Sex on Six Legs

Marlene Zuk

18 annotations • Dec 2023 • data

Foreword

Beetles and earwigs take care of their young, fireflies and crickets flash and chirp for mates, and ants construct elaborate societies, with internal politics that put the U.S. Congress to shame.
A group of scientists working in Brazil recently discovered that caterpillars parasitized by a wasp continue to make an unwitting sacrifice even after the wasp larvae have emerged from their host to pupate on a nearby stem. The ravaged caterpillar stands guard over the developing wasps and defends them against intruders with vigorous swings of its body, a most uncaterpillar-like behavior. Apparently the wasps exert a kind of mind control over their host that persists even after they leave it, doomed to die before it will ever become a moth.
Bees convey the location of food using symbols.
As the famous evolutionist Richard Dawkins said in an article about the intelligent design controversy, "Many people cannot bear to think that they are cousins not just of chimpanzees and monkeys, but of tapeworms, spiders, and bacteria."
If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos. —E. O. WILSON
Crickets are usually rather secretive animals, with the males staying hidden in burrows or leaf litter while they produce their melodic songs. But here, we kept seeing males out walking around on the surface of the grass, brazen as could be, and what was more, they weren't calling. Since calling is the only way male crickets can attract a mate, and since attracting a mate is a cricket's—any insect's—raison d'être, I was puzzled. What were the silent males doing?
As you can probably guess, the next day I was dissecting the previous night's catch of crickets when a white maggot popped out of the body cavity of one of them, like a ghoulish jack-in-the-box. A little more work established that indeed, the crickets in Hilo—and, as it turned out, on Kauai and Oahu as well—didn't only attract the attention of amorous females when they called. They also risked being discovered by flies that use the chirps in a much more sinister way. Once a female fly locates a calling cricket, she deposits tiny larvae on him. A larva, usually one but sometimes two or even three, burrows inside the cricket's body and starts, ever so slowly, to eat his flesh while he is still alive. First it feeds on his body fat, but eventually, as the fly maggot grows until it occupies the entire body, from head to abdomen, it consumes the male's other organs, so that he is a shell that looks like a cricket but is pulsing inside with fly.
I am interested in this grisly process for many reasons, but mainly because it exquisitely illustrates an evolutionary conflict for the males: it is terribly dangerous to call, because males risk attracting the attention of the flies, but calling is the only way to attract a mate.

Chapter 1

THE LIKELIEST candidates for insect intelligence, or at least the first ones to be considered by naturalists, have always been the bees, wasps, and ants.
But grasshoppers and their relatives the locusts can be taught to determine the nutritional content of different plants and feed preferentially on the most nourishing ones.
In one study, groups of locusts were given food lacking either protein or digestible carbohydrates. The experimenters gave one food in a yellow tube and one in a green tube, alternating the association between subjects, and then let the insects feed on a balanced diet for a few days to make sure they didn't become malnourished. Then, the locusts were deprived of food for four hours, a rather long time between meals for the insects, which usually eat more or less nonstop. When the locusts were placed in a test chamber containing yellow and green tubes, but no food, they went to the color associated with the nutrient—either protein or carbs—they had been lacking. This feat is particularly impressive because it isn't just the grasshoppers having some holistic instinct for eating what is good for them, but a learned association between color and a nutritional deficit.
What was novel was the kind of image in his experiments: a black-and-white photograph of a man from a stock collection, compared with a photo of a different person, the same face upside down, and a drawing. Not all the bees got it right, but those that did could remember an individual face several days after their initial training.
If crickets are placed in a container with other crickets that have been hiding under leaves from predatory spiders, they are more likely to find a shelter and hide themselves.
"The intimate interaction between leader and follower in a pair of tandemly running ants at first sight bears all the hallmarks of a parent teaching a child to ride a bicycle."
And if it is, why haven't all animals evolved to be smarter? The answers to these questions come from an unlikely source: the humble fruit fly. Now, I can usually sell people on crickets, and ladybugs, ants, and bees already get their own movies, toys, and children's songs. People are less than enthusiastic, though, about the possibility of a sparkling intellect lurking in the sesame seed-sized flies that buzz in clouds around decaying fruit. But in Tad Kawecki's laboratory at the University of Fribourg in Switzerland, fruit flies are contestants in an unending game of Jeopardy, insect style. And some of them are big winners.
Despite these setbacks, one generation of flies led to another. Through the selective breeding process, the flies rapidly improved their ability to remember which substance was attractive and which was not, and after about twenty generations, Kawecki had flies that could go to the bug equivalent of Harvard or Princeton. Instead of taking three hours to learn which substance has quinine in it, the new and improved flies knocked the task out in less than an hour. What's more, they could generalize their ability to other tasks that required them to avoid or prefer one odor to another, and even to other stimuli besides odor, which means that the flies were not simply evolving better discrimination of pineapple versus orange, they were actually getting smarter.
Within the lifetime of the fly, the energy a fly acquires could go either to helping it survive longer, or to nervous system machinery, but not both. It may be cheap to upgrade the memory in your laptop, but doing so in the brain is going to cost you.
Over many generations, a different process may be at work. Say that a gene makes a fly smart, but because most genes have more than one effect, it also makes the fly vulnerable to starvation, or maybe more susceptible to infections. If being smart is advantageous enough—in Kawecki's lab, it made the difference between reproducing or not—then the gene conferring it will persist in the population, even if it also has some downsides.