3 results
Contributors
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- By Zachary W. Adams, Margarita Alegría, Atalay Alem, Jordi Alonso, Victor Aparicio, Rifat Atun, Florence Baingana, Emily Baron, Marco Bertelli, Dinesh Bhugra, Sanchita Biswas, José Miguel Caldas de Almeida, Edwin Cameron, Somnath Chatterji, Erminia Colucci, Janice L. Cooper, Carla Kmett Danielson, Diego De Leo, Mary-Jo DelVecchio Good, Marten W. de Vries, Maureen S. Durkin, Xiangming Fang, Julia W. Felton, Sally Field, Andrea Fiorillo, Lance Gable, Teddy Gafna, Sandro Galea, Patrick Gatonga, Sofia Halperin-Goldstein, Yanling He, Grace A. Herbert, Sabrina Hermosilla, Simone Honikman, Takashi Izutsu, Ruwan M. Jayatunge, Janis H. Jenkins, Rachel Jenkins, Lynne Jones, Jayanthi Karunaratne, Ronald C. Kessler, Rob Keukens, Lincoln I. Khasakhala, Hanna Kienzler, Sarah Kippen Wood, M. Thomas Kishore, Robert Kohn, Natasja Koitzsch Jensen, Sheri Lapatin, Anna Lessios, Isabel Louro Bernal, Feijun Luo, Laura MacPherson, Matthew J. Maenner, Anne W. Mbwayo, David McDaid, Ingrid Meintjes, Victoria N. Mutiso, David M. Ndetei, Samuel O. Okpaku, Lijing Ouyang, Ramachandran Padmavati, Clare Pain, Duncan Pedersen, Jordan Pfau, Felipe Picon, Rodney D. Presley, Reima Pryor, Shoba Raja, Thara Rangaswamy, Jorge Rodriguez, Diana Rose, Moosa Salie, Norman Sartorius, Ester Shapiro, Manuela Silva, Daya Somasundaram, Katherine Sorsdahl, Dan J. Stein, Deborah M. Stone, Heather Stuart, Athula Sumathipala, Hema Tharoor, Rita Thom, Lay San Too, Atsuro Tsutsumi, Chris Underhill, Anne Valentine, Claire van der Westhuizen, Thandi van Heyningen, Robert van Voren, Inka Weissbecker, Gail Wyatt
- Edited by Samuel O. Okpaku
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- Book:
- Essentials of Global Mental Health
- Published online:
- 05 March 2014
- Print publication:
- 27 February 2014, pp x-xiv
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- Chapter
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22 - Reptile reproduction and endocrinology
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- By Valentine A. Lance, Center for Reproduction of Endangered Species, Zoological Society of San Diego, PO Box 120551, San Diego CA 92112, U.S.A.
- Edited by William V. Holt, Zoological Society of London, Amanda R. Pickard, Zoological Society of London, John C. Rodger, David E. Wildt, Smithsonian National Zoological Park, Washington DC
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- Book:
- Reproductive Science and Integrated Conservation
- Published online:
- 21 January 2010
- Print publication:
- 05 December 2002, pp 338-358
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Summary
INTRODUCTION AND BACKGROUND
The alarming pace of the global decline in amphibians has alerted both biologists and the general public to the accelerating rate of habitat loss, fragmentation and degradation (Roth & Obringer, Chapter 23). However, as Gibbons et al. (2000) recently pointed out, ‘Although the amphibian decline problem is a serious threat, reptiles appear to be in even greater danger of extinction worldwide.’ For example, one of the most spectacular and enigmatic reptiles, the leatherback sea turtle (Dermochelys coriacea) appears to be on a direct course for extinction, while little continues to be known of its unusual physiology and life history (Spotila et al., 1996). In fact, many reptile species are destined to disappear before anything is discovered of their basic biology, including reproduction.
Reptiles were the first truly terrestrial vertebrates. The evolution of the amniote egg, ‘the most marvelous “invention” in vertebrate history’ (Romer, 1967), freed reptiles from dependence on an aquatic environment for reproduction, thus allowing exploitation of terrestrial habitats. The increase in yolk mass, completion of development within an egg and abandonment of a larval stage resulted in an explosion of forms that typified the ‘age of reptiles’ during which at least 17 orders appeared.
Of this extraordinary diversity, only four orders remain today in the class Reptilia: Chelonia or Testudinata (turtles and tortoises, 260 species), Crocodilia (crocodiles, alligators and the gharial, 22 species), Squamata (snakes, lizards and amphisbaenids, >6800 species) and Rhynchocephalia or Sphenodontida (represented by the genus Sphenodon, the tuatara, two species).
Sex ratios of American alligators (Crocodylidae): male or female biased?
- Valentine A. Lance, Ruth M. Elsey, Jeffrey W. Lang
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- Journal:
- Journal of Zoology / Volume 252 / Issue 1 / September 2000
- Published online by Cambridge University Press:
- 01 September 2000, pp. 71-78
- Print publication:
- September 2000
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- Article
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Recent theoretical papers on temperature-dependent sex determination in reptiles are based on the assumption that crocodilian populations, particularly adults, are markedly female biased. While there is evidence that some crocodile populations may conform to this expectation, there is no compelling evidence that American alligator populations are female biased anywhere in the species' range. Previous data had indicated that some populations of juvenile and/or adult alligators were significantly male biased. However, these studies were criticized for sampling errors. Adult males typically occupy a different habitat from that of females, and males frequent areas where they are more likely to be caught. In contrast, in juveniles, both sexes occupy the same habitat. We determined the sex ratios of c. 3000 juvenile alligators collected from 11 sites over 6 years in south Louisiana. Our results indicate a significant sex bias (58% male), but variation was evident among samples. Sex ratios varied by year and site, and the interaction of these factors was significant. At one site in one year, there was a female bias (71%), but in no year was there an overall female bias across sites. From this study and earlier reports, we conclude that there is no evidence at present of female-biased sex ratios in the juvenile and/or adult alligator populations, and consequently, that certain models of temperature-dependent sex determination in reptiles require re-evaluation. Furthermore, our data suggest a pattern of differential mortality of females vs males during the first years of life, a pattern consistent with a key prediction of several differential fitness models for the adaptive significance of temperature-dependent sex determination in reptiles.