The fitness consequences of kin-biased dispersal in a cooperatively breeding bird

Abstract

Cooperative alliances among kin may not only lead to indirect fitness benefits for group-living species, but can also provide direct benefits through access to mates or higher social rank. However, the immigrant sex in most species loses any potential benefits of living with kin unless immigrants disperse together or recruit relatives into the group in subsequent years. To look for evidence of small subgroups of related immigrants within social groups (kin substructure), we used microsatellites to assess relatedness between immigrant females of the cooperatively breeding superb starling, Lamprotornis superbus. We determined how timing of immigration led to kin subgroup formation and if being part of one influenced female fitness. Although mean relatedness in groups was higher for males than females, 26% of immigrant females were part of a kin subgroup with a sister. These immigrant sibships formed through kin recruitment across years more often than through coalitions immigrating together in the same year. Furthermore, females were more likely to breed when part of a kin subgroup than when alone, suggesting that female siblings form alliances that may positively influence their fitness. Ultimately, kin substructure should be considered when determining the role of relatedness in the evolution of animal societies.

How cooperatively breeding birds identify relatives and avoid incest: New insights into dispersal and kin recognition

“…This detailed analysis, drawing on more than a decade of data from individually marked individuals, is one of several recent field studies demonstrating the extent and impact of kin substructure in cooperative avian societies. Contrary to previous models, these studies find that sexbiased dispersal does not necessarily eliminate kin associations between members of the dispersing sex, since such alliances can persist during dispersal or form after dispersal [14,15,12]. Nor does sex-biased dispersal necessarily eliminate the risk of inbreeding in cooperative societies, since kin recruitment and short-distance movements can lead to unexpectedly high levels of local genetic relatedness [16][17][18].…”

“…In superb starlings, however, Pollack and Rubenstein [12] found that sister alliances form via a different, less common, route. Some sisters did emigrate together from their natal group, as discussed above, but the majority of sister pairs involved individuals that joined the same social group in different years.…”

“…A recent study by Pollack and Rubenstein [12] provides new evidence that, in cooperatively breeding superb starlings (Lamprotornis superbus), the relationship between dispersal and genetic structure may not be so straightforward. Superb starlings have an unusually complex social system known as plural breeding: social groups are composed of up to six pairs that each build a nest and raise young separately, assisted by a variable number of helpers.…”

“…As in most cooperative breeders, the majority of helpers are male relatives of the breeding pair and females almost always disperse rather than staying in their natal group to breed [13]. However, Pollack and Rubenstein [12] found that females do not join groups randomly with respect to relatedness; rather, about a quarter of immigrant females belonged to a social group that contained a full sister (confirmed through color-banding records and microsatellite analysis). Interestingly, immigrant females were more likely to breed when a sister was present, suggesting that young females may be better able to achieve a dominant breeding position when they have social support from a sibling.…”

Song in a Social and Sexual Context: Vocalizations Signal Identity and Rank in Both Sexes of a Cooperative Breeder

“…Audio files were saved as 16-bit, 44 kHz wav files and were automatically time-stamped upon recording. Focal birds were identified using a spotting scope, and age, breeding status, and the total number of seasons spent breeding were obtained from behavioral observations and long-term census records (Pollack and Rubenstein, 2015;Rubenstein, 2016).…”