Impulse to Exchange Gifts isn't Limited to Humans

Here are some last-minute gift ideas to suit even the most discriminating individuals on your list.

For the female scorpionfly: an extremely large, glittering, nutrient-laced ball of spit, equivalent to five per cent to 10 per cent of a male fly’s body mass. Gentlemen: Too worn down by the holidays to cough up such an expensive package? Try giving her a dead insect instead. You can always steal it back later.

For the male Zeus bug: a monthlong excursion aboard the luxury liner that is the much larger female’s back, with its scooped-out seat tailored to his dimensions and a pair of dorsal glands to supply the passenger with all the proteinaceous wax he can swallow.

For the bonobo you’ve just met: half your food, at least. Just shovel it over. Sharing is fun!

For the bonobos you’ve known your whole life: Eh, maybe nothing this year. It’s not like they’ll stop being your friend if you “forget” to toss them a banana.

We may denounce the hyper-consumerism of the Christmas season until were Hanukkah blue in the face, but much of our economy relies on the strength of the gift-giving impulse and with good reason: The drive to exchange presents is ancient, transcultural and by no means limited to Homo sapiens. Researchers have found striking examples of gift-giving across the phyletic landscape in insects, spiders, mollusks, birds and mammals.

Many of these donations fall under the rubric of nuptial gifts, items or services offered up during the elaborate haggle of animal courtship to better the odds that one’s gametes will find purchase in the next generation. Hungry? Why don’t you go ahead and chew on the droplets oozing from my hind-leg spur while I just take a few moments to deposit a sperm packet in the neighborhood of your genitals?

Nuptial gifts can also be a gift for researchers, allowing them to precisely quantify a donor animal’s investment in mating and reproduction and to track the subtleties of sexual competition and collusion by analyzing the chemical composition of a given bag of courtship swag.

“This is an incredibly cool and important topic in sexual selection that we’re just beginning to explore,” said Sara M. Lewis, a professor of biology at Tufts University who has written extensively about nuptial gifts. “The bright side of nuptial gifts is, here’s a way that males can contribute things that are essential to his mate and to his future offspring.

“On the other hand, the gifts can be a source of sexual conflict, a way of manipulating the female into doing what he wants,” she said. “So there is a lot of back and forth over evolutionary time.”

Other researchers are studying how animals use gifts socially to foster alliances or appease dominant members of the group. Grooming among primates is considered a form of gift-giving, and, in most cases, it’s the subordinates who do the tick-picking: betas groom alphas, females groom males.

A nuptial or other animal gift is, by definition, something that is voluntarily given, Lewis said. “But that doesn’t mean its voluntarily received,” she added. “We’ve all gotten gifts that we didn’t want and wished we could return.”

One example of a possibly unwelcome gift, she said, is the snail’s love dart. Land snails like the ones in a garden are hermaphroditic, meaning they produce both eggs and sperm, and they mate by swapping sperm with other snails, often promiscuously. This is why, before copulation, a snail will try to pierce its partner with a love dart, a harpoon-like structure made of calcium carbonate and produced in the snails genital region.

Barely an eighth of an inch long, coated in mucus and ejected with considerable force, the dart may penetrate anywhere on the other snail’s body: through the shell, the head, even the eye. And when it does, it delivers a “gift” of potent hormones, which scientists have lately determined offer little obvious benefit to the recipient, but, instead, help promote the retention of the donor’s sperm over that of competing snails. No mere victim, the punctured mollusk retorts with a flirty fléchette of its own, at which point the dueling Cupids will copulate.

In most cases, though, a male’s nuptial gift is something the female wants or needs. Martin Edvardsson, an evolutionary biologist at Australian National University, studies Callosobruchus maculatus, a small, spotted beetle that is a major pest on beans and stored grains. Given their chosen meal plan, the beetles have little access to water, and the females get very thirsty while making eggs. What does a girl have to do to get a drink around here? Mate with a male.

As it turns out, a male sequesters most of the liquid he encounters as a larva inside a bean and adds it to his ejaculate. Should a parched female solicit him, hell mount and pump in the stored water along with his sperm packet, for seven or eight minutes at a time. The emission is a veritable cataract.

“When I’ve given talks, I use props,” Edvardsson said. “I’ll bring in four two-liter containers of milk” proportionally speaking, that is the human equivalent of the male beetles ejaculate “and I’ll hold up a little soy sauce packet from a takeout restaurant”: the actual volume of a human ejaculate. Edvardsson and his colleagues have shown that the thirstier a female beetle is, the more often she mates; and the more water she secures, the more eggs she lays.

Gifts can be costly to make or acquire. The salivary mass that a male scorpionfly secretes to lure in a peckish female is packed with so much protein and nutrients that a less-robust suitor may forgo the effort and resort to offering a female a dead insect, instead. Unlike a spitball, the insect corpse has the benefit of being reclaimable, at least in part, after mating is through.

-New York Times Service.