Abstract
Inbreeding can affect fitness-related traits at different life history stages and may interact with environmental variation to induce even larger effects. We used genetic parentage assignment based on 22 microsatellite loci to determine a 25 year long pedigree for a newly established island population of moose with 20–40 reproducing individuals annually. We used the pedigree to calculate individual inbreeding coefficients and examined for effects of individual inbreeding (f) and heterozygosity on fitness-related traits. We found negative effects of f on birth date, calf body mass and twinning rate. The relationship between f and calf body mass and twinning rate were found to be separate but weaker after accounting for birth date. We found no support for an inbreeding effect on the age-specific lifetime reproductive success of females. The influence of f on birth date was related to climatic conditions during the spring prior to birth, indicating that calves with a low f were born earlier after a cold spring than calves with high f. In years with a warm spring, calf f did not affect birth date. The results suggest that severe inbreeding in moose has both indirect effects on fitness through delayed birth and lower juvenile body mass, as well as separate direct effects, as there still was a significant relationship between f and twinning rate after accounting for birth date and body mass as calf. Consequently, severe inbreeding as found in the study population may have consequences for population growth and extinction risk.
Highlights
Small and isolated populations have an increased risk of extinction from genetic drift and inbreeding as opportunities for mating become restricted and the probability of mating between relatives increases (Lande 1988; Frankham 2005; Wright et al 2008)
Ecology and Evolution published by John Wiley & Sons Ltd
We investigated whether inbreeding (f) and heterozygosity (MLH) affected the following individual fitness-related traits: birth date, calf body mass, and cow twinning rate and age-specific lifetime reproductive success
Summary
Small and isolated populations have an increased risk of extinction from genetic drift and inbreeding as opportunities for mating become restricted and the probability of mating between relatives increases (Lande 1988; Frankham 2005; Wright et al 2008). Inbreeding depression may for instance be reduced if detrimental and lethal recessive alleles are purged from the population (Keller and Waller 2002). Immigration may on the other hand restore genetic variation, reduce inbreeding, and increase population viability (Hedrick and Kalinowski 2000; Vila et al 2003), but may re-introduce purged alleles and the positive effects may be short term (Liberg et al 2005; Bijlsma et al 2010; Hedrick and Fredrickson 2010). The magnitude of inbreeding depression seems to increase with environmental stress (Keller and Waller 2002; Marr et al 2006; Bijlsma and Loeschcke 2012).
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