Sexual dimorphism in Amphisbaena nigricauda (Reptilia, Squamata, Amphisbaenidae) from Southeastern Brazil

Francco A N De Souza E Lima,Antonio De Padua Almeida,Tamí Mott,João Luiz Gasparini,Marcos V C Vital

doi:10.1590/1678-476620141043299307

Abstract

Amphisbaena nigricauda Gans, 1966 is a small, poorly known amphisbaenid endemic to the restinga of the states of Espírito Santo and Bahia, Brazil. We analyze 178 specimens collected in Vitória municipality, state of Espírito Santo, Brazil, to investigate whether this species show sexual dimorphism in pre-cloacal pores and in morphological characters. Sex was determined by a ventral incision and direct inspection of gonads. A PCA analysis was performed to generate a general body size measurement. A T test and the non-parametric Mann-Whitney test were used to assess whether this species show sexual dimorphism on five morphometric and five meristic characters, respectively. Sex could not be determined in 36 specimens because they were mutilated in the posterior portion of their bodies. The diagnosis of the species is redefined based on this sample size: the smallest number of body annuli changes from 222 to 192, the number of dorsal and ventral segments in an annulus in the middle of the body changes to 9-11/13-16 (instead of 10/16), and the autotomic tail annulus lies between annulus 7-10 (instead of 6-9). The number of tail annuli remained within the known range of variation of the species (19-24). None of the 80 females analyzed showed pre-cloacal pores, whereas within males 59 out of 62 specimens displayed four and two specimens displayed five pre-cloacal pores. A single male did not possess pre-cloacal pores, but showed irregular scales on its cloacal region. Sex-based difference based on presence or absence of pre-cloacal pores as well as males with wider head was seen in other Neotropical amphisbaenids. However, a pattern of body size differences between males and females has not been identified so far in the few amphisbaenid species studied in this regard. Further studies on this taxonomic group are still needed to elucidate the existence of general patterns of sexual dimorphism and to identify the selective pressures driving these patterns.

Highlights

The diagnosis of the species is redefined based on this sample size: the smallest number of body annuli changes from 222 to 192, the number of dorsal and ventral segments in an annulus in the middle of the body changes to 9–11/13–16, and the autotomic tail annulus lies between annulus 7–10
Brazil harbors the highest diversity of amphisbaenians worldwide (Mott & Vieites, 2009) with 69 species currently catalogued in the country (Bérnils & Costa, 2012; Roberto et al, 2014)
A total of 178 specimens of Amphisbaena nigricauda were analyzed, 36 of which were excluded because they were mutilated. Based on these specimens the morphological diagnosis of A. nigricauda is redefined: the smallest number of body annuli changes from 222 to 192, the number of dorsal and ventral segments in an annulus in the middle of the body changes from 10/16 to 9–11/13–16, and the autotomic tail annulus lies between annulus 7 and 10 instead of 6–9

Summary

Introduction

For Neotropical amphisbaenids, sex-based morphological differences were investigated for Amphisbaena alba Linnaeus, 1758 (Colli & Zamboni, 1999); Amphisbaena kingii (Bell, 1833) and Amphisbaena munoai Klappenbach, 1960 (Balestrin & Cappellari, 2011); Amphisbaena ibijara Rodrigues, Andrade & Lima, 2003 and Leposternon polystegum (Duméril, 1851) (Gomes et al, 2009); Leposternon wuchereri (Peters, 1879) and Leposternon microcephalum Wagler, 1824 (Filogonio et al, 2009); and Amphisbaena prunicolor (Cope, 1885) (Maciel et al, 2012) These studies generally found that females are larger than males (exception to Leposternon microcephalum whereas total length do not differ, and L. polystegum whereas males are larger than females), following the same pattern found in other squamate reptiles (Shine, 1994). 1924, A. heathi Schmidt, 1936 (Vanzolini, 2002), A. uroxena Mott, Rodrigues, Freitas & Silva, 2008 and A. anaemariae Vanzolini, 1997 (Mott et al, 2011) do not show pores

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Conclusion