The sex lives of fruit flies are influenced by temperature, a new study has found, with warm conditions favoring monogamy and colder environments suiting promiscuity.
The mating habits of the fruit fly Drosophila pseudoobscura have previously attracted interest from entomologists since the males produce more sperm than any other Drosophila species, a consequence of frequently having to compete with other suitors who have mated with the same female. However, the rate of multiple mating varies substantially between populations.
In a case of multiple loves in a cold climate, biologists from the University of Exeter compared the sexual behavior of D. pseudoobscura collected from the very different climates of Arizona and Montana.
"This is a textbook example of the role of genes versus environment," said lead researcher Dr. Michelle Taylor in a statement. "Sexual behavior is really hardwired into females. It makes sense biologically for females to have a number of partners as they will produce more offspring that are more genetically diverse and survive better."
Cold weather may inspire mammals to snuggle, but in Behavioral Ecology, Taylor and her co-authors note that for species that rely on external energy for their body heat, it might be high temperatures, and thus more energy, that boost mating activity.
Indeed, some species have shown a positive relationship between temperatures and multiple partnering. On the flip side, certain fruit flies have been found to be more promiscuous in colder climates. To learn more, Taylor and her co-authors inbred the flies through 40 generations at the University's lab in Cornwall and then had them mate at different temperatures.
“We found that temperature experienced at the time of mating significantly influenced female remating,” the authors report. “However, we also found that genotype retained a significant influence.”
“Females of all genotypes were more likely to remate at cooler temperatures,” the authors report, with 26% having two or more partners at 17°C and just 15% at 25°C, a finding they acknowledge is “in direct contrast to the patterns emerging from other insect studies.”
Sex also lasted substantially longer in the cold, but the authors report, “We found no evidence that rearing temperature had any effect on remating.”
The authors acknowledge that increased sexual activity at lower temperatures is harder to explain than the reverse, but note, “High temperatures can also impose time constraints on courtship and mating through risk of desiccation.” The team hope to test other factors, such as humidity, in a follow-up study.
“These results are an important step towards understanding how genes and environment contribute towards behavior and ultimately how behavior affects the success or failure of natural populations,” added Taylor. “Mating with many different males can change the genetic make-up of a population because it increases the number of combinations of genes represented in each generation. Evolutionarily speaking, this could be one reason why some populations are able to adapt to changing environments while others go extinct.”
More generally, she added, “What is interesting, and what needs further research, is the question of why some females stay with one partner. We don’t know what maintains monogamy."
