First the researchers had to find out if both sexes indicate mate preference. They randomly paired virgin females with virgin males, put each couple into a “mating arena,” videotaped the interaction and then analyzed each fly’s behavior.

In the "mating arena" designed by UGA behavioral geneticist Yong-Kyu Kim, a virgin fruit fly (in the larger main chamber) has a choice of two potential mates, one in each smaller chamber at either end of the main arena. A chooser can see, smell, and hear both suitors. To be included in the next phase of experiments — the actual mating game — the chooser must select the same mate twice by standing near the preferred fruit fly for at least 60 percent of the time during two separate mate-choice trials.

“The flies didn’t really tell us who they liked,” Gowaty said, “but they behaved in certain ways that allowed us to infer whether they liked each other. One way in which a passionate, ardent female indicates this, for example, is to go still.”

Hundreds of observations later, the team announced that both sexes in two fruit-fly species displayed ardent and discriminating behaviors — findings that contradicted earlier accounts of fly courtship.

“I’m guessing that earlier observations were done under a microscope with flies in very confined spaces,” Anderson said.

The research team — which included students and post-doctoral fellows — randomly assigned virgin flies to one of four matchmaking possibilities. The ideal match — mutual attraction between the female and male — was considered unconstrained. Constrained matches included: a preferred female and non- preferred male; a non-preferred female and preferred male; and a non-preferred female and non-preferred male.

To make the mate-choice criteria more rigorous, team member Yong-Kyu Kim, a UGA behavioral geneticist, modified the mating-preference arena to better fit the experimental conditions for subjected flies. His arena, made from flexible, clear tubing, allowed a chooser to see and smell two potential mates or to completely avoid one or both suitors. The arena also eliminated interaction — competition, posturing or intimidation — between the two candidates. For a mate to be considered preferred, the chooser had to select him or her twice, spending at least 60 percent of the time near the preferred mate.

“About 40 percent of the time females chose the same male twice,” Kim said, “while males chose the same female about 50 percent of the time.”

To compare reproductive success among the variously matched fly couples, the team relied on Kim to direct the tedious work of counting numbers of eggs laid and hatched, measuring offspring fitness and calculating the percentage of young that survived to adulthood.

The data revealed small but noticeable differences: In ideal matches, moms laid fewer eggs and dads delivered less sperm.

“It appears that an unconstrained female doesn’t have to have as many kids,” Gowaty said. “She’s with her preferred partner and her offspring are probably more variable, which may explain why they are healthier and survive better.”

Meanwhile, though constrained moms laid more eggs and constrained dads inseminated with more sperm, their larger biological investments yielded fewer adulthood offspring.

More surprising was that mate choice among males also affected the ratio of eggs to adult offspring. “By insisting we also test male choice, Wyatt saved me from that grandest of sexist mistakes,” Gowaty said.

The researchers are now comparing long-term survival rates for constrained and unconstrained moms. “A main longevity cost for females is egg production,” said team member Beth Tyler LeBow, a UGA doctoral student. “If females are laying more eggs, you would predict they’d die sooner because egg-laying is very expensive.”

Accordingly, LeBow, who has shown that environmental stress decreases a fly’s life span, is studying how stress affects both egg production and lifespan among moms with preferred and non-preferred mates.

The researchers also are investigating offspring fitness among moms who had either one or many partners.

Jessica Laverentz, a recent UGA undergraduate, has studied offspring outcomes when a mom is mated either with the same male throughout her reproductive life or with a series of partners. Her preliminary findings show that females mated with multiple partners have greater reproductive success in that their young have higher survival rates.