The ecomorphological diversity of Amazonian stream fishes is constrained by phylogenetic relationships

Abstract

Phylogenetic history and environmental conditions determine the trait diversity of species pools. Stream fishes have diversified into a wide range of body and oral shapes that allow a similarly wide range of functional traits, but that can be determined by habitat type and taxon. Herein, we analyzed 16 ecomorphological traits of nearly 400 fishes inhabiting streams distributed across the Brazilian Amazon to (i) describe the main axes of ecomorphological variation of Amazonian stream fishes; (ii) quantify the proportion of the potential combination of traits that is displayed by the regional pool of species; (iii) evaluate the distribution of different taxonomic groups in those axes; (iii) determine the overall contributions of the taxonomic groups to regional ecomorphological diversity. Our results show that Amazonian stream fishes concentrate around multiple combinations of traits defined by five axes of ecomorphological variation. The benthic-nektonic axis segregates fishes with upper-positioned eyes and wide mouth gapes from fishes with lower-positioned eyes and narrow mouth gapes related to narrower body shapes. Benthic fishes further differ in three groups of species depending on ecomorphological traits coupling different strategies for feeding and swimming. Taxonomic order and family constrained species position along these axes of variation and consequently determined their contribution to overall ecomorphological variation. Overall, we show that five axes related to habitat and food partitioning explain most of the ecomorphological diversity of Amazonian stream fishes, but taxonomic identity determines species suite of traits.