Tiny bushcricket named as animal with the world's biggest testicles

Cricket balls: Tiny insect named as animal with the world's biggest testicles

It may only be half the size of a human finger, but this cricket is hiding a big secret: it has the largest testicles in relation to its body weight in the world.
Scientists have discovered that the male Tuberous Bushcricket has testes which are 14 per cent of its whole body mass.

To put this into perspective, a man with the same proportions would have to carry testicles weighing as much as five bags of sugar each.
This beats a species of fruit fly (Drosophila bifurca), thought to be the previous record holder for the biggest testes as a percentage of male body mass, at 10.6 per cent.

But despite this, the bushcricket does not necessarily produce the largest amount of sperm - contrary to traditional thinking - according to the study.
The research, led by biologists at the University of Derby, is published today in Royal Society Journal Biology Letters.

Lead researcher Dr Karim Vahed, Reader in Behavioural Ecology at the university, said: 'We couldn't believe the size of these organs; they seemed to fill the entire abdomen.

'We are also interested in the reason why they are so large.

'An almost universal evolutionary rule appears to be that such variation in relative testes size is linked to female mating behaviour.
'Testes tend to be larger in species where females are more promiscuous, as has been demonstrated in various species in fish, birds, insects and mammals.

'But at least two hypotheses could account for this pattern - sperm competition on the one hand and male mating rate on the other.
'Yet our study appears to be the first study to show that, in the case of the Tuberous Bushcricket, bigger testes don't necessarily produce more sperm per ejaculate.'

In the study Dr Vahed, Derby biology graduate Darren Parker, and Dr James Gilbert from the University of Cambridge compared relative testes size across 21 species of bushcricket.

They found testes were proportionately larger in species where females mated with more males - female Tuberous bushcrickets mate with up to 23 different males in their two-month adult life.

But they also found the bushcricket did not produce more sperm - in fact they produced less ejaculate.

They said a traditional assumption was that larger testes produce more sperm per ejaculate, giving males an advantage in sperm competition.
That competition is most intense when a female of a species mates with many males, so the male who produces the most sperm is often assumed to have an advantage, leading to development of larger testes in such species.

But more promiscuous females also increase the number of mating opportunities available for the male.
So it is possible larger testes have evolved in species that mate with more than one partner, allowing more ejaculate to be produced so they can have more successive matings, the scientists said.

'Traditionally it has been pretty safe to assume that when females are promiscuous, males use monstrously sized testicles to deliver huge numbers of sperm to swamp the competition - even in primates,' Dr Gilbert said.
'Our study shows that we have to rethink this assumption.

'It looks as though the testes may be that big simply to allow males to mate repeatedly without their sperm reserves being exhausted.'
Dr Vahed added: 'This strongly suggests that extra large testes in bushcrickets allow males to transfer relatively small ejaculates to a greater number of females.

'Males don't put all their eggs (or rather sperm!) in one basket.'

The scientists said their findings could give insight into links between endowment, promiscuity and reproduction within insects in the biological world.

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Tiny bushcricket named as animal with the world's biggest testicles

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