Sex-differential effects of inbreeding on overwinter survival, birth date and mass of bighorn lambs

Abstract

Although it is generally expected that inbreeding would lower fitness, few studies have directly quantified the effects of inbreeding in wild mammals. We investigated the effects of inbreeding using long‐term data from bighorn sheep on Ram Mountain, Alberta, Canada, over 20 years. This population underwent a drastic decline from 1992 to 2002 and has since failed to recover. We used a pedigree to calculate inbreeding coefficients and examined their impact on lamb growth, birth date and survival. Inbreeding had a substantial effect on female survival: for a given mass in September, the probability of overwinter survival for inbred female lambs was about 40% lower than that of noninbred ones. Contrary to our expectations, inbred female lambs were born earlier than noninbred ones. Earlier birth led to inbred female lambs being heavier by mid‐September than noninbred ones. There was a nonsignificant trend for inbred female yearlings to weigh more than noninbred ones. A stronger mass‐dependent viability selection for inbred compared to noninbred female lambs may explain why surviving inbred females were heavier than noninbred ones. Survival of male lambs was not affected by inbreeding. Sex‐differential effects of inbreeding may be a general pattern in sexually dimorphic mammals, because of sex‐biased maternal care or sexual differences in early development strategies.

Low incidence of inbreeding in a long-lived primate population isolated for 75 years

“…For instance, a pedigree study of an isolated population of bighorn sheep ( Ovis canadensis ) maintained at about 30 females revealed that 18.1% of the lambs had an F  > 0 (Rioux-Paquette et al 2011). In addition, the probability of lamb survival for inbred females was 40% lower than for non-inbred ones (Rioux-Paquette et al 2011).…”

Genetic population structure of Peninsular bighorn sheep (Ovis canadensis nelsoni) indicates substantial gene flow across US–Mexico border

“…We detected no evidence of low heterozygosity or close inbreeding in the three populations (F IS = À0.01 to 0.03; mean IR = 0.013), however PBS population densities should be carefully monitored. Research has demonstrated bighorn sheep show no behavioral mechanism for inbreeding avoidance when mate choice becomes demographically limited (Rioux-Paquette et al, 2010), and that inbreeding reduces survivorship among female lambs (Rioux-Paquette et al, 2011). In addition, there is evidence that population growth and dispersal rates are correlated with N e (Singer et al, 2000).…”

Heterozygosity–fitness correlations in blue tit nestlings (Cyanistis caeruleus) under contrasting rearing conditions

“…Interestingly, differences in the strength and direction of HFCs may also differ between sexes and these differences may result from sex-specific genetic structure or different sensitivity of males and females to environmental limitations (Rossiter et al 2001;Foerster et al 2003). Sex-specific effects of inbreeding have indeed been found in a variety of species (Saccheri et al 2005;Charpentier et al 2006;Reid et al 2007;Rioux-Paquette et al 2011). In most cases, the negative effects of inbreeding (or the positive effects of outbreeding) have been found more often among females than males.…”