Understanding lifelong and multigenerational inbreeding effects in the Seychelles warbler

Inbreeding depression needs to be measured in natural populations where environmental stresses exposes its detrimental effects However, such studies probably greatly underestimate inbreeding depression because accuracy is undermined by factors such as dispersal, inaccurate parentage assignment or problems quantifying inbreeding. Importantly, they also normally only focus on the survival or reproduction of inbred individuals (and not inbreeding events)- often over limited periods of their lives - thus missing key components that impact fitness such as prenatal inviability, mating success or transgenerational effects. To encompass these effects an individual's genetic contribution to the population over generations should be assessed. Studies also rarely account for fluctuating environmental stresses1 or map age-dependent effects.

The small Seychelles warbler population on Cousin is an excellent system in which to study inbreeding depression. Since 1993 nearly all individuals have been monitored throughout their lives. No migration occurs, so dispersal does not confound survival estimates. All reproduction is monitored and molecularly verified, and a pedigree of >2000 individuals spanning >12 generations exists. Individuals differ greatly in how inbred they are, and limited assessments indicate that inbreeding depression occurs.

Methods
Fieldwork will be used to further strengthen the individual-based survival and senescence dataset, understand the system, gain fieldwork skills and liaise with in-country conservation stakeholders. The student will use genomic resequencing information already available on 1600 individuals to calculate genome-wide homozygosity (how inbred an individual is). A genome-based approach is more accurate than using pedigree-based estimates and also allows inbreeding events to be identified based on genomic similarity between both social and genetic partners. The database on individuals will allow the student to calculate life-time reproductive success, determine how differential survival and reproductive success contribute to this, and whether that differs for females and males. They can also determine if inbreeding influences among-individual variation in senescence, an important phenomenon in many species. The pedigree will be used to assess how inbreeding affects an individual's contribution to the population over multiple generations. Finally, determining how past inbreeding in the pedigree affects the impact of subsequent inbreeding events can test whether sustained inbreeding can lead to purging and reduced inbreeding depression. Hierarchical Bayesian models will be used to separate the effects of factors i.e. being inbred, how inbred parents are, inbreeding events, control for environmental variation, and allow assessment of age and sex effects.