Abstract
Punishment is claimed as an important mechanism to stabilise costly cooperation in humans, but its importance in social animals has been questioned recently due to both conceptual considerations and a lack of empirical evidence (only few published studies). We empirically tested whether there is evidence for punishment in communally nursing house mice (Mus musculus domesticus, direct descendants of “wild” animals). Communally breeding females pool their litters and raise all offspring together, indiscriminately caring for own and other offspring. Such a situation resembles a public good and provides scope for exploitation if females vary in their relative contributions to the joint nest (offspring number). We allowed two females to communally breed and conducted removal experiments both in the presence and absence of pups. We aimed to test whether reduced investment by one of the females (induced through separation from the partner and their combined offspring for 4 or 12 hours) leads to increased aggression by the other female after the reunion. We found no evidence for punishment, on the contrary, females increased socio-positive behaviours. The costs of losing a partner in a communally breeding species might be too high and hinder the evolution of punishment. Our findings add to a growing list of examples questioning the role of punishment in cooperating non-human animals and emphasise the importance of empirical testing of its assumptions and predictions.
Highlights
Cooperative offspring care is a wide spread phenomenon in different taxa [1, 2] and refers to the situation in which individuals help to raise offspring that is not their own
Twelve out of 25 pairs of females had to be separated before the first female gave birth, because of aggression between the females
We found an increase in socio-positive behaviours after the “removed” female was returned, both in the presence and absence of pups, indicating that “resident” females may encourage their partner to stay in the group, as we would expect if the costs of losing a partner are high
Summary
Cooperative offspring care is a wide spread phenomenon in different taxa [1, 2] and refers to the situation in which individuals help to raise offspring that is not their own. Reproductive skew varies among caring individuals, ranging from despotic systems with one breeding pair and several non-reproducing helpers (cooperative breeding), to egalitarian groups with several breeding females raising their offspring together in one nest (communal breeding) [3,4,5]. Caring for another female’s offspring and especially nursing non-offspring requires an evolutionary explanation, considering the high energetic costs of parental care in general and in particular of lactation in mammals [6]. Cooperation in these situations is expected to be evolutionary stable only when individuals gain indirect or direct fitness benefits [7,8,9].
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