title: Resolving the conundrum of inbreeding depression but no inbreeding avoidance: Estimating sex-specific selection on inbreeding by song sparrows (Melospiza melodia).
abstract: Inbreeding avoidance among interacting females and males is not always observed despite inbreeding depression in offspring fitness, creating an apparent "inbreeding paradox." This paradox could be resolved if selection against inbreeding was in fact weak, despite inbreeding depression. However, the net magnitude and direction of selection on the degree to which females and males inbreed by pairing with relatives has not been explicitly estimated. We used long-term pedigree data to estimate phenotypic selection gradients on the degree of inbreeding that female and male song sparrows (Melospiza melodia) expressed by forming socially persistent breeding pairs with relatives. Fitness was measured as the total numbers of offspring and grand offspring contributed to the population, and as corresponding expected numbers of identical-by-descent allele copies, thereby accounting for variation in offspring survival, reproduction, and relatedness associated with variation in parental inbreeding. Estimated selection gradients on the degree to which individuals paired with relatives were weakly positive in females, but negative in males that formed at least one socially persistent pairing. However, males that paired had higher mean fitness than males that remained socially unpaired. These analyses suggest that net selection against inbreeding may be weak in both sexes despite strong inbreeding depression, thereby resolving the "inbreeding paradox."
authors.affiliation: Institute of Biological and Environmental Sciences, School of Biological Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland. jane.reid@abdn.ac.uk.
authors.forename: Jane M
authors.initials: JM
authors.lastname: Reid
authors.affiliation: Department of Forest and Conservation Sciences, University of British Columbia, 2424 Main Mall, Vancouver, BC, Canada, V6T 1Z4.
authors.forename: Peter
authors.initials: P
authors.lastname: Arcese
authors.affiliation: Institute of Biological and Environmental Sciences, School of Biological Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland.
authors.forename: Greta
authors.initials: G
authors.lastname: Bocedi
authors.affiliation: Institute of Biological and Environmental Sciences, School of Biological Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland.
authors.forename: A Bradley
authors.initials: AB
authors.lastname: Duthie
authors.affiliation: Institute of Biological and Environmental Sciences, School of Biological Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Wolak
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
authors.forename: Lukas F
authors.initials: LF
authors.lastname: Keller
mesh_terms: D000818:Animals; D005260:Female; D056084:Genetic Fitness; D007178:Inbreeding; D008297:Male; D010375:Pedigree; D010641:Phenotype; D012098:Reproduction / Q000235:genetics*; D012726:Sexual Behavior, Animal; D046370:Sparrows / Q000235:genetics*
keywords: Fitness; mate choice; mating system; pedigree; relatedness; selection gradient