Abstract
Inbreeding depression, or the reduction in fitness due to mating between close relatives, is a key issue in biology today. Inbreeding negatively affects many fitness-related traits, including survival and reproductive success. Despite this, very few studies have quantified the effects of inbreeding on vertebrate gamete traits under controlled breeding conditions using a full-sib mating approach. Here, we provide comprehensive evidence for the negative effect of inbreeding on sperm traits in a bird, the zebra finch Taeniopygia guttata. We compared sperm characteristics of both inbred (pedigree F=0.25) and outbred (pedigree F=0) individuals from two captive populations, one domesticated and one recently wild-derived, raised under standardized conditions. As normal spermatozoa morphology did not differ consistently between inbred and outbred individuals, our study confirms the hypothesis that sperm morphology is not particularly susceptible to inbreeding depression. Inbreeding did, however, lead to significantly lower sperm motility and a substantially higher percentage of abnormal spermatozoa in ejaculate. These results were consistent across both study populations, confirming the generality and reliability of our findings.
Highlights
Inbreeding, or mating between close relatives, is known to have a detrimental effect on the phenotypes and performance traits of offspring (Keller and Waller 2002)
Ecology and Evolution published by John Wiley & Sons Ltd
Our study, which was based on a controlled breeding design with offspring raised under standardized conditions, demonstrated a clear effect of inbreeding on the sperm characteristics of a songbird species, with inbred males having more abnormal spermatozoa and lower sperm velocity than outbred males kept under the same conditions
Summary
Inbreeding, or mating between close relatives, is known to have a detrimental effect on the phenotypes and performance traits of offspring (Keller and Waller 2002). Knowledge of the extent to which traits are susceptible to inbreeding depression has wide implications for evolutionary (Charlesworth and Charlesworth 1987; Lynch and Walsh 1998) and conservation biology (Crnokrak and Roff 1999; Bijlsma et al 2000; Leberg and Firmin 2008; Knief et al.2015) and agricultural sciences (Sewalem et al 1999; Ko€nig et al 2010; Makina et al 2014). Inbreeding depression is thought to arise primarily from deleterious recessive mutations whose detrimental effects are only revealed once they become homozygous (identical by descent) in inbred individuals (Falconer and Mackay 1996; Lynch and Walsh 1998; Charlesworth and Willis 2009).
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