Temperature effects on Wolbachia-infected brown widow spiders

REU Fellow: Caroline Willis, Davidson College

Mentor: Dr. J. Scott Harrison

Brown widow spiders (L. geometricus) are an introduced species and have recently spread north from south Florida into Georgia. This spider is infected with Wolbachia, an intracellular bacterium that infects the majority of arthropods and is transmitted through the maternal line. In other species, Wolbachia is known to manipulate the host’s fitness and reproductive ecology, but its effect on the brown widow spider is not very well known. A northward trend in decreasing infection frequency has recently been found in southeastern US populations. This pattern led us to hypothesize that temperature might be affecting the host-Wolbachia interaction. We split 8 egg sacs, 4 positive and 4 negative, and incubated each half at a high or low temperature cycle. We predicted infected eggs incubated in lower temperatures would have either an increased mortality rate or a decreased Wolbachia titer compared to those incubated in higher temperatures. We also predicted there would be a correlation between Wolbachia and mitochondrial densities. No difference in mortality rate was detected, but we did see a significant decrease in Wolbachia density in a lower temperature cycle (p=0.0008). We also saw a significant positive correlation between mitochondria and Wolbachia densities in both treatments.