Reproductive Isolating Mechanisms Between Two Sympatric Sibling Species of Sea Snakes

Abstract

Mechanisms that maintain species isolation within sympatric congeners have attracted analysis in many kinds of organisms, but not in snakes. We studied two sibling species of amphibious sea snakes (Laticauda colubrina and L. frontalis) on the island of Efate, in the Pacific Ocean republic of Vanuatu. The two taxa are almost identical morphologically, except that L. colubrina grows much larger than L. frontalis. No natural hybrids have been reported, and geographic distributions of the two taxa suggest the possibility of sympatric speciation. Our fieldwork shows that the two taxa are often syntopic and overlap in breeding seasons. Behavioral studies in outdoor arenas show that the separation between these two taxa is maintained by species-specific cues that control male courtship. Males of both species courted conspecific females but not heterospecific females. The proximate mechanism driving this separation involves chemical cues. Adult females of both taxa possess distinctive lipids in the skin. Males directed courtship behavior (chin-pressing) to hexane-extracted samples of lipids from conspecific but not heterospecific females. Males of the dwarf species (L frontalis) were more selective courters than were those of the larger taxon (L. colubrina), perhaps because a preference for courting larger females means that L. colubrina males would be unlikely to court L. frontalis-sized (i.e., small) females even in the absence of pheromonal barriers.

Interpopulational variation in chemosensory responses to selected steroids from femoral secretions of male lizards, Podarcis hispanica, mirrors population differences in chemical signals

“…Differences in chemical signals preclude interspecific mating between related sympatric species (e.g., Cooper andVitt 1986, 1987;Shine et al 2002;Mas and Jallon 2005;Barbosa et al 2006). Different environments may select for different chemical signals in order to, for example, maximize their efficiency (Alberts 1992;Boughman 2002;Symonds and Elgar 2009).…”

Interpopulational differences in chemical composition and chemosensory recognition of femoral gland secretions of male lizards Podarcis hispanica: implications for sexual isolation in a species complex

“…Sexual selection is one of the mechanisms that may facilitate speciation due to divergence in male mating signals and female preferences (Boughman 2001;Panhuis et al 2001), and, thereafter, several species recognition mechanisms may prevent interspecific matings (e.g., Shaw & Parsons 2002;Shine et al 2002). Sex pheromones are important for species recognition in many taxa, and like other signals favored by sexual selection, they may play important roles in speciation (Phelan & Baker 1987;McLennan & Ryan 1999;Wyatt 2003).…”

“…For example, two sympatric sea snakes species might be reproductively isolated due to differences in skin scents (Shine et al 2002). Similarly, sexual isolation exists to a degree among populations of red-garter snakes due to variations in female sexual attractiveness pheromones (LeMaster & Mason 2003).…”

Androgenic control of male-typical behavior, morphology and sex recognition is independent of the mode of sex determination: A case study on Lichtenfelder's gecko (Eublepharidae: Goniurosaurus lichtenfelderi)

“…Reptiles use non-behavioral chemical cues of conspecifics to distinguish between the sexes (Brillet, 1993;Cooper and Steele, 1997;Greenberg, 1943;Houck, 2009;Martin and Lopez, 2011;Mason and Gutzke, 1990;Shine et al, 2002). Additionally, studies on E. macularius suggest that sex steroids alter the chemical cues used for sexrecognition (Flores and Crews, 1995;.…”

“…Studies have also demonstrated that chemical or pheromonal cues play an important role in social interactions of several species of reptiles, including the eublepharid gecko E. macularius, such as for the identification of conspecifics and distinguishing between the sexes (Brillet, 1993;Cooper and Steele, 1997;Greenberg, 1943;Mason and Gutzke, 1990;Shine et al, 2002;reviewed in Houck, 2009;Martin and Lopez, 2011; but see Hews et al, 2011). Furthermore, studies suggest that these chemical cues used for sex recognition may be altered by manipulation of sex steroid levels (Flores and Crews, 1995;.…”