Leonard - Sexual Selection and Mating Systems in the Genus Ariolimax (Stylommatophora: Gastropoda)

Sexual Selection and Mating Systems in the Genus Ariolimax(Stylommatophora: Gastropoda)

Janet L. Leonard¹ , Jane A. Westfall² , and John S. Pearse¹

¹ Joseph M. Long Marine Laboratory, University of California-Santa Cruz, Santa Cruz, CA 95060, jlleonar@ucsc.edu; ² Department of Anatomy & Physiology, Kansas State University, Manhattan, KS 66506-5802

It has been hypothesized that where genital characters are taxonomically important at the species level, sexual selection has been important. The taxonomy of the genus Ariolimax, the banana slugs of North America, has been based on genital characters. Behavioral and morphological studies of Ariolimax spp. provide substantial evidence for sexual selection. Morphological studies show a previously undescribed genital polymorphism in Ariolimax buttoni. Aphallate individuals of this specieswere previously termed Aphallarion buttoni whereas euphallate forms had been synonymized with A. columbianus. This phally polymorphism would reduce the number of individuals capable of mating as males in populations of A. buttoni, thereby producing a skewed sex ratio. Behavioral data show that all three species of the Meadarion subgenus (A. californicus, A. brachyphallus and A. dolichophallus), share a lengthy courtship behavior. A. brachyphallus may also show penial stroking. A. stramineus of the subgenus Ariolimax has a very different courtship behavior involving brief (20 m) mutual exploration with early penis eversion.Apophallation has been observed in A. californicus and A. dolichophallus. Mating encounters involve a single 2h simultaneously reciprocal intromission in A. dolichophallus; bouts of briefunilateral intromissions in A. californicus and A. brachyphallus; a 2h simultaneously reciprocal intromission preceeded by a brief unilateral intromission in A. stramineus and a > 24 h reciprocal intromission in A. buttoni. Phally polymorphism, apophallation, lengthy and elaborate courtship and the patterns of reciprocity observed provide circumstantial evidence for sexual selection in this genus.