Abstract
Infanticide, the killing of unrelated young, is widespread and frequently driven by sexual conflict. Especially in mammals with exclusive maternal care, infanticide by males is common and females suffer fitness costs. Recognizing infanticide risk and adjusting offspring protection accordingly should therefore be adaptive in female mammals. Using a small mammal (Myodes glareolus) in outdoor enclosures, we investigated whether lactating mothers adjust offspring protection, and potential mate search behaviour, in response to different infanticide risk levels. We presented the scent of the litter’s sire or of a stranger male near the female’s nest, and observed female nest presence and movement by radiotracking. While both scents simulated a mating opportunity, they represented lower (sire) and higher (stranger) infanticide risk. Compared to the sire treatment, females in the stranger treatment left their nest more often, showed increased activity and stayed closer to the nest, suggesting offspring protection from outside the nest through elevated alertness and vigilance. Females with larger litters spent more time investigating scents and used more space in the sire but not in the stranger treatment. Thus, current investment size affected odour inspection and resource acquisition under higher risk. Adjusting nest protection and resource acquisition to infanticide risk could allow mothers to elicit appropriate (fitness-saving) counterstrategies, and thus, may be widespread.
Highlights
The killing of conspecific young by males, i.e. infanticide[1,2], is a widespread phenomenon that occurs throughout the animal kingdom[2,3]
To determine whether infanticide risk leads to adjustments in behaviour driven by fundamental trade-offs between investment in current and future reproduction, we studied the nest defence and explorative behaviour, e.g. for acquiring mates or food resources, of lactating, non-pregnant rodent females exposed to the scent of males presenting differing levels of infanticide risk
Females received the scent of the familiar sire of their current litter, which poses a lower risk to the offspring, while in the stranger treatment, females received the scent of an unfamiliar male, which poses a higher infanticide risk in microtine rodents[17,23]
Summary
The killing of conspecific young by males, i.e. infanticide[1,2], is a widespread phenomenon that occurs throughout the animal kingdom[2,3]. To determine whether infanticide risk leads to adjustments in behaviour driven by fundamental trade-offs between investment in current and future reproduction, we studied the nest defence and explorative behaviour, e.g. for acquiring mates or food resources, of lactating, non-pregnant rodent females exposed to the scent of males (potential mates) presenting differing levels of infanticide risk. We predicted that under a higher infanticide risk females will increase investment in current reproduction to avoid losing offspring, for instance, by staying in or near the nest, by increasing vigilance behaviour, or by deterring potential intruders. In the treatment simulating a lower infanticide risk, we predicted females to invest less time in offspring protection, and, potentially, more time in future reproduction, for instance, by leaving their litter more often to encounter a mating partner. Since a female’s fitness costs of infanticide depend on the value of the current parental investment[29], we predicted litter size to influence the magnitude of a female’s behavioural response to infanticide risk
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