Sex on Six Legs Page 8

  Be that as it may, scientists don't try to replicate the five commonly used axes for personality in humans: extraversion/introversion, antagonism/agreeableness, conscientiousness, neuroticism, and openness to experience. Too many of those criteria require self-reporting, but equivalents can often be measured, for example, the frequency of fighting that occurs when animals are in a group, or the length of time it takes an animal to move through its enclosure. Gosling cautions that it is important to know the standards against which the measures are being compared; after all, he points out, if one asked whether a deadly black mamba in a room was aggressive, it would be possible to respond that it was not, if "it has attacked only two people in the last hour, well below the norm for this species of snake." Nevertheless, one would still be ill-advised to enter. There is also something called The Horse Personality Questionnaire, with categories of Dominance, Anxiousness, Excitability, Protection, Sociability, and Inquisitiveness; why horses require six descriptors while humans only need five is an interesting question.

  Keeping this in mind, a wide range of animals, including several insects and spiders, show consistency in their behavior. For example, fishing spiders live at the edge of ponds and feed on insects near the water. Different individuals attack their prey with differing degrees of alacrity, and the individuals that leap upon their prey more quickly get more food. This seems like an all-around good thing, until you learn that predatory eagerness in females is also associated with a greater likelihood of killing and eating one's potential mate. Fishing spiders also respond to the threat of attack by a potential predator by quickly diving under the water and remaining submerged in an air bubble until the danger is perceived to have passed, a period that can exceed 90 minutes. J. Chadwick Johnson and Andy Sih at the University of California, Davis, found that the length of time female spiders spent submerged varied among individuals, and bold spiders—ones that emerged relatively quickly from their underwater shelter—were also likely to go after food more decisively and to respond to males that were courting them by tapping the water surface.

  Because I study them, I am biased toward crickets and have always thought they had plenty of personality, with more of it, not to mention charm, than their relatives the grasshoppers. Male crickets are rather pugnacious, and the ancient Chinese often pitted them against each other in specially constructed arenas, much like miniature cockfights. Some individuals were highly prized as winners, with poems written about their prowess. And indeed, my intuition was upheld; recently, Raine Kortet and Ann Hedrick found that fighting ability in a North American cricket was not only variable among different males, but winners were more brazen about emerging from a refuge in their container after they had been disturbed in a manner simulating a predator.

  Water striders are the leggy insects that dimple the water of streams and ponds all over North America; they skate over the surface, grabbing both prey and, during mating season, each other. More accurately, male water striders jump on females and attempt to mate, while the females often try to shake them off. Although they all look similarly jittery to the casual observer, the striders, too, vary among themselves in their level of activity, with relatively sluggish individuals and more perky ones. More active individuals also tend to be more aggressive. Andy Sih, working with Jason Watters this time, created groups of male water striders in semi-natural streams by putting like-minded, or at least like-behaving, individuals together, so that some groups had members that were more laid-back overall, and others those that were more likely to hustle. The scientists then put females into the mix and measured the success of the males in obtaining mates. Somewhat to their surprise, the groups that measured the highest on the hard-driving scale didn't end up with the most overall mates. Watters and Sih discovered that such groups were likely to have "hyperaggressive" individuals whose overenthusiastic pursuit apparently drove the females away. As with humans, it's easy to overdo the hard sell.

  Even those poster insects for uniformity, tent caterpillars, turn out to have some inner uniqueness. Tent caterpillars live in rather messy webs spun in tree branches and can number in the thousands during outbreaks, when they are serious forest pests. Their munching, marching armies can defoliate tens of thousands of acres. Understanding variations in their behavior is important for controlling them, so the topic has received considerable study, and it turns out that individual caterpillars show consistent distinctive patterns of sluggishness or activity over several days. Admittedly, how much a caterpillar walks or eats during an hour-long observation period, and whether it is more or less than the amount attributable to another caterpillar, is not what most people think of when they imagine an animal with a characteristic personality, but it still differs from that Borg-like image that is traditionally held.

  As for Wart's—and T. H. White's—stereotypes about ants, they too may not be well founded. In his delightfully titled 1928 paper Psychological Experiments with Ants, G. Kolozsvary studied the escape behavior of the insects and found that they varied in what he termed nervousness. Other more recent papers have found individual differences in how ants cared for the pupae in the nest and how they responded to the others in the colony.

  So personality is everywhere, even if Arthur, the once and future king, remained unconvinced. One of the most interesting implications of this realization is that scientists are starting to have what might be termed a more holistic view of animal behavior. If how an individual behaves now can be predicted based on the way it behaved before, we should probably stop acting as if every day, and every experiment, is a world made new—looking at an ant or fish or cricket under one set of experimental circumstances isn't independent of looking at that same animal under another set. This means that even biologists should see the animals they study as unique individuals at least sometimes, rather than interchangeable subjects. We've shied away from this before lest we appear anthropomorphic, but now it seems as though there are solid scientific reasons not to assume that all ants are the same.

  She Must Get That from Your Side of the Family

  WHERE do personalities come from? In other words, are we—and other animals—born with them, or are they shaped by our experiences? It's particularly instructive to ask these questions about insects, because with humans and other cognitively complex vertebrates, it's virtually impossible to disentangle the two. We humans are interacting with others nearly nonstop from the moment we are born, and maybe even before that if the exhortations about talking, reading, or playing music to the developing fetus are to be believed. Other social animals such as dogs or primates are almost the same. But insects have a much more modest amount of input from others, and as I have said repeatedly, we can manipulate their environments much more easily as well. Therefore, any behavior that persists despite a change in juvenile milieu must be genetic, and conversely, a behavior that is different in genetically similar individuals, for example, siblings, that are reared apart is likely to be due to learning.

  Like many traits, shyness and boldness seem to be at least partly heritable; if an individual's father or mother was bold, chances are that it will be too, even if it is reared apart from its parents. Using fruit flies, Marla Sokolowski has been able to find not only a single gene, but its coded protein that lies behind a tendency to either move around as a larval fly (rovers) or have a more couch potato-like persona (called, reasonably enough, a sitter). Humans have also been able to domesticate breeds of horses, dogs, and other animals that possess not only particular body types but also characteristic behavioral traits, including willingness to fetch (retrievers) and aggressiveness (think pit bull), which means that such characteristics must be able to be passed from parents to offspring. Bold and shy people have different responses in their brains when they are presented with the same photographs of familiar or unfamiliar people, suggesting that these differences are an integral part of our makeup.

  But as is also the case for many traits, the environment affects how much boldness or shyness (or any oth
er aspect of personality) is expressed. Early experiences such as how much a mother interacts with her offspring can modify the tendency for an animal or person to be reckless or reserved, docile or rebellious. For many insects that lack any parental care, later behavior can still be affected by the place where a mother lays her eggs. In Wilson's sunfish, boldness means that you explore a new object in your pond sooner than the other fish do, and you are more willing to come out of hiding when a predator approaches. These differences between bold and shy individuals persisted in the wild for as long as Wilson and his crew were willing to look for them. And immediately after they were brought into aquaria in the lab, the bold fish were more willing to eat fish flakes, a novel food, instead of sulking in a corner, dreaming of scrumptious snails. But after a few weeks of getting used to the glass and plastic of their new digs, the distinction between the two types disappeared, and the formerly bold and shy sunfish were equally likely to approach a new object. The real world, it seems, keeps us—or at least some animals—different. These results make it tempting to speculate about the homogenizing effects of institutions such as prisons, or maybe even just urban living, on us humans; but of course we don't have a similar controlled experiment on people to use for comparison.

  This universality of personalities across many different kinds of animals, including insects with their tiny brains, has two crucial implications. First, it means that the mechanism behind personalities can't be all that important, or at least that different parts of our physiology must account for the existence of personalities in different groups. In people and other mammals, we attribute, maybe even excuse, being laid-back or anxious to our hormones. Our stress levels are up because of cortisol or adrenaline, our neighbor is phlegmatic because his testosterone has decreased as he's aged. It isn't that hormones cause us to have particular traits, but that we have to have some physiological manifestation of our psychic differences. Even things that seem to be all in our head have to come from somewhere in the body, whether that is hormones coursing in the blood or electrical signals leaping in the brain.

  Invertebrates, however, lack the same kind of hormonal system that mammals have, so their tendency to dart across a pond or cower under a leaf must arise from a different physiological source. The hormones are a handy means to an end, but they are not the only one. If fish, ants, and crickets have personalities too, we have to look somewhere other than our vertebrate types of tissues and organs for where they come from.

  Second, when something seems to have evolved independently over and over again, such as wings in bats, birds, and butterflies, you have to suspect that nature is onto a good thing. So the existence of something that looks so much like our personalities, but is obviously evolutionarily independent, suggests that having a personality serves an important function.

  The Face Is Familiar, but the Sting Is Different

  IMPLICIT in the existence of different personality types is the ability to tell each other apart. If you can't keep track of whom you're dealing with, knowing that someone is rude and someone else magnanimous is useless. Young Wart was taken aback by the sameness of the ants he encountered, each distinguishable only by a set of letters and numbers (the Borg, too, were designated by numbers, with the voluptuous Seven of Nine, taken into the Voyager starship community, using her lack of a humanoid name as an indication of her loss of humanity). The implication was that since all the individuals behaved the same, there was no point in distinguishing among them, either by appearance or appellation. And yet if animals have personalities, and others react to them as individuals, they must not be indistinguishable. We can tell our pets apart, and we are perfectly happy to watch nature shows that differentiate—and name—individual elephants or meerkats. But what about insects?

  One roach or ant may look just like the next to us, but when Liz Tibbetts of the University of Michigan puts up a slide of the paper wasps she studies, she calls the array of face shots portraits, and she does it unselfconsciously. To her, they are just as distinctive as a series of family holiday photos, or a row of oil paintings of ancestors on the manor wall. And indeed, once you scrutinize the lineup, the yellow triangular faces do differ: a couple of black dots across the forehead of one, a big dark triangle across the chin of another. For over a century, conventional entomological wisdom held that given the large numbers of individuals in a social insect colony, the most one could hope for in terms of individual recognition would be a rough ability to classify other wasps (or bees, or ants) into categories: male versus female, or nest mate, to be fed or at least tolerated, versus foreigner, to be attacked. Maybe it is the opposite of anthropomorphism: instead of assuming animals are like us, we assume they are not. Both are risky generalizations that turn out not to be borne out by the facts. Increasingly, biologists such as Tibbetts are discovering that at least some insects can do far more than peer nearsightedly at their neighbor and call it friend or foe.

  Paper wasps, unlike honeybees, live in relatively small groups of females, all of which are capable of laying eggs, so they lack the clear distinction between worker and queen. The females of one of the species Tibbetts studies, Polistes fuscatus, fight vigorously for dominance at the beginning of the season. The rank an individual attains is crucial, because the higher up a wasp is in the hierarchy, the more food she can garner, the less work she does, and, most important, the more eggs she contributes to the colony's reproduction, giving her a larger share of genes in the next generation. But Tibbetts noticed that, as with other species that live in socially stratified groups, for example, baboons, the overall amount of aggression in a wasp nest subsides with time, and the wasps do not have to fight each time they meet to reestablish who's boss.

  Tibbetts suspected that the wasps used their variable facial patterns to recognize and remember individuals, and she tested her idea in an ingenious if simple way: she painted the faces of wasps so that they no longer seemed familiar to their nest mates. To minimize her risk of getting stung, she nabbed the wasps early in the morning, when the wasps were chilly and less inclined to object to being handled. Once the redecorated insects were returned to their nests, Tibbetts watched the reaction of the rest of the colony. As she had predicted, the wasps were much more aggressive to the altered individuals than they had been before, although the aggression subsided after about half an hour, indicating that they had learned the new facial pattern of their nest mate. It was clear that the wasps were not simply reclassifying the painted females into rough categories, such as "familiar" or "unfamiliar," because paper wasps use chemicals on their outer surface for that purpose; furthermore, a female perceived to be from outside the colony would have been ripped to shreds or chased away, not simply pushed around a bit more than before. What is more, the wasps didn't seem to care how the apparent interlopers were painted—a bit more yellow on the chin garnered no more or fewer attacks than a larger brown stripe between the eyes. That means that the wasps are not using the face patterns as an indicator of size or age or some other quality of an individual, but instead as genuine identity tags; having two black spots, for example, doesn't say, "Stay away from me, I am large and fierce," but rather, "Sam I am" (or Samantha, in this case).

  In another species of paper wasp, P. dominulus, facial patterns do indicate both size and dominance, and females pay particular attention to the blotchiness of the black marks. A more broken pattern means a robust, higher-quality individual, for reasons that aren't yet clear. This time, Tibbetts painted the faces of the females so as to either make them look more or less dominant, and then allowed the wasps to guard a sugar cube in the lab; in the wild, the wasps eat nectar, but they happily consume sugar in captivity. Pairs of wasps, one painted to look like a subordinate and one to look like a dominant individual, were each assigned their own sugar cube, and then another wasp was introduced to the container. The wasps share food, but dominant individuals are harder to coax into contributing than submissive ones. As you might expect, the supplicating wasp was more likely to c
hoose a cube being defended by a wasp whose facial pattern suggested she was a loser. What's more, when Tibbetts staged encounters between wasps that were strangers to each other, a subordinate individual painted to look like a dominant one was much more likely to be beaten up by the real dominant wasp, showing that even wasps dislike a cheater. Interestingly, other researchers studying the same species of wasp found that body size, rather than pattern, was important in determining social rank in a population from Italy (Tibbetts works in North America); the reasons for the difference are not well understood but may have something to do with the timing of food shortages and, hence, growth of the young insects.

  It turns out that individual recognition is more likely to evolve in wasp species that show more complex social behavior than in those with more short-lived or simple interactions. In some species of paper wasps, a single female always starts a nest, and her daughters then contribute to the growth of the colony. In others, several females build the cells and attempt to lay their eggs simultaneously, giving rise to the jockeying for social status described above. Among yet a third group, either approach is seen. Each of these scenarios calls for an increasingly astute approach to social politics. As one might expect, species that are likely to have complicated group dynamics, as indicated by the likelihood that multiple individuals will have to work out their hierarchy, are more likely to show a lot of variability in their markings.