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Social parasite bees fight to survive

Between parasites and hosts there is often a high stakes evolutionary arms race. As hosts develop defenses to ward off parasites, the parasites in turn evolve abilities to avoid these defenses. Such is the case of social bees, Exoneura, and their social parasite bee species, Inquilina.

Social parasites live in the colonies of their hosts, essentially getting a free ride. The scientists wanted to take a look at evolution and this case of social parasitism, so they conducted a study. 

“These parasitic species spend their entire life cycle within the nest of the host species and have extreme adaptations to social parasitism, they are not able to survive without their hosts,” explained study first author Dr. Nahid Shokri-Bousjein.

The researchers were curious how parasitism evolved when the parasite and host had differently sized populations. Because evolution depends on random novel mutations, larger populations are likely to have an evolutionary advantage. This means that a parasite with a greater population than its host might be able to “out maneuver” them. It’s a bit tricky though, because if a parasite becomes too good at parasitizing it could kill off its host and thus itself. 

“We can see this problem play out with COVID-19. The virus has a much bigger population size than its host (us!), so its ability to evolve around our defenses is great,” said Dr. Shokri-Bousjein. “We see this in terms of new COVID variants emerging and then spreading.”

Interestingly, previous research shows that the host and parasite are evolving at the same pace, keeping in step with each other, despite the difference in population size between the two. 

“Evolutionary wars between species and their enemies may be much more complex than we have thought. Large population sizes might allow more strategies to arise, but maybe the critical issue is how effective those strategies are,” said Professor Mike Schwarz of Flinders University.

“Species like these bee social parasites are on the very edge of survival: they might tell us something about how you can survive when your very existence is under threat.”

The study is published in the journal Ecology and Evolution.

By Zach Fitzner, Staff Writer

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