"Infanticide" is the term used for the termination of a neonate after it has been born, and in zoology this often applies to the termination and/or consumption of newborn animals by either a parent or an unrelated adult. In rodents, it is not uncommon for the mother to commit infanticide shortly after parturition (giving birth) under conditions of extreme stress (parental infanticide), or for an unrelated male to kill neonates not his own (nonparental infanticide).
Contents |
Parental infanticide is perhaps the most confusing behaviour to understand, as in many cases it can seem maladaptive for a parent to terminate offspring carrying its own genetic material. However, studies in mice have indicated infanticide may be a gentically heritable trait,[1] and may even have a learned element,[2] so there is clearly more to the behaviour than might be expected. The occurrence of infanticide seems to vary within rodent species between parents. For example, male meadow voles and house mice can be classed as either 'infanticidal' or 'non-infanticidal' depending on their history with other litters they have sired, although studies have shown that females do not discriminate between these classes when choosing a mate.[3]
Some rodent species (most typically males) will take the chance to kill neonates that are unrelated to them should opportunity permit. There is thought to be several benefits by doing so, which not only include nutrition benefits (particularly where food is in short supply[4]) but also non-direct benefits, such as allowing access to more resources, improving reproductive opportunities and the retainment of energy and resources that might otherwise be spent on unrelated offspring.[5] A common causal factor of infanticide, particularly among sciurid rodents, is direct resource competition, therefore killing the pups of an unrelated neighbour would prevent resource competition with those individuals in the future.[6]
Work by Blumstein (2000)[7] highlighted the following rodent species which have previously been associated with infanticide in published scientific literature. Assessment of these traits lead Blumstein to conclude that infanticide evolved independently in sciuromorphs, myomorphs and caviomorphs.
Not all rodent species commit infanticide, and in fact some species are remarkable for their lack of this behaviour. One such species is the degu, a highly social caviomorph rodent from central Chile. Degus have been found not to harm even unfamiliar pups, and male degus will even accept other males' litters into a group without problems.[8] This is thought to be related to the communal nesting habits of the species[9] and reflects genetic trends rather than a lack of the conditions that lead to infanticide.