The biology of night and day

How do we know when to sleep, wake, eat? Professor Bernard Possidente’s biological-clock research suggests some answers, which he’ll share in the annual Edwin M. Moseley Faculty Research Lecture on Feb. 20.

Internal clocks regulate the timing of many biological processes, from trees dropping their leaves to humans fighting jet lag. In animals these timers tend to be very small anatomically, yet they can control complex activities. A specialist in this field is Skidmore geneticist Bernard Possidente, professor of biology, who will discuss his fruit-fly studies in the College’s 2013 Moseley Faculty Research Lecture, “Circadian Biological Clocks: How Flies Time When They’re Having Fun.”

Scheduled to begin at 8 p.m. Wednesday, Feb. 20, the talk will be in Gannett Auditorium, Palamountain Hall. Admission is free. A reception will follow in the Palamountain/Dana lobby.

The lecture title refers to a recent project in which Possidente and his students investigated the role of biological clocks in fruit-fly mating behaviors. It’s known that the flies, like most organisms, have strong circadian rhythms: even when kept in 24-hour darkness, fruit flies adhere to their usual sleep and wake cycles. “Our first question,” he says, “was whether those rhythms affect patterns of courtship and mating behavior.” By placing male and female flies together at different times of day, they found that “their preferred mating time was five hours after the lights come on. And when we removed the photoperiod, they still mated at about the same time,” indicating that their mating was regulated by an internal clock and not simply by environmental light cycles.

“We already know which cells constitute a fruit fly’s biological clock; it’s only about 10 neurons,” he says. (That compares to a human’s 10,000 or so—still a minuscule part of the brain.) As expected, when Possidente tested flies that had a genetic mutation known to turn off their biological clocks, the insects showed no preferred time to mate.

Possidente’s lecture will discuss this and related research on fruit flies, mice, and humans. He explains that flies made good subjects for his recent study because of their courtship rituals. “There are hundreds of species of fruit fly that look similar, and of course it’s important to mate with the right species,” he says. Helping the females distinguish which males to mate with, each species has evolved its own courtship displays “with elaborate dances and love songs,” laughs Possidente. “In the wild, if a male is displaying but the female isn’t interested, she just flies away. In our lab, we placed them in little clear-plastic chambers, where the male eventually got his way 90 percent of the time. What we measured was how long it took before the female allowed the mating.” The research also proved that the female’s biological clock is more influential than the male’s; a male will mate whenever the female accepts him, but she rebuffs him for an extra minute or two during her non-preferred times of day.

Possidente’s research at Skidmore has also probed the disruption to sleep-wake cycles caused by dementia such as Alzheimer’s disease, how lead or ethanol exposure affects biological clocks, and related questions, with funding from the National Institutes of Health, the Whitehall Foundation, and other agencies. Although flies’ neurological systems are far less complex than humans’, he points out that the genetics of circadian rhythm in both species “are very similar—in fact, we share 70 percent of all our genes.”

Possidente holds a Ph.D. in genetics from the University of Iowa. He was a researcher in its zoology department and in Florida State University’s psychology department before joining the Skidmore faculty in 1983.

Selection as the Moseley lecturer is the highest honor that the Skidmore faculty confers upon one of its own. The series is named in memory of the Skidmore provost and English scholar Edwin M. Moseley.