An epoch abroad: how & when Cyprinodon may have reached the Great Basin (& points along the way)

Authors: Christopher Hoagstrom, Megan Osborne

Year: 2022

Abstract

Most native fishes of the Colorado River drainage are evolutionary affiliated with rivers of the Pacific Coast. Genus Cyprinodon is an exception, affiliated instead with the Gulf of México. In the Late Miocene, this genus produced five western mitochondrial lineages in relative synchrony. Four of these have clear affiliations with Late Miocene drainages then tributary to the Gulf of México. A fifth (western clade) occupies the Río Grande Rift, lower Colorado River drainage, and adjacent Southern Great Basin, but has no clear route from the Gulf of México to these regions. Although present in several other Cyprinodon clades, the western clade shows no evidence of secondary contact with other clades, consistent with a hypothesis that it remained isolated after its origin. Geomorphic evidence suggests a possible Late Miocene route into the nascent Río Grande Rift (Albuquerque Basin) from an area of widespread dissolution subsidence on the southern High Plains. From there, an isolated founder population could have expanded in distribution downstream as the upper Río Grande expanded southward along the rift. Populations in the southern rift potentially had westward access through the Cochise Filter Barrier via a series of closed basins that held warmwater lakes in the middle Pliocene. A possible route into the Safford Basin could have established the clade in the Colorado River drainage, allowing colonization of Gila River and Lower Colorado River, along the eastern boundary of the Southern Great Basin. Divergence estimates for the above evolutionary events correspond with timings of potential access based on geological and environmental evidence, but more focused study is needed to better support or refute each event.