Kinship and genetic mating system of the Grayish Baywing (Agelaioides badius), a cooperatively breeding Neotropical blackbird

Abstract

Kin selection theory predicts that extrapair mating should be rare in cooperatively breeding birds. However, most cooperative breeders are not genetically monogamous and the relationship between promiscuity and cooperative breeding remains unclear. This relationship is further complicated by a lack of data. The majority of cooperatively breeding birds live in the tropics, and their genetic mating systems are little known. Here we studied the genetic mating system of the Grayish Baywing (Agelaioides badius), a socially monogamous Neotropical blackbird in which most nesting pairs are assisted by helpers, previously assumed to be offspring of the breeding pair. Grayish Baywings are the primary host of the parasitic Screaming Cowbird (Molothrus rufoaxillaris), and previous studies have found a positive association between brood parasitism and helper recruitment in the last part of the nestling period. We used microsatellite markers to analyze the kinship of 192 individuals in 47 breeding groups, finding that 13% of 153 nestlings (in 38% of 47 nests) resulted from extrapair mating. We also documented 2 instances of conspecific brood parasitism and 1 instance of quasiparasitism (the nestling was sired by the social father, but was unrelated to the social mother). Of 8 helpers that were genotyped, 4 (all males) were offspring of the breeding pair and 4 (2 males, 2 females) were unrelated to both members of the breeding pair. None of the helpers produced offspring within the clutch. These results suggest that, although cooperative breeding is frequent, genetic relatedness between Grayish Baywing helpers and the offspring that they raise is highly variable. Future studies are needed to determine why unrelated helpers assist at Grayish Baywing nests, and to understand the role that brood parasitism may have played in the evolution of cooperative breeding in this species.

Non-mimetic shiny cowbird nestlings escape discrimination by baywings in absence of host nest mates

“…Data were collected during two consecutive breeding seasons (late November-early February) in 2016-2017 and 2017-2018. Baywings are secondary cavity-nesters that breed mostly in the domed nests of many furnariid species (Anumbius annumbi, Furnarius rufus, Phacellodomus sp., Synalaxis sp.). They are socially monogamous cooperative breeders (Fraga 1991;Ursino et al 2017) and single-brooders (De Mársico et al 2010). Breeding pairs can have one to four helpers at the nest that typically join them after hatching and participate in brood provisioning and nest defence (Fraga 1991;Ursino et al 2011).…”

Family ties in a neotropical cooperative breeder: within‐group relatedness and fine‐scale genetic structure in the greyish Baywing (Agelaioides badius)

“…We also included in our analysis an additional set of blood samples from 28 individuals that were colour‐banded before 2015 (Ursino et al . 2017) and re‐sighted as breeders or helpers during the present study period. DNA from these 28 samples was extracted using a DNeasy Blood and Tissue kit (Qiagen, Hilden, Germany) following the manufacturer's protocol.…”

“…Breeding pairs can have one to four helpers that join almost exclusively during the nestling and fledgling stages. Previous studies suggest that helpers are predominantly males and may be young adults that did not disperse after fledging, although there is also evidence of adult individuals redirecting help after failing with their own breeding attempt (Fraga 1991, Ursino et al 2017. However, the main patterns of relatedness within and between social groups are not well understood.…”

“…Based on banding data, Fraga (1991) reported nine out of 12 helpers marked as nestlings that assisted either one or both parents, but also observed an unrelated helper. Ursino et al (2017) assessed within-group relatedness for eight helpers using a panel of seven microsatellites and showed that half of them (all males) were the previous offspring of the assisted pair, and the other half (two males and two females) were unrelated to both breeders. This study also revealed extra-pair paternity at 38% of 47 sampled nests and occasional intraspecific brood parasitism (i.e.…”

Evolutionary origins of cooperative and communal breeding: Lessons from the crotophagine cuckoos

“…Even assuming that their evolutionary origins are distinct, the selective pressures maintaining social behavior in the two systems often appear to be convergent. First, it has long been appreciated that genetic relatedness in many helper‐at‐the‐nest systems is not particularly high (Brouwer et al., 2011; Dunn et al., 1995; Ursino et al., 2017; Webster et al., 2004). Turnover among breeders and extra‐pair mating can greatly reduce kinship in family groups, suggesting that while monogamy and the accompanying inclusive fitness benefits may play a role in the initial formation of family groups, direct fitness benefits may become more important once cooperative breeding is established.…”