2010, pp 465-483
Date: 20 Jun 2010

Beyond Sympatric Speciation: Radiation of Sailfin Silverside Fishes in the Malili Lakes (Sulawesi)

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Adaptive radiations of plants and animals play an important role as model systems in speciation research. Rapid emergence of biological diversity provides opportunities to study adaptive and non-adaptive factors leading to speciation, including the role of spatial factors and ecological, behavioral and genetic mechanisms potentially driving speciation processes. The radiation of sailfin silversides (Atheriniformes: Telmatherinidae) endemic to “Wallace’s Dreamponds”, i.e., the Malili Lakes in Central Sulawesi (Indonesia), allows for testing hypotheses of speciation processes under different geographic settings. Compared with other well-known freshwater fish radiations, the Telmatherinid system is of intermediate size in terms of both, geographical size and organismic diversity. Phylogenetic analyses provide evidence for multiple clades that were connected secondarily through reticulate evolution, but combined analyses support an ancient monophyletic origin of all Telmatherinidae clades in Lake Matano. The consensus view is that the lake contains two reciprocally monophyletic groups of sailfin silversides, highly diverse “sharpfins” heavily introgressed by stream populations, and less diverse “roundfins” not affected by allochthonous introgression. Genetic, morphological, habitat-utilization, trophic, and mate-choice data demonstrate that the most plausible hypothesis for the origin of roundfins is by sympatric speciation. Substantial but not absolute restrictions in gene flow coupled with morphological and behavioral adaptations to distinct ecological niches support the hypothesis that natural selection coupled with assortative mating drives speciation processes in roundfins. In contrast, discrete male color polymorphisms can be explained by sexual selection, but appear not to be associated with population divergence. In line with evidence for adaptive radiation in sharpfins, natural selection for distinct resources is certainly a major force shaping diversity in this lacustrine radiation. However, the role of divergent sexual selection on divergence of ecologically diverse sharpfins remains to be tested.