Species lose functions when others work for them

A parasitic wasp which cannot reproduce independently because a bacterium has taken over its egg production; such loss of function occurs is more widespread in nature than scientists previously assumed. This was shown in a new evolutionary theory formulated by researchers at VU University Amsterdam and the University of Wisconsin. They publish their findings today in the journal Ecology Letters.

When two species have a prolonged ecological relationship, one species sometimes loses an essential function because it is provided by the other. “As a result of natural selection, species stop producing a compound if an ecological partner in their environment is already producing it,” says VU University professor Jacintha Ellers. “Species therefore take advantage of others working for them. Such compensated trait loss is a result of co-evolution of species. However, dependence on others can become a major disadvantage if the ecological partner disappears, for example due to climate change. Without the partner the chance of survival is small,” says Ellers.

For a long time scientists have underestimated the scale of compensated trait loss because its effects remain hidden as long as one species works for the other. Ellers: “But now there is an increasing number of species whose entire genome has been sequenced. That makes it easier to find genes that have lost their function. Therefore, more and more cases of compensated loss of function will come to light.” The scientists reviewed the scientific literature and found evidence for over forty cases of compensated trait loss in ecological interactions such as mutualism, parasitism and herbivory.

Apart from no longer being able to reproduce independently, parasitic wasps also cannot produce fat anymore because they eat the fat from their host. Corals do not produce certain amino acids anymore because a bacterium provides them. And leaf cutter ants are unable to digest proteins because they grow a fungus that provides them with amino acids. It has been known for many years that humans and other primates no longer produce vitamin C because the fruit they consume already contains enough of it.

Compensated trait loss is common in parasites and pathogenic fungi. The researchers therefore believe that
their findings can be used for agricultural pest control. “Pest control should not only focus on the parasite or
fungus, but also on other species that have taken over their lost function,” says Ellers. “For example, the
blight fungus Rhizopus microspores is dependent on a bacterium for its reproduction. So by controlling the
bacteria the fungus will be unable to reproduce, which may be a promising way to slow its spread.”

Science news reference: 

Ecological interactions drive evolutionary loss of traits. Jacintha Ellers, E. Toby Kiers, Cameron R. Currie, Bradon R. McDonald, Bertanne Visser. Ecology Letters, 2 JUL 2012. DOI: 10.1111/j.1461-0248.2012.01830.x

Science news source: 

VU University of Amsterdam