By Jody Bourton
Earth News reporter
Hot stuff, a thermal image of a male damselfly
Female damselflies prefer hot males, scientists have revealed.
Male damselflies perform elaborate courtship displays, attracting females with high-speed flying manoeuvres.
Now a new imaging study can reveal that males that warm their bodies by flying in the sun are indeed 'hot stuff' and attract more females.
Hot-bodied males may benefit females by having access to the warmest territories, which in turn are optimal sites to lay eggs, the scientists say.
The study is published in the journal Behavioral Ecology and Sociobiology.
In a bid to attract females, some male damselflies perform intricate courtship displays, using specialised wings to fly at high speeds.
This courtship display can indicate to females the quality of the male damselfly and potentially the quality of the territory he defends.
Now new filming techniques have helped reveal a previously unknown aspect to the mating behaviour of Japanese damselflies (Mnais costalis), that are endemic to Japan, living along fast-flowing mountain streams.
"The key approach was to combine two technologies that have become cheap enough to use in the field," says Professor Michael Siva-Jothy from the University of Sheffield, UK who undertook the study with Professor Yoshitaka Tsubaki and Dr Yuka Samejima from Kyoto University, Shiga, Japan.
The team used a thermal imaging camera to measure the body temperature of the insect while in flight. The camera was originally designed for use by the food industry.
They also used a specialist high-speed digital camera.
"This was designed for elite sports coaches but it allows us to capture high speed images of behaviours that occur very rapidly and unpredictably," says Prof Siva-Jothy.
Using these techniques they discovered that hotter male damselflies get more mates.
Males flying in warm spots of sunlight have enhanced courtship displays as they attain higher body temperatures for longer, enabling them to court more females.
Previous research has found higher body temperature enhances flight performance in insects.
The team also reveals that the fortunes of a male damselfly can change depending on the amount of sun it gets.
"A female can change her preference for the same male depending on how hot he is. A 'wimp' can become a 'hunk' by sitting in the sun. And then become a 'wimp' again because his territory is in the shade," Prof Siva-Jothy explains.
It seems females prefer hot males, as they must have access to the sunnier spots along a river.
Eggs laid in these warmer spots may develop faster and have a higher survival rate.
Mating with a male in a sunny patch may also allow a female to stay warm while laying her eggs in the cold water. That will increase her ability to escape from predators and other male damselflies.
Hotter males may also be better at defending their mates, say the researchers.
They hope to learn more details about the behaviour, including how common it is among other damselflies.