Fighting for mates: the importance of individual size in mating contests in rocky shore littorinids

Abstract

they generally challenged defenders that were smaller than themselves, suggesting an ability to detect rival size before entering into a contest in this species. When sizes of the contestants were similar, defenders were more likely to win contests in E. malaccana but not in E. radiata. Evidence for pure self-assessment of RHP and the ability to assess resource value in challengers was found in E. malaccana. Different fighting strategies appear to have evolved in these congeneric marine snail species, and decisions based on male and female sizes play an important role in determining male reproductive success.

The causal relationship between sexual selection and sexual size dimorphism in marine gastropods

“…The male sexual selection pattern (SSm from Table 2), on the other hand, can be caused by male-male competition. Aggressive physical male-male contests, for example, have been reported in E. malaccana and E. radiata (Ng et al, 2016) as well as in several other littorinids (Gibson, 1965;Ng & Williams, 2014;Zahradnik et al, 2008) and other marine gastropods (e.g. Strombus pugilis, Bradshaw-Hawkins and Sander 1981).…”

“…Strombus pugilis, Bradshaw-Hawkins and Sander 1981). In the littorinid species where such contests were observed, larger m s m ft w t s 'm t g tt s' w t sm m s pu t g with females were displaced (Ng et al, 2016;Ng & Williams, 2014).…”

“…In this study, field measurements of the whole mating process (i.e. from trail following to copulation, see detailed text and video descriptions in Ng & Williams, 2014) (Ng et al, 2016).…”

“…To test for generality in the patterns of sexual selection on size, we used published material from Littoraria flava, Littorina saxatilis (Cardoso, Costa, & Loureiro, 2007; Erlandsson & Rolán-Alvarez, 1998), and Echinolittorna malaccana and E. radiata (Ng et al, 2016). In this study, we also incorporated unpublished data from The distance of these reference snails to the mating pair depended on snail density…”

“…During copulation, selection occurs via inter-individual interactions. Male-male competition can, for example, occur when a rival male physically challenges a mating male (Gibson, 1965;Ng, Davies, Stafford, & Williams, 2016;Zahradnik et al, 2008). In a few species, females may reject males, through mechanisms such as pushing away or even biting the penis (e.g.…”