Abstract
BackgroundSnakes exhibit sexual dimorphism in both head size and shape. Such differences are often attributed to different reproductive roles and feeding habits. We aim to investigate how sexual dimorphism is displayed in the highly specialised fish-egg-eating snake, Aipysurus eydouxii, by analysing two complementary features: body size and skull morphology.MethodsWe used data on body length, weight, and skull shape from 27 measurements of 116 males and females of A. eydouxii. We investigated both sexual dimorphism and allometric (multivariate and bi-variate) properties of skull growth in the analysed data set.ResultsWe found that although there was female-biased sexual size dimorphism in body length, females were not heavier than males, contrary to what is commonly observed pattern among snakes. Moreover, females tend to possess relatively smaller heads than males. However, we only found very subtle differences in skull shape reflected in nasal width, mandibular fossa, quadrate crest and quadrate length.DiscussionWe suggest that the feeding specialisation in A. eydouxii does not allow for an increase in body thickness and the size of the head above a certain threshold. Our results may be interpreted as support for prey-size divergence as a factor driving skull dimorphism since such species in which the sexes do not differ in prey size also shows very subtle or no differences in skull morphology.
Highlights
The differences between sexes have attracted the attention of biologists for decades; do they refer to reproductive investments or sex-related traits, but consequences of differential reproductive output can be observable among many other features (Darwin, 1871)
There was no sexual dimorphism in body weight (BW) when corrected for snout-to-vent length (SVL) (ANCOVA test F1, 41 = 0.244, p = 0.624)
MANCOVA showed that males had relatively longer, higher, and wider skulls than females at the same SVL (Wilks’ ƛ = 0.772, F3,42 = 4,127, p = 0.012) (Tables 2 and 3, Fig. 2)
Summary
The differences between sexes have attracted the attention of biologists for decades; do they refer to reproductive investments or sex-related traits, but consequences of differential reproductive output can be observable among many other features (Darwin, 1871). 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 ecological properties (like habitats, preferences towards appropriate food resources, or feeding niche divergence) and of morphology (Camilleri & Shine, 1990). Methods: We used data on body length, weight, and skull shape from 27 measurements of 116 males and females of A. eydouxii. We investigated both sexual dimorphism and allometric (multivariate and bi-variate) properties of skull growth in the analysed data set. Our results may be interpreted as support for prey-size divergence as a factor driving skull dimorphism since such species in which the sexes do not differ in prey size shows very subtle or no differences in skull morphology
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