Phenotypic traits meet patterns of resource use in the radiation of “sharpfin” sailfin silverside fish in Lake Matano

Abstract

Disruptive natural selection on traits related to resource exploitation may lead to differential adaptation and finally to speciation. Trait utility, the performance of traits in terms of fitness, is a central criterion for the recognition of adaptive radiation. Utility of morphological structures involved in foraging can be detected by relating their variation to individual resource use. Here, we test for trophic adaptations in the radiation of ''sharpfin'' sailfin silversides (Atheriniformes: Telmatherinidae), endemic to ancient graben-lake Matano in central Sulawesi (Indonesia). This small species-flock is characterized by high phenotypic diversity, including traits most likely related to feeding ecology. Previous analyses suggest that species boundaries are porous, indicating very recent or possibly ongoing processes of species flock formation. To test for adaptation to resource use in this radiation, we compared morphological traits among trophic groups of individuals as identified by stomach content analyses. We analyzed variation in candidate structures or structural complexes commonly recognized as indicative of trophic adaptation in fish radiations, including shapes of body, oral and pharyngeal jaws, gill rakers and body size. We found fine-scaled morphological differentiation according to feeding habits, covering all traits analyzed. Fish-, shrimp-and egg-feeders were most distinct, with major axes of morphological variation fitting patterns of adaptation reported from other lacustrine fish radiations. Thus, the present results are consistent with fine-scaled morphological adaptation to resource use, supporting the adaptive character of the sharpfin sailfin silverside radiation.Electronic supplementary material The online version of this article (

Rugged adaptive landscapes shape a complex, sympatric radiation

“…Morphological differentiation among sharpfin morphotypes (figures 2a and 3) is consistent with adaptations predicted by their respective ecological niches [23,38,62,63,66]. These include short and widely spaced gill rakers in fish and shrimp predators, and long and closely spaced gill rakers in sharpfins feeding on fish eggs, zooplankton or insects (figures 2a and 3).…”

“…The species flock is endemic to Lake Matano [20] and consists of several ecological specialists with conspicuous morphological and behavioural adaptations to various ecological niches [21][22][23]. However, specific morphotypes do not form well-sorted clades in phylogenetic analyses based on mitochondrial markers [24].…”

DNA Barcoding Indonesian freshwater fishes: challenges and prospects

“…73,76,79]. The absence of species-level resolution in mitochondrial markers is not unexpected in evolving radiations, particularly when ecological speciation takes place in the absence of geographical barriers, as observed in the endemic lacustrine species of Lake Matano [80,81]. Introgressive hybridization among closely related species is also known to blur phylogenetic signal, particularly for maternally inherited mitochondrial markers.…”

Alternative egg-feeding tactics in Telmatherina sarasinorum, a trophic specialist of Lake Matano’s evolving sailfin silversides fish radiation

“…Egg-feeding, among other trophic specialisations, has also been reported in the adaptive radiation of sailfin silverside fishes (Teleostei: Atheriniformes: Telmatherinidae) endemic to the ancient graben Lake Matano in the central highlands of Sulawesi (Kottelat, 1991;Gray & McKinnon, 2006;Pfaender et al, 2010). This ultraoligotrophic (Haffner et al, 2001) and extraordinarily deep ([590 m) lake is the hydrological head of 'Wallace's dreamponds', i.e.…”