Unexpected positive and negative effects of continuing inbreeding in one of the world's most inbred wild animals

Abstract

Inbreeding depression, the reduced fitness of offspring of related individuals, is a central theme in evolutionary biology. Inbreeding effects are influenced by the genetic makeup of a population, which is driven by any history of genetic bottlenecks and genetic drift. The Chatham Island black robin represents a case of extreme inbreeding following two severe population bottlenecks. We tested whether inbreeding measured by a 20-year pedigree predicted variation in fitness among individuals, despite the high mean level of inbreeding and low genetic diversity in this species. We found that paternal and maternal inbreeding reduced fledgling survival and individual inbreeding reduced juvenile survival, indicating that inbreeding depression affects even this highly inbred population. Close inbreeding also reduced survival for fledglings with less-inbred mothers, but unexpectedly improved survival for fledglings with highly inbred mothers. This counterintuitive interaction could not be explained by various potentially confounding variables. We propose a genetic mechanism, whereby a highly inbred chick with a highly inbred parent inherits a "proven" genotype and thus experiences a fitness advantage, which could explain the interaction. The positive and negative effects we found emphasize that continuing inbreeding can have important effects on individual fitness, even in populations that are already highly inbred.

Indirect fitness benefits through extra‐pair mating are large for an inbred minority, but cannot explain widespread infidelity among red‐winged fairy‐wrens

“…This could simply result from the inbred individuals not being exposed to the cost of raising fledglings (since they produced fewer offspring), although this is rather unlikely as even though helpers of both sexes and dominant males might not have sired offspring, they routinely take care of young on their home territory. A few other studies have reported positive associations between inbreeding and fitness components, which were suggested to be the result of these offspring inheriting a "proven genotype" (i.e., high quality genotype) from a highly inbred parent (Weiser et al 2016) or by purging and partial dominance of deleterious alleles (Moreno et al 2015). Despite the limited dispersal in our study population, purging is extremely unlikely as there is no evidence for a recent bottleneck.…”

“…A few other studies have reported positive associations between inbreeding and fitness components, which were suggested to be the result of these offspring inheriting a “proven genotype” (i.e., high quality genotype) from a highly inbred parent (Weiser et al. ) or by purging and partial dominance of deleterious alleles (Moreno et al. ).…”

Inconsistent inbreeding effects during lizard ontogeny

“…Other researchers have found no such effects of inbreeding on direct measures of offspring survival (Kempenaers et al 1996;Kruuk et al 2002) or on other traits that could indirectly affect survival, such as the incidence of malformations in larval tiger salamanders (Ambystoma tigrinum tigrinum) (Williams et al 2008). Finally, somewhat surprisingly, a number of studies have found positive effects of inbreeding on offspring survival (Richardson et al 2004;Weiser et al 2016;Bichet et al 2018). Additionally, it is important to recognize sources of error in calculating effects of inbreeding, which can change across life stages.…”

Inter-aviary distance and visual access influence conservation breeding outcomes in a territorial, endangered bird

“…We used Pearson correlation coefficients to identify and exclude highly correlated fixed effects prior to analysis and, in all but one case, dropped correlated fixed effects with coefficients ≥ 0.60 (Table S2). Location and inter-aviary distance were correlated at 0.79, but both were essential to include as predictors of reproductive success; thus, we retained them in our global GLMM and subsequently evaluated multicollinearity within the GLMM using variance inflation factors (VIF) to ensure that the covariates used in model averaging had VIF < 5 (e.g., Belsley et al, 1980;Weiser et al 2015). VIFs were calculated using the vif command from the car package (Fox & Weisberg, 2011).…”