Apparent inbreeding preference despite inbreeding depression in the American crow

Abstract

Although matings between relatives can have negative effects on offspring fitness, apparent inbreeding preference has been reported in a growing number of systems, including those with documented inbreeding depression. Here, we examined evidence for inbreeding depression and inbreeding preference in two populations (Clinton, New York and Davis, California, USA) of the cooperatively breeding American crow (Corvus brachyrhynchos). We then compared observed inbreeding strategies with theoretical expectations for optimal, adaptive levels of inbreeding, given the inclusive fitness benefits and population-specific magnitude of inbreeding depression. We found that low heterozygosity at a panel of 33 microsatellite markers was associated with low survival probability (fledging success) and low white blood cell counts among offspring in both populations. Despite these costs, our data were more consistent with inbreeding preference than avoidance: the observed heterozygosity among 396 sampled crow offspring was significantly lower than expected if local adults were mating by random chance. This pattern was consistent across a range of spatial scales in both populations. Theoretically adaptive levels of inbreeding, given the magnitude of inbreeding depression, were predicted to be very low in the California population, whereas complete disassociative mating was predicted in the New York population. Sexual conflict might have contributed to the apparent absence of inbreeding avoidance in crows. These data add to an increasing number of examples of an "inbreeding paradox," where inbreeding appears to be preferred despite inbreeding depression. This article is protected by copyright. All rights reserved.

Why don't all animals avoid inbreeding?

“…(d) Random mating does not necessarily increase the risk of inbreeding Different mechanisms of inbreeding avoidance were equally effective at reducing relatedness between pairs among species with inbreeding depression. Species where mate choice was random with respect to relatedness, were equally successful at avoiding inbreeding as species where mating with relatives was actively avoided (figure 2; electronic supplementary material, figure S8, table S6 However, we did find that species with sex-bias dispersal and post-mating avoidance were more likely to choose their mates at random with respect to relatedness (figure 3; electronic supplementary material, table S8 In some species with inbreeding depression, mechanisms of inbreeding avoidance were not reported (N Species = 10), a phenomenon often referred to as an 'inbreeding paradox' [53,54]. Relatedness between partners in these species, although higher, was not statistically significantly different from species where mechanisms of inbreeding avoidance were known (electronic supplementary material, figure S8, table S6, Model 5, mean relatedness between breeding pairs ± s.e.…”

Mosquito blood-feeding patterns and nesting behavior of American crows, an amplifying host of West Nile virus

“…We recorded the territory from which each feather was collected. A previous analysis of parentage and relatedness in this population showed that this sample of adult crow feathers included many parents of the nestlings sampled between 2012 and 2014 as well as non-breeding group members [ 48 ].…”

“…Samples were genotyped using a panel of 27 microsatellite loci developed for American crows [ 54 , 55 ] and other corvids [ 56 – 58 ]. PCR conditions were described previously [ 48 ]. Individuals were scored at a minimum of 25 loci; 91% were scored at all loci.…”

“…Results from a previous parentage analysis that utilized the maximum likelihood method in CERVUS (described in [ 48 ]) was used to evaluate the relationship between nestlings sampled in 2012–2014 and the adults that were identified as crow blood meals. In brief, all sampled adult males were specified as “potential fathers” and females as “potential mothers.” The potential typing error was specified at 5%, the proportion of sampled candidate parents at 65% and relatedness among 10% of candidate parents at 0.25.…”

Significant Genetic Impacts Accompany an Urban Rat Control Campaign in Salvador, Brazil

“…Increasing relatedness can have fitness consequences, and has been found to reduced reproductive success, competitive ability and growth rates in invasive plant species (Burns, 2006;Elam et al, 2007). Yet there is evidence that some social animals prefer inbreeding despite documented deleterious impacts, such as elevated susceptibility to disease in American crows (Townsend et al, 2018). This raises the question of what tradeoffs exist between tight social relationships, inclusive fitness, and inbreeding depression.…”