Honors College Theses

Publication Date

2017

Major

Biology (B.S.B.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. J. Scott Harrison

Abstract

The brown widow spider (Latrodectus geometricus) is thought to be native to South America or Southern Africa, but its distribution has expanded to most continents by human introduction. In the continental USA, L. geometricus was first documented in south Florida in the 1930’s. In the early 2000’s a population expansion occurred, and this species is now found in Florida, Georgia, South Carolina, Alabama, Mississippi, Louisiana, Texas, and southern California. Introduced species may face many obstacles when establishing a new population. One common obstacle might be severe inbreeding following founder events or genetic bottlenecks. The purpose of this study was to quantify inbreeding depression in an introduced population of L. geometricus. I predicted that if inbreeding was common for many generations during the introduction, many deleterious alleles should have been purged resulting in lower genetic load and consequently minimal fitness differences between inbred and outbred offspring. To assess the consequences of inbreeding, I compared hatching number between clutches produced by full-sibling crosses and crosses between unrelated individuals. The percentage of unhatched eggs/clutch was roughly 3-fold higher in inbred relative to outbred offspring, indicating a fitness cost to inbreeding. The results suggest that significant inbreeding has been avoided during the introduction of this species in the southeastern US. This may be the result of multiple and continued introductions being common during the recent range expansion leading to a minimization of inbreeding.

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