Meeting Abstract

27.3  Wednesday, Jan. 5  The depths of divergence: A phylogenetic analysis of troglomorphic spiders in the genus Usofila (Araneae, Telemidae) AUDISIO, T.L.*; LEDFORD, J.M.; GRISWOLD, C.E.; California State University, Sacramento; California Academy of Sciences, San Francisco tracy@troglophile.com

Spiders in the genus Usofila thrive in cold, moist, dark microhabitats and are exapted for life in caves. Cave obligate, or troglobiotic, Usofila exhibit a suite of troglomorphic characters, however, species delimitation is problematic due to a high degree of morphological homogeneity. Although these taxa lack traditional diagnostic features, they have evolved relatively deep molecular divergence. The evolution of troglobionts can be explained either by the Climatic Relict Hypothesis (CRH) or by the Adaptive Shift Hypothesis (ASH). According to the CRH, troglobionts are relicts of a previously widespread fauna. A climatic shift occurred which pushed these species into caves. Alternatively, the ASH predicts an adaptive shift to troglobiotic life prompted by resource availability. We used a combination of morphological and molecular data to assess species limits within Usofila and test hypotheses of evolution in caves. Scanning electron microscopy and automontage were used to assess morphological variation, including both somatic and genitalic characters. Our molecular data is based on 28S rDNA and CO1 mtDNA from a sample of 51 individuals. Parsimony, Maximum Likelihood, and Bayesian analyses were used to determine phylogenetic relationships and trait data were then mapped on the resulting trees. Independent analysis of CO1 resulted in strong support for several terminal groups but was unable to resolve deeper nodes on the tree. A concatenated analysis resolved the deeper nodes and suggested that troglobionts in the genus Usofila have evolved four times. These results are consistent with the ASH hypothesis, in which multiple independent origins of the troglobiotic lifestyle have occurred.