What do you do when your only means of attracting members of the
opposite sex also puts your life in jeopardy? For field crickets on the
Hawaiian island of Kauai, shutting up seems to work.
According to a new study, rapid evolution in the Kauain population of
the oceanic field cricket Teleogryllus oceanicus has rendered
nine-tenths of the males there incapable of producing their iconic
night-time call. The genetic mutation, which changes the shape of the
male's wing to make it silent, means the crickets are better adapted
to avoid a deadly parasite.
The finding dumbfounded biologist Marlene Zuk, at the University of
California in Riverside, US, who first thought the dwindling population
of crickets she was studying had gone extinct when she no longer heard
"If you're a cricket and you're a male, your life is defined by
calling," Zuk explains. "How are you going to find a female, and
once you do, how are you going to get her to mate with you without your
Zuk found that the quiet crickets maintained their reproductive chances
by congregating near to the few remaining male crickets that are still
capable of calling.
In laboratory tests involving speakers that broadcast cricket calls,
males that were physically unable to call would approach as close as 1
centimetre to the speakers. In contrast, males that could make their
own calls usually settled more than a metre away.
The reason, says Zuk, for such a dramatic physical and behavioural
change is the small fly, Ormia ochracea. The fly uses highly sensitive
ears to hone in on the male cricket's call before depositing its
larvae on the cricket's back. The larvae then dig into the
cricket's body where they eat their host alive in about a week.
In previous studies, Zuk noticed that the hopping insects behaved
differently around the flies. Populations of crickets that lived in
areas where the flies were present were more likely to wait until it
was completely dark to start calling. They were also more reluctant to
resume calling in laboratory tests after they had been disturbed by the
simulated sound of a fly buzzing by.
Zuk calculates that the new wing mutation first occurred on the island
of Kauai sometime in the late 1990s and spread to 91% of males there by
Loss of calling has resulted in a strong reduction in mortality for the
male crickets. Out of 121 males that had the non-calling mutation, only
one harboured the fly larvae compared to previous infestation rates of
greater than 30% in normal-winged males.
William Cade, a researcher of cricket biology at the University of
Lethbridge in Alberta, Canada, says the study substantiates prior
theories: "It confirms our predictions from years ago that
acoustically orienting enemies, especially flies, can have a profound
effect on the evolution of mating signals in crickets."
Now that just 10% of males on Kauai still have normal wings and can
call, what happens next open to debate. The silent flatwing crickets
depend on a certain proportion of males still being able to attract
females, so extinction is a possibility, says Zuk.
Another possibility, she says, is that the proportions of flatwings and
normal-wings will cycle, so that the normal-wings will be at an
advantage now since they get more mates, but that would mean parasite
fly populations increase, which then puts the flatwings at more of an
advantage, and so forth.
This kind of oscillation has been predicted for other host-parasite or
predator-prey systems, but seldom demonstrated, Zuk says.
Journal reference: Biology Letters (DOI: 10.1098/rsbl.2006.0539)
What the hell was Schaffer and Rosenzweig teaching me then?
> c'bert wrote:
> "This kind of oscillation has been predicted for other host-parasite or
> predator-prey systems, but seldom demonstrated, Zuk says."
> What the hell was Schaffer and Rosenzweig teaching me then?
You studied with Rosenzweig? Wow...
John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project
University of Queensland - Blog: scienceblogs.com/evolvingthoughts
"He used... sarcasm. He knew all the tricks, dramatic irony, metaphor,
bathos, puns, parody, litotes and... satire. He was vicious."
He teaches (or did ten years ago) an undergrad class at the U of A. For
an EEB course it was very popular. Rosenzweig is a very interesting
teacher. Between him and Schaffer (my advisor) it sure didn't seem like
this was seldom demonstrated.
My guess is that the cricket/fly system can be modeled and it will turn
out that the system is chaotic and not a regular oscillation as there
are at least two attractors.
>... The fly uses highly sensitive
>ears to hone in on the male cricket's call before depositing its
>larvae on the cricket's back. The larvae then dig into the
>cricket's body where they eat their host alive in about a week.
Me too. Same course as 'jet'.
Always worked for me - until I lost interest in crickets.