Batty bigamy and worse
July 20, 2010 Leave a comment
Normally, inbreeding isn’t such a good thing
The idea that three generations of related females might share the same mate is, frankly, abhorrent and strange to us humans, but among bats, this tactic may be a fairly common phenomenon.
Generally, animals avoid inbreeding with one another because doing so results in the development of “inbreeding depression” in a population. This depression refers to falling rates of reproduction and survival that result when relatives interbreed. An example of what happens with inbreeding can be found among the royal houses of Europe in previous centuries. The members of these families would often receive papal dispensations to ignore the rules about consanguinity—close relatedness—to be allowed to marry another royal personage. There just weren’t that many eligible royal folk wandering around Europe and inbreeding was the ultimate result.
Hidden disorders emerge
Because of this inbreeding, often with third or second cousins marrying through several generations, the royal families would manifest disorders that normally would remain hidden. Some of these disorders required the inheritance of two alleles, both carrying mutations, for them to manifest. If the royal families had not constantly been intermarrying, the two recessive alleles would have been much less likely to come together in a single person. As it was, many royal households had children who were sickly, who could not reproduce successfully, or who manifested mental illness or retardation. One particularly notable trait that arose through several families was the “Hapsburg jaw,” a severe underbite and jutting jawbone that traced its way through the European royal chessboard. One potentate had a jaw deformity so severe that he could not chew his food.
Horseshoe bats don’t care
But the greater horseshoe bat appears to be untroubled by such issues of consanguinity, at least in the sense that related females from several generations will mate with the same male. In the world of the horseshoe bat, it pays to be a male bat who attracts a female. If the male attracts the daughter, he has a good chance of also mating with the mother and the grandmother, too. And he may be set for his relatively long bat-life; greater horseshoe bats can live up to 30 years, and females will consistently select the same male for the annual bat mating ritual, which results in a single offspring per female each year.
In spite of this inbreeding and polygyny, in which several females mate with the same male, the females apparently are quite adept at avoiding mating with their own fathers. A female will only mate with her mother’s partner if her mother has switched partners and is no longer mating with the daughter’s father.
Beat that, Belgium
This complex mating web results in a bat family tree that is more confusing than that of all the royal houses of Europe combined. It is possible for a female bat and her maternal half-aunt to be half-sisters on their father’s side.
How did researchers unravel this remarkable complexity? They identified a colony of female bats—who spend most of the year living in single-sex groups—in an old mansion in Great Britain. DNA analysis showed that the several hundred females lived in about 20 groups of related females who shared mates. The females met up with the males, who lived in a permanent stag party condition in a nearby cave, only once a year. Researchers speculate that females use smell to avoid mating with their fathers.
What benefit this interbreeding?
Why risk interbreeding in the first place? Actually, many species exhibit tactics that lead to closer kinship among individuals. Researchers speculate that closer kinships result in better teamwork to protect the genetic investment. In the world of team-playing ants, for example, female siblings can be 75% related, rather than the 50% most sexually producing species share genetically with their siblings. Experts believe that this extra genetic relatedness enhances the teamwork atmosphere of an ant colony. In much the same way, the related groups of female bats work together to raise the young. Researchers believe that this horseshoe bat tactic may extend beyond the greater horseshoe to other bat species.