Tasmanian devils evolving early motherhood, according to reports in ScienceNOW 14 July 2008, BBC News and ABC News in Science, 15 July 2008. Over the past decade Tasmanian Devils have been dying off due to a facial tumour disease that is spread when the animals bite one another, especially during mating. Since the disease has spread through the population many of the animals die around age three. Normally the females start breeding around age two years, and have a lifespan of five to six years, so they could raise several litters in a lifetime. Females with the disease only breed once, and may not live long enough to raise one litter to independence.
Menna Jones of University of Tasmania has found that since the spread of the disease females are breeding earlier. In one location, prior to the disease only 13.3 percent of females were breeding at one year of age. This increased to 83.3 percent after the spread of the disease. The researchers suggest the animals are able to breed at an earlier age due to reduced competition from food and mates in populations that are affected by the disease. The ScienceNOW article goes on to say: “The shift toward early breeding could be an evolutionary response, says Jones. By killing any adults that breed after age 2, the cancer could be selecting for younger breeding females, she notes. If so, the findings would make the devil the first known mammal to rapidly evolve its reproductive pattern in response to a disease.” The change is not defeating the disease, however, because the animals bite one anther during mating, and the younger breeding animals are starting to get the tumours.
Editorial Comment: The recent history of the Tasmanian Devil is one of death, disease and struggle – the very processes that are supposed to make living creatures evolve upwards, but the Tasmanian Devil is definitely going down, and may soon be out, as natural selection kills off the animals with tumours. The facial tumours first arose as a result of damaged genes, i.e. mutations. The spread of the tumours is caused by violent behaviour. This is Darwin’s “war of nature” at work, but it is simply diminishing the population to a subgroup that can breed early, not making them evolve into anything else.
It will be interesting to see if the early breeding decreases the average size of the animals. Fossil Tasmanian Devils were larger than their living descendents. By putting their resources into breeding early, rather than continuing to grow, could be one reason they became diminished in size. But, what has also been discovered since the above research was completed is that since mating in Tasmania Devils involves lots of face biting – this is only spreading facial tumours and increasing their rate of demise – this claimed evolution is really devolution. (Ref. marsupials, oncology, reproduction)
Evidence News 24 September 2008