Researchers from the University of Cambridge's Department of Zoology found that female species developed a strategy called "sperm competition" to save their offspring from infanticide.
Infanticide involves mature species killing off its young offspring and is common among animals. Scientists have been studying this significant occurrence as it might provide insight on human infanticide.
Earlier studies showed the behavior is commonly observed in groups dominated by one or a few males. Since the group is mostly females, the male must compete with other males for control and this is often done violently – including killing their young offspring. But there also some instances of females committing infanticide to limit resources and defend their territory from the males.
A new study has provided evidence that female species learned to fight back against infanticide without making it obvious to the males. Researchers have observed that the mouse lemur species seems to have developed a smart strategy to prevent males from killing their offspring: sperm competition.
Sperm competition happens when a female mates with different males in a short period. This approach leads to "paternity dilution" or confusion regarding the paternity of infants that reduces the risks of killing their infants. Male lemurs attempt to counter this biological move by increasing their testis to produce more sperm, which increases the chances of these spern winning the race to fertilize a female's egg. Researchers found that the testes of mouse lemurs swell to ten times their normal size during breeding season.
"Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears – since males face the risk of killing their own offspring, and might not get the benefit of siring the next offspring," said lead author Dr. Dieter Lukas from the University of Cambridge's Department of Zoology.
The study's findings imply that infanticide is not an instinctive behavior among species, but rather a strategy for dominance and power. On a brighter side, the researchers proved that the practice is reversible.
"Male infanticide appears and disappears over evolutionary times according to the state of the evolutionary arms race between the sexes. Although infanticide may not have contributed to shape the diversity of mammalian social systems, it has deeply influenced the evolution of sexual behaviour and sex roles," said study co-author Dr. Elise Huchard from the CNRS Centre d'Ecologie Fonctionnelle et Evolutive in Montpellier.
Further details of the study were published in the Nov. 14 issue of Science.
