V. Jormalainen et al., Reproductive anatomy, precopulatory mate guarding, and paternity in the socorro isopod, Thermosphaeroma thermophilum, MAR FRESH B, 32(1), 1999, pp. 39-56
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.