Reproductive behaviour of mangrove littorinid snails: how do males successfully mate with females?

Abstract

Diverse reproductive behaviours in animals are developed to increase individual fitness. Some behavioural traits are selected to overcome environmental constraints, whereas others are evolved through sexual selection to maximize reproductive success. Most littorinid snails in the genus Littoraria inhabit mangrove trees in the Indo-Pacific region. Searching for mates within the complex 3-dimensional habitat of tree leaves, branches and trunks would appear a difficult task for these snails. Field studies of two co-occurring species in Hong Kong, Littoraria ardouiniana and L. melanostoma, however, showed that these species can successfully locate mates as overv 90% of mating pairs were 'true' pairs (a male mating with a conspecific female). This success is achieved through males of both species following mucus trails to locate conspecific females during the mating season. In both species, males were also capable of detecting the direction (polarity) of the trails of conspecific females. “Fighting” behaviour, which involves two males aggressively pushing each other when they encounter a female, was also observed in L. ardouiniana but not in L. melanostoma. Such aggressive behaviour during mate acquisition can be attributed to the male-biased sex ratio in natural populations of L. ardouiniana, which may drive competition for mates amongst males.