Biology (B.S.B.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. J Scott Harrison


The Brown widow spider, Latrodectus geometricus, is an introduced species to the southern United States (Brown 2008). The Brown widow is a member of the widow spider genus Latrodectus which includes the southern Black widow (L. mactans) and 29 other venomous species. All species of widow spiders produce venom which is used against both predator and prey. These venoms are composed of several different species-specific toxins, each encoded by a different gene (Graudins 2012). Previous research has shown that positive selection pressures affect the venom of snakes and snails, thus aiding in adaptive potential of the species (Gibbs 2008; Duda 1999). The study presented here was designed to sequence and characterize the α-latroinsectotoxin gene for the Brown and southern Black widow spiders. The sequence data was used to address two objectives: 1) quantify the nucleotide and amino acid divergence in the a-latroinsectotoxin gene between the Brown widow, southern Black widow, and Mediterranean Black widow spiders; and 2) compare levels of divergence to that of α-latrotoxin and a non-toxin gene Cytochrome Oxidase I. Results showed that nucleotide difference lead to large amino acid differences between species in the toxin genes. Nucleotide divergence between species was similar at all three genes while amino acid divergence was 2.3 to 3.2 times higher in the toxin genes relative to the non-toxin gene (COI). High amino acid variation in the toxin genes between species suggests a structural basis exists for potential differences in functionality and toxicity.