Overprotective Mice Mothers

At some point in our lives we have all thought our mothers were overprotective, but have you ever wondered if there was a reason for this behavior other than the common explanation that it is for your own good and because they care? Many species of animals give parental care and protection to their young in the early stages in life so as to increase the survival rate of those offspring, but different animals exhibit this behaviour in different ways. In mice, females have been observed to become more anxious and aggressive as their pregnancies progress with the most aggressive behavior exhibited just prior to giving birth and during lactation.

Research into the causes of aggression in prospective mice mothers by F.R. D'Amato, R. Rizzi, and A. Moles was published in the October 2006 issue of Animal Behaviour. These scientists hypothesized that the overall number of pups and the male to female ratio in the litter would determine female agressive behavior. Scientists believed that as the number of pups in a litter increased the level of aggression of the mother would also increase, and that a mother mouse about to have more male than female babies would also show higher levels of agression than a mouse about to have a litter with more female than male pups. The experimental results showed that aggression does indeed increase with the number of pups in a litter, but does not show a relation to the male to female ratio of the litter.

To explain this behavior D'Amato, Rizzi, and Moles point out that maternal aggression is key in the survival of the pups because the behavior of the mother provides some protection for the young from both predators and fratricidal male mice. Scientists suggest that certain internal and external stimulii that the femal recieves from her litter give her an idea as to the reproductive value of that particular litter. A larger litter means that a mother's genes will be passed on to the next generation in higher frequency so it maks sense that the female will have more to gain in an evolutionary sense if a larger litter survives.

So in the end it comes down to a matter of weighing benefits against losses. When confronted with a predator or intruding male a female must decide to run or try to chace it off. If she runs her pups are likely to die, but she will live to breed another day, whereas if the mother stays she may die her pups have a greater chance of survival. This explains why female mice show less fear and more agression when confronted with a predator or male while she is carrying and nursing a large litter of pups. If a female has a litter of 10 or 12 pups her genes better represented in the next generation than if she has a litter of 6 or 7 pups. When we consider this it makes sense that the mother will be less likely to run and more likely to stay and try to chase off an intruding predator or male mouse when she has more babies on the line, because she has more to gain from an evolutionary stand point if a litter of 12 survives than she does from the survival of a litter of 6.

posted by MFP