Communal nursing in wild house mice is not a by-product of group living: Females choose

Andrea Weidt,Anna K Lindholm,Barbara König

doi:10.1007/s00114-013-1130-6

Abstract

Communal nursing, the provision of milk to non-offspring, has been argued to be a non-adaptive by-product of group living. We used 2 years of field data from a wild house mouse population to investigate this question. Communal nursing never occurred among females that previously lacked overlap in nest box use. Females nursed communally in only 33 % of cases in which there was a communal nursing partner available from the same social group. Solitarily nursing females were not socially isolated in their group; nevertheless, high spatial associations prior to reproduction predict which potential female partner was chosen for communal nursing. An increase in partner availability increased the probability of communal nursing, but population density itself had a negative effect, which may reflect increased female reproductive competition during summer. These results argue that females are selective in their choice of nursing partners and provide further support that communal nursing with the right partner is adaptive.Electronic supplementary materialThe online version of this article (doi:10.1007/s00114-013-1130-6) contains supplementary material, which is available to authorized users.

Highlights

A controversial example of altruism in mammals is communal nursing, where milk is shared between own pups and young produced by another mother
Using females that overlapped for at least 5 days, we found that mothers had a significantly higher index of spatial association during the non-reproductive period with their actual nursing partners than with their potential, but not chosen, Determinants of communal nursing decisions
We predicted that if communal nursing is a by-product of group living, females would communally nurse whenever a litter had been born to another female with overlapping nest box use

Summary

Introduction

A controversial example of altruism in mammals is communal nursing, where milk is shared between own pups and young produced by another mother. Communal nursing occurs in all major mammalian taxa and is relatively common among rodents, carnivores and pigs (Packer et al 1992). Some authors consider it a non-adaptive trait as lactation in mammals involves high energetic investment and can result in future reproductive costs (see Lewis and Pusey 1997; Hayes 2000; Roulin 2002). Manning et al (1992) observed, in their study of house mice in seminatural enclosures, that solitary nests mainly occurred when there was no opportunity to nest communally They suggested that communal nursing is a side effect of sharing the same nest. Other non-adaptive explanations of non-offspring nursing are milk theft by parasitic young, misdirected maternal care or sexual conflict (for reviews see Lewis and Pusey 1997; Hayes 2000; Roulin 2002; Roulin and Hager 2003)

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