| Abstract
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Understanding factors generating biodiversity are critical in a world where continued anthropogenic disturbances threaten the survival of an increasing number of species. Ancient lakes provide ideal systems for the study of such factors as early invading species have a high potential for speciation and adaptive radiation. Lake Matano, a tropical island lake located on Sulawesi, Indonesia, is estimated to be 2-4 million years old. This isolated lake is characterized by very low productivity and has a high degree of endemism. The purpose of this research was to assess the potential for adaptive radiation within the fish community of this system and determine its causal root(s). First, genetic data demonstrated that, of the endemic fish genera in this system, Telmatherina is monophyletic and demonstrates greater genetic diversity than any other genus in this system. Telmatherina are also characterized by more numerous colouration patterns and exhibits higher variation in feeding traits than the other genera in this lake as determined from standard morphometrics. These data support the radiation of Telmatherina in Lake Matano due to either sexual selection among the varied colouration types, or resource partitioning in this trophically limited system. A second investigation used genetic, shape and trophic data to identify the number of Telmatherina species present in Lake Matano and determine if feeding trait differences among them were of an adaptive nature. Genetic data revealed that all Telmatherina previously described could be categorized into three distinct lineages. Skull and pharyngeal jaw features showed clear distinction among the three lineages and these data corresponded to lineage-specific diets determined from gut content and stable isotope analyses. Results separated the 3 Telmatherina lineages into a littoral specialist, a pelagic specialist and a generalist making use of both littoral and pelagic resources. The generalist was also found to be genetically basal to the two specialist lineages suggesting that the generalist is the most recent common ancestor to both specialists and that the radiation of Telmatherina is ongoing. A third study used genetic, colouration and geometric shape analyses to assess whether or not the sympatric radiation of Telmatherina was primarily driven by sexual selection, specifically among colouration types, or if body shapes were more important to initial divergence. Results confirmed the Telmatherina genetic lineages and showed that colouration had little to do with initial divergence. Rather, body shape differences, most notably along the axis of body compression, but also in fin shape, caudal peduncle and head region, were key features segregating Telmatherina into three genetic lineages. Accrued data from this research provide strong support for the adaptive radiation of Telmatherina in Lake Matano, as a consequence of ecological selection within this trophically limited system and demonstrates one of the clearest examples of this phenomenon in a natural setting.
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