Dr. Tatiana's Sex Advice to All Creation

by Olivia Judson

  Neglected Househusband in Tamil Nadu

  Talk louder, shout, yell yourself hoarse. Among bronze-winged jacanas, that’s about all that gets a female’s attention as she skitters across the lily pads on her elegant long toes. After all, she’s a busy bird. She has a big territory to defend, other males to mate with, eggs to lay. You’re not going to get anywhere by hanging around like a wet feather—you have to make yourself heard.

  Female jacanas have matters well in hand. They mate with all the males in their harem (often as many as four), lay a clutch for one, then repeat. Males do all the child care—so a male who is sitting on eggs or feeding chicks is excused from copulation. A female with a harem may thus have four times as many chicks as a female who has one partner. It just shows what you can do if you’ve got good help.

  More help is one reason lots of females are promiscuous. Consider the greater rhea, a flightless South American bird that resembles the ostrich. A male receives eggs from several females. He incubates all the eggs and rears all the chicks. At the right time of year on the pampas, you can see males and their little flocks wandering about, the male whistling softly to keep them all together. The females, meanwhile, go off to mate and lay other clutches for other males to look after. Indeed, this system—where males look after the young from several females, and females spread their broods between several males—is common, especially among fish.

  Even in systems where females are not so shamelessly promiscuous, they may still get more help if they sleep around. Among red-winged blackbirds—which have not red wings but red epaulettes—every male a female has bonked will come flying to her defense if her nest is attacked. This can be a delicate balance to strike: if a female’s main squeeze suspects her of cheating, he may stop helping her. For example, among reed buntings, small brown songbirds, males won’t make as much effort to feed the chicks if they suspect the chicks aren’t theirs.

  This kind of thing doesn’t seem to bother bronze-winged jacanas, though. As far as we can tell—although the genetic analyses are not yet complete—males routinely rear some chicks that are not theirs. Why do they put up with it? They don’t have a choice. In jacanas, females rule the roost. A female bronze-winged jacana is 60 percent heavier than a male; he has to toe the line or leave the game. How did such a system evolve? I wish I could tell you. I’m sure a lot of women out there would like to know.

  Dear Dr. Tatiana,

  I’m an orange-rumped honeyguide, and I own prime real estate: a cliff face that has several giant-honeybee nests. Lots of girls visit me, and they always let me have sex with them. They say they do it because they love me, but I worry that the real reason is that afterward they get to gorge on beeswax. Indeed, I’m starting to suspect they act the same with all the guys. Can you reassure me?

  Waxing Suspicious in the Himalayas

  Honeypot for honeycomb? Sounds like a fair trade to me. After all, you have something they want—beeswax. And they have something you want—eggs to be fertilized. So I see no reason why the girls should give sex for free or why they should limit themselves to a single sugar daddy. Here’s a thought you can comfort yourself with, though. Female orange-rumped hon-eyguides may not be paragons of virtue, but they are not indiscriminate birds—oh no. They only mate with males who hold territories—and who thus have beeswax to offer—so that rules out a lot of fellows.

  Boys, I’m afraid the way to a woman’s bed is often through her stomach. Remember the long-tailed dance fly? Well, females in many other species insist on trading sex for food. There are several ways you can meet a girl’s appetites. First, like our orange-rumped friend, you can defend a territory that contains food that females need, and charge females at least one copulation per admission to the site. Second, you can hunt for food to give the female. Third, you can secrete gifts using food that you have eaten—although I wouldn’t recommend this unless you are an insect.

  Unfortunately, however, while food can buy you sex, it can’t buy you love. In species where females swap sex for food, loose females typically eat better—and have more offspring. Take the common field grasshopper. Given a choice, females will exchange nourishment for sex with as many as twenty-five different males. Promiscuous females lay more batches of eggs—and more eggs per batch—than females who only get to mate once. Particularly when times are hard and food is scarce, this easily makes up for the hour and a half it takes to have grasshopping sex. In the green-veined white butterfly, a critter fond of damp meadows, a virgin male ejaculates a sperm packet roughly 15 percent of his weight. As well as sperm, the packet contains nutritious substances, and females who have sex with several virgins lay more and bigger eggs, and live longer, than females who do it with only one. But if their lovers are not virgins, females are even more inclined to promiscuity. Males who’ve already mated cannot come up with the goods: their sperm packet is a mere half the size of their virgin glory. Females compensate for the loss of nutrients by copulating with other fellows all the more.

  Life’s tough. Girls, don’t forget that boys go to tremendous effort to find or produce food—and yet, your screwing a fellow doesn’t even guarantee that you’ll use his sperm. This observation has generated a vigorous controversy about why boys bother to feed girls at all. Some people argue that a good meal is just a way for a guy to get into a girl’s pants. Others say that he’s trying to be a good father, giving essential nutrients to the female so that she can incorporate them in her eggs—and thus give his children a good start in life. The eggs of hundreds of species have been analyzed to see whether any substances handed over by the males have indeed been incorporated. The results vary. Sometimes a female channels the nutrients to her eggs. Sometimes she nourishes herself. And sometimes nutrients given by one male go into eggs sired by another. But this shouldn’t surprise you. A girl is always going to want to copulate with the males who offer the most; what she does with the offerings is up to her. All a guy can do is hope he satisfied her. Here’s hoping.

  Dear Dr. Tatiana,

  I’m a male shiner perch, and I’ve heard that loose women are taking over my species because they have more children than anyone else. How can I stop this dreadful fraying of the moral fiber of tomorrow’s perches?

  Outraged in Baja

  It is true that in many species the females who mate the most have more and healthier children than girls who restrain themselves. But you can relax: this doesn’t seem to be true in yours. Yes, female shiner perches are forward fishes, chasing males through the surf rather than waiting to be chased. But even the big females, who are likely to seduce several males, don’t have more, bigger, or healthier embryos than the females who mate only once.

  So why do female shiners chase guys? No one knows for sure. One thought is that they are hedging their bets against the possible sterility of their mates. In general, I don’t think this is a convincing explanation for promiscuous behavior: in most species, females mate much more than is necessary to avoid sterility. Nor do I accept the popular notion that females who store sperm only remate because they’ve run out of it. To be sure, females can run out of sperm. In most species, though, they leap back into bed long before sperm depletion becomes a problem. And while I’m dismissing ideas, let me also put to rest the idea that females are promiscuous in order to increase the genetic diversity of their offspring. Genetic diversity is always a consequence of female promiscuity but rarely a cause.

  To get back to shiner perch, however, the theory that promiscuous females are hedging against male sterility is plausible. Shiner perch are unusual fish. Rather than shed eggs and sperm into the sea as so many fish do, they copulate, the male placing sperm packets into the female’s genital orifice. What’s more, the females don’t lay eggs—they actually give birth. But there’s a long delay—several months—between the time females mate and the time they fertilize their eggs. By then, males have lost interest in sex and their testes have shriveled for the winter. If a female had only one mate and he turned out to be sterile, s
he would lose out on breeding for the whole year. Surely you wouldn’t want that?

  You do, though, raise an interesting matter. If a proclivity for promiscuity is genetic, then yes, promiscuous behavior will become more common if loose females tend to have more children than their monogamous peers. That’s how natural selection works. Unfortunately, though, we don’t know much about the genes that influence female sexual behavior in any animal, let alone in shiner perch. What I can say is that in both the fruit fly Drosophila melanogaster and the field cricket Gryllus integer, females do differ in their inclination to have fun, and this can largely be accounted for by genetic differences. So, boys, take a long look at your girlfriend’s mother—if she was a good-time girl, the odds are on that your girlfriend will be too.

  Dear Dr. Tatiana,

  I’m consumed with existential angst. I’m a stalk-eyed fly, Cyrtodiopsis dalmanni, and every night girls line up to mate with me, but I rarely see the same girls twice. Worse, few of my visitors are virgins—and I know that they’ll go on to other guys night after night after night. What are they looking for, and why can’t I satisfy them?

  Feeling Inadequate in Malaysia

  True, female stalk-eyed flies are massively promiscuous. But they have exacting taste. Females of your species are irresistibly drawn to a fellow with stalks so imperial that his eyes are set farther apart than his body is long. When dusk falls in the tropics, as you know from personal experience, stalk-eyed flies gather at streams, where they settle for the night on the fine root hairs that stick out under the banks. Females head for the root hairs presided over by the male with the longest stalks—and in the morning, they copulate with him before flying off for another day’s foraging.

  You see, girls may say they want a kind, sensitive, devoted guy—that personality matters more than looks—but the truth is, in many species, females are body fascists. That’s why as a rule it’s the males that have ridiculously long tails or fancy headdresses—or eyes perched on the ends of long, stiff stalks.

  Darwin was perplexed by the extravagant ornaments and decorations that grace the features of so many males. The evolution of weapons was easy to explain. Not so ornaments. All too often, ornaments seem to work against natural selection by making it much harder to survive. The peacock’s tail might look superb—but have you ever seen peacocks fly? It’s a ludicrous sight. They lumber through the air, an easy snack for a tiger.

  To explain how huge tails and other frivolities could evolve despite the obviously greater risk of being eaten, Darwin came up with an idea even more radical than evolution by natural selection. He called it “sexual selection.” That is, males have these ornaments because females prefer to mate with the most beautiful males. Since beautiful males would therefore go on to have more children, enhanced sex appeal could more than make up for the risks involved in having a huge tail.

  Darwin was ridiculed. Females have a sense of beauty? Ludicrous. Females the ones who choose? Absurd. But as usual, he was right. These days, no one would dispute that females in many species actively decide whom to have sex with or that their preferences can drive the evolution of extravagant ornaments. What is still fiercely argued, though, is what they get by choosing the longest eyestalks or the biggest tail. Is it just sex appeal? Or is it something more?

  In theory, it could be either. Sheer sex appeal can evolve through something known as “Fisher’s runaway process,” or the advantage of having “sexy sons.” Who’s Fisher? Ronald Fisher was one of the great mathematical geneticists of the twentieth century. According to his model, female taste is initially arbitrary: girls like long tails, say, just because they do. But because of this, males with the longest tails mate the most. Females who prefer the males with the longest tails have sons with the longest tails (the sexy sons)—who also mate the most. And so on. The result? Tails get longer and longer. When does it stop? One way it could stop is when the disadvantage of having a slightly longer tail—like becoming a predator’s lunch—outweighs the advantage of being just that little bit sexier.

  Alternatively, beauty might be more than skin deep. According to the “good genes” hypothesis, ridiculously long tails, fancy headdresses, or absurdly long eyestalks tell a girl not only that a boy has genes for long tails, fancy headdresses, and so on but that he has good genes in general. In other words, males with the longest tails are simply the best: they’re in the best shape because they have the best genes—and their offspring will be more likely to survive.

  Both the runaway process and the good genes theory make sense in principle. As usual, though, it’s difficult to work out what Mother Nature’s been up to in any particular case. Let me give you a couple of examples.

  When biologists study wild birds, they often put little colored bracelets on the birds’ legs so that they can tell who’s who from far away. Evidently, bracelets are not a characteristic that can be inherited. Yet it turns out that female zebra finches find a male sporting red bracelets to be extremely sexy. So sexy, indeed, that they will lay him an extra clutch of eggs. Green bracelets, however, have no such charm. Perhaps females find that green clashes with a fellow’s orange legs; in any case, males wearing green bracelets have no luck with the girls.

  But although this preference shows females can pick a mate based on sex appeal alone—the basic requirement for a runaway process—in more natural situations it is often exceedingly hard to tell whether females are mating because they find the males sexy or because they’re hoping for good genes. An example of the difficulties comes from peacocks. Peachicks sired by males with fancier tails survive at a higher rate than those fathered by more humdrum-looking males—which at first glance supports the good genes hypothesis. The trouble is, there’s always the possibility that the effect appears simply because females who mate with sexy males take more trouble over their offspring. Among mallards, a duck who mates with the sexiest drake lays larger eggs than she does for an ugly fellow. Big eggs are a crucial factor in a chick’s early survival. But it turns out that a drake’s genes have no bearing on the size of the eggs. The difference in bigness can be explained entirely by the mother’s tender loving care. So why does she bother? Who knows. Perhaps it’s Fisher coming through the back door: perhaps ducks with sexy mates put more effort into their offspring because they know their ducklings will grow up to be sexy too. Is something like this also going on in peacocks? We don’t know. Although peahens don’t alter the size of their eggs, they could be making more subtle adjustments. Female zebra finches mated to attractive males, for example, increase the testosterone composition of their eggs—thus accelerating the speed at which the chicks grow.

  Your situation is similarly complex, my stalky friend. When females mate with you, are they after good genes or sexy sons? There is evidence that if the larval environment is harsh, only a few males have the genes to grow great stalks. Again, at first glance, this supports the good genes idea: females select the males most able to cope with a tough environment. Alas, without information on whether these males have offspring who are more likely to survive than the offspring of other males, we cannot arbitrate. In picking males with the longest eyestalks, the females also increase the odds that their sons will be sexy too.

  Dear Dr. Tatiana,

  I’m a harlequin-beetle-riding pseudoscorpion. At least, I should be. But when I found a beetle to ride, I wasn’t allowed on board. Some big thug of a pseudoscorpion helped my girlfriend on but pushed me away as the beetle took off. ,She went with him happily, and I just know she’s having sex with him, the tramp. Meanwhile, here I am marooned, a stuck-on-a-rotting-log pseudoscorpion. I’ve tried waving my pincers at harlequin beetles flying overhead, but none has landed. How can I get off this log and find a girl who will be true?

  Stranded in Panama

  Boy, have you got a bundle of problems. Let’s start with the most pressing one—getting you off that log. You won’t get anywhere by waving your pincers, I’m afraid. Here’s the scoop. Harlequin-beetle-riding pseudosco
rpions live on rotting logs—the fallen branches of fig trees, preferably. The only problem with this otherwise excellent arrangement is that sooner or later a given log will decay completely; when it does, anyone in residence will perish. So, how can you escape from the log before it has rotted to nothing? Enter the harlequin beetle.

  Harlequin beetles are magnificent, their jet-black wing covers decorated with jagged red stripes. More germane than their looks, however, is where they make their homes—in rotting logs. The cycle begins when a female harlequin beetle lays her eggs in a freshly fallen fig tree. Her children develop in the wood; after several months, they emerge fully grown. This is your moment. Pseudoscorpions are tiny—far smaller than proper scorpions (although the real distinction is that you have no sting). This means that you can stow away under a harlequin beetle’s wing covers and fly off to a new home when the harlequin beetle flies to fresh logs to find mates and lay eggs.

  But as you found out, space under the wings is limited. Even on a large beetle, no more than about thirty pseudoscorpions can clamber on board. Worse, a big male pseudoscorpion can easily defend this space from rivals. With bogus gallantry, he lets females on and keeps other males off. Then, when they take to the skies, he will have sex with as many of his companions as possible. Right now, just as you feared, your girlfriend is probably squatting over a packet of sperm that the “big thug” has deposited for her on the harlequin beetle’s back. Sorry about that. And I’m afraid I have some other bad news. Harlequin beetles already out in the world are not attracted to old logs, so there will be no casual passersby. If you can’t find and board another beetle as it emerges, you’ll be marooned forever, a helpless member of a doomed population.