), but there were a Chi-square test and incubation period by a two-way differences among years (Table 1). During 1996, there SHORTER COMMUNICATIONS 201

TABLE 1. Hatching success of four treatments in TABLE 2. Percentage of survivorship of Caiman la- each year of experiment. Total HS refers to hatching tirostris hatchlings during their ﬁrst year of life. N.D. success of each treatment in the period 1996/1999. ϭ no data, Total ϭ survivorship of both years. Sample N.D. ϭ no data. Sample size in parentheses. size in parentheses.

Treatments Incubation temperature Year 29ЊC31ЊC33ЊC 34.5ЊC Year 29ЊC31ЊC33ЊC 34.5ЊC 1996 52.9 (70) 57.1 (70) 12.9 (70) N.D. 1997 81.3 (16) 56.3 (16) 71.4 (14) N.D. 1997 76.2 (21) 76.2 (21) 66.7 (21) N.D. 1998 80 (5) 44.4 (9) 50 (14) 0 (6) 1998 33.3 (15) 60 (15) 87.5 (16) 33.3 (18) Total 81 (21) 52 (25) 60.7 (28) 0 (6) 1999 80 (15) 93.3 (15) 80 (15) 0 (19) Total HS 57.9 (121) 65.3 (121) 40.2 (122) 16.2 (37)

date, except Alligator mississippiensis (Lang and An- drews, 1994). was low hatching success at 33ЊC, but during 1998 the Incubation temperature influences hatching success same treatment had the highest hatching rate. The best in C. latirostris. We found the lowest hatching success mean hatching success occurred in 1999. We assume at 34.5ЊC. Lang and Andrews (1994) reported that low hatching success was because of excess humidity eggs of Alligator incubated at 34.5ЊChadarateof condensed to drops of water in the environment. In- hatching of 29%, but incubation at 35ЊC reduced cubation at 34.5ЊC produced a lower percentage of hatching success to 11%. Results for other species re- hatchlings than any other treatment: 16.2%, just six ported by Lang and Andrews (1994), and Webb et al. animals from 37 eggs (␹2 ϭ 9.16, df ϭ 3, P ϭ 0.028). (1987) show that incubation at 34ЊC is a lethal tem- Survivorship.—Survivorship to one year was unaf- perature for most species (Caiman crocodilus, Crocody- fected by incubation temperature (Table 2; ␹2 ϭ 4.64, lus palustris, C. moreletii, Crocodylus siamensis, C. poro- df ϭ 3, P ϭ 0.201). We must note that incubation at sus,andGavialis gangeticus). These species produced 34.5ЊC had zero survivorship (76% of ␹2-value, 3.53/ no hatchlings at 34ЊC, or higher, incubation tempera- 4.64); this indicates temperature effects were not de- tures. It is interesting note that the two species of Al- tected because of small sample size. ligatoridae having the highest latitudinal distributions (Alligator mississippiensis and C. latirostris) produce DISCUSSION hatchlings at temperatures higher than 34ЊC. Crocod- Incubation period in C. latirostris was negatively re- ylus johnstoni develop at 34ЊC but do not produce more lated to temperature. Results indicate that temperature than 39% males at any constant incubation tempera- could act by producing an increase in metabolism as ture. Some wild nests of C. johnstoni produce 100% temperature rises (Zug, 1993), thus reducing the time male hatchlings. Webb et al. (1987) attributed this to required for development within the 29–33ЊC range. daily fluctuation of temperature in nests of C. johnstoni Temperature does not modify incubation period line- and the steadily increasing temperature during natu- arly; effects were higher from 29ЊCto31ЊC than from ral incubation that allows eggs to develop at temper- 31ЊCto33ЊC (Lang and Andrews, 1994, and this ex- ature as high as 34ЊC. periment). Hatchlings from one nest at 34.5ЊC suggest In this study, survivorship during the first year was that differences from 33ЊC to 34.5ЊC are insignificant. unaffected by incubation temperature, but the lack of Our results are similar to previous studies reported differences could be a result of low number of hatch- for crocodilians: temperature affects incubation period lings produced at 34.5ЊC. Survivorship was highest at up to 33ЊC. C. latirostris has the shortest incubation 29ЊC (89%) and 33ЊC (61%), female and male produc- period reported at 29ЊC, and one of the longest at ing temperatures, respectively. Caiman eggs incubat- 33ЊC, exceeded only by Caiman crocodilus and Crocod- ed at 31ЊC had a survivorship of 52%, and it was null ylus moreletii (Lang and Andrews, 1994) and Crocody- at 34.5ЊC (0%). These results are similar to those re- lus porosus (Webb et al., 1987). ported by Janzen (1995), in which snapping turtles Incubation temperature determinates sex in C. lati- incubated at temperatures that produced mixed sex rostris. Low incubation temperatures (29ЊCand31ЊC) ratios had lower survivorship than hatchlings incu- produce 100% females, 33ЊC produces only males bated at temperature that produced only males or fe- (100%), but higher temperature (34.5ЊC) produces males. both males and females. It appears C. latirostris has Our results suggest that hatchlings produced at pattern II of TSD (female-male-female, as defined by 34.5ЊC have lower fitness than hatchlings incubated at Ewert et al., 1994) as do other crocodilians (Lang and 29ЊC, 31ЊC, or 33ЊC, because the former had the lowest Andrews, 1994). We obtained animals incubated at hatching success (16%) and survivorship (0%). We did 34.5ЊC from only one nest, so inferences concerning not use incubation temperatures between 31ЊCand sex ratios are not limited this incubation temperature. 33ЊC (which probably produce both sexes) to deter- Clutch is a significant source of variation for sex of mine whether lower fitness of animals incubated at hatchlings at temperatures that produce both sexes 34.5ЊC was because of production of both sexes or be- (Conley et al., 1997; Lang and Andrews, 1994; Rhen cause this incubation temperature is detrimental for and Lang 1998). Caiman latirostris produces 100% C. latirostris. Further experiments are needed to an- males at constant incubation temperature of 33ЊC, con- swer this question. trasting with other species of crocodilians studied to Woodward and Murray (1993) suggested a possible 202 SHORTER COMMUNICATIONS selective advantage because of TSD on the ability of LANG,J.,AND H. ANDREWS. 1994. Temperature-de- crocodilians to produce skewed sex ratios. We found pendent sex determination in crocodilians. Journal higher hatching success and survivorship from the of Experimental Zoology 270:28–44. eggs incubated at 29ЊC, which is consistent with this LARRIERA, A. 1993. La conservacioń y el manejo de hypothesis, but recent data on alligators (Lance et al., Caiman latirostris en Santa Fe, Argentina. In:L.M. 2000) challenge this idea. Results of our experiments Verdade, I. U. Packer, M. B. Rocha, F. B. Molina, P. do not provide evidence of a clear evolutionary ad- G. Duarte, and L. A. Lula (eds.), Anais do III Work- vantage for TSD in C. latirostris, other than the lower shop sobre Conservaçaõ e Manejo do jacare´do fitness of those eggs incubated at 34.5ЊC. In this ex- papo amarelo, pp. 61–69. Piracicaba, Sa˜ o Paulo, periment, we demonstrated that another crocodilian Brazil. species has TSD, rising the total to 12 of 22 extant MROSOVSKY, N. 1994. Sex ratios of sea turtles. Journal species. of Experimental Zoology 270:28–44. RHEN,T.,AND D. CREWS. 1999. Embryonic tempera- Acknowledgments.—We thank all the crew of Proy- ture and gonadal sex organize male-typical sexual ecto Yacare´ (P. Sirosky, P. Donayo, P. Amavet, M. Me- and aggressive behavior in a lizard with temper- dina, A. Imhof, and N. Frutos) who helped during egg ature-dependent sex determination. Endocrinology collection, incubation, and hatching. Comments on the 140:4501–4508. manuscript by two anonymous reviewers are appre- RHEN,T.,AND J. LANG. 1998. Among-family variation ciated. A. Woodward helped with English revision for environmental sex determination in reptiles. and comments on the manuscript. Partial support for Evolution 52:1514–1520. this study was provided by a grant from the Orga- WEBB, G. J. W., S. C. MANOLIS, AND G. C. SACK. 1984. nization for Tropical Studies (O.T.S.) to CIP. CIP was Cloacal sexing of hatchling crocodiles. Australian a postgraduate fellow from CONICET, Argentina, and Wildlife Research 11:201–202. MRC is a researcher from CONICET. WEBB, G. J. W., A. M. BEAL,S.C.MANOLIS, AND K. E. DEMPSEY. 1987. The effects of incubation temper- LITERATURE CITED ature on sex determination and embryonic devel- ALLSTEADT,J.,AND J. W. LANG. 1995. Sexual dimor- opment rate in Crocodylus johnstoni and Crocodylus phism in the genital morphology of young amer- porosus. In G. J. W. Webb, C. Manolis, and P. J. ican alligators, Alligator mississippiensis. Herpeto- Whitehead (eds.), Wildlife Management of Croco- logica 51:314–325. diles and Alligators, pp. 507–531. Surrey Beatty CONLEY,A.J.,P.ELF,C.J.CORBIN,S.DUBOWSKY,A. and Sons Pty. Ltd. in association with the Conser- FIVIZZANI, AND J. W. LANG. 1997. Yolk steroids de- vation Commission of the Northern Territory, Can- cline during sexual differentiation in the Alligator. berra, Australian Capital Territory, Australia. General and Comparative Endocrinology 107:191– WIBBLES,T.,J.BULL, AND D. CREWS. 1994. Tempera- 200. ture-dependent sex determination: a mechanistic EWERT,M.,D.JACKSON, AND C. NELSON. 1994. Pat- approach. Journal of Experimental Zoology 270: terns of temperature-dependent sex determination 71–78. in turtles. Journal of Experimental Zoology 270:3– WOODWARD,D.E.,AND J. D. MURRAY. 1993. On the 15. effect of temperature-dependent sex determination JANZEN, F. J. 1995. Experimental evidence for the evo- on sex ratio and survivorship in crocodilians. Pro- lutionary significance of temperature sex determi- ceedings of Royal Society, London 252:149–155. nation. Evolution 49:864–873. ZUG, G. R. 1993. Herpetology: An Introductory Biol- LANCE, V., R. ELSEY, AND J. LANG. 2000. Sex ratios of ogy of Amphibians and Reptiles. Academic Press, American alligators (Crocodylidae): Male or fe- San Diego, CA. male biased? Journal of Zoology, London 252:71– 78. Accepted: 8 May 2002.