Kinship affects investment by helpers in a cooperatively breeding bird

Abstract

Helping behaviour in cooperative breeding systems has been attributed to kin selection, but the relative roles of direct and indirect fitness benefits in the evolution of such systems remain a matter of debate. In theory, helpers could maximize the indirect fitness benefits of cooperation by investing more in broods with whom they are more closely related, but there is little evidence for such fine-scale adjustment in helper effort among cooperative vertebrates. In this study, we used the unusual cooperative breeding system of the long-tailed tit Aegithalos caudatus to test the hypothesis that the provisioning effort of helpers was positively correlated with their kinship to broods. We first use pedigrees and microsatellite genotypes to characterize the relatedness between helpers and breeders from a 14 year field study. We used both pedigree and genetic approaches because long-tailed tits have access to pedigree information acquired through social relationships, but any fitness consequences will be determined by genetic relatedness. We then show using both pedigrees and genetic relatedness estimates that alloparental investment by helpers increases as their relatedness to the recipients of their care increases. We conclude that kin selection has played a critical role in moulding the investment decisions of helpers in this cooperatively breeding species.

Kinship reduces alloparental care in cooperative cichlids where helpers pay-to-stay

“…Subordinate, non-reproductive members of social groups can gain indirect fitness benefits if they are related to the dominant breeders and distribute their help according to kinship 4 . Among vertebrates, evidence for the importance of indirect fitness benefits exists for some bird species, for example, Seychelles warblers 5 , Long-tailed tits 6,7 and Bell miners 8,9 . However, several studies did not find kinship effects on helping behaviour as predicted by kin-selection theory (in mammals 10 ; fish 11 ; birds 12 ; insects 13 ) and substantial help is sometimes shown by unrelated individuals 9,[14][15][16] .…”

The Right Tools for the Job: Cooperative Breeding Theory and an Evaluation of the Methodological Approaches to Understanding the Evolution and Maintenance of Sociality

“…For these reasons, observational studies should be augmented by comparative and experimental work to gain a holistic view of social evolution. Observational studies are particularly well suited to investigating animals which live in groups on discrete habitat patches or well defined territories (e.g., Nam et al, 2010;Marino et al, 2012). Similar to comparative analyses, there is a pervading taxonomic bias in observational studies leaning toward terrestrial taxa (Figure 1).…”

“…These methods have been used to demonstrate preferential provisioning of close kin in many species such as long-tailed tits (Nam et al, 2010), carrion crows (Canestrari et al, 2005), and gray mouse lemurs (Eberle and Kappeler, 2006). However, there is some ambiguity as to whether related individuals actively choose to remain philopatric and provision care to related young in order to maximize indirect benefits, or whether family groups form due to some direct benefit of remaining at the natal habitat and the provision of help to close kin is merely a result of nesting in family groups.…”

“…Observational studies have played a key role in informing this debate. For example, Nam et al (2010) examined the investment of helpers of the cooperatively breeding long-tailed tit, Aegithalos caudatus, using group history pedigrees and microsatellite genotypes from a 14 year field study to show that investment by helpers increased with relatedness. Likewise, Bruintjes et al (2011) found that subordinate cichlids, Neolamprologus pulcher, raised their levels of helping behavior when they had bred successfully and their offspring were present in the clutch.…”

Bell miner provisioning calls are more similar among relatives and are used by helpers at the nest to bias their effort towards kin

“…Nestlings are attended by 8-10 helpers throughout most of the nestling period [26,28], of which approximately onethird are unrelated to the broods that they provision [20]. Substantial costly helper investment and adaptive adjustment of effort according to brood kinship argue against recognition errors predominating in this system [20], with bell miners providing one of the best examples of fine-scale facultative adjustment of helping effort according to kinship ([20; see also [29]). …”