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Leuteritz, T. E. J., & Gantz, D. T. , Sexual dimorphism in radiated tortoises (astrochelys radiata). Unpublished paper presented at Turtles on the Brink in Madagascar: Proceedings of Two Workshops on the Status, Conservation, and Biology of Malagasy Tortoises and Freshwater Turtles. 
Added by: Admin (06 Jan 2014 18:24:48 UTC)
Resource type: Conference Paper
DOI: 10.3854/crm.6
BibTeX citation key: Leuteritz2013
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Categories: General
Keywords: Astrochelys radiata, Fortpflanzung - reproduction, Habitat - habitat, Haltung - husbandry, Madagaskar - Madagascar, Schildkröten - turtles + tortoises, Testudinidae
Creators: Gantz, Leuteritz
Collection: Turtles on the Brink in Madagascar: Proceedings of Two Workshops on the Status, Conservation, and Biology of Malagasy Tortoises and Freshwater Turtles
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Testudinidae Geochelone Turtles exhibit a wide variety of size differences between the sexes. In addition to body size, a suite of other divergent characters exist that have often been used to determine the sex of turtles. The visual determination of sex in radiated tortoises can often be subjective and misleading, especially for tortoises around the size of sexual maturity or somewhat smaller. The purpose of this paper was to: 1) quantify and evaluate morphological characteristics that may be sexually dimorphic in the radiated tortoise, Astrochelys radiata; 2) develop a discriminant function that can accurately identify the sex of individual A. radiata based on these characteristics; and, 3) provide this function as a tool to help sex juvenile tortoises in captive breeding conservation programs. Two linear discriminant function equations were developed using morphological variables as raw or size corrected (ratio) values based on known-sex animals and comparing them to other tortoises in a population at Cap Sainte Marie (CSM), Madagascar. Although both equations are equal at classifying males, the raw + ratio variables equation did a better job of predicting females in the test data set from the CSM population. Incorporating data based on known-sex juveniles would be the next step in developing a more comprehensive discriminant function. Male radiated tortoises were found to be the same size, or slightly larger than females. The data fit Berry and Shine’s mating system model, in which male combat or forcible insemination is used to explain why males are as large, or larger than females. Although male-male combat did occur at CSM, its frequency was low. It is unlikely that a significantly smaller male radiated tortoise could successfully copulate with a larger female because of the physical strength needed to restrain her and their sheer size disparity. Forced insemination is therefore a plausible explanation for equal or larger size in male radiated tortoises.
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