THE EFFECTS OF BODY SIZE ON MATING FEATURES IN A FIELD POPULATION OF THE HERMAPHRODITIC SEA HARE APLYSIA KURODAI BABA, 1937 (GASTROPODA: OPISTHOBRANCHIA)

Abstract

Mating behaviour of the hermaphroditic sea hare Aplysia kurodai Baba was observed in the field to investigate the effects of body size on various mating features. Compared with small individuals, large gastropods mated with more partners both as males and as females, and also with larger partners (size-assor-tative mating). Large gastropods also mated more frequently as females but not as males, and tended to be selected as female mating partners more often than small ones by neighbouring individuals but not as male partners. All these results suggest some mating advantage of large individuals over small ones as females, probably because of the preference by male partners for large female partners. At the same time, the results suggest that the mating advantage of large size as males may be limited, if any. The preference for large female partners is also consistent with the fact that their mating was longer than that of small ones. The greater advantage of large size in mating as females, than as males, means that sexual selection at mate determination acts more strongly on female size than on male size and that the direction of total sexual selection at mating is probably reversed in this hermaphrodite