A Beginner’s Guide to Animal Behavior John A. Byers Contact Information 2480 Blaine Road Moscow, ID 83843 USA 208 230 0643 [email protected] Chapter One The Biology of Behavior Imagine that you are sitting at your kitchen table. It is a beautiful summer morning and the screen door slaps shut after the dog has pushed it open with her nose to go outside. As you take your ?irst sip of coffee, a house?ly that entered when the dog exited suddenly claims your attention. Like a tiny vulture, the ?ly circles above the table, slowly descending, until she lands close to the sugar bowl. The ly walks toward the bowl, and stops where a few grains of sugar spilled when you lifted your spoon from the bowl two minutes earlier. The ?ly in?lates her proboscis and begins to dab at the sugar. As you watch this, you probably begin to feel a mild sense of outrage, not because the ?ly is stealing sugar, but because the ?ly’s moist, spongy proboscis, now dabbing at your table, was recently outside, probably dabbing at dog feces or at rotten chicken in the garbage can. You wave your free hand at the ly and she jumps into the air and hovers nearby before quickly landing at the sugar. You bring your hand rapidly down, attempting to crush the ?ly, but she is too quick for you. You put your coffee cup down, rise, and reach for the ly swatter, a tool that humans with their big brains have invented to crush ?lies. The ?lyswatter effectively doubles the length of your forearm and so doubles the speed of your strike. As you swing the ?lyswatter at the ?ly, that has resumed dabbing at the sugar, you also ?lex your wrist, further increasing speed. The ly sees the rapidly approaching head of the ?lyswatter. She jumps and begins to ?ly, but the broad head of your simple tool stops her ?light and crushes her with enormous force into the table top. Her internal organs, including her brain, are crushed beyond repair. A tiny marvel of Byers - A Beginnerʼs Guide to Animal Behavior 2 miniaturized circuitry and engineering lies mangled on your table. In your own brain, the circuits that would trigger shame or remorse do not light up. You brush the twitching carcass to the loor and step toward the door, where the dog is scratching to be let in. The ?irst thing that I want to say about this ordinary moment in life is to note how extraordinary the performances of you, the ?ly, and the dog were. The three of you used sensors that are tuned to radiation in certain parts of the electromagnetic spectrum, as well as sensors (in the dog and the ?ly) tuned to detect certain chemicals in the environment, to extract useful information about your environments. Your brains then issued precise sets of commands to muscles that pulled in a complex way on your skeletons, causing your bodies or parts of your bodies to move through space in a smooth, goal directed way. The performance of the three of you was far more impressive than anything that modern human technology can create. Robots that act like Commander Data, in the continuing voyages of the Starship Enterprise, are still entirely in the realm of science ?iction, as are robots that could emulate a dog or a house?ly. Unlike the Roomba, with a behavioral repertoire that consists of rolling on a lat surface and sucking dust, real animals move through a complex three-dimensional environment, detect and analyze information in multiple domains, acquire their own energy, repair themselves, and reproduce! Byers - A Beginnerʼs Guide to Animal Behavior 3 A neurobiologist who studies the cerebellum, a part of the brain that controls movements, once remarked that, “Moving the skeleton is an engineer’s nightmare.” Yet animals, such as you, the dog, and the ?ly, make very smooth, precisely timed and impeccably directed movements. The way that each of you produces movements is essentially identical. You, the dog, and the ly have sense organs, which transduce environmental energy or materials into patterns of nerve signals. Each of you uses sense organs called eyes to transduce light, energy from a narrow band of the electromagnetic spectrum. Each of you has sensors that bind to certain chemicals in the environment and transduce this event into patterns of nerve signals. For you and the dog, these chemical sensors are in the nose; in the ?ly, the sensors are on many parts of the outer body, including the feet – that’s how the ?ly knew to stop and extend her proboscis when she walked into that sweet spot on your table. Animals have a variety of sense organs, each tuned to a different source of environmental energy or materials, and across animal species, the same class of sensors may be tuned differently. The dog cannot see all the colors that you do, but the ly can. The ly can see the pattern of polarized light in the sky, but you and the dog cannot. The dog and the ?ly have chemical sensitivity that is greater than yours. Given the sense organs that it possesses, as well as the sensitivity and tuning characteristics of those sense organs, each animal species has its own perceptual world. I will return to this point in the next chapter. Each animal species also has a rich variety of internal sensors, which report information about the current functioning of the body. You and the dog have Byers - A Beginnerʼs Guide to Animal Behavior 4 receptors that report on blood temperature, sugar level, and acidity, the amount that each muscle is stretched, the likelihood that damage is occurring, mechanical pressure at most parts of the skin, how much the muscular walls of each blood vessel are contracted, the position of your head and of your eyes, to list a few examples. In summary the internal sensors report on the biochemical and mechanical integrity of the body, as well as on body part position. Now, where do all of these reports, from the sense organs and from the internal sensors, go? They go, in you, the dog, and the ?ly, to the brain. A brain is an integration and command center. A brain receives reports from the sense organs and the internal sensors, integrates the information to create priorities and then, based on the priority list, issues commands. These commands are of two sorts. First, there are commands to the organs – to the heart, lungs, gut, blood vessels, and endocrine glands. These commands are concerned with the essential task of keeping the body running. Howver, as we saw in our summer tableau, an animal must do more than simply rest, plant-like, in a steady state; it must also move through its environment. This is where the second sort of commands comes in. These are the commands to the muscles that pull on the skeleton and produce movements. We call these movements behavior. Muscle is tissue that is specialized to do one thing: to shorten on command. Muscle tissue is evolutionarily ancient and in all animals, muscle operates the same way. A command from the brain, traveling along what we call a motor nerve, reaches a Byers - A Beginnerʼs Guide to Animal Behavior 5 muscle. The muscle, in response to the commands, uses stored energy to contract: to become shorter. The exact molecular mechanism by which shortening occurs is complicated and is now almost completely described and understood. Muscle shortening produces movement in most animals because each muscle is attached to a rigid skeleton (internal in you and in the dog, external in the ly) at two points that are on opposite sides of a ?lexible skeletal joint. When the muscle shortens, one part of the skeleton moves with respect to the other. For example, your biceps brachii muscle has two close points (biceps = 2 heads) of attachment (what we call the origin, or relatively ixed location) on your shoulder blade and its other point of attachment (what we call the insertion, or moveable location) on the arm bone below your elbow. When the biceps contracts, the forearm moves toward the shoulder. Essentially all animal movement is produced this way – by muscles pulling at the skeleton. A cheetah sprinting in pursuit of a gazelle, a bumblebee ?lying over a meadow to land on a ?lower, a great blue heron stabbing at a ?ish, a bird of paradise hopping electrically around his display area to attract a female, bullfrogs calling, crickets chirping, Hillary Hahn playing the Bach D minor Ciaccona, a baby smiling – all are the outcomes of patterns of muscle contraction. I mentioned that animal brains are integration and command centers that receive internal and external sensory information and then issue commands. The commands to skeletal muscles cause the movements that we call behavior. How does the brain make a decision about which commands to issue? Although biologists do not understand very much about brain decision making, they are quite Byers - A Beginnerʼs Guide to Animal Behavior 6 certain about the general design features that they expect. In other words, we can predict the general decision making rules that brains should use. In animal behavior, we make a single, quite powerful assumption about the way that brains are organized. We assume that brains are organized so that from moment to moment, individual animals act as if they are asking themselves the following question: “What should I be doing at this moment to maximize my lifetime reproductive success?” In the past 20 years we have learned is that animals in nature really do act this way and that they give the impression of being aware of the complex contingencies that go into such a calculation.