Doctoral Dissertations

Date of Award

5-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Ecology and Evolutionary Biology

Major Professor

Susan E. Riechert

Committee Members

Gordon M. Burghardt, James A. Fordyce, Todd M. Freeberg

Abstract

The genus Agelenopsis (Araneae, Agelenidae) is a group of morphologically similar funnel-web spiders with overlapping habitat requirements and geographic ranges. Yet, molecular evidence suggests this group has undergone recent speciation with no evidence of hybridization. In this dissertation, I explored courtship divergence as a possible explanation for the formation and coexistence of these species. Courtship behavior patterns, sequences, and vibratory signals were compared across 12 Agelenopsis species and three related outgroup species. Courtship in Agelenopsis was found to be comparatively long but not completely species-specific. To investigate mechanisms of reproductive isolation within the genus, interspecific crosses were staged in the lab between species for two closely related species pairs, one pair being sympatric in distribution and the other peripatric. Vibratory courtship did not function as a reproductive isolating mechanism for either pair. In the sympatric species pair, males displayed significantly less courtship toward heterospecific females than to conspecific females and no interspecific copulations were attempted. Females did not reject males based on their vibratory courtship, rather males rejected females, apparently based on chemical cues. In contrast, there was interspecific courtship and copulation in the peripatric species pair. However, males appeared to encounter mechanical difficulties copulating with heterospecific females and no hybrid offspring were produced. Thus, the sympatric pair was reproductively isolated by barriers acting early in the mating process, while the geographically isolated pair appeared to be isolated by barriers acting very late in the mating process. Though these results did not support a role for vibratory courtship in reproductive isolation, vibratory courtship appeared to be quite important in Agelenopsis. Males continued to court females even after females accepted them, and even behavior occurring late in the courtship sequence varied among species. In comparison to the two more distantly related outgroup species, vibratory courtship in Agelenopsis seems to be under relatively strong sexual selection for long, complex displays.

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