No evidence of size-assortative mating or sex-dependent trail following and temporal and spatial variation in sexual size dimorphism and sexual selection in <i>Nerita yoldii</i>

ABSTRACT Size-assortative mating is a well-documented pattern in a wide diversity of animals, including marine gastropods. In most cases, positive assortative mating by size is due to males mating with larger, more fecund females, which is often mediated by males following female mucus trails in gastropods. Fecundity selection has been invoked to explain not only size-assortative mating but also sexual size dimorphism in most taxa studied to date. To widen the generality of these hypotheses, we tested for these patterns in the intertidal, dioecious gastropod Nerita yoldii across sites and years in Hong Kong. In N. yoldii, females were larger than males in most mating pairs, and size was generally a predictor of fecundity in females. There was, however, no evidence of size-assortative mating or sex-dependent mucus trail following. There was also no clear pattern of sexual selection, measured using sexual selection intensity, which varied between sites and years. Overall, the reproductive behaviour of N. yoldii was dependent on site and year and did not conform to the common patterns found in other marine gastropods. Evidence from this tropical nerite, therefore, suggests sexual selection should be considered as only one of several potential mechanisms underlying these common patterns.