GARB, J.G.*; GILLESPIE, R.G.; HAYASHI, C.Y.; Univ. of California, Riverside; Univ. of California, Berkeley; Univ. of California, Riverside: A toxic tale: evolution of the vertebrate toxin gene, α-latrotoxin, in black widow spiders.

The venom of black widow spiders (Theridiidae: Latrodectus) contains multiple neurotoxic proteins, including the vertebrate neurotoxin alpha-latrotoxin (α-LTX). Though the function, structure and gene sequence of α-LTX has been thoroughly characterized in one species of the genus (L. tredecimguttatus), the phylogenetic distribution and evolutionary origin of the α-LTX gene is unknown. In addition to α-LTX, venom of L. tredecimguttatus contains insect and crustacean-specific neurotoxic proteins possessing structural motifs and sequence homology at the amino acid and nucleotide level similar to α-LTX. We hypothesize that these different toxins (expressed by a single individual) are products of a gene family whose members arose via duplication events. Here we investigated the evolution of the vertebrate specific α-LTX toxin by sequencing a fragment of this gene from multiple Latrodectus species in addition to constructing an independent species phylogeny for the genus using the mitochondrial gene COI. Our data indicates that α-LTX occurs across a broad phylogenetic spectrum of Latrodectus species, suggesting that this gene existed in the common ancestor of the genus and that it likely occurs in closely related genera. Across the sequenced region, we observed substantial nucleotide variation, translating into amino acid differences, suggesting the gene is rapidly evolving.