Female Pygmy Squid Cryptically Favour Small Males and Fast Copulation as Observed by Removal of Spermatangia

摘要

Females can express mate (or fertilisation) preferences after copulation. In the Japanese pygmy squid, Idiosepius paradoxus, in which males do not show any conspicuous pre-copulatory displays, the females remove the spermatangia attached to their bodies after copulation. In this study, we observed pre- and post-copulatory behaviours and analysed which variables associated with copulation were correlated with spermatangia removal. When females mated with larger males or copulation lasted longer female squid elongated their buccal mass after copulation and removed more spermatangia. We also investigated the effects of spermatangia removal on the retained spermatangia to predict whether cryptic female choice (CFC) influenced fertilisation success. Spermatangia removal by females had a stronger effect on the number of spermatangia retained than did the number of spermatangia ejaculated by males. These results suggest that spermatangia removal after copulation by buccal mass elongation works as a CFC in Japanese pygmy squid, and females cryptically favoured small males and fast copulation.