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Junxia Zhang
Graduate student
University of British Columbia
Zoology
Vancouver, BC Canada
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| Intersexual coevolution of genitalia in euophryine jumping spiders (Araneae: Salticidae): sexual selection or “lock-and-key”? |
| Author(s) |
Junxia Zhang, Wayne P Maddison |
| Info |
Talk category:
Behavior |
| Abstract |
A long-standing question in spider evolution is the extent to which genitalia are sexually selected or serve as species recognition mechanism (“lock-and-key”). We investigated the lengths of the male embolus and female copulatory duct of euophryine jumping spiders, and found they are positively correlated among species. This correlation confirms an interaction, but it does not indicate the selective mechanism involved. Intra-specific variation of these traits in ‘Sidusa’ recondita and ‘Cobanus’ cambridgei shows negative allometry. While this may appear to favor the “lock-and-key” scenario, it could also occur via post-copulatory sexual selection. The size-corrected intra-specific variation is high for genitalia, which has been argued to indicate sexual selection, but could also arise through developmental mechanisms to achieve negative allometry. However, if high intra-specific variation is indicative of sexual selection, there remains the question of the mechanism: cryptic female choice or sexual antagonistic coevolution. An antagonistic arms race of ever-increasing embolus and CD length can be rejected, as decreases appear to occur as often as increases on the phylogeny. Unlike the genitalic traits, the pre-copulatory sexually-selected traits (male chelicerae) tend to show positive intra-specific allometry, and thus may have evolved under strong directional selection. The fact that the species with stronger somatic sexual dimorphism (‘Cobanus’ cambridgei) has the lower intra-specific variation in genitalia may imply a trade-off between pre- and post-copulatory sexual selection. The mechanisms underlying the variability of euophryine genitalia remain unclear, and in fact sexual selection and species isolation mechanisms in principle could coexist. |
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