Kin grouping is insufficient to explain the inclusive fitness gains of conspecific brood parasitism in the common eider

Abstract

Conspecific brood parasitism allows females to exploit other females' nests and enhance their reproductive output. Here, we test a recent theoretical model of how host females gain inclusive fitness from brood parasitism. High levels of relatedness between host and parasitizer can be maintained either by: (a) kin recognizing and parasitizing each other as a form of cooperative breeding or (b) natal philopatry and nest site fidelity facilitating the formation of kin groups, thereby increasing the probability of parasitism between relatives nesting in close proximity. To address these two hypotheses we genotyped feathers and hatch membranes of common eiders (Somateria mollissima) from western Hudson Bay, Canada, using a noninvasive sampling methodology. We found that most instances of brood parasitism do result in inclusive fitness gains. Furthermore, females with failed nests moved an average of 492 m from their previous year's nest site, while successful females only moved an average of 13 m. Therefore, we observed host–parasite relatedness can occur at levels higher than would be expected by chance even in the absence of kin grouping, suggesting that closely related females nesting near one another is not essential to maintain high host–parasitizer relatedness. In addition, kin grouping is only a transient phenomenon that cannot occur every year due to the propensity for females of failed nests to nest farther away from their nest site in subsequent years than females with successful nests, which provides support for kin recognition as a more likely mechanism to maintain high host–parasitizer relatedness over time.

Pedigree simulations reveal that maternity assignment is reliable in populations with conspecific brood parasitism, incomplete parental sampling and kin structure

“…As cervus was developed 12 years before colony , it is not surprising that the majority of the studies used the program cervus (17 of 28) to assign parentage, while three used colony , and one study used both. Several studies (seven) did not use either parentage assignment program but instead relied on methods such as comparing the genotypes of females and offspring and assigning maternity based on the occurrence of mismatches (often only at one or two loci) relative to that expected given allele frequencies, expected mutation rates, genotyping error, null alleles or allele drop‐out (e.g., Hervey et al, 2019; Šťovíček et al, 2013; Tiedemann et al, 2011). The choice to use exclusion by mismatch instead of parentage assignment may reflect a discomfort with available programs, including the limitations that we have tried to address in the present study (Anderholm et al, 2009); however, despite the appeal of simplicity, exclusion is somewhat arbitrary (Flanagan & Jones, 2019).…”

“…(often only at one or two loci) relative to that expected given allele frequencies, expected mutation rates, genotyping error, null alleles or allele drop-out (e.g., Hervey et al, 2019;Šťovíček et al, 2013;Tiedemann et al, 2011). The choice to use exclusion by mismatch instead of parentage assignment may reflect a discomfort with available programs, including the limitations that we have tried to address in the present study (Anderholm et al, 2009); however, despite the appeal of simplicity, exclusion is somewhat arbitrary (Flanagan & Jones, 2019).…”

Full Issue PDF

“…First, individuals may get confused in dense colonies during disturbance events, lose awareness of their nest location, and submit to the strong visual stimulus to cover an unattended clutch of eggs (even those not their own). While other Arctic birds such as Common Murre (Uria aalge) and Thick-billed Murre (Uria lomvia) can recognize their own eggs (Gaston et al 1993), high rates of conspecific nest parasitism in eider colonies (Waldeck and Andersson 2006;Hervey et al 2019) suggest that they are poor at egg recognition. The combination of disturbance induced by a large predator and the inability to recognize their own nest suggests that general confusion is a highly likely explanation for conspecific nest attendance in eiders, but other explanations deserve consideration.…”

“…Third, the focal eider has a reproductive investment in other unattended nests because she has laid parasitic eggs in them (Hervey et al 2019), and fourth, the focal eider is genetically related to the female of the unattended nest (McKinnon et al 2006) and, therefore, gains direct fitness benefits from concealing the exposed eggs of relatives. Both of these hypotheses are plausible as high rates of conspecific nest parasitism (Waldeck and Andersson 2006;Hervey et al 2019) and kin-grouping (McKinnon et al 2006) occur in eider colonies. These hypotheses are intriguing and require further investigation.…”

Estimating nest‐switching in free‐ranging wild birds: an assessment of the most common methodologies, illustrated in the White Stork (Ciconia ciconia)

“…2018, Hervey et al . 2019). There is still a problem of missing birds (feathers sampled in only 1 year), similar to resighting biases.…”