Having an STI could benefit male animals

  Last updated May 21, 2019 at 3:25 pm

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New research has found that having an STI isn’t bad news for male animals and could actually benefit them in reproduction.


mating animals sexual conflict reproduction

Mating beetles. Credit: Damien Esquerre, ANU


New Australian research has found that sexually transmitted infections (STIs) can act to benefit male animal reproductive success when the evolutionary interests of males and females don’t align.


Megan Head from The Australian National University (ANU) says that the sexual interests of male and female animals are almost never the same.


“For males, it’s often good for them if they spread their sperm around, as they have more offspring and contribute more genes to future generations.”


“For females, it often pays to be a bit more choosey. Producing eggs can be quite taxing, and they have to invest a lot more time and effort after they’re fertilised as well.”


Sexual conflict causes unusual traits


Sexual conflict causes some species to develop unusual traits that increase the male’s reproductive success, like spiny genitalia, or mating plugs that stop a female from mating with partners until her eggs have been successfully fertilised.


The research suggests that STIs in males could work the same way.


“When animals become infected with a virus or bacteria they usually respond in one of two ways,” says Head.


“The first is: ‘oh no I’m sick, I better have lots of offspring now, because I’m not going to survive into the future to have them’. We call this terminal investment.”


“At other end of the spectrum, they invest everything in fighting the infection and getting better first, then hopefully go on to reproduce later.”


The ANU study shows if females take the ‘terminal investment’ approach and ramp up reproduction after becoming infected with an STI, this could benefit the male who’s passed on the disease to his partner.


“It means the female is more likely to use that particular male’s sperm to fertilise more of her eggs before mating again with anyone else,” explains Head.


Males evolve to have lower immunity


“Some studies show that males have lower immunity than females. It’s possible that in some species the males evolve lower immunity because for them, there’s a benefit to catching an STI.”


While this new research proves Dr Head’s theory is mathematically possible, she’s now keen to test it in lab scenario.


To do this, she’s studying Eucalypt beetles, which have a sexually transmitted mite that lives underneath their wing case.


The research is published in the journal Evolutionary Ecology.


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