You’ll have noticed I’ve said nothing so far about fighting male wasps. That’s because pollinating wasps are generally peaceable types. They are not, however, the only occupants of a fig. As well as having a pollinator species, each fig species has to put up with parasitic wasps—sometimes as many as twenty-five different species. A few are pollinators that have gone bad. They live off the fig, but the pockets they once, long ago, filled with pollen stay empty. Others simply prey on the pollinators. For the most part the biology of these parasites is poorly understood, but we do know that they are often prone to violence.
The difference stems from the way that female parasitic wasps lay their eggs. Rather than crawling into the urn, most of the parasites lay their eggs by drilling through the outside. This means that these females do not have to lay all their eggs in one place as pollinators do but instead can lay a few eggs in many. At the right time of year, you can see speckles on the fig skins from the drilling of different females.
Spreading a brood among several figs will have one of two consequences. In species where population densities are low, males risk finding themselves alone in a fig. So it is not surprising that where this is likely, males have wings so that they can fly off to search for lovers outside the fig of their birth. But in species—and yours is one—where figs tend to be crowded, males do not fly. Any given fig will probably also be home to mates. The trouble is, of course, it will probably also be home to rivals. Hence the slaughter.
Mortal combat is an effective but risky way of eliminating rivals. Males are not usually interested in fighting to the death unless they have a lot to gain—and little to lose—by doing so. Dying, after all, precludes further reproduction. Thus, lethal fighting is most likely to occur in species like yours that live for only one breeding season. One-shot breeding does not by itself, however, produce routine violence. Two other factors are crucial. First, receptive females must be clumped in space and time such that a fellow’s only chance to mate is here, now. Second, fighting must increase the number of females he can mate with: there is no point wasting time fighting if in doing so he is missing out on sex. For example, if females are abundant but they mate only once, then males who copulate will do better than males who fight—a dynamic thought to explain why fighting is virtually unheard of among pollinator wasps.
Only a handful of other creatures have a reputation for extreme violence, and what little we know of them is consistent with this scenario. Take the “annual” fishes of Africa and South America. Their lifestyle is almost magical. They live in puddles, ponds, and ditches that dry up for part of the year. When the puddles dry up, they die. Only their eggs survive, buried under the dried mud, waiting for the next rains. Collect mud, add water—and presto, you get fish! You can see why people believed in spontaneous generation. When the rains come, time is short. As there is no chance to move to a new neighborhood, everyone tries to be the big fish in the small pond: the males of some of these species are among the most pugnacious fishes known. If I had to bet, I’d predict that the more ephemeral the puddle, the fiercer the fighting.
Or take gladiator frogs. These brown tropical frogs have evolved switchblades: on each hand, just above the thumb, males have a sharp, retractable spine that is shaped like a scythe. Most of the time, they keep it sheathed in folds of flesh. But when two male frogs fight, they rake these spines across each other’s faces, aiming for the eyes and eardrums of their opponent. Although we don’t know the death toll in the wild, we do know fights can be lethal. As you would expect, competition for mates is fierce. And also consistent with the hypothesis, gladiator frogs have short lives. Even without the fighting, few survive from one breeding season to the next.
Perhaps the strangest example of violence is not from an animal but from a plant, the orchid Catasetum ochraceum, and its relations. In these species, female flowers receive pollen from only one pollinator. Immediately after pollination, they swell shut and set about making fruit. Competition between male flowers to be “the one” is therefore fierce. But since they are plants, they can hardly fight it out man to man. Instead, they direct their aggression at a hapless intermediary—a bee. The male flowers assault any bee who ventures inside them, throwing sticky sacks of pollen onto the bees’ backs. In one species, the flower throws the pollen at the staggering velocity of 323 centimeters per second. Since the pollen sacs are also large—they can be as much as 23 percent of a bee’s weight—the bees don’t like this treatment. After one such attack, they avoid all other males, visiting only the gentle female flowers.
But for brutality, nothing rivals wasps in a fig. One scientist I know tried to study fighting in fig wasps—only to find that he was never there in time. Whenever he slit open a fig, there would be just one male left alive, celebrating his victories by mating with all the females in the fruit. So as you see, there’s a reason all the guys you know have such terrifying demeanors—and maybe now that you understand, you can forgive them for being such maniacs.
Dear Dr. Tatiana,
Perhaps you can help. I don’t know what’s happened to me. I’m a twenty-seven-year-old African elephant, and I used to enjoy showering at the water hole and other idle pleasures. But the joy has gone from life. I feel angry all the time—if I see another bull elephant, I want to kill him. And I’m obsessed with sex. Night after night I have erotic dreams, and the sight of a beautiful cow sends me into a frenzy. Worst of all, my penis has turned green. Am I ill?
Anxious in Amboseli
Uncontrollable aggression, obsessive lust, morbid anxiety about your sexual health: this all sounds normal for a fellow in his late twenties. It’s nothing to worry about. You’ve just got a case of SINBAD: Single Income, No Babe, Absolutely Desperate. Unfortunately for you, however, you’re likely to be in this state for much of the next twenty years. Female elephants prefer older males. Until you’re bigger, the cows will run away from you—and their mothers and sisters will bellow for older bulls in the area to come and send you packing.
I’m afraid that females in many species often provoke males into fighting over them. When the mood strikes, they make themselves conspicuous—then stand back and watch the battle, before mating with the winner. Female northern elephant seals, for example, create a rumpus whenever a male tries to mount them; this has the immediate effect of summoning every other fellow on the beach, even waking those who’ve been snoozing. The Burmese jungle fowl—the ancestor of the farmyard chicken—gives a loud squawk after laying an egg, an odd thing to do given that it immediately tells hungry predators there are eggs on the menu. But it also, apparently, goads any roosters in the area into fisticuffs over the chance to fertilize her next egg. In my opinion, though, the worst offenders are found in Zootermopsis nevadensis, a termite that lives in rotting wood. In this species, males and females usually live together as couples. They meet each other on a suitable log and found a nest. During this initial period, if a male finds he doesn’t like his mate, he’ll probably leave. But a female will typically invite a new male into the nest, which almost always results in the two males dueling. Between bouts, the female will groom first one and then the other. (On rare occasions, a male will invite a new female into the nest—and will then encourage the girls to fight.) Finally, although female cheetahs do not, as far as I know, goad their admirers into fighting, they do find fights arousing and come into heat shortly after watching one.
Female provocation does not usually lead to a pileup of corpses, however. As the saying goes, “He who fights and runs away lives to mate another day.” There’s no point in fighting if you know you’re going to lose—especially if by bowing out, you may be able to find another mate elsewhere. That’s why even in one-shot breeders, fighting to the death is rare. If a male arrives to discover that another guy got there first, there may be some argy-bargy, but it’s more likely to be a show of strength than all-out war. Take two-spotted spider mites. These tiny creatures are agricultural pests: they feed on plant cells, stabbing each cell with thei
r mouthparts and drinking it dry. Although they are mites, they have the ability to make silk just like their spider cousins. In this species, males hunt for adolescent females—those about to undergo their final molt and become adults—and stand guard, so that they can be first come, first served. A guarding male sits on the female, with his legs draped over her body. If a second male arrives and refuses to leave when threatened, some sort of fight will break out. The two males will wave their front legs and grapple with each other, often trying to trip their opponent by attaching strands of silk to his legs. Fights can end in death, but that’s rare. Usually, the smaller male retreats before it comes to that.
Size is crucial in hand-to-hand fighting. In animals from boa constrictors to humans, the larger combatant typically enjoys a large advantage, so smaller males usually back off. As a rule, savage fighting breaks out only when both contestants figure they can win—that is, when they are about the same size. Consequently, many animals have evolved bizarre rituals to assess their opponents. Remember those flies with eyes perched on the ends of long, stiff stalks? Males measure their strength by going head-to-head to compare eye spans. If there isn’t a clear difference, they’ll fight; otherwise, the male with the smaller eyespan leaves. Thus, you can tell when fighting is important in determining who gets to mate: males will typically have evolved to be big. Male elephants, for example, have evolved to grow throughout their lives rather than stopping after puberty like most mammals. Whereas most mammals cannot grow beyond puberty because their bones fuse together, a male elephant’s bones don’t fuse until he is middle-aged. That’s how male elephants can grow to be more than twice the size of females.
Among elephants, though, it’s not only size that matters. Bull elephants, even the largest and oldest of them, feel like fighting only at certain times of the year, when they are in the grip of a fury known as musth. For young males, a bout of musth lasts only a few days at a time, but for the oldest bulls it can continue for as long as four months. When a bull is in musth, the amount of testosterone in his blood soars to levels fifty times higher than usual. Unsurprisingly, this has profound effects on a fellow’s behavior.
Males in musth display all the symptoms you complain of, and more. They wave their ears and shake their heads and constantly dribble strong-smelling urine—this is what causes the penis to develop the unfortunate greenish tinge you mentioned. Musth even affects their conversation. Most elephant conversations take place in the infrasound, well below the range of human ears but audible to other elephants for miles around. Male elephants are usually the strong, silent type—probably because, unlike the females, they haven’t got large vocabularies. (In fact, it’s not just that male elephants have smaller vocabularies but that male and female elephants have vocabularies that are almost entirely mutually exclusive. Elephant girls and boys couldn’t discuss the same subjects even if they wanted to. I know the feeling.) But an elephant in musth rumbles constantly, announcing his desperate lust and aggressive anger to any elephant in earshot. Males in musth are also much more likely to pick fights with one another than with other males, and if the males are the same size, fights are more likely to escalate. That’s bad news. A big fight can last for hours in the heat of the African sun and can certainly be fatal. In between rounds, fighting elephants uproot trees and throw logs, and if, at the end of all this, both contestants are still standing, the fight finishes with the winner chasing the loser for several miles. This is probably why large males in musth often try to avoid one another—and why even large males who are not in musth stay well away from any male who is.
Dear Dr. Tatiana,
My name’s Rob, and I’m a bedbug, Xylocoris maculipennis. I’ve read that if I have sex with my friend Fergus, he’ll deliver my sperm when he next has sex with Samantha. Is this for real?
Making Mischief between the Sheets
First, you’re not a real bedbug but a pirate bug, a close cousin. No use pretending. As to your question, it sounds to me like you’ve been reading too much naughty French literature (although to be fair, I’ve read the same stuff myself). The claim is that because you have a penis like a hypodermic needle—and because in species like yours, you jab it through the body wall—sperm injected into another male will migrate through his body and arrive in his gonads. Exciting though this sounds, it has always struck me as one of those facts journalists call “too good to check.” The short answer is yes, it’s possible—but it’s unlikely.
I have two reasons, one practical and one theoretical, for being skeptical. On a practical level, the original claim is flimsy—based on poor data—and the experiments have never been repeated on your species. Moreover, experiments on a related species, the European bedbug, have found no evidence for males injecting each other. Theoretically, the situation you describe would be highly unstable: any male who could resist acting as a proxy would have a big advantage over one who could not, and genes for resistance should swiftly spread through the population. Which is exactly what has happened in the sea squirt Botryllus schlosseri.
This creature undergoes cycles of both sexual and asexual reproduction. It lives in colonies on rocks and reefs. A sea squirt looks like a tiny barrel with two siphons on the top; in a sea squirt colony, the barrels are embedded in a gel-like matrix. Looking at the adult, you’d probably never guess that these organisms are animals, let alone close relations of animals with backbones. Only the larvae, which look like simplified tadpoles, give the game away. When a larva settles on a new rock, it metamorphoses into a grown-up sea squirt and begins to reproduce asexually to form a group of genetically identical individuals that share a common blood supply.
As neighboring colonies expand, they may run into each other. At this point, they have a choice. They can either join forces and become one big colony or they can reject each other, creating a physical border, a line in the sand that neither can cross. If the colonies fuse, something sinister can happen. Cells from the individuals of one colony can travel through the common blood supply and invade the gonads of all the individuals from the other colony. It’s a hostile takeover: when the time comes to reproduce sexually, members of the losing colony are forced to make eggs and sperm carrying genes that are not their own. Predictably enough, this has led to the evolution of mechanisms to avoid having your gonads hijacked. Botryllus colonies are highly particular about whom they fuse with: whether or not fusion goes ahead depends on a complex system that ensures close matching between genes of the two colonies. Colonies fuse only when they have similar genes—and therefore, are probably closely related. In pirate bugs and bedbugs, however, there is no evidence of measures to counter gonadal hijacking—and I bet it doesn’t happen in the first place.
The males of some species do, however, have another, more plausible way of eliminating their rivals: they render them impotent. Such nastiness has been claimed for at least one spiny-headed worm, the gloriously named Moniliformis dubius, a scourge of cockroaches and rats. Baby worms live in the guts of cockroaches; when a cockroach is eaten by a rat, the worms grow up and have sex in the rat’s intestines. Not exactly romantic, but there you go. What’s important to us is that female worms mature at the same time, a situation that, as you know, promotes fierce contests. But here the contest is not fighting but sabotage by “cementing.” When a male mates with a female, you see, he finishes off by capping her genitalia with a chastity belt made of a kind of cement. It turns out that males aren’t shy about cementing up each other either: by applying cement to another guy’s genitals, they prevent the other guy from copulating. Is it just that male spiny-headed worms can’t tell the difference between males and females? Maybe. But there is some tentative evidence that when a male cements a male he doesn’t transfer sperm, so perhaps the aim really is to make his rivals impotent.
Spoiling tactics have been proposed to explain mysterious goings-on in other species too. For instance, among African bat bedbugs—large bedbugs that suck the blood of roosting bats—females have a peculiar gen
ital structure on their bellies for receiving sperm. This structure is entirely separate from where the eggs are fertilized. Curiously enough, the males have the same structure. One possibility is that they use it to sabotage rivals by fooling them into depositing sperm there, thus wasting their reproductive effort. However, since any male who could tell the difference between a male and a female would have a significant advantage, I’d be astonished if this is the real reason the males have this structure.
I suspect that such spoiling tactics are most likely to evolve when males do not pass on their sperm directly but put it into a packet—a spermatophore—that they leave lying around in the hopes that a female might pass by or that they try to persuade her to pick up. In some species, males have been reported to trample or eat any spermatophores they encounter; in others, males deposit their own packet on top, forming a kind of sperm stalagmite. And some males come between a mating couple as the sperm deposition is about to take place. The Jordan salamander, an amphibian that looks like a lizard, is an accomplished third wheel. During courtship, male and female Jordan salamanders do a dance in which he leads and she follows behind, straddling his tail until he deposits his spermatophore. Occasionally, a second male slips between the courting couple and waddles along as if he’s the female. When the first male is duped into depositing his packet of sperm, the second then goes off with the bride, and the unhappy loser has to wait several days before he can make a new spermatophore. But either Jordan salamanders are fools or the risks of this happening are low enough that most of the time a male doesn’t have to look over his shoulder while making love.
Dr. Tatiana's Sex Advice to All Creation Page 6
