The importance of inbreeding and drift in conservation of subdivided populations

In conservation biology we still lack the information needed to properly evaluate genetic risks of population extinction. Specifically, we need a better understanding of how population fragmentation, fluctuations in population sizes, inbreeding depression and loss of genetic variation affect population viability. Our study populations of house sparrows (Passer domesticus) at the coast of northern Norway represent a study system well suited to improve our understanding of how inbreeding depression and loss of genetic variation may affect the growth and viability of small and fragmented populations. Our work will be divided into five interconnected work packages (WPs). WP 1 will start by combining genomic analyses of inbreeding and loss of genetic variation with high-quality ecological data to study reasons for why the level of inbreeding and rate of loss of genetic variation vary between populations and years. Next, we will quantify how much spatial and temporal variation there is in the negative effects that inbreeding and loss of genetic variation have on reproduction and survival (fitness), and investigate the reasons for such variation. In WP 2 we will explore the genetic basis for negative fitness effects of inbreeding and loss of genetic variation. We will then follow up these results in WP 3 by using data from large-scale experiments in three natural populations to examine fitness effects of changes in allele and genotype frequencies at putative candidate genes found in WP 2. Next, how inbreeding and loss of genetic variation reduce ability to adapt to any changes in the environmental will be examined in WP 4. Finally, in WP 5 we will use results from WP 1-4 as input in statistical models and simulations to evaluate the importance of genetic processes for the growth and viability of fragmented populations.

A major challenge in conservation biology is the lack of information needed to properly evaluate risk of population extinction. In particular, we lack understanding of how population fragmentation, fluctuations in subpopulation sizes, and the genetic architecture of genetic load affect population viability. Our study populations represent an outstanding empirical study system uniquely suited to go beyond the current state-of-the-art regarding our understanding of the mechanisms underlying inbreeding load and drift load in nature, and the importance that these processes have for the growth and viability of fragmented populations. We will divide our conceptually rigorous research program into five connected and complementary work packages (WPs). In WP 1, we integrate genomic analyses of inbreeding and drift with unique high-quality demographic data to identify the causes of spatio-temporal variation in inbreeding and inbreeding depression, and examine the occurrence and strength of drift load in a subdivided vertebrate population. WP 2 will build on on-going cross-disciplinary collaboration between biologists and statisticians to explore of the genetic architecture of inbreeding depression and heterosis. In WP 3 we will follow up these results by using data from extraordinary and large-scale experiments in three natural populations to examine fitness effects of changes in allele and genotype frequencies at putative candidate loci/regions involved in inbreeding depression and heterosis. Inbreeding and drift is expected to reduce adaptive potential, and in WP 4 we use our team's cutting edge knowledge in quantitative genetics and genomics to quantify the importance of inbreeding (depression) and drift (load) for the additive genetic variance of subdivided populations. Finally, in WP 5 we extend current methods and use simulations to evaluate the importance of genetic processes and spatial structure for the growth and viability of fragmented populations.