Different feeding preferences of males and females of three sunray fish species reduce competition for food supply

Food preferences and occurrence of the three different Telmatherina species (“roundfin”).


Sexual dimorphisms in sunray fishes probably reduce competition for ecological resources and thus avoid intraspecific competition.

On the Indonesian island of Sulawesi lives the small group of “round fins”. Here we are dealing with three fish species that evolved within the adaptive radiation of the sunray fishes. The three species have specific adaptations to different prey and different habitats in their habitat, thus occupying their own ecological niche. We have known for several years that roundfin biology and ecology differ not only between species, but also between sexes within a species. For example, females of a species eat significantly more insects, whereas males eat significantly more snails.

This study was designed to find out whether these ecological differences are also reflected in the morphology of the fish. For this purpose, three ecologically relevant head structures were examined in more detail: the gill cover, the “pharyngeal jaw apparatus” for grinding food, and the oral cavity. We were able to show that these structures differ significantly between the sexes. The more the sexes differ in their ecological adaptations, the stronger the morphological differences between the sexes. These sexual dimorphisms likely represent adaptations to the respective ecological niches of the sexes. The ability to use different foods reduces competition for prey and habitat within a species, and thus reduces intraspecific competition for ecological resources. This sexual differentiation could allow emerging species to become better established in their habitat.

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