Traits of a lineage with extraordinary geographical range: ecology, behavior and life-history of the sailfin tetra Crenuchus spilurus

Abstract

Current broad geographical distributions of species can only exist because individuals dispersed from their natal sites. The Amazon’s sailfin tetra Crenuchus spilurus has a geographical range of over 3 million km2, an area 5.7 times larger than France, which includes regions of very distinct abiotic and biotic conditions. What traits may aid in explaining such a broad geographical range, and which make the range exceptional? Here we investigate the species’ ecology and behavior using several approaches: direct field observations, ecological surveys, analyses of reproductive parameters, and diet. Broad trophic niche and frequent reproduction may help explain the wide geographical range, whereas most other traits are typical of short-ranged species: small body size, specific habitat requirements, small populations, low mobility, site-fidelity, low fecundity, and large relative size at maturation. We propose that the broad geographical range of C. spilurus is better explained by passive processes related to river dynamics. Interestingly, this species is one of few strongly dichromatic species of Amazon fish, having mutual signaling during courtship, and males exerting exclusive parental care of eggs and early larval stages. While the combination of such behavioral and ecological characteristics should promote differences among lineages and (eventually) speciation, populations far apart are remarkably morphologically similar. We suggest that ecology along with sexual selection may interplay and contribute to the inter-population morphological similarity, criterion on which Crenuchus is considered a monotypic genus.