Early in his career, USC marine biologist Dennis Hedgecock explored a pair of hypotheses that since have significantly influenced science’s understanding of how marine animals pass genes on to future generations.
In 1986, he published an unassuming 14-page article in the Bulletin of Marine Science that investigated the importance of gene flow caused by the dispersal of larval sea life to the adaptation and evolution of a given species.
It became one of the most cited articles in the journal’s 60-year history. In honor of that fact, the journal invited Hedgecock to contribute a feature for its anniversary issue this month.
Hedgecock, now a professor of biological sciences in USC Dornsife, opted to review the ramifications of another of his hypotheses, which he first published in 1982. In it, he suggested that marine animals were subject to Sweepstakes Reproductive Success (SRS) — the counterintuitive idea that they have an “extremely large variance in individual reproductive success.”
The idea is counterintuitive because, with highly fecund marine life, scientists easily can watch the majority of marine creatures doing their best to reproduce and pass their genetic material along.
“Most of them do spawn,” said Hedgecock, Paxson H. Offield Professor in Fisheries Ecology and professor of biological sciences. “You can see that just by making observations.”
Simply put, Hedgecock thought that the chaotic nature of the marine reproductive environment — with currents sweeping gametes and fertilized eggs away — could mean that a tiny minority of adults will wind up being the parents of the vast majority of the next generation.
The topic is not even one Hedgecock deals with much anymore. He wrote the article while working at the Bodega Marine Laboratory at the University of California, Davis. His work took a different turn, and he eventually moved to Los Angeles to teach at USC in 2003.
And yet hundreds of other scientists tested his hypothesis about SRS, finding his predictions to be correct time and time again.
“I was pleased, naturally, that other people thought the idea important enough to go out and test it,” he said. “Moreover, in the last several years, this idea has attracted the attention of some top-notch theoretical scientists.”
Those top-notch scientists include Harvard University’s John Wakeley, whose team that explored the theoretical implications of Hedgecock’s hypothesis on coalescent theory — the model of population genetics that mathematically predicts how many generations back you have to go to find a common ancestor for a defined population.
Up until now, scientists based coalescent theory calculations on a bifurcating process, regardless of the species. While that works well for humans, in which most adults procreate and create an average of two offspring, SRS predicts more of a multifurcating process for marine life, in which the adults that successfully procreate generate dozens or even hundreds of offspring.
“That changes the game completely,” Hedgecock said.
Nowadays, Hedgecock mostly does experimental work exploring the growth, survival and reproduction of oysters.
“Dennis Hedgecock is one of our first-rank scientists applying population genetics approaches to economically important marine species in order to more carefully manage their stocks and commercial exploitation,” said Doug Capone, Wrigley Professor of Environmental Biology and chair of USC Dornsife’s Department of Biological Sciences.
However, Hedgecock said he is excited about the future of theoretical marine biology and its potential to impact aquaculture.
“I think that there’s much more to learn now,” he said.