Microgeographic population structuring in a genus of California trapdoor spiders and discovery of an enigmatic new species (Euctenizidae: sp. nov.).

The recognition and delineation of cryptic species remains a perplexing problem in systematics, evolution, and species delimitation. Once recognized as such, cryptic species complexes provide fertile ground for studying genetic divergence within the context of phenotypic and ecological divergence (or lack thereof). Herein we document the discovery of a new cryptic species of trapdoor spider, sp. nov. Using subgenomic data obtained via target enrichment, we document the phylogeography of the California endemic genus and its constituent species, which also includes and . Based on these data we show a pattern of strong geographic structuring among populations but cannot entirely discount recent gene flow among populations that are parapatric, particularly for deeply diverged lineages within . The genetic data, in addition to revealing a new undescribed species, also allude to a pattern of potential phenotypic differentiation where species likely come into close contact. Alternatively, phenotypic cohesion among genetically divergent lineages suggests that some level of gene flow is ongoing or occurred in the recent past. Despite considerable field collection efforts over many years, additional sampling in potential zones of contact for both species and lineages is needed to completely resolve the dynamics of divergence in at the population-species interface.