Phylogeography and conservation genetics of Californian coastal terrestrial communities: a comparative study using three beetles

1. The coastal beach and dune environments of California host a diverse fauna of specialist arthropods, but are heavily and increasingly impacted by human activities. Little phylogeographical work has examined arthropods in these habitats, despite the importance of arthropods to community health. 2. We analysed the COI mitochondrial gene for approximately 80 individuals from nine dune systems in central and southern California for each of three coastal beetle species, Coelus ciliatus (Tenebrionidae), Hypocaccus lucidulus (Histeridae), and Cercyon fimbriatus (Hydrophilidae), examining overall phylogeographical patterns, inter-population connectedness, and concordance in these among species. 3. All species exhibited significant intra-specific diversity, with Co. ciliatus exhibiting both the lowest overall diversity and the strongest geographical structure. Cercyon fimbriatus was at the other extreme, exhibiting high diversity and essentially no geographical structure. None showed strong concordance with phylogeographical breaks common in either terrestrial or marine organisms, suggesting that coastal specialists may occupy their own unique realm. 4. Few populations of any species are monophyletic, but FST values for Co. ciliatus and H. lucidulus indicated moderately restricted gene flow; populations of Ce. fimbriatus appear panmictic. 5. Our results suggest that coastal beetles may be relatively good colonists, and likely to repopulate appropriate areas where management permits habitat to return to natural conditions.