LEONARD, J.L.*; PEARSE, J.S.; BREUGHELMANS, K.; BACKELJAU, T.; DIEP, P.J.; ROBLES, M.; TOWNSEND, R.C.; Univ. of California, Santa Cruz; Royal Belgian Institute of Natural Sciences, Brussels: Rapid Evolution in Banana Slugs (Ariolimax spp.) (Gastropoda; Stylommatophora: Arionidae): Life History Parameters.

Although the banana slugs of the west coast rain forests are superficially identical from San Diego County to southern Alaska, five largely allopatric taxa have been described on the basis of genital morphology. However, trees derived from a combination of sequence data from mitochondrial DNA CO1 and 16S rRNA genes present a somewhat different picture. The molecular data demonstrate that A. columbianus columbianus is not monophyletic. Populations to the south of Humboldt County, CA are clearly genetically distinct from a northern clade extending to Alaska. The sister taxon of the northern clade of A. c. columbianus is A. columbianus stramineus, and the southern populations previously classified as A. c. columbianus represent a basal clade. Life history data support the separation of A. c. columbianus into two species since under common garden conditions laboratory populations of the northern and southern clades of A. c. columbianus differ in growth rate, egg size and larval coloration. Hatchling color supports the close relationship of the northern A. c. columbianus and A. c. stramineus. Hatchlings of the southern clade of A. c. columbianus are intermediate in color between the dark hatchlings of A. c. columbianus and A. c. stramineus and the very pale hatchlings of A. californicus and A. dolichophallus. Growth rates vary greatly even within clutches for all taxa, with some individuals showing very slow growth. These �midgets� have so far failed to reproduce under laboratory conditions although individuals collected from the field have shown this growth pattern in the laboratory.