Inbreeding Depression Accumulation across Life‐History Stages of the Endangered Takahe

Abstract

Studies evaluating the impact of inbreeding depression on population viability of threatened species tend to focus on the effects of inbreeding at a single life-history stage (e.g., juvenile survival). We examined the effects of inbreeding across the full life-history continuum, from survival up to adulthood, to subsequent reproductive success, and to the recruitment of second-generation offspring, in wild Takahe ( Porphyrio hochstetteri ) by analyzing pedigree and fitness data collected over 21 breeding seasons. Although the effect size of inbreeding at individual life-history stages was small, inbreeding depression accumulated across multiple life-history stages and ultimately reduced long-term fitness (i.e., successful recruitment of second-generation offspring). The estimated total lethal equivalents (2B) summed across all life-history stages were substantial (16.05, 95% CI 0.08-90.8) and equivalent to an 88% reduction in recruitment of second-generation offspring for closely related pairs (e.g., sib-sib pairings) relative to unrelated pairs (according to the pedigree). A history of small population size in the Takahe could have contributed to partial purging of the genetic load and the low level of inbreeding depression detected at each single life-history stage. Nevertheless, our results indicate that such "purged" populations can still exhibit substantial inbreeding depression, especially when small but negative fitness effects accumulate across the species' life history. Because inbreeding depression can ultimately affect population viability of small, isolated populations, our results illustrate the importance of measuring the effects of inbreeding across the full life-history continuum.

Inbreeding depression across the lifespan in a wild mammal population

“…By foregoing the cost of reproduction on survival (M8) and subsequent fecundity (M10), the net effect of a female's inbreeding coefficient on LBS is diminished, and so was undetectable among those who bred at least once (M12). Similar discrepancies between effects on annual or seasonal and lifetime measures of fitness due to compensation can be found, for example, when inbreeding affects brood success in birds, but inbred females increase the number of breeding attempts (35). These results emphasize the importance of considering the entire life cycle, including effects of parental inbreeding coefficients on juvenile survival, when estimating the total effect of inbreeding depression.…”

High genetic load in an old isolated butterfly population

“…As purging of highly deleterious mutations is more efficient than purging of mildly deleterious mutations, other things being equal, the high inbreeding depression of egg viability in the PT population is surprising. Other studies have previously reported that purging may not effectively reduce inbreeding depression in all traits (63,64).…”

Factors affecting the local occurrence of the near-threatened bitterling (Tanakia lanceolata) in agricultural canal networks: strong attachment to its potential host mussels

“…Our set of candidate models was defined as those with DAIC B 2. The ''natural'' average was used in model averaging (Burnham & Anderson, 2002;Grueber et al, 2010). This analysis produces two outputs: parameter estimates (and their unconditional standard errors, which incorporate model-selection uncertainty) and the relative importance of each variable in explaining the variance in the response variable.…”