Saltwater tolerance and the Holarctic distribution of freshwater percid fishes

Freshwater organisms have long been valuable indicators in historical biogeography due to their habitat specificity. This study focuses on Percidae, a species-rich lineage of freshwater fishes with a Holarctic distribution, comprising nearly 25% of North America's freshwater fish species diversity. Despite their ecological significance, the evolutionary relationships within Percidae and their biogeographic implications remain incompletely understood. We estimated the ancestral geographic distributions of Percidae using a fossil-calibrated phylogeny based on newly generated ultraconserved element data. Our results indicate an initial vicariance event followed by two independent dispersal events from Eurasia to North America. While the precise timing of these biogeographic events remains challenging to correlate with hypothesized paleogeographic connections or the fracture thereof, ancestral state reconstruction suggests that early Percidae evolution involved tolerance to brackish habitats. This finding challenges the necessity of ephemeral land bridges in explaining the geographic distribution of Holarctic freshwater fishes. Instead, it proposes a more complex dispersal scenario involving saltwater tolerance. These results contribute to our understanding of the processes that shaped the temperate freshwater biodiversity hotspot in eastern North America and provide new insights into the biogeographic relationships between Eurasia and North America.