Sensitive males: inbreeding depression in an endangered bird

Abstract

Attempts to conserve threatened species by establishing new populations via reintroduction are controversial. Theory predicts that genetic bottlenecks result in increased mating between relatives and inbreeding depression. However, few studies of wild sourced reintroductions have carefully examined these genetic consequences. Our study assesses inbreeding and inbreeding depression in a free-living reintroduced population of an endangered New Zealand bird, the hihi (Notiomystis cincta). Using molecular sexing and marker-based inbreeding coefficients estimated from 19 autosomal microsatellite loci, we show that (i) inbreeding depresses offspring survival, (ii) male embryos are more inbred on average than female embryos, (iii) the effect of inbreeding depression is male-biased and (iv) this population has a substantial genetic load. Male susceptibility to inbreeding during embryo and nestling development may be due to size dimorphism, resulting in faster growth rates and more stressful development for male embryos and nestlings compared with females. This work highlights the effects of inbreeding at early life-history stages and the repercussions for the long-term population viability of threatened species.

Figure 1.

Frequency distribution of inbreeding coefficients for all hihi individuals shown by the grey hatched columns (n = 230) and specifically for males shown in the dashed columns (n = 133) and for females shown in the dotted columns (n = 94), sampled from the 2006–2007 breeding season.

Figure 2.

Mean inbreeding values are shown for (a) all males and females, and (b,c) dead and surviving hihi of either sex at each stage of development, with vertical bars showing standard error distribution. Sample sizes are: (a) males at all stages of development, M = 133; females at all stages of development, F = 94; (b) dead embryos: M = 28, F = 9; surviving embryos: M = 105, F = 85; (c) dead nestlings: M = 37, F = 15; surviving nestlings: M = 69, F = 70, from the 2006–2007 cohort. (b,c) hatched column, male; dotted column, female.