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

Abstract

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)(20)(21)(22)(23)(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. KEYWORDS.Amphisbaenia, Espírito Santo, restinga, sexual dimorphism.RESUMO. Dimorfismo sexual em Amphisbaena nigricauda (Reptilia, Squamata, Amphisbaenidae) do Sudeste do Brasil. Amphisbaena nigricauda Gans, 1966 é uma pequena anfisbênia pouco conhecida endêmica da restinga dos estados do Espírito Santo e Bahia, Brasil. Analisamos 178 indivíduos coletados no município de Vitória, Espírito Santo, Brasil, para verificar se esta espécie apresenta dimorfismo sexual nos poros pré-cloacais e em caracteres morfológicos. O sexo foi determinado por uma incisão ventral e inspeção direta das gônadas. Uma análise de PCA foi realizada para gerar uma medida geral do tamanho do corpo. O test-T e o teste de Mann-Whitney não paramétrico foram utilizados para avaliar se esta espécie apresenta dimorfismo sexual em cinco caracteres morfométricos e cinco merísticos, respectivamente. O sexo não pode ser determinado em 36 indivíduos porque eles estavam mutilados na parte posterior do corpo. O diagnóstico da espécie é redefinido com base nesta amostra: o menor número ...

Ontogenetic allometry constrains cranial shape of the head‐first burrowing worm lizard Cynisca leucura (Squamata: Amphisbaenidae)

“…We found no evidence of sexual dimorphism in C. leucura, either during ontogeny or among adults. Whether this reflects the absence of sexual selection pressures (e.g., competition for mates, female fecundity) in this and other species is still unknown, since reproductive behavior of amphisbaenians has rarely been observed (Souza e Lima et al, 2014;but see Cooper et al, 1994, Filogonio et al, 2009.…”

“…In addition to body length, head shape is one of the most consistently dimorphic traits in lizards (Olsson et al, ), with larger male heads associated with enhanced success in male‐male competition (Vitt and Cooper, ; Anderson and Vitt, ) and increased bite force and prey handling efficiency (Verwaijen et al, ). Evidence of sexual dimorphism in amphisbaenians is mixed: males can be larger than females ( Amphisbaena nigricaudata , Souza e Lima et al, ; Leposternon polystegum , Gomes et al, ), females can be larger than males ( Anops kingii , Vega, ; Zygaspis quadrifrons , Webb et al, ), sexes can have similar body lengths but larger heads in one (males in Trogonophis wiegmanni , Martín et al, ; Blanus cinereus , Gil et al, ; Leposternon microcephalum and L. wuchereri , Filogonio et al, ; and females in Monopeltis anchietae , Webb et al, ), or sexes can be the same in both body length and head size ( Bipes biporus , Kearney, ; Amphisbaena ibijara , Gomes et al, ). We found no evidence of sexual dimorphism in C. leucura , either during ontogeny or among adults.…”

A new tale of lost tails: Correlates of tail breakage in the worm lizard Amphisbaena vermicularis

“…Despite the lack of empirical evidence of male–male competition in amphisbaenians, experiments show that males respond aggressively to scents of conspecific males (López & Martín, 2009; Martín et al, 2020). Thus, sexually dimorphic species where males are larger than females (e.g., Gomes et al 2009; Souza e Lima et al 2014) could indicate male–male competition, ultimately leading to tail breakage. There is no sexual dimorphism in Amphisbaena vermicularis , and we found no sexual differences in the frequency of urotomy between sexes, which suggests that tail loss does not involve differential survival between males and females (Costa et al., 2014).…”

Microanatomy of the testes and testicular ducts of the butterfly lizard, Leiolepis ocellata Peters, 1971 (Reptilia: Squamata: Agamidae) during the active reproductive period

“…The testes are typically ovoid in lizards and elongated in snakes (Gribbins & Rheubert, ; Lombardi, ). In general, lizards and snakes have paired testes with asymmetric placement in the way that the right testis is anterior to the left one (Fox, ; Gans & Parsons, ; Gribbins & Rheubert, ; Mott, Rodrigues, & de Freitas, ; Navega‐Gonçalves, ; Rheubert et al, ; Sever, ; Siegel, Sever, Rheubert, & Gribbins, ), while Amphisbaena nigricauda reveals intraspecific variation in the testis disposition, with 86%, 4% and 10% of the male population showing the more anterior right testis, the more anterior left testis and the symmetrically positioned testes, respectively (de Souza e Lima, Gasparini, de Padua Almeida, Vital, & Mott, ). However, L. ocellata have comparably sized, almost symmetrically disposed, bilateral testes.…”