Investigating the genetic basis of boldness and reproductive performance traits in the grey seal (Halichoerus grypus)
Creators: Bubac, Christine Marie
Publisher: name: University of Alberta Library
Year: 2022

<p>Individual variation provides the material for natural selection to act upon, influencing ecological and evolutionary processes. Much phenotypic variation in traits, such as behaviour and life-history, have a moderate to high heritable component, suggesting that these traits may have adaptive potential and are genetically influenced. Yet, investigating the genetic basis of complex traits remains limited to few natural systems – partly due to the difficulty of sampling phenotypes in the wild, a lack of existing genomic resources, and detailed pedigree information – and remains a great challenge in biology today. Advances in DNA sequencing technologies now permit investigations into the evolutionary potential of traits as well as the genetic architecture underlying phenotypic variation in the wild. In this dissertation, I examine the genetic basis of maternal performance traits in free-ranging grey seals (Halichoerus grypus), a long-lived, iteroparous species that has rebounded following a long history of overexploitation. First, I performed a literature review and meta-analysis to examine trends in analytical molecular approaches used to elucidate the genetic basis of animal behaviour. Analyzing nearly 150 studies focused on candidate gene, quantitative trait locus mapping, and genome-wide association analyses, I discovered evidence of limited taxonomic breadth in the literature. I highlighted commonly studied candidate genes and behaviours, and further reported global genetic effect sizes for each approach undertaken. Second, I determined the existence of an animal personality signal along the shy-bold continuum in the Sable Island National Park Preserve (Nova Scotia, Canada) population of female grey seals. Using behavioural data collected over a nine-year period (2008-2016), I showed that boldness is highly repeatable both between and within years. Boldness was influenced by maternal age, such that younger females were generally less bold than older, more experienced females providing some support for the life-history trade-off hypothesis. Seal pups produced by bolder females were on average ~2 kg heavier than pups of shy females. Third, I used a candidate gene approach to investigate relationships between genetic variants and repeated measures of boldness, offspring weaning mass, and lactation duration in grey seals. I isolated and re-sequenced five candidate genes commonly screened in primates, rodents, and passerines. Here, I found genetic effects of the serotonin transporter (SERT) and dopamine receptor D4 (DRD4) genes on boldness and offspring weaning mass. Genotypes explained 6.52-13.66% of total trait variation. Lastly, using a reduced representation DNA sequencing method, I obtained genome-wide genotypic data for over 450 female grey seals and determined that eight maternal traits, representing morphological, life-history, and behavioural traits, had low to moderate heritability (h2 = 0.08-0.38). Genome-wide association analyses did not reveal any loci that were significantly associated with the traits examined, suggesting these traits are polygenic. Altogether, this thesis integrated molecular genetic methodologies and statistical approaches with a longitudinal field program, and presented support for the adaptive potential of fitness-related traits in Sable Island grey seals. Results further provided insights into factors and mechanisms underlying maternal performance variation in this ecologically important marine predator. Though challenges exist in investigating the genetic basis of quantitative traits, such analyses give insight into the evolutionary dynamics and capacity for adaptation in natural populations, especially relevant as biodiversity is exposed to novel selection pressures and changing environmental conditions.</p>