Molecular Ecology (2001)

10, 899–910

Blackwell Science, Ltd

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

Aptostichus simus

J. E. BOND,* M. C. HEDIN,† M. G. RAMIREZ‡ and B. D. OPELL§

*Department of Zoology— Insect Division, Field Museum of Natural History, Roosevelt Road at Lake Shore Drive, Chicago, IL 60605 USA,

†Department of Biology, San Diego State University, San Diego, CA 92182 – 4614 USA,

‡Department of Biology, Loyola Marymount University, 7900 Loyola Boulevard, Los Angeles, CA 90045 – 8220 USA,

§Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24060 USA

Abstract

Aptostichus simusis a trapdoor spider endemic to the coastal dunes of central and southern California and, on morphological grounds, is recognized as a single species. Mitochondrial DNA 16S rRNA sequences demonstrate that most populations are fixed for the same haplotype and that the population haplotypes from San Diego County, Los Angeles County, Santa Rosa Island, and Monterey County are extremely divergent (6 –12%), with estimated separation times ranging from 2 to 6 million years. A statistical cluster analysis of morphological features demonstrates that this genetic divergence is not reflected in anatomical features that might signify ecological differentiation among these lineages. The species status of these divergent populations of A. simus depends upon the species concept utilized. If a time-limited genealogical perspective is employed, A. simus would be separated at the base into two genetically distinct species. This study suggests that species concepts based on morphological distinctiveness, in spider groups with limited dispersal capabilities, probably underestimate true evolutionary diversity.

Keywords: Araneae, biogeography, phylogenetics, phylogeography, ribosomal RNA, spider taxonomy

Received 25 May 2000; revision received 3 October 2000; accepted 16 October 2000