Innate behaviour: reflexes, fight or flight, taxes and kineses – Behaviour and Response in Mammals (Senior 5 Biology) | Ganzaa

Behaviour and Response in Mammals

Lessons

Senior 5 · Biology

Behaviour and Response in Mammals

4 lessons

Lesson 1 of 4

Innate behaviour: reflexes, fight or flight, taxes and kineses

25 min

Born knowing

A calf born on a farm in Nyagatare stands within an hour and pushes its mouth against its mother's udder until it finds a teat and begins to suck. Nobody taught it. Turn over a log in a damp garden and the woodlice beneath it scurry away, then gather again in the darkest, dampest corner. Nobody taught them either. Behaviour that an animal performs correctly the first time, without learning, is called innate. This unit is about how animals respond to their world; this first lesson deals with responses that are built in by the genes.

Definition

Behaviour: everything an animal does in response to a stimulus from its surroundings or from inside its body.

Innate behaviour: behaviour that is inherited, performed in the same way by all members of a species, and needs no learning. Examples: reflexes, taxes, kineses and instincts.

Taxis (plural taxes): a movement of the whole organism towards (positive) or away from (negative) the direction of a stimulus. Example: positive phototaxis, moving towards light.

Kinesis (plural kineses): a non-directional response in which the speed of movement or the rate of turning changes with the intensity of a stimulus.

Instinct: a complex, inherited sequence of behaviour, such as nest building.

Features of innate behaviour

It is inherited, coded by genes and shaped by natural selection.
It is stereotyped: performed in the same way each time and by all members of the species.
It works the first time, which matters when there is no chance to learn, as when escaping a predator or finding milk at birth.
It is inflexible: it cannot easily be changed when conditions change.

Reflexes

A reflex is a rapid, automatic response to a stimulus, such as pulling your hand away from a hot pan, blinking when something approaches your eye, or the knee-jerk. The impulse passes along a reflex arc: receptor → sensory neurone → relay neurone in the spinal cord → motor neurone → effector. Because the brain is not needed to start the response, it is very fast and protects the body from harm. You will study the reflex arc in detail in Senior 6.

Fight or flight

When a mammal meets a sudden threat, the hypothalamus triggers the sympathetic nervous system, and the adrenal medulla releases the hormone adrenaline into the blood. Together they prepare the body to fight or to run.

Change	How it helps
Heart rate and stroke volume rise	More blood, carrying oxygen and glucose, reaches the muscles
Bronchioles widen; breathing deepens	More oxygen enters the blood
Liver glycogen broken down to glucose	More fuel for respiration in muscles
Arterioles to gut and skin narrow; those to muscles widen	Blood is redirected to where it is needed
Pupils dilate	More light enters the eye, widening the field of view
Digestion slows; hairs stand on end	Energy saved for action; the animal looks larger

Worked example 1: the heart in fight or flight

A student's resting heart rate is 70 beats per minute and her stroke volume (blood pumped per beat) is $70\,\mathrm{cm^3}$ . A sudden loud bang raises them to 112 beats per minute and $90\,\mathrm{cm^3}$ . Calculate (a) the percentage increase in heart rate, (b) the cardiac output before and after, and the factor by which it rises.

(a) $\frac{112 - 70}{70} \times 100 = 60\%$
(b) Cardiac output $= \text{heart rate} \times \text{stroke volume}$ . Before: $70 \times 70 = 4\,900\,\mathrm{cm^3\,min^{-1}} = 4.9\,\mathrm{dm^3\,min^{-1}}$ . After: $112 \times 90 = 10\,080\,\mathrm{cm^3\,min^{-1}} \approx 10.1\,\mathrm{dm^3\,min^{-1}}$ .
Factor: $\frac{10.08}{4.9} = 2.1$ .

Meaning: within seconds, adrenaline and the sympathetic nerves roughly double the blood supply available to the muscles, before any exercise has started.

Taxes and kineses

Simple animals such as woodlice, maggots and flatworms, and single-celled organisms, use two kinds of simple response to stay in favourable places (Figure 2).

Taxes are aimed at the stimulus. Euglena, a single-celled alga, swims towards light (positive phototaxis), where it can photosynthesise. Blowfly maggots crawl away from light (negative phototaxis), which takes them into dark places where they are less likely to dry out or be eaten. Bacteria swim towards nutrients (positive chemotaxis).
Kineses are not aimed. A woodlouse in dry air moves faster and turns more often; in humid air it slows down and stops. Without ever "aiming" for damp places, woodlice end up gathered in them, because they stop moving there. This is useful because woodlice lose water quickly through their body surface.

Investigating with a choice chamber

A choice chamber gives animals a choice of two conditions. Place ten woodlice in the centre, cover the chamber, and count how many are on each side every minute for 10 minutes. To make it a fair test, change only one factor (here, humidity), keep the chamber evenly lit or dark, and repeat with fresh animals. Handle woodlice gently with a soft brush, and return them to where they were found afterwards.

Worked example 2: analysing choice chamber results

Illustrative results: in five trials, each with 10 woodlice, the numbers on the humid side after 10 minutes were 8, 9, 7, 8 and 9.

Total on the humid side: $8 + 9 + 7 + 8 + 9 = 41$ out of 50, which is $\frac{41}{50} \times 100 = 82\%$ .
If the woodlice had no preference, we would expect about half, 25 out of 50, on each side.
Every trial gave a majority on the humid side, so the result is consistent; a statistical test (you will meet the chi-squared test in Unit 12) would show whether the difference from 25 : 25 is significant.
To decide whether the response is a taxis or a kinesis, watch the paths: woodlice that wander fast and turn often in the dry half and slow down in the humid half show a kinesis.

Instincts

Instincts are long, complex chains of innate behaviour, each step triggered by the one before. A male weaver bird builds an intricate woven nest the first time it tries; a newborn mammal searches for a teat and sucks; a spider spins a web of the right pattern for its species without ever having seen one built. Instincts are adaptive because they work without practice, but because they are inflexible, an animal cannot easily change them when its surroundings change.

Warning

Common mistakes

Mixing up taxis and kinesis. A taxis is directional (towards or away from the stimulus); a kinesis only changes the rate of moving or turning.
"Woodlice move towards damp places." In a kinesis they do not aim at anything; they collect in damp places because they slow down there.
"Innate behaviour cannot be adaptive because it does not change." It is highly adaptive in the conditions in which it evolved; its weakness is in new conditions.

Miss Estruch Biology: "Taxes and Kinesis: Simple responses in organisms to their environment". Watch for the difference between a directional and a non-directional response, and for the woodlouse example; then compare the paths in Figure 2.

Tip

Memory hook: a taxi takes you directly to where you want to go: taxis is directional. A kinesis is about kinetic energy, how much you move, not where.

✦

Practice: innate behaviour

List three features of innate behaviour.
Give one example each of positive phototaxis and negative phototaxis, and explain how each helps the organism survive.
Explain the difference between a taxis and a kinesis.
Describe how you would use a choice chamber to test whether maggots prefer light or dark. State two variables you would control.
A man's heart rate rises from 72 to 95 beats per minute when he is frightened. Calculate the percentage increase, to the nearest whole number.
Explain why the fight-or-flight response includes the narrowing of arterioles to the gut.
Suggest why innate behaviour is especially important in animals with short lives and no parental care.
Woodlice placed in very dry air at first move fast and turn often. Explain how this behaviour increases their chance of survival.

Show answersHide answers

Any three: inherited; stereotyped; performed by all members of a species; correct the first time; inflexible.
Positive: Euglena swims towards light, so it can photosynthesise. Negative: maggots move away from light, into dark places where they are less likely to dry out or be eaten.
A taxis is a directional movement towards or away from a stimulus; a kinesis is non-directional, with the rate of movement or turning changing with the intensity of the stimulus.
Cover one half of the chamber with black paper and leave the other half lit; place maggots in the centre, count the number on each side at intervals, and repeat. Control: humidity on both sides, temperature, the number and age of maggots, the time allowed.
$\frac{95 - 72}{72} \times 100 = 31.9\%$ , about 32%.
It diverts blood away from digestion, which is not urgent, to the muscles, which need extra oxygen and glucose for fighting or running.
They have no time and no parent to learn from, so behaviour that works the first time, without practice, is essential for survival.
Moving fast and turning often makes it likely that they will soon reach a damper place, where they slow down and stay, so they lose less water.

Key points

Innate behaviour is inherited, stereotyped, correct the first time and inflexible.
Reflexes are rapid automatic responses; fight or flight is driven by the sympathetic nervous system and adrenaline.
Taxis: directional movement towards or away from a stimulus. Kinesis: non-directional change in speed or turning rate.
Instincts are complex inherited chains of behaviour, such as nest building.

Sources and credits

Written by Ganzaa. Facts were checked against 45.7 Behavioral Biology: Proximate and Ultimate Causes of Behavior, from Biology 2e by Mary Ann Clark, Matthew Douglas and Jung Choi, OpenStax, licensed under CC BY 4.0. No text was copied.
Photo: Porcellio scaber, Alexis, CC BY 4.0, via Wikimedia Commons.
Video: Taxes and Kinesis: Simple responses in organisms to their environment, Miss Estruch Biology, embedded from YouTube.

Figures 1 and 2, the tables, the worked examples and the practice questions are by Ganzaa. The results in Worked example 2 and the values in Worked example 1 are illustrative.

1Born knowing

2Features of innate behaviour

3Reflexes

4Fight or flight

5Taxes and kineses

6Investigating with a choice chamber

7Instincts