Fruit Fly Mating Mixup May Be Driving Species Toward Extinction

Fruit Fly Mating Mixup May Be Driving Species to Extinction
March 17, 2017

Be honest, how many times have you looked at a hornet and called it a yellowjacket, seen a stink bug in your home and worried it could be a kissing bug or mixed up the various species of flies and ticks?

Don’t feel bad, as it is very easy to confuse insect species. They are small and hard to see, and the millions of insect species around the world often look so similar that even entomologists with years of experience will argue over what species a given insect might belong to. Even blown up, many people might have trouble identifying the pictures in this article as different fly species.

Even bugs, it turns out, can get confused. Invasive male fruit flies will mate not only with females of their own species, but also with females of the native species, and according to a new study, that confusion could have dire consequences for the native fruit flies.

Drosophila hydeiDuke University biology professor Mohamed Noor found that the decline of a major fruit fly species in the American and Canadian West called Drosophila persimilis and the rise of the invasive Drosophila subobscura could be due, in large part to, these mating mix ups. The paper describing the study is published in the journal Ecology and Evolution.

Noor and his colleagues captured both persimilis and subobscura fruit flies, and isolated the female persimilis flies with males of either the native or invasive species. Over the course of one hour, one-third of the females placed with invasive males were forced—as evidenced by the females trying to shake off the males—into mating.

These interspecies matings occurred just as frequently as mating with the correct species, but they lasted twice as long. So not only do the invasive males mate with females that could be mating with their own species, but they take more time, during which the female is vulnerable to attack and not producing offspring.

To make matters worse, once the females mated with the invasive males, they were less likely to mate again in the next few hours than the females mating with the native males. The researchers are not exactly sure why this happens, but previous studies have shown that some fruit fly species have an allergy-type reaction to the sperm of other species, causing pain and swelling in the abdomen.

One of the things that separates one species from another is the ability to produce fertile offspring. Grey squirrels can mate with other grey squirrels to make grey squirrel babies that can make more grey squirrel babies because they are the same species. The best case scenario when two different species mate is viable but infertile offspring, like a donkey and a horse mating to create a usually infertile mule. In most cases, however, fertilization does not occur if the offspring are not viable.

Drosophila melanogasterThe interspecies mating of fruit flies do not result in any offspring and the researchers hypothesize that the confusion of the invasive subobscura flies—which studies have shown will attempt to mate with a ball of wax if it jiggles like a fly—could be causing the population decline of the native persimilis flies.

In a separate experiment, Noor placed one population of female persimilis flies with male persimilis flies and another with both persimilis and subobscura flies. The same-species group produced roughly 50 more offspring over four weeks than the mixed-species population did.

In the wild, this phenomenon is known as reproductive interference and could represent a threat imposed by invasive species beyond predation and competition. Reproductive interference has been repeatedly seen in controlled experiments in species like bean weevils and toads, but researchers have yet to observe reproductive interference by an invasive species in the wild.

Noor says he would like to observe these flies in their natural habitat, to rule out other explanations for their results, like the subobscura flies doing something else to harm persimilis young, like secreting a toxin or eating the young. It is also possible that in the wild, the invasive flies do not interact with the native flies at all.

If it does turn out that the invasive flies are causing the decline of the native ones, invasive species could be posing a whole new danger to native habitats. 

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.

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