LEONARD, J.L.*; PEARSE, J.S.; BREUGHELMANS, K.; BACKELJAU, T.; Univ. of California, Santa Cruz; Royal Belgian Institute of Natural Sciences, Brussels: Rapid Evolution in Banana Slugs (Ariolimax spp.) (Gastropoda; Stylommatophora: Arionidae): Sexual Behavior Indicates the Direction of Evolution.

The diversity of genital morphology in the genus Ariolimax is suggestive of rapid evolution. This view is supported by sequence data from the mitochondrial DNA CO1 ,and 16S rRNA, genes and observations on sexual behavior. In the molecular data, A. californicus and A. dolichophallus are indistinguishable. Comparison of the courtship and mating behavior of Ariolimax spp. suggests that the bouts of brief, unilateral copulations characteristic of A. californicus are a derived character; the pattern of a single, 2 h long, simultaneously reciprocal copulation found in A. dolichophallus is more similar to the reciprocal copulation found in A. columbianus stramineus and the southern clade of A. c. columbianus. This supports a phylogeny based on molecular data in which the californicus/dolichophallus clade is derived from a more basal clade including A. c. stramineus . The californicus/dolichophallus clade has a derived courtship behavior involving obvious swelling of the genital area, prolonged (2h), vigorous, Biting and Head-swinging, and a penis eversion behavior involving initial protrusion and intromission of a basal segment of the penis. In contrast, courtship in A. c. stramineus is brief (20 min) and much less conspicuous, with occasional Biting and low amplitude Head-swinging. Penis eversion occurs earlier in courtship and genital swelling is not obvious. The molecular data suggest that the southern clade of A. c. columbianus, with its long (sometimes greater than 24 h) simultaneously reciprocal copulations and aphallic morph may be basal. This suggests that the apophallation behavior described in the californicus/dolichophallus clade is derived.