A reduced propensity to cooperate under enhanced exploitation risk in a social mammal

Abstract

Conditional adjustment of cooperativeness to the expected pay-off might be a useful strategy to avoid being exploited in public good situations. Parental care provided towards all offspring in a communal nest (containing offspring of several females) resembles a public good. Females indiscriminately caring for all young share the costs equally, but the pay-off may vary depending on their contribution to the joint nest (number of own offspring). Females with fewer offspring in the joint nest will be exploited and overinvest relative to their contribution. We experimentally created a situation of high conflict in communally nursing house mice, by using a genetic tool to create a difference in birth litter sizes. Females in the high conflict situation (unequal litter sizes at birth) showed a reduced propensity to give birth as part of a communal nest, therefore adjusting their cooperativeness to the circumstances.

Oxytocin administration during early pair formation delays communal nursing in female house mice

“…A communal litter in this study was determined when the second female gave birth within 16 days of the first female and pups were raised in a single nest (this definition has been used in other studies (Ferrari et al, 2016;König, 1994b)). Day 16 was chosen as weaning commences one day later when pups begin to eat solid food and reduce milk consumption (König and Markl, 1987).…”

“…Within a communal litter, under our previous definition, litters can differ by up to 16 days in age (Ferrari et al, 2015;König, 1994b), and when heavily pregnant the female giving birth second in a communal litter may kill some or all of her partners young before giving birth herself (Ferrari et al, 2016;König, 1994b, such infanticide has never been observed after offspring reached 17 days of age).…”

“…We were able to monitor litter loss (infanticide) as pups were typically found with their head bitten off or wounds to the neck region. Infanticide is common in pregnant female house mice (McCarthy and Saal, 1985), and pregnant females often kill pups already present in the nest before giving birth themselves (Ferrari et al, 2016;König, 1994b).…”

“…Therefore, any elevated maternal aggression could be analogous to the natural behaviour of females postpartum. Especially as female house mice are known to kill pups of another female when heavily pregnant (Ferrari et al, 2016;König, 1994b;1994a;McCarthy et al, 1986). Alternatively, females have been shown to kill own pups under stressful situations (Poley, 1974).…”

Evolution of strategic cooperation

“…For example, pairs of female house mice have been shown to adjust their contribution to communal care in response to unequal litter sizes, increasing the time spent caring for the group's offspring when their own offspring make up a larger fraction of the group (Ferrari et al. 2016). Similarly, soldier‐producing aphids increase their contributions toward gall defense behavior when in highly related groups, which comes at a cost to their personal reproduction (Abbot et al.…”