Evidence for multiple paternity in the trapdoor spider Bothriocyrtum californicum (O. Pickard-Cambridge, 1874) (Araneae: Halonoproctidae)

Inbreeding avoidance via polyandry is a common response to combat inbreeding depression across multiple taxa, but has never been investigated in the Halonoproctidae. With a member of this family, the trapdoor spider Bothriocyrtum californicum (O. Pickard-Cambridge, 1874), Ramirez et al. (2013) found no evidence for inbreeding in several southern California populations, but did not examine polyandry. Hence, in this study, we determined the extent of multiple paternity in broods of B. californicum. To do so, we gathered broods and mothers from two sites in Los Angeles, CA, and then genotyped each mother and up to 50 spiderlings for variation at the phosphoglucomutase locus. Among nine sets of broods, six showed significant deviations from the Mendelian genotype ratios expected under the hypothesis of single paternity. This indicates that B. californicum females sometimes mate with multiple male partners. This is certainly an adaptive feature for a low-dispersal trapdoor spider residing in island-like units where inbreeding may be more likely.