Masked behind Cnesterodon decemmaculatus (Cyprinodontiformes: Poeciliidae): integrative taxonomy uncovers a new Cnesterodon species with broad ecological and biogeographic implications

Abstract

A new species of poeciliid, Cnesterodon pampeanus (Cyprinodontiformes), is described from Pampean streams, Argentina, based on integrative taxonomy. Generalised discriminant analysis of morphometric data allowed to discriminate the new species from its congeners, providing a reliable tool for an accurate identification of Cnesterodon species. Additionally, phylogenetic reconstructions of COI sequences revealed that the new species is grouped in a well-supported clade, validating the erection of a new Cnesterodon species. Up to the present, only Cnesterodon decemmaculatus (Jenyns, 1842) has been recorded inhabiting freshwater environments south of La Plata River, being considered one of the most widespread fish species in the Pampa biome. However, the geographic distribution of sequenced specimens, previously misidentified as Cnesterodon decemmaculatus, suggests that the newly described species actually has the southernmost distribution, having remained masked behind Cnesterodon decemmaculatus for years. The sympatric and syntopic presence of at least two species of Cnesterodon in thePampas region implies that caution should be exercised when using Cnesterodon decemmaculatus to study processes that shape their genetic structure, since differences among populations can be overestimated if both species are considered as a single one. Additionally, differences in the morphology of Cnesterodon decemmaculatus previously attributed to the effect of pollutantsmay instead be interspecific variability.