Sexual dimorphism in skull size and shape of Laticauda colubrina (Serpentes: Elapidae)

Abstract

Background Sexual dimorphism in size and shape is widespread among squamate reptiles. Sex differences in snake skull size and shape are often accompanied by intersexual feeding niche separation. However, allometric trajectories underlying these differences remain largely unstudied in several lineages. The sea krait Laticauda colubrina (Serpentes: Elapidae) exhibits very clear sexual dimorphism in body size, with previous studies having reported females to be larger and to have a relatively longer and wider head. The two sexes also differ in feeding habits: males tend to prey in shallow water on muraenid eels, whereas females prey in deeper water on congerid eels. Methods I investigated sexual dimorphism in skull shape and size as well as the pattern of skull growth, to determine whether males and females follow the same ontogenetic trajectories. I studied skull characteristics and body length in 61 male and female sea kraits. Results The sexes differ in skull shape. Males and females follow distinct allometric trajectories. Structures associated with feeding performance are female-biased, whereas rostral and orbital regions are male-biased. The two sexes differ in allometric trajectories of feeding-related structures (female biased) that correspond to dietary divergence between the sexes. Conclusions Sea kraits exhibit clear sexual dimorphism in the skull form that may be explained by intersexual differences in the feeding habits as well as reproductive roles. The overall skull growth pattern resembles the typical pattern observed in other tetrapods.

Sexual dimorphism and allometry in the head and body size of two viperid snakes (genus Vipera)

“…Variation in internarial distance has rarely been studied in the context of male-female differences in snakes. et al (2021) and Borczyk (2023), we assume that this characteristic may also be dimorphic in other species and suggest that such variation may be linked to the chemosensory system in snakes. Males rely strongly on olfactory cues (andrén 1982), so the olfactory bulbs, and also the vomeronasal organ, which is involved in pheromone detection, may be better developed, thus making mate searching more effective.…”

“…Thus, the differences in sensory structures may be reflected in the skull bones supporting these structures (and thus affecting the head shape). Sexual dimorphism in the skull bones supporting the eyes and nasal region (housing chemosensory structures) exists in at least some snake species (andjelKović et al 2016;Borczyk et al 2021;Borczyk 2023).…”

“…The quadrate length strongly contributes to the gape size in viperids (haMPton & Moon 2013), and in many other species it shows positive allometry with respect to skull length (Borczyk 2023); moreover, its elongation may enhance snake feeding performance. Furthermore, in many snake species there is a shift in the preferred prey during ontogeny (from small cylindrical, usually reptilian, prey to bulky mammalian and avian prey), which may be reflected by a complete 'switch' to a new category of prey or else by the inclusion of a new prey type in addition to the previous one after some threshold size has been attained (arnold 1993;Vincent et al 2007;lóPez et al 2013).…”

“…This is reflected in the tongue, which is relatively longer and more deeply bifurcated in males (sMith et al 2008) and may be associated with further modification of the head, i.e., with males having a relatively wider rostral region (bearing the olfactory structures). However, the question of sexual dimorphism in reproduction-related head dimensions is underrepresented in published studies (saint-Girons 1957;steward 1971;ForsMan 1991a), although subtle intersexual differences have been recently reported in nasal bones in Natrix species (andjelKović et al 2016), and in the nasal and orbital regions in two elapid species -Aipysurus eydouxii (Borczyk et al 2021) and Laticauda colubrina (Borczyk 2023).…”