Relationships between sexual dimorphism and niche partitioning within a clade of sea-snakes (Laticaudinae)

Abstract

Previous studies in Fiji have shown that females of the amphibious sea-krait Laticauda colubrina are much larger than males, and have larger heads relative to body size. The dimorphism has been interpreted in terms of adaptation to a sex divergence in prey-size: females primarily eat large (conger) eels rather than smaller (moray) eels. The hypothesis that dimorphism is affected by niche divergence predicts that the degree of sex dimorphism will shift when such a species invades a habitat with a different range of potential prey sizes. On the island of Efate in Vanuatu, L. colubrina and a regionally endemic sibling species (L. frontalis) both consume smaller eels (in absolute terms, and relative to the snake's body size) than do the previously-studied Fijian snakes. Patterns of morphology and sexual dimorphism have shifted also. Both Vanuatu taxa are slender-bodied, and frontalis is smaller and less dimorphic than L. colubrina. Females grow larger than males in all taxa, and have larger heads (relative to body length), but the degree of sexual divergence is lower in Vanuatu (especially in frontalis). Dietary overlap (in prey species as well as size) is high between adult frontalis and juvenile colubrina, but the two taxa differ in prey size/predator size relationships. In particular, male frontalis eat very small prey and have very short heads. Our results are consistent with the hypothesis that sex differences in the mean adult body sizes and relative head sizes of laticaudine snakes are linked to sex differences in feeding biology.

Sex differences in population genetics, home range size and habitat use of the parti-colored bat (Vespertilio murinus, Linnaeus 1758) in Switzerland and their consequences for conservation

“…For example, sex-specific habitat use explained sex-specific mortality rates and subsequent shifts in adult sex-ratios in several maritime bird species owing to incidental mortality caused by long-line and trawl fisheries (Gonzalez-Solis et al 2000;Lewis et al 2002;Phillips et al 2005;Phillips et al 2004). Our finding that the sexes in the parti-colored bats display strong "ecological dimorphism" (Shine et al 2002) underlines the importance of including sex as a factor when studying the ecology and population genetics of a species.…”

Dietary resource partitioning among sympatric New Zealand and Australian fur seals

“…In sexually dimorphic species, 2 hypotheses have been developed to explain how differences in resource exploitation by adult males and females have evolved (Stewart 1997). The ecological divergence hypothesis suggests that sexual dimorphism evolved as a consequence of males and females utilising different prey resources (Shine et al 2002). In contrast, the intra-sexual competition hypothesis predicts that sexual dimorphism has evolved as a consequence of sexual selection and intra-sexual competition -for example, males segregate to increase their competitive ability against other males.…”

The South-American rattlesnake Crotalus durissus: feeding ecology in the central region of Brazil

“…This could be one of the reasons that this species is more frequently consumed rather than other ectothermic prey. Additionally, some factors such as adaptations related to competition, niche utilization, foraging strategies, costs of time and energy and prey availability (Schoener 1969;Shine 1986;Shine et al 2002), could reflect important characteristics in the understanding of feeding ecology of C. durissus from the central region of Brazil.…”