One for the evolutionary biologists and entomologists... speciation in crickets?

Question

A recent study in Biology Letters has shown that a mutation causing a silent chirping in crickets has been spreading rapidly in a hawaiian cricket population.

http://www.newscientist.com/article.ns?id=dn10121&feedId=online-news_rss20

The article comments on what may happen in the future, but doesn't mention the possibility that the crickets with the flatwing mutation will eventually constitute a separate species from those that remain able to call.

This seems like a perfect example to me of what may promote speciation in a population. Am I missing something?

Answer 1

That is an interesting article, thank you!
Well, at this point, it does not seem like speciation because this particular mutation drastically decreases the chances of mating... So far, it has spread in the population because there are still males capable of producing sound. But what will happen if all the chirping males disappear?
I think it's too severe a handicap for this population, unless as you say, they could develop some other type of reproductive communication cues (chemical, tactile, etc). In that sense, I think crickets may already be too constrained by their previous history, and it would be improbable.

For sympatric speciation to occur, this mutation in the males should be accompanied by some shift in the preferences of the females, so that the mutant ones should be attracted by the silent males. If that were the case, you'd have a pretty case of instantaneous speciation. Regrettably, the females still prefer the singing guys.

Another possibility that's mentioned in the article is that frequency-dependent selection ensues. That would produce a shifting balance of both morphotypes in the population, thus maintaining the polymorphism.
http://www.blackwellpublishing.com/ridley/a-z/Frequency-dependent_selection.asp
- The silent crickets have higher survival rates, but are reproductively handicapped
- The chirping ones do better reproductively, but are more exposed to the parasites.

I think I'll keep tabs on this case... quite interesting!

Answer 2

I agree with you regarding the probability of a speciation event, it might be a form of sympatric!? speciation if they continue to survive and diverge genetically. However, from an ecological perspective they have a big problem in potentially going extinct before they have a chance of evolving into a new species.
By avoiding the parasitic flies they have reduced their potential to find mates which in turn reduces the chance of this chirpless mutation being passed onto the next generation. It seems like most of the chirpless males are placing themselves in proximity to chirping males to find a mate but this strategy is still likely to put the chirpless males at a reproductive disadvantage unless the females maybe attracted by some other cue such as pheromones?

Answer 3

That is incredibly interesting, thanks for posting this.

The possibility of speciation would definitely require that the flatwing males develop another method of securing females for reproductive purposes.

Considering that 90% of the current population appears to be flatwing it would be interesting to find if the flatwing gene is dominant or recessive.

If it is dominant, then the huge population proportion could be due to survivorship in the last generation (with many of the singing recessives taken out by parasitoids, but still successfully reproducing - and helping some of their flatwinged brethren by attracting mates).

If the flatwing gene is recessive though, that would indicate that the parasitoid fly is creating some major selective pressure on the population. So much so that the population could very easily be wiped out before it has a chance to adapt a new reproductive strategy.

I wonder if the females show the same population ratio.

Many interesting fields of study to follow up on!

Answer 4

Eh my answer won't be as long and edumacated as the other people but I was under the impression that something is considered a different species when the ability to breed and produce fertile offspring is lost. This is why a chihuahua and an Irish setter aren't considered different species despite the wildly different physical characteristics. Perhaps the quiet and normal crickets can still breed normally??