PEARSE, J.S.*; LEONARD, J.L.; BREUGELMANS, K.; BACKELJAU, T.; Univ. of California, Santa Cruz; Univ. of California, Santa Cruz; Royal Belgian Istitute of Natural Sciences, Brussels; Royal Belgian Istitute of Natural Sciences, Brussels: COI data reveal surprises in clades of banana slugs (Stylommatophoa: Arionidae, genus Ariolimax).
Banana slugs occur along the west coast of North America, from Alaska to southern California. Using genital morphology, workers in the early and mid 20th century established 5 allopatric taxa: A. columbianus (SE Alaska to central California, including the Sierras), A. columbianus stramineus (central and southern California), and 3 taxa restricted mainly to the San Francisco Peninsula: A. dolichophallus (Santa Cruz and western Santa Clara counties), A. californicus (San Mateo County), and A. californicus brachyphallus (San Francisco County). Phylogenetic analyses of COI data for 130 individual banana slugs from Alaska to San Diego County, along with preliminary ITS-1 and 16S rRNA data, modify this picture. Our data suggest two clades within the northern columbianus clade: one occurring from SE Alaska and the Queen Charlotte Islands to extreme northern California displays the least structure, and a second occurring in north-central California, including San Francisco, the islands in the Sacramento River Delta, and the Sierras, displays the most structure. The stramineus clade was distinct and found in south-central coastal California and the Channel Islands, and an undescribed taxon was found on Mount Palomar, San Diego County. The californicus and dolichophallus forms remain restricted mainly to the San Francisco Peninsula, but dolichophallus is paraphyletic with respect to californicus, which is only weakly monophyletic. No specimens were collected with sequences that could be assigned to brachyphallus. In californicus and dolichophallus, despite their close relationship, mating behavior and egg size are notably distinct, as are the genitalia; sexual selection appears to be leading to incipient speciation.
