Sexual dimorphism of sharks from the amazonian equatorial coast

Jorge Luiz Silva Nunes,Ednaldo Da Silva Filho,Zafira Da Silva De Almeida,Luiz Phelipe Nunes E Silva,Leonardo Manir Feitosa,Ana Paula Barbosa Martins

doi:10.11144/javeriana.sc20-3.sdos

Jorge Luiz Silva Nunes, Ednaldo Da Silva Filho + Show 4 more

Open Access

https://doi.org/10.11144/javeriana.sc20-3.sdos

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Abstract

Sexual dimorphism is a widespread feature in several groups of vertebrates. Chondrichthyans differ sexually due to the presence of the clasper, a structure for internal fertilization, and other sexual differences in secondary characteristics. Nevertheless, studies assessing these variations are fairly rare. The main goal of this study is to identify differences in sexual dimorphism in three species of sharks from the Carcharhinidae family (Rhizoprionodon porosus, Carcharhinus porosus and Isogomphodon oxyrhynchus) using morphometric tools. A total of 213 specimens were captured in the Amazonian Equatorial Coast and analyzed using 65 morphometric characters. Discriminant analysis and The Student's t-test were used to demonstrate the morphological differences among sexes. Sexual dimorphism was reported at different levels for the three species. This study suggests that the most likely explanation for the presence of these variations is related to their reproductive characteristics and mating behavior.

Highlights

Sexual dimorphism is common among vertebrates (Kajiura et al 2005)
Since updated data about these species is scarce and consistent knowledge is required for developing management strategies for local species, this study aims to evaluate the presence of sexual dimorphism within three Carcharhinidae sharks captured off the coast of Maranhão state, Amazonian Equatorial Coast, Brazil
The sharks were stored in thermal coolers with ice and taken to the Ichthyology Laboratory of the Universidade Federal do Maranhão (Federal University of Maranhão) for morphometric analysis

Summary

Introduction

Sexual dimorphism is common among vertebrates (Kajiura et al 2005). With regard to fishes, in mature specimens the internal differences between genders are usually clear, but externally they are not differentiated (Moyle & Cech 2004). All cartilaginous fishes exhibit external sexual dimorphism brought about by the modification of males’ pelvic fins. This results in a specialized structure for internal fertilization, called clasper. Beyond this evident characteristic, many other species exhibit sexual dimorphism through other morphological features (Orlov et al 2010, Orlov & Cotton 2011).

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