Subterranean Fishes of the World

5247

2008

Bulletin of Fish Biology

69-80

10

Summary: Atlantic mollies (Poecilia mexicana) in the southern Mexican Cueva del Azufre system inhabit a variety of different habitat types, some of which are characterized by perpetual darkness (caves) and/or the presence of toxic hydrogen sulfide. Previous studies demonstrated heritable differences among populations from adjacent but ecologically divergent habitat types in morphology, behavior and life history. Here we examined male mating behavior in fish from the most extreme habitat, the sulfidic Cueva del Azufre (“cave mollies”), and a nearby non-sulfidic river (i.e., the least extreme habitat type) as well as hybrids (F1 and F2) between both populations. Compared to surface-dwelling males, mollies showed strongly reduced sexual activity, which may be an adaptation to life in a stressful, energy-poor environment. However, sexual activity of first-generation hybrids even exceeded the level of the surface fish, suggesting that a heterosis effect leads to strongly increased sexual activity. To avoid unwanted copulations, surface females are more vigilant in the presence of a male than in the presence of a female, which detracts from the time spent feeding. Reduced sexual activity in cave mollies comes along with reduced vigilance in females, so cave molly females do not feed less when accompanied by a male. Despite increased sexual activity in F1 hybrid males, F1 females did not feed less in the presence of a male (i.e., resumed feeding even though males frequently attempted to mate) and also no effect was seen in the F2 hybrids. This could indicate a breakdown of coevolved gene complexes of (i) male persistence traits (i.e., population-specific levels of male sexual activity) and (ii) female resistance traits (vigilance and flight behavior). Key words : cavefish, coercive mating, heterosis effect, hydrogen sulfide, sexual conflict

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