Broken ring speciation in California mygalomorph spiders (Nemesiidae, Calisoga)
Abstract
Idealized ring species, with approximately continuous gene flow around a geographic barrier but
singular reproductive isolation at a ring terminus, are rare in nature. A broken ring species model
preserves the geographic setting and fundamental features of an idealized model but
accommodates varying degrees of gene flow restriction over complex landscapes through
evolutionary time. Here we examine broken ring species dynamics in Calisoga spiders, which
like the classic ring-species Ensatina salamanders, are distributed around the Central Valley of
California. Using nuclear and mitogenomic data we test key predictions of common ancestry,
ring-like biogeography, biogeographic timing, population connectivity and terminal overlap. We
show that a ring complex of populations shares a single common ancestor, and from an ancestral
area in the Sierra Nevada mountains, two distributional and phylogenomic arms encircle the
Central Valley. Isolation by distance occurs along these distributional arms, although gene flow
restriction is also evident. Where divergent lineages meet in the South Coast Ranges we find rare
lineage sympatry, without evidence for nuclear gene flow, and with clear evidence for
morphological and ecological divergence. We discuss general insights provided by broken ring
species, and how such a model could be explored and extended in other systems and future
studies.
Monjaraz-Ruedas, R., Starret, J., Leavitt, D., & Hedin, M. (2024). Broken ring speciation in California mygalomorph spiders (Nemesiidae, Calisoga).
https://doi.org/10.1086/730262
