The role of contextual and individual factors in male mate choice for size in a marine snail

Echinolittorina malaccana , a marine gastropod living on rocky shores along the Indo-West Pacific coasts, shows consistent mate choice in which males prefer to mate with females slightly larger than themselves. Previous studies suggest that the strength of this preference is, to a certain extent, context dependent, being influenced by both demographic and individual (potentially genetic) factors. To disentangle how exactly these factors contribute to male mate choice for size in E. malaccana, we employed modified versions of a previous mate choice experiment using a range of female and male size classes. Mate choice was measured from the same male individuals across different experimental days, thus allowing the analysis of the repeatability of male preferences, as well as the comparison of the strength of mate choice with previous experimental designs and data from wild populations. Two parallel experiments (presenting either the same or different female individuals to males across days) were conducted, which allowed the inference of whether size alone, or additionally with other traits, influences mate choice. Results showed that male preference for females slightly larger than themselves remained consistent in both experiments, although its specific characteristics (e.g. strength of preference, extent of size bias) differed from previous studies. This suggests that the estimation of mate choice in E. malaccana is sensitive to experimental approaches and, to a certain extent, context dependent. The repeatability of mate choice (0–0.36) was only significant in the experiments where males were presented with the same female individuals. Mate choice is, therefore, primarily based on size, but other factors such as female quality or imprinting may modify this choice and lead to discrepancies in repeatability between experiments. • Echinolittorina malaccana shows male mate choice for slightly larger females. • The strength of mate choice depends on contextual and demographic factors. • Mate choice shows low to mid repeatability depending on experimental conditions. • Mate choice likely evolved as a trade-off between fecundity and partner availability.