Reproductive anatomy, precopulatory mate guarding, and paternity in the socorro isopod, Thermosphaeroma thermophilum

We examine the reproductive anatomy of both sexes of the isopod Thermosphae roma thermophilum using SEM and light microscopy, and study the occurrence of multiple paternity using allozyme electrophoresis. Female reproductive o penings are found ventrally, under the cuticular plate covering the body be tween the fifth and seventh pereonites. Receptivity for copulation is short during the sexual moult. Sperm from copulation are stored within the ovidu cts, close to the ovary, for up to two weeks before fertilisation and ovipo sition into ventral brood pouches. Sperm are not stored between broods. Mal e genitalia consist of penes with erectile extensions, and curved, channell ed appendices masculinae. We suggest that appendices masculinae either chan nel sperm from the penes to oviduct openings located beneath the cuticular plate, or are used to push aside the cuticular plate for penile intromissio n. Paternity analyses suggest that multiple paternity is uncommon and that precopulatory guarding is an effective mate monopolisation strategy for mal es. We discuss the evolution of reproductive anatomy in the context of inte rsexual conflict, and suggest that conflict resolution may play a prominent role in the evolution of temporally restricted receptivity, male mate guar ding, sperm storage, and delayed oviposition.