Divergence in trophic ecology characterizes colonization of extreme habitats

Abstract

Extreme habitats are characterized by the presence of physio-chemical stressors, but also differ in aspects of the biotic environment, such as resource availability or the presence of competitors. The present study quantifies variation in trophic ecology of a small livebearing fish (Poecilia mexicana, Poeciliidae) across four different habitats that included nonsulphidic and sulphidic surface waters, as well as a nonsulphidic and a sulphidic cave. Resource use in different habitat types was investigated using gut content analysis. Populations diverged in resource use from a diet dominated by algae and detritus in nonsulfidic surface habitats to a diet including invertebrate food items in the other habitats. Poecilia mexicana in cave habitats further exhibited a higher dietary niche width than conspecifics from surface habitats. The condition of P. mexicana was analysed using storage lipid extractions. Fish from sulphidic and cave habitats exhibited a very poor condition, suggesting resource limitation and/or high costs of coping with extreme conditions. Finally, divergence in resource use was correlated with variation in viscerocranial morphology. A common garden experiment indicated both a genetic and plastic basis to the morphological variation observed among field populations. It is suggested that the morphological diversification is an adaptation to the differential use of resources among populations.

Reduced opsin gene expression in a cave-dwelling fish

“…selection on the latter two structures may directly affect eye development (Yamamoto et al 2009). Incidentally, cave mollies-like Astyanax cavefish-have also diverged in taste bud density (Parzefall 2001) and jaw morphology (Tobler 2008). This raises the question as to whether common developmental trade-offs underlie the convergent evolution of troglodytic phenotypes.…”

Diet shift of Red Belly Pacu Piaractus brachypomus (Cuvier, 1818) (Characiformes: Serrasalmidae), a Neotropical fish, in the Sepik-Ramu River Basin, Papua New Guinea

“…Niche shifts are not uncommon following the natural expansion of a species distribution range, the colonization of new habitats, or habitat alterations (e.g., Koch et al, 1995;Wanink & Witte, 2000;Tobler, 2008). Despite the preference by both juvenile and adult P. brachypomus for foods derived from terrestrial plants (Knab-Vispo et al, 2003;Lucas, 2008), the species is naturally adapted to live in a variable environment where annual hydrological fluctuation causes major shifts in the availability of food and other resources.…”

Feeding efficiency and food competition in coexisting sexual and asexual livebearing fishes of the genus Poecilia

“…As the main food source of mollies is detritus (Darnell 1962;Winemiller 1993;Tobler 2008;Scharnweber et al unpubl. data), which is rarely limiting (Moyle and Light 1996), it is likely that food competition generally plays a minor role in mollies.…”