Effects of caste on the constitutive and induced expression of genes associated with immunity and detoxification in Formosan subterranean termites

Abstract

Simms, Dawn M., B.S., Louisiana State University, 1997 Master of Science, Spring Commencement, 2013 Major: Entomology Effects of Caste on the Constitutive and Induced Expression of Genes Associated with Immunity and Detoxification in Formosan Subterranean Termites Thesis directed by Associate Professor Claudia Husseneder Pages in thesis, 74. Words in abstract, 268. ABSTRACT Formosan subterranean termites (FSTs) live in dense populations and nest conditions that are conducive to microbial growth. Furthermore, termites are exposed to potential toxic substances in the soil and in their lignocellulose diet. These characteristics, in combination with the specialized caste system of FSTs, make this termite a valuable model for studying insect immunity and detoxification mechanisms. Since workers forage for food, feed their nest mates and care for the brood, they are more likely than soldiers to encounter pathogens and/or toxins. They must, therefore, be better able to defend against these challenges. This study tested the hypothesis that genes associated with immunity and/or detoxification via xenobiotic metabolism in FST have higher constitutive expression level and/or are more readily inducible in workers than in soldiers. FST workers and soldiers were challenged either by bacterial injection or by no-choice feeding with a sublethal concentration (0.5%) of Phenobarbital. Constitutive and induced expression of 5 putative immune response and 5 detoxification genes was measured via quantitative real time qRT-PCR and compared within and between 1) colonies, 2) treatment groups and 3) castes via non-parametric, multivariate analysis of variance. Of the 10 total target genes, none were found to be differentially expressed as an effect of colony. However, treatment type had a significant (P< 0.05) effect on the expression of each of the 8 target genes that were inducible. Caste effects on expression levels were significant in 6 of the 8 inducible target genes. In many cases, target genes were only inducible in the worker caste. Overall, constitutive and induced expression of target genes was significantly higher in workers than in soldiers.