Frigid Flies, It's In His Buzz

For people with late-summer birthdays, merrymaking on a frigid winter's day during the holidays likely led to their conception. But for some insects, cold periods aren't opportunities for snuggle time with a loved one but are times of selfish resource hoarding.

Among Drosophila melanogaster FRUIT FLIES, for example, those exposed to repeated cold periods trade survival of the species for their own survival, according to a study by Brent J. Sinclair, a professor in the University of Western Ontario's biology department, and Ph.D. student Katie E. Marshall (Proc. R. Soc. B, DOI: 10.1098/rspb.2009.1807). "Each organism has finite resources," Marshall says. When exposed to stress events, fruit flies have to decide whether to use those resources to be tough and survive or to reproduce and hope that their offspring survive. "It's a trade-off between reproduction and repair," she says.

For the study, the researchers exposed groups of D. melanogaster to a single 10-hour cold period or a series of five two-hour cold periods with 22-hour warm periods in between to give the flies time to repair. The flies exposed to cold periods multiple times had higher survival rates than the single-exposure flies, but they also had a significantly lower rate of population increase.

"There is a fitness consequence to repeated cold exposure," the researchers write. By analyzing triglycerides and glycogen at intervals after treatment, they determined that repeated stress events affect the flies' metabolic reserves. The multiple-exposure flies had lower levels of both compounds than the single-exposure group. Because the multiple-exposure flies are not reproducing at the same rate as single-exposure and control groups, they are likely allocating their metabolic resources to survival rather than to reproduction, Marshall says.

"In nature, animals are exposed to thermal stress on a regular and repeated basis," Marshall says. "Understanding the consequences of these repeated stresses is essential to interpreting and predicting climate-change effects in the natural world." For example, such research could aid in designing population models of agricultural and pathogen-vector pests such as tsetse flies and mosquitoes, whose geographical ranges could change as Earth heats up.

Although a mosquito's choice of domicile might be expanding because of climate change, its choice of mates is limited by its musical ear.

Anopheles gambiae is a complex group of seven species and several genetic forms of MOSQUITOES that host the malaria pathogen. Their genetic diversity allows them to adapt to new environments and is maintained by reproductive isolation, even when different types coexist within the same swarm. Scientists in the U.K. and the African country Burkina Faso report that these mosquitoes maintain reproductive selectivity by "singing" vibratory ballads to one another and harmonizing to find the perfect mate (Curr. Biol., DOI: 10.1016/j.cub.2009.11.040).

The tones mosquitoes use to identify their partners are produced by their wings during flight. Two mosquitoes don't harmonize properly if they are of different types or of the same sex, the researchers show, and eventually dissonant pairs give up and move on.

"Even the most 'lowly creatures,' such as mosquitoes, have highly evolved neurosensory systems that can process relatively simple auditory inputs to produce motor outputs enabling them to distinguish between other types of mosquito that are so closely related we need to analyze their DNA to tell them apart," Gabriella Gibson, one of the report's authors and an entomologist at the University of Greenwich's Natural Resources Institute, says in a press release.