"Teen Sex" Rising for Cancer-Affected Tasmanian Devils
"Teen Sex" Rising for Cancer-Affected Tasmanian Devils"Teen Sex" Rising for Cancer-Affected Tasmanian Devils
Ker Than
for National Geographic News
July 15, 2008
Tasmanian devils affected by a deadly cancer epidemic are engaging in teenage sex as a matter of survival, a new study finds.
The famously feisty mammals found on the Australian island of Tasmania typically live for five to six years and don't begin mating until age two. But in some populations threatened by the contagious and disfiguring facial tumor disease (see video), more than half of females one year old or younger have begun breeding.
"This represents a sixteen-fold increase in precocious sex for the species," said study leader Menna Jones of the University of Tasmania in Australia."Teen Sex" Rising for Cancer-Affected Tasmanian Devils
The team believes some females are reaching sexual maturity faster and reproducing sooner because the hefty toll of the disease has freed up food and created less competition for mates.
The finding is detailed in this week's issue of the journal for the Proceedings of the National Academy of Sciences.
Survival Advantage
Early breeding could help explain how some devil populations have survived despite being ravaged by the rare facial cancer for more than a decade, said study co-author Clare Hawkins, also of the University of Tasmania.
Yet "despite these compensations, the numbers in all diseased areas are continuing to steadily decrease," Hawkins added. "The compensation doesn't appear—at least so far—to be sufficient."
Scientists fear that, if trends continue, wild Tasmanian devils could disappear as soon as 2030. (See story.)
While early breeding alone may not be enough to prevent extinction, it could buy the animals enough time to adapt to the disease.
"Because the disease is consistently fatal, devils are under very, very strong selection on a number of fronts," Jones said.
The natural selection could be for "disease resistance, early breeding, or behaviors that keep the devils out of trouble," Jones said.
For example, scientists think the facial tumor disease is spread by devils biting each other while mating."Teen Sex" Rising for Cancer-Affected Tasmanian Devils
If the species can hang on long enough, devils that bite less or that are better able to avoid bites will have more chances to reproduce, Jones said.
Eventually these milder-tempered devils could form the bulk of their populations because they are less likely to pass on the disease.
"Teen Sex" to Stay?
Since early breeding allows female devils to give birth at least once before falling victim to the disease, it could become an "evolutionarily fixed" trait for the species, scientists say.
"Most animals are dying at about two-and-a-half years old, so they may die halfway through raising their young," Jones said. "Any animal that breeds as a one-year-old is going to have a better chance of passing on its genes."
This trait makes sense, said Esben Moland Olsen, a biologist at the University of Oslo in Norway who was not involved in the study.
Olsen has documented a similar shift toward younger breeding in populations of cod threatened by overfishing. His studies suggest early reproduction is already becoming a fixed part of the fish's life cycle.
"Based on the latest data I have seen, the change seems to be holding," Olsen said.
"Although cod populations have not fully recovered, I tend to think that things would have looked even worse in the absence of a life-history change towards early maturation."
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