Body shape vs. colour associated initial divergence in the Telmatherina radiation in Lake Matano, Sulawesi, Indonesia.

Highly polymorphic colouration patterns are often associated with sexual selection in fish and can be the initial cause of divergence among closely related taxa. Here we use genetic, body colour and geometric morphometric data collected on 118 fish from Lake Matano, Sulawesi, Indonesia to test if colouration is the initial cause of divergence in the radiating Telmatherina genus. Results reveal that all Telmatherina previously described in this system can be categorized into three mitochondrial lineages and that colouration is only weakly associated with early divergence. Clade-specific body shapes, however, likely adapted to microenvironments are key to the initial divergence in this system. Data also show that although colourations were not likely instrumental in seeding divergence in these fish, they appear to have developed in parallel within each clade. Our results are consistent with an emerging pattern repeated in many vertebrate radiations, whereby divergence by colouration or other display traits is preceded by specialization to environmental adaptive peaks.