Deep molecular divergence in the absence of morphological and ecological change in the Californian coastal dune endemic trapdoor spider Aptostichus simus

Aptostichus simus is a trapdoor spider endemic to the coastal dunes of cent ral and southern California and, on morphological grounds, is recognized as a single species. Mitochondrial DNA 16S rRNA sequences demonstrate that mo st populations are fixed for the same haplotype and that the population hap lotypes from San Diego County Los Angeles County, Santa Rosa island, and Mo nterey County are extremely divergent (6-12%), with estimated separation ti mes ranging from 2 to 6 million years. A statistical cluster analysis of mo rphological features demonstrates that this genetic divergence is not refle cted in anatomical features that might signify ecological differentiation a mong these lineages. The species status of these divergent populations of A . simus depends upon the species concept utilized. if a time-limited geneal ogical perspective is employed, A. simus would be separated at the base int o two genetically distinct species. This study suggests that species concep ts based on morphological distinctiveness, in spider groups with limited di spersal capabilities, probably underestimate true evolutionary diversity.