The decision to cooperate: kin recognition mechanisms in female house mice

This project addresses mechanisms underlying kin recognition, and the importance of kinship in cooperative breeding between females. Cooperative breeding occurs when animals assist in rearing offspring that are not their own. For example, female house mice frequently rear their offspring communally with another breeding female, providing milk to all pups in the communal nest. This decision is facultative - they can choose to cooperate with a particular partner or not. However, the factors that underlie social partner choice, and how this choice influences an individual female's investment in own and other pups, are poorly understood. It is generally assumed that kinship drives such cooperative behaviour by increasing the success of relatives that share genes. Implicitly, this requires reliable recognition of close kin in species where related and unrelated individuals mix, although we have surprisingly poor understanding of the abilities of animals to recognize kin and the mechanisms that might underlie this. Recently, we discovered a highly polymorphic genetic identity signal that is used to avoid inbreeding with close kin by house mice. This has provided clear evidence of a genetic recognition mechanism that is used to identify close kin sharing the same highly polymorphic genetic marker. We will use this proven genetic marker to test whether female house mice prefer known kin as cooperative partners. We will also use a novel non-invasive approach to label the milk of individual mothers and measure investment in each pup in communal nests for the first time. This will allow us to address whether those cooperating with known kin show more egalitarian investment in their own and other offspring than those cooperating with other females. This type of simple genetic kin recognition mechanism is limited, though, because it identifies only a small proportion of close kin. Through modeling, we have generated testable predictions concerning the proportion of sibs and unrelated animals that would be recognized using alternative genetic kin recognition mechanisms. Theoretically, behavioural imprinting on maternal alleles detected through a mother's phenotype during rearing could allow reliable recognition of a very high proportion of close kin. However, the key requirements for recognition of kin using this mechanism have yet to be tested. In this project, we will establish whether normal, genetically variable house mice can recognize maternal kin through behavioural imprinting on maternal alleles. We will determine whether they imprint specifically on three highly polymorphic gene clusters that encode established genetic identity signals in mouse scents, or on other genetic loci. We will also test whether a common maternal environment, which influences the scents of inbred genetically homozygous laboratory mice, contributes to any recognition of maternal sibs and half-sibs. Our findings will have general relevance for understanding the extent to which animals are able to recognize close kin in a broad range of social contexts. Kinship is unlikely to be the only factor influencing the decision to cooperate among breeding females. Mice can gain considerable information about female physiological status through urinary proteins and metabolites (steroid sulphates) detected through the vomeronasal olfactory subsystem. We will test whether individual partner preferences that are not determined by kinship correlate with expression of these physiologically-variable scent components. We will also test whether females avoid inbred partners (from sib matings) that would have significantly poorer success in raising offspring to weaning.