Oct. 13, 2000 ATHENS, Ga. - In centuries past, natural historians like William Bartram collected and identified the world's plants and animals, making clear the rich diversity of the planet. The new pioneers, however, are molecular natural historians, and they stand at the brink of an entirely new discipline - one that is beginning to expand our understanding of nature.
One area in which scientists are using the techniques of molecular biology with great success is in examining animal mating systems. Studies of these genetic systems in mammals and birds are now extensive, but until recently, almost no such research had been done on fishes or other cold-blooded vertebrates.
A team of geneticists at the University of Georgia is helping change all that and has published a series of research papers that is altering how science views the diverse reproductive strategies of these creatures.
"When it comes to the oft-secret world of mating strategies, field observations alone often provide poor or even misleading descriptions of the full panoply of reproductive tactics," said Dr. John Avise. "This is where molecular genetic techniques can help."
Avise describes the advances from his lab in an essay, "Natural History, Early 21st Century Style," which was just published in Intecol, the newsletter of the International Association of Ecology.
While Avise has done path-breaking work on birds for many years, his laboratory since the mid-90s has been deeply involved in studying reproductive behavior in fishes and turtles. Among the discoveries from his lab:
* Some fish get divorces. Seahorses, he writes, are quite unusual in the fish world for being socially monogamous. His lab's studies on the Western Australian seahorse showed that while the study population was genetically monogamous within a breeding period, more than 40 percent of the couples get "divorces" and "remarry" between successive reproductive bouts.
* Gender roles are sometimes reversed. In the more than 300 species of pipefishes and seahorses, "traditional" gender roles are turned on their heads. Researchers already knew that males of these species receive eggs from females, fertilize them and hold them in a brood pouch until the young are born live. Avise's lab was the first to discover, using the techniques of molecular genetics, that a pregnant male often has received eggs from two or more females.
* Female turtles can store sperm for years. In one of the most dramatic examples of a bizarre reproductive behavior, female painted turtles, the geneticists found, can store and use viable sperm for at least three years following mating. Although this capability has been noted in captive animals in the past, Avise's lab was the first to document this phenomenon in nature.
* Some male fishes steal eggs from another nest, perhaps "priming the pump" for spawning by their own mates. This amazing behavior was genetically documented in the euphoniously named fifteen-spine stickleback. Egg thievery, Avise notes, might seem to be counterproductive because the male would wind up with foster young to tend, since the males are the "nest-sitters." It is suspected, however, that the presence of eggs - even those stolen from a nearby nest - prompt a male's mates to lay additional eggs that he himself can fertilize, thereby making him a more prolific father.
* Females often "sleep around." In several fish species, Avise's lab showed, using genetic markers, that individual females sometimes have spawned in more than one male's nest.
"It's remarkable that so little study has been done on these taxonomic groups of vertebrates, since they have a vast array of reproductive behaviors that are simply begging for explanations," said Avise. "We're fortunate now that we have the genetic tools to assist with the job."
Among these tools are new DNA profiling methods based on molecular markers called microsatellites that can, along with a technique called the polymerase chain reaction, identify parents and their offspring using only tiny bits of tissue.
The researchers have continued to document numerous unexpected behaviors, and one of the strangest may be "filial cannibalism." Scientists had suspected for years that some nest-guarding fish were actually eating their own offspring, though the reasons seemed obscure from an evolutionary point of view.
Avise's team tested another idea, though. What if these parents were actually eating only the young of other parents? In years past, such behavior would have been nearly impossible to disprove. Using the techniques of the molecular natural historian, however, the geneticists examined recently consumed fry in the guts of adult redbreast sunfish and tessellated darters. The genetic data confirmed that filial cannibalism does indeed occur: Dads truly do eat some of their own kids.
Avise's essay stemmed from a symposium that was held in June at Yale University, bringing together for the first time researchers studying the mating systems of reptiles, fishes and amphibians. The event was moderated by Avise, who is president of the American Genetic Association (AGA), which sponsored the event.
Early next year, the Journal of Heredity, the AGA's official publication will devote a special issue to the topic.
In the meantime, Avise has plenty to study, including the strange behavior of nest kidnappers. These males, it turns out, are tending nests in which they have sired none of the young, having "evicted" the rightful males or taken their places when some deadbeat dads may simply have fled the area.
"This might be especially common in species or in ecological settings where suitable nesting sites are in short supply," said Avise.
Whatever the reason for these intriguing behaviors, such studies by this new breed of molecular natural historian will undoubtedly continue to turn up many surprises about nature's operations.
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