Allometric Relationship Between Genitalic Size and Body Size in Two Species of Mordellid Beetles (Coleoptera: Mordellidae)

Abstract

Abstract Although there is often an isometric relationship between the size of nongenital parts and body size, data on insects and spiders indicate that male genitalic size is only slightly influenced by variation in body size. Eberhard et al. (1998) interpreted the low influence of body size on genitalic size as evidence of stabilizing selection based on cryptic female choice. Data on this aspect of sexual selection are rare. We compared the variation in genitalic size with the variation in elytra length as an indicator for body size in the males of two mordellid beetle species, Mordellistena weisei Schilsky and M. bicoloripilosa Ermisch (Coleoptera: Mordellidae), to find additional indications of stabilizing selection on genital traits. The slopes of the allometric regressions between paramere size and elytra length were <1 for left and right parameres in both species, and significantly less in three of the four comparisons. There was no significant correlation between elytra length and genitalic size i...