Thesis Format

Monograph

The correspondence between genotype at bacterial and viral-facing Toll-like receptors and preen oil chemical composition in song sparrows

Justin To, Western UniversityFollow

Degree

Master of Science

Program

Biology

Supervisor

MacDougall-Shackleton B.

Abstract

Mate choice can optimize immune genotypes of offspring and thus reinforce parasite-mediated selection on immune genes. Information about genotype at class II major histocompatibility complex (MHC) is conveyed through body odour, possibly mediated by symbiotic odour-producing bacteria. This can influence mate choice: many jawed vertebrates prefer mates dissimilar to themselves (‘compatible’) at MHC. However, whether odour conveys information about genotype at other immune loci remains unknown. I assessed whether preen oil chemical composition (a proxy for body odour in birds) varies with genotype at viral-facing (TLR3) and bacterial-facing (TLR4) Toll-like receptors in song sparrows (Melospiza melodia). Pairwise distance of preen oil chemical composition did not covary in most cases with pairwise genetic distance at either TLR3 or TLR4, nor did heterozygosity at either locus predict preen oil chemical diversity. Despite evidence of nonrandom mating at TLR3, the mechanism by which song sparrows assess genetic similarity at TLR loci remains elusive.

Summary for Lay Audience

Throughout evolutionary history, organisms have had to defend themselves against infectious disease caused by bacteria, viruses and other microbes. Individuals with different versions of immune genes (alleles) can recognize, and are defended against, different kinds of infections. At one kind of immune gene, the major histocompatibility complex (MHC), animals often prefer mates with alleles different from their own: they detect this difference through body odour, which may be influenced by the bacteria living on them. In birds, feather preen oil is the main source of body odour, and in song sparrows, the chemicals present in preen oil provide information about MHC alleles. Song sparrows use this information to choose mates that are similar or different to themselves at MHC. Toll-like receptors (TLRs) are another important part of immune defence: they detect infection by viruses, bacteria or other microbes and help activate immune responses. Song sparrows tend to choose mates similar to themselves at the Toll-like receptor TLR3 (which recognizes viral infection), suggesting they must have some way to assess TLR3 similarity. I asked whether the preen oil of song sparrows reflects the individual’s alleles at TLR3, and/or at another TLR (TLR4) which recognizes bacterial infections. I collected DNA and preen oil from wild song sparrows, then determined which TLR3 and TLR4 alleles, and which preen oil chemicals, each individual carried. Pairs of individuals with similar preen oil chemistry were not necessarily more similar at either TLR3 or TLR4 in most cases, suggesting that odour cues in preen oil do not provide information on similarity at these genes. The next step is to find other ways that similarity at TLR genes might be communicated by song sparrows.

Recommended Citation

To, Justin, "The correspondence between genotype at bacterial and viral-facing Toll-like receptors and preen oil chemical composition in song sparrows" (2024). Electronic Thesis and Dissertation Repository. 10335.
https://ir.lib.uwo.ca/etd/10335