Cranial sexual discrimination in hatchling broad-snouted caiman (Caiman latirostris)

Carlos Piña,Luciano M Verdade,Pablo Siroski,Alejandro Larriera

doi:10.1590/s0073-47212007000100003

Abstract

Broad-snouted caiman (Caiman latirostris) hatchlings present a consistent sexual dimorphism in their cranium shape and size. Male hatchlings have smaller crania than females. Using multivariate statistical analyses it is possible to discriminate sex in broad-snouted caiman hatchlings by their cranial shape with a reasonable efficiency. The understanding of sexual dimorphism of crocodilian hatchlings might be possibly improved by experimental approach considering, genetic and phenotypic variables such as incubation temperature and clutch of origin.

Highlights

The evolution of sexual dimorphism can result from sexual selection and/or intraespecific niche divergence (HEDRICK & TEMELES, 1989; SHINE, 1989)
Adult crocodilians are sexed by direct inspection of the cloaca (CHABRECK, 1963; BRAZAITIS, 1969), the sex of hatchlings is difficult to determine because cloacal examination usually leads to a high rate of misclassification, up to 90% (JOANEN & MCNEASE, 1978)
If multivariate analyses of hatchlings sex discrimination became as effective as they are for adult crocodilians (VERDADE, 2003) they might replace the currently available techniques: surgical examination of the gonads (MAGNUSSON et al, 1990) which is an invasive method; delaying sexing until animals are big enough which is time consuming; or, sacrificing animals for necropsy which is not recommended for endangered species

Summary

Introduction

Los neonatos de yacaré overo (Caiman latirostris) presentan un dimorfismo sexual en la forma y tamaño de su cráneo. Young and adult crocodilians (from 40 to 120 cm snout-vent length) have sexually dimorphic heads (WEBB & MESSEL, 1978; HALL & PORTIER, 1994; VERDADE, 2003), but there is no available data for hatchlings. If multivariate analyses of hatchlings sex discrimination became as effective as they are for adult crocodilians (VERDADE, 2003) they might replace the currently available techniques: surgical examination of the gonads (MAGNUSSON et al, 1990) which is an invasive method; delaying sexing until animals are big enough which is time consuming; or, sacrificing animals for necropsy which is not recommended for endangered species. We aimed to answer the following questions concerning sexual dimorphism of broad-snouted caiman hatchlings, Caiman latirostris (Daudin, 1802): 1) does the species present cranial sexual dimorphism in hatchlings?; 2) can we efficiently discriminate gender in hatchlings based on their cranial morphometrics?; 3) what cranial measurements are more relevant for this purpose?

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