Abstract
A common pattern of adaptive diversification in freshwater fishes is the repeated evolution of elongated open water (limnetic) species and high-bodied shore (benthic) species from generalist ancestors. Studies on phenotype-diet correlations have suggested that population-wide individual specialization occurs at an early evolutionary and ecological stage of divergence and niche partitioning. This variable restricted niche use across individuals can provide the raw material for earliest stages of sympatric divergence. We investigated variation in morphology and diet as well as their correlations along the benthic-limnetic axis in an extremely young Midas cichlid species, Amphilophus tolteca, endemic to the Nicaraguan crater lake Asososca Managua. We found that A. tolteca varied continuously in ecologically relevant traits such as body shape and lower pharyngeal jaw morphology. The correlation of these phenotypes with niche suggested that individuals are specialized along the benthic-limnetic axis. No genetic differentiation within the crater lake was detected based on genotypes from 13 microsatellite loci. Overall, we found that individual specialization in this young crater lake species encompasses the limnetic-as well as the benthic macro-habitat. Yet there is no evidence for any diversification within the species, making this a candidate system for studying what might be the early stages preceding sympatric divergence.A common pattern of adaptive diversification in freshwater fishes is the repeated evolution of open water (limnetic) species and of shore (benthic) species. Individual specialization can reflect earliest stages of evolutionary and ecological divergence. We here demonstrate individual specialization along the benthic–limnetic axis in a young adaptive radiation of crater lake cichlid fishes.
Highlights
Understanding how ecological, morphological, and genetic variation is created and maintained is of central interest in evolutionary biology
Ecology and Evolution published by John Wiley & Sons Ltd
A range of lower pharyngeal jaw (LPJ)-morphologies were detected within A. tolteca, which varied along the benthic–limnetic axis as typified by the extent of characteristic robust molariform or slender papilliform shape (Fig. 2B) (e.g., Meyer 1990a, b)
Summary
Understanding how ecological, morphological, and genetic variation is created and maintained is of central interest in evolutionary biology. Individual specialization, and divergence along the benthic–limnetic axis in Amphilophus tolteca (Recknagel et al 2013), an extremely young species of Midas cichlids endemic to the maximally 1245 year old crater lake Asososca Managua (Pardo et al 2008). It has been suggested, though not previously tested, that this variable species has differentiated into macrohabitats, and that discrete morphs (or even species) might have evolved within such a short period of time (Elmer et al 2010a). We demonstrated that this young Midas cichlid species has not diverged into discrete ecomorphs or subpopulations along the benthic–limnetic axis as has been previously suspected (Elmer et al 2010a) and rather represents continuous ecological variation and individual specialization
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