Species-specificity of male genitalia is characterized by shape, size, and complexity
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While species-specificity of male genitalia is a well-documented pattern among insects which can be explained by sexual selection, there are a number of species that appear to lack species-specific male genitalia despite the presence of stimulation of female genitalia by male genitalia and remating by females which are the conditions for the sexual selection by cryptic female choice. Such contradiction to the general pattern is found in the species belonging to the grasshopper genus Schistocerca whose male genitalia are known to be very similar across species and not useful taxonomically. In this study shapes and sizes of two functionally different genital structures of four Schistocera species were examined using geometric morphometic analyses. Both shape and size fail as a species-specific character when examined individually because there were extensive overlaps of both variables among species. However, when both variables were examined simultaneously, distinct species-specific clusters were recovered in each genital structure, as well as two structures combined. This finding suggests that the male genitalia of Schistocerca should be considered species-specific because the combination of shape and size of both genital structures is unique for each species even if the individual feature might be similar between species. The idea of speciesspecificity in insect systematics when applied to male genitalia, therefore, needs to be re-examined and should be applied to the shape and size and the composite nature of the structure. © Koninklijke Brill NV, Leiden, 2009.
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