Estimating selection on the act of inbreeding in a population with strong inbreeding depression

Abstract

Inbreeding depression is widely regarded as a driving force in the evolution of dispersal, mate choice and sperm selection. However, due to likely costs of inbreeding avoidance, which are poorly understood, it is unclear to what extent selection to avoid inbreeding is expected in nature. Moreover, there are currently very few empirical estimates of the strength of selection against the act of inbreeding (mating with a relative), as opposed to the fitness costs of being inbred. Here, we use data from the individual-based study of red deer on the Scottish island of Rum, a strongly polygynous system which harbours a large inbreeding load, to estimate selection against the act of inbreeding for each sex. We use pedigree and genomic estimates of relatedness between individuals and measure fitness using both lifetime breeding success (number of calves born) and lifetime reproductive success (number of calves surviving to independence), with the latter incorporating inbreeding depression in calf survival. We find for both sexes that the repeatability of the act of inbreeding was low (< 0.1), suggesting little among-individual variation for this trait on which selection can act. Using the genomic measures, there was significant selection against the act of inbreeding in males, but not in females, and there was considerable uncertainty in the estimate in both sexes. We discuss possible explanations for these patterns and their implications for understanding the evolution of inbreeding avoidance in natural populations.

Lifetime Fitness Costs of Inbreeding and Being Inbred in a Critically Endangered Bird

“…Our study is unusual in quantifying the relative fitness costs associated with an individual being inbred and an individual engaging in inbreeding within the same analytical framework [18,19]. Studies that have tested for sex-specific fitness costs associated with individuals engaging in inbreeding (as distinct from sex-specific fitness costs associated with ''being inbred'') in polygynous red deer [19] and in socially monogamous song sparrows [18] have reported reproductive costs of engaging in inbreeding for males, but not females.…”

“…Our study is unusual in quantifying the relative fitness costs associated with an individual being inbred and an individual engaging in inbreeding within the same analytical framework [18,19]. Studies that have tested for sex-specific fitness costs associated with individuals engaging in inbreeding (as distinct from sex-specific fitness costs associated with ''being inbred'') in polygynous red deer [19] and in socially monogamous song sparrows [18] have reported reproductive costs of engaging in inbreeding for males, but not females. In the present study, we found evidence of fitness costs associated with engaging in inbreeding in both sexes, although it remains to be tested whether helmeted honeyeaters are making active choices to avoid breeding with genetically similar mates (i.e., exhibiting inbreeding avoidance behavior).…”

Effect of MHC and inbreeding on disassortative reproduction: A data revisit, extension and inclusion of fertilization in sand lizards

“…In a previous study on the same population, we showed that offspring standardized heterozygosity SH (Coltman et al, 1999 ) was positively associated with hatching success (Bererhi et al, 2019 ). That said, it is important to distinguish between selection on “being inbred” and selection on “inbreeding” (Troianou et al, 2018 ). Pedigree‐based inbreeding coefficients are approximations of the proportion of the genome that is autozygous (Franklin, 1977 ; Hill & Weir, 2011 ).…”

Quantitative genetics of extreme insular dwarfing: The case of red deer on Jersey

“…Although we did not keep the complete ancestry record among simulated individuals, we evaluated inbreeding by Markovian approximation, tracking whether the pairs generating offspring were siblings, and keeping the overall mean inbreeding level in the previous generation as the background level. For instance, data interpolation allows the estimation that, under inbreeding depression, the fitness of an individual derived from a brother‐sister couple in mammals ( f = 0.5) will be reduced by around 73% (see below for kinship estimation) (Huisman et al, 2016; Troianou et al, 2018; Walling et al, 2011). We defined an overall level of population inbreeding f that was assigned to “unbred” individuals.…”