Looking spiffy to draw the attention of a lover – and staying attractive – is tough at the best of times. But for male Australian painted dragons, which sport a bright yellow and orange head at the start of the mating season, keeping their sexy signals on means a faster death.
Researchers in Austalia and Poland found those that remain colourful for longer aged faster than their fading counterparts.
The work was published in Biology Letters.
Colourful mating displays, and the fading that follows, are common in the animal kingdom. Many pigments, such as yellow and orange carotenoids, double as antioxidants and combat the destructive effects of reactive oxygen species.
Reactive oxygen species, as their name suggests, are molecules containing oxygen that readily react with other chemicals. They can damage DNA and accelerate ageing.
They do this by eroding the caps on the ends of chromosomes called telomeres. As long strings of repeating DNA, telomeres protect the chromosome from deteriorating. But with each cell division, telomeres shorten. Once they reach a critical length, the DNA is no longer protected and is prone to damage. Some cancers arise from short telomeres.
Mathieu Giraudeau, then at the University of Sydney in Australia, and colleagues thought: if an animal directs its stock of antioxidants to its skin, what does this mean for its longevity?
A handy test subject was the painted dragon (Ctenophorus pictus), a species of lizard endemic to southern and central Australia. Males live just one year, so they have to make their breeding season count. At the start of the season, their head blushes yellow, orange and red, thanks to carotenoids and another antioxidant pigment, pteridine.
But some males start fading faster than others.
So the researchers collected 53 male painted dragons from Yathong Nature Reserve – around 650 kilometres west of Sydney – and monitored them during the second half of the breeding season.
They took blood tests to measure telomere length and levels of reactive oxygen species in the animals and photographed the left side of their head to keep track of colouration.
Indeed, the lizards that maintained a colourful glow longer ended up with shorter telomeres than the faders.
Surprisingly, though, reactive oxygen species levels weren’t related to colouration or telomere erosion. This may be, the researchers suggest, because they measured reactive oxygen species as a whole. If they’d picked out specific reactive oxygen species, such as superoxide, they might have found a link.
Given it seems to be a bad thing to be colourful for longer, why do male painted dragons do it?
It comes down to the females, the researchers write. They’re able to hold on to sperm to use later, so a bright male able to make a large number of “deposits” early in the breeding season may well sire offspring even after he’s dead.
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