Peripheral Budding Following Range Expansion Explains Diversity and Distribution of One-Sided Livebearing Fish.

Peripheral budding occurs when populations diverge from a widespread parental population and speciate along its periphery, facilitated by the interaction of ecological and geographic barriers. This phenomenon results in species that contrast in range size and ecological tolerance and can lead to confounding phylogenies. Here we examine patterns of peripheral budding in the Jenynsia lineata species complex using a genomic approach. The J. lineata species complex is a group of live-bearing fish in South America that shows signals of peripheral budding through asymmetric range sizes, J. lineata being widespread, and with a confounding and unresolved phylogeny. Our goal was to adequately classify the J. lineata species complex, delimit species within the complex, and identify signals of introgression to better understand the underlying evolutionary patterns. We collected 85 samples from the species complex for DNA extraction and performed RAD sequencing to generate genome-wide molecular markers for phylogenetic analyses. We found evidence of six distinct genetic groups within the complex and delimited at least five species, with a new species of Jenynsia in Northern Argentina along the periphery of J. lineata. Jenynsia lineata was recovered as the most recently diverged species in our phylogeny. This placement, along with observed patterns of introgression between species, suggests peripheral budding to have facilitated speciation in the J. lineata species complex, following a range expansion of a parental J. lineata. Our results show genomic patterns associated with peripheral budding and support the utility of using peripheral budding to better understand confounding phylogenetic patterns.