Fruit Flies Produce More Diverse Offspring When Threatened By Parasites

Fruit flies are very smart insects. When they're attacked by parasites or bacteria, they produce offspring with greater genetic variability--increasing chances of survival when faced with dangerous pathogens in the future ahead. A new study suggests that fruit fly parents may purposefully alter the genotypes of their offspring in the hopes of increasing longevity. 

Fruit flies typically have haploid cells, meaning that there is only one copy of each chromosome in the cell's nucleus instead of two. During meiosis, the form of cell division creates eggs in females and sperm in males, in which female fruit flies produce eggs that contain only one set of chromosomes. It's uncertain which set the offspring may get, however. A chromosome set may be a copy of the mother's chromosome or it may be a copy of the father's or even a mixture of both. The study notes that, "Under normal conditions each offspring of a female fruit fly has a 25 percent chance of getting a maternal copy of a chromosome, a 25 percent chance of receiving a paternal copy, and a 50 percent chance of receiving a recombinant chromosome."

During the study, researchers worked to determine if fruit flies could evolve a strategy for coping with infections by bacteria or parasitic wasps. Study authors Nadia Singh, an assistant professor of biological sciences at NC State, and her colleague and co-author of a paper describing the work, Todd Schlenke of Reed College, exposed the fruit flies to two different pathogenic bacteria and to parasitic wasp Leptopilina clavipes, which lays its eggs inside fruit fly larvae and devours the fly from the inside out unless it is killed by the fly immune system.

Females who survived wasp infection or bacteria produced a greater proportion of recombinant offspring than those who were not infected. Mother survivors, thus made more diverse offspring. 

"We believe that this is an example of what has been called transmission distortion. In this case, something is signaling these female fruit flies to produce a higher proportion of offspring with recombined chromosomes than they would normally," added Singh, in a news release. "The result is that they're hedging their bets, genetically speaking -- creating a large number of very different offspring means that at least some of those offspring may be genetically better suited to surviving future threats from these bacteria or parasites."

More information regarding the findings can be seen via the journal Science.

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