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Design experiments to investigate taxis and kinesis
aaResearch on animal behaviour
- Quantitative evidence from carefully controlled experiments is necessary to make conclusions about the relative influence of ‘learning’ and ‘heredity’ on animal behavior.
- Using your knowledge of independent, dependent and controlled variables you can design your own research on innate behavior in invertebrates. Go for it!
- Innate behaviors are controlled by genes, independent of learning. They ‘pre-program’ an individual for ‘success’ in its natural environment. In evolutionary terms, ‘success’ means surviving, reproducing and passing on genes to the next generation.
- Taxis and kinesis are categories of innate behavior. Kinesis is the random movement of an animal in which the rate of movement is related to the intensity of a stimulus but not to its direction. (e.g. the positive relationship between humidity and the rate of movement in sowbugs). Taxis is the movement of an animal in response to the direction of a stimulus. Movement towards a stimulus is positive and movement away from a stimulus is negative. (e.g. positive chemotaxis guides male promethia moths towards female pheremones).
- In order to pass on his genes, a male promethia moth must avoid being eaten by predators and he must find a fertile female to copulate with. This isn’t an easy task because females spend most of their time hiding under branches, and they are distributed very sparsely over large forest landscapes.
- Through natural selection, male promethia moths have adapted two innate behaviors - menotaxis and chemotaxis - to help them locate mates. Menotaxis refers to an animal in motion that maintains a constant angle to a stimulus. Chemotaxis is movement in response to chemicals.
- Male promethia moths fly at an angle (menotaxis) perpendicular to the direction of the wind (stimulus). Once a male detects a female’s scent trail (stimulus), he turns upwind and follows the chemical gradient (chemotaxis) of the trail, which leads to the female.
- The menotaxis response increases the male’s chance of successful reproduction by: 1) reducing his searching time; 2) lowering his energy costs; 3) decreasing his risk of being eaten by predators; and 4) increasing his chance of finding a female.
aaaExample of kinesis – the sowbug
- Organisms that settle in more favorable areas enjoy a reproductive advantage over those settling in less favorable areas. Therefore, natural selection favors animal behaviors that help individuals to move to, and remain in, ideal habitat.
- Humidity is one factor that affects the reproductive success and survival of the sowbug. Sowbugs are land animals with external gills that must remain moist. Therefore, sowbugs are restricted to humid areas and are commonly found under damp logs, rocks, and fallen leaves.
- To settle in a suitable habitat, a sowbug must perceive, and respond to, changes in humidity. When humidity is favorable, a sowbug will remain (more or less) in the same place. When humidity is unfavorable, a sowbug will emigrate to a new location.
- Sowbugs respond to humidity with a form of kinesis called hygrokinesis. In hygrokinesis, sowbugs respond to changes in humidity by altering the rate of locomotion and/or the rate of change in direction.
- When conditions are ideal, sowbugs move slowly and change directions frequently, which has the effect of keeping them in the ideal microhabitat? When conditions become dry, sowbugs increase their speed of travel and change direction less frequently, which has the effect of taking them far away. Once a sowbug reaches a moister microhabitat it will move slower and change directions more frequently.
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