Allometry of head size and shape dimorphism in the grass snake (Natrix natrix L.)

Abstract

Sexual dimorphism is a common phenomenon in the animal kingdom and has been reported in numerous snake species (see Shine, 1993 for review). In most colubrids (sensu lato) females are the larger sex (Shine, 1994). Body size differences are often accompanied by body shape and scalation differences, e.g., proportionally longer male tails or longer female trunks (

The impact of diet, habitat use, and behaviour on head shape evolution in homalopsid snakes

“…Surprisingly few studies on head shape evolution in snakes have been conducted despite the suggested relevance of head shape to diet in gape‐limited predators like snakes (Gans, ; Savitzky, ). Most studies exploring snake head shape have used linear descriptors in an attempt to explore growth allometries and sexual dimorphism (Arnold & Peterson, ; Vincent, Herrel & Irschick, ,b; Vincent & Herrel, ; Henao‐Duque & Ceballos, ; Borczyk, ) or to explore the role of head shape and head triangulation as a predator deterrent (Valkonen, Nokelainen & Mappes, ; Dalbosco et al ., ). Studies using geometric morphometrics are relatively rare and have mostly focused on head shape variation from a systematic perspective (Gentilli et al ., ; Mangiacotti et al ., ).…”

Sexual dimorphism and skull size and shape in the highly specialized snake species,Aipysurus eydouxii(Elapidae: Hydrophiinae)

“…Females grow larger in approximately two thirds of snake species studied so far and usually females possesses larger heads (Shine, 1993). These differences can be a result of a disproportional (allometric) head growth (Borczyk, 2015). However, this is not the case in A. eydouxi.…”

“…Differences in head size and shape often result from selective pressure on dietary/ feeding niche separation, as they are usually accompanied by differences in average prey size, type, or both (e.g. Shine, 1986Shine, , 1991Shine, , 1993Houston & Shine, 1993;Forsman & Shine, 1997;Keogh, Branch & Shine, 2000;Shine et al, 2002;Gregory & Isaac, 2004;Vincent, Herrel & Irschick, 2004;Shine et al, 2012;Borczyk, 2015). The species in this study is one of the very few snake species that feed on fish eggs.…”

“…It is thought to be one means of compensating for greater energy expenditures (maintaining larger bodies and, in the case of females, providing nutritional components for developing embryos) (e.g. Elgee & Blouin-Demers, 2011;Borczyk, 2015). Females grow larger in approximately two thirds of snake species studied so far and usually females possesses larger heads (Shine, 1993).…”

“…For example, Arafura File Snakes (Acrochordus arafurae) reaching extremes with females being up to 10 times heavier than males (Shine, 1991). Sexual size dimorphism is followed by differentiated energy requirements that can manifest as food intake and type or size of prey (Elgee & Blouin-Demers, 2011;Borczyk, 2015). The latter aspect is of specific interest since, in many instances, it requires adjustment of not only ecological properties (like habitats, preferences towards appropriate food resources, or feeding niche divergence) but also of morphology (Camilleri & Shine, 1990).…”