Violent sex means chameleons die young
- Violent sex means chameleons die young* 22:00 30 June 2008* NewScientist.com news service* Nora SchultzImages and full article at: http://www.newscientist.com/article/dn14226-violent-sex-means-chameleons-die-young.htmlTalk about staying stuck in childhood – a tiny chameleon from Madagascar spends two-thirds of its life inside its egg. Once it hatches, it engages in brutal sex, then dies before its offspring see the light of day.The astonishing life-history of Furcifer labordi, which researchers have unravelled for the first time, is more reminiscent of an insect than a vertebrate. The lizard is also one of the smallest known chameleons: males are 9 centimetres long, and females reach just 7cm."I thought it was really bizarre that I could only find adults of this species," says Kris Karsten at Oklahoma State University in Stillwater, US. A few weeks into his first season observing the lizards in their natural habitat, all the adults died as Karsten looked on, bewildered.Over four years, Karsten and his colleagues marked 400 chameleons and followed seven with radio tags to study their growth patterns, lifespans and behaviour. They discovered that juveniles hatch in synchrony in early November, grow into adults within just seven weeks, mate, and all die without exception by April, just before the harsh dry season settles in.Around this time, they seem to lose much of their strength. Karsten and his colleagues saw several falling out of trees for no apparent reason.Just before dying, females produce about a dozen eggs, just 12 millimetres long. These incubate in the ground for 8 months and hatch in November – and the entire cycle starts over again.This life-history is common in plants and invertebrates. But of some 28,000 species of four-limbed vertebrates just 20, including other lizards and some male marsupials, are thought to have annual life-cycles.Death by sexKarsten thinks sex might be what kills the adults off after just 4 to 5 months. In as-yet-unpublished experiments, he studied the mating behaviour of F. labordi in enclosures and discovered that courtship is a risky business for both sexes."These males will fight fiercely in long, rather drawn-out combats, and their courtship behaviour is also rather violent," Karsten told New Scientist.The dry season in Madagascar is so inhospitable that many native species of chameleon hibernate through it to save energy. But it appears that F. labordi die instead.Live fastHeinz Grillitsch at the Natural History Museum in Vienna, Austria, says that when harsh physical and social environments lead to high adult death rates, it can make sense for a species to put all its energy into a single reproductive effort. He says a similar strategy may be more common among chameleons than previously thought."I have often seen pregnant females that are filled to the brim with eggs lose two-thirds of their body weight when they lay them. They turn into a bag of skin and bones and die soon after," Grillitsch says.Karsten now wants to find out why F. labordi die instead of hibernating. He thinks the chameleons may have high levels of androgens – a class of sex hormones – or be particularly sensitive to them.This could explain their aggressive mating behaviour and relatively early death. Animals with high levels of androgens expend a lot of energy and can have suppressed immune systems. As a result they tend to have short life-cycles.