By Roger Segelken
Most vacationers complain to the travel agent when deadly spiders infest their warm weather getaway. Maydianne C.B. Andrade is delighted.
The Cornell biology graduate student spent her winter break in the blazing heat of Western Australia. At night she donned a miner's head lamp to watch one of the most extreme forms of self-sacrifice in the animal kingdom. Days were spent painting color codes on spider legs or giving interviews to journalists from around the world. And trying to catch some sleep.
The news media were drawn to Andrade like moths to a flame because she had just published (Science, Jan. 5, 1996) the solution to a long-standing puzzle in evolutionary biology: the adaptive advantage of male complicity in sexual suicide and cannibalism. Allowing oneself to be eaten during mating makes sense in an adaptive sense, she proposed.
The facts that landmark experiments with Australian redback spiders were con ducted by a young student and that Andrade was the sole author of an article in a prestigious journal were remarkable enough. But a healthy dose of sex and violence helped sell the story.
"Love Really Is to Die For" The New York Times wrote in an article filling most of the Jan. 9 science section front page and another page inside. "Sex as Suicide," the Jan. 15 Time magazine titled its "girl-eats-boy" tale, noting, "On the face of it, this seems insane." Broadcast and print media journalists were calling the Mudd Hall office Andrade shares with four other graduate students, only to learn that their quarry was 13 time zones away.
Some interviews were conducted by e-mail. Fax machines helped, too, and Andrade conscientiously returned phone calls to reporters. Everyone wanted to know: Who are these spiders that put up with such nonsense?
Hardly an endangered species, the redback spider (Latrodectus hasselti) is too omnipresent for comfort in parts of Australia. "Mothers have to warn their children not to touch the female redbacks,"Andrade said of attractively colored, jellybean-sized arachnids with a crimson blaze on their backs. Venom from a female redback bite can kill a child or an elderly person.
Compared to the female redback, the males aren't much to look at. So small and light (about 2 percent of the female's mass), the males might be mistaken foranother species. "Males hang around the web for days or weeks, waiting for the female to mature," Andrade said.
What happens next defies logic: A "lucky" male is chosen for mating and inserts his intromittent organ. Then, as recounted in Andrade's Science article, he performs a spectacular somersault that positions his abdomen directly over the female's mouth parts. He remains there throughout copulation -- as long as half an hour. If the female is hungry enough (and they are about 65 percent of the time, according to Andrade's experimental observations), the male is a meal.
One reason why complicity in cannibalism might be sexually selected for and genetically adapted into redback behavior involves food for the next generation. Perhaps extra nutrients, passed along to offspring in the female's eggs, give young redbacks carrying the male's genes a head start in life, and they "remember" to do the same when it's their turn to mate. Evolutionary theorists call that strategy paternal effort, but it didn't make sense to Andrade. For one thing, there's not much of the minuscule redback male to go around.
So she looked for a more direct advantage. In a series of painstaking experiments conducted while she was a master's degree student at the University of Toronto, Andrade irradiated certain male spiders. That left their sperm intact and viable -- but genetically damaged so that any eggs they reached would not develop. Other, "normal" males were not irradiated and were capable of fertilization.
Thus, males were labeled and Andrade would know whose sperm was reaching which eggs in a female spider that sometimes mates with more than one suitor. Then, with the clock running, the biologist allowed "normal" and irradiated males to mate sequentially with one female at a time.
The experiment successfully demonstrated that the longer the male has to transfer his sperm, the more eggs he fertilizes. Sometimes the female is so satisfied -- sexually and gustatorially -- that she doesn't seek another mate. Contestant number one wins the great genetic lottery of life.
Of course he's dead, but the short-lived male would have passed away, anyway. As Andrade wrote in Science, "paternity advantages of sexual cannibalism outweigh the low cost of suicide for males. Male facilitation of cannibalism probably evolved through sexual selection as the most extreme mating gift."
Such extreme reaches of evolutionary theory fascinate Andrade, and she will try to nail down more in her doctoral research at Cornell. "I guess I've always been interested in cannibalism," she said, recovering from a jet-lagging journey from Perth last month. "First it was praying mantids, but their males don't volunteer to be eaten. They run like crazy to get away from the females.
"Then I read about the redback spider's somersault, and I thought: This must be the most extreme example of male investment in mating," she said. "This is not survival of the individual organism. It is overall reproductive success. If it means dying for mating, that's what they will do."
Coming to Cornell, she has joined a department where evolutionary "decisions" are viewed in terms of cost-benefit analyses. Neurobiology and Behavior's Stephen Emlen analyzes decision-making in birds that forsake mating to help their closest kin. Paul Sherman questions why naked mole-rats choose to live like bees, devoting their efforts to serving their colony's queen. Hudson Kern Reeve started with mole-rats and now studies wasps.
Andrade said she was first attracted to Cornell when she heard Sherman lecture at the University of Toronto about the mysterious mole-rats. "This has to be one of the best places on the continent to study behavioral ecology," she said.
Born in Jamaica, Andrade was reared in Vancouver, B.C., from age 2. After the Pacific Northwest, Toronto's climate was something of a shock, but she finally got used to weather in the East. Or so she thought until her first winter in an even-colder Ithaca.
This spring Andrade will head to Florida. There's some extreme behavior in brown widow spiders she wants to observe.