Biological Timing Responses in Animals

Biological Clocks These are internal timing system which continue without external time cues. They control the timing activities of plants and animals.

Uses of Biological Clocks Control of daily body rhythms such as sleep, blood pressure, temperature, blood cell count, alertness, urine composition, metabolic rate and sex drive. Reproductive timing i.e. animals in heat, courtship rituals, simultaneous release of sperm and eggs into water.

Uses of Biological Clocks Preparation for migration by eating a lot. Preparation for winter by storing food, increasing coat thickness or colour and hibernating. Solar (sun) or Stellar (stars) navigation

Endogenous Rhythms Controlled by an internal Biological clock. Circadian – daily activity period (24hrs) Circatidal – Tidal period (12.4hrs) Circasemilunar – spring/neap tide (14.7 days) Circalunar – monthly activity (29 days) Circannual – yearly activity (365 days)

Exogenous Rhythms This is a rhythm that is controlled by the external environmental stimuli detected by the organisms.

Circadian Rhythms Animals are active at different times of day: Diurnal Active during the day, inactive at night. Nocturnal Active at night, inactive during the day. Crepuscular Active at dawn and dusk e.g. fruit flies

Circadian Rhythms Arrhythmic No regular pattern These organisms are usually found in areas where changes in the microclimate are negligible. E.g. in caves, deep under the ocean or soil.

Circadian Rhythms in Humans Sleep – Awake rhythms Vary from person to person Children sleep about 12 hrs per night Teenagers sleep about 9 hrs per night Adults on average sleep about 7-8 hrs Elderly people make do with 6hrs (and nap during the day.)

Circadian Rhythms in Humans Temperature This rises during the day and drops at night, the lowest point being at 3 am. Heart Rate This keeps in step with temperature.

Circadian Rhythms in Humans Pain This varies during the day. We are more sensitive to the pain of a needle at noon, but are more sensitive to the pain of cold at night.

Circadian Rhythms in Humans Alcohol Metabolism We break down alcohol most efficiently between 4pm and 11pm.

Circadian Rhythms in Humans Efficiency of Learning This follows the temperature curve except it takes an unexplained dip at lunch time which is not related to eating lunch.

Circadian Rhythms in Humans Renal Excretions The kidneys are the blood filters, they control the amount of ions in the blood by excreting any excess and holding back ions if their blood level is low. These follow a rhythm of excretion of chemicals such as calcium and potassium and of volume.

Circadian Rhythms in Humans Birth and Death You are most likely to be born or to die in the early morning

Circadian Rhythms in Humans Hormone Secretion Varies but most are secreted at night.

Disturbing Sleep Rhythm Jet Lag These days when travelling great distances is possible in a very short time, we can cause a complete reversal of our day and night. Our biological clock has a phase shift of 12 hrs.

Things to Note. It takes about 3 days to sleep at the new time. All our other rhythms take longer to adjust, so they get out of phase with the sleep/awake cycles and with each other. It can take about 10 days to synchronise. Until then, we do not feel so good and do not perform as well as usual.

Things to Note All these symptoms together are what we call Jet Lag.

Think About This…. After the holidays, when you don’t use your alarm clock, you are tired when you come back to school. It is because you were free running during the holidays. Most students shift their clock by at least 2 hours, many by up to 4 hours. You are suffering from Jet Lag

Shift Work Sleepiness can cause mistakes, a common sign is using the wrong words in conversations or forgetting the end to a sentence. Shift work causes more distress than jet lag, as the days off-duty return the person to normal time. Shifts of 10 days on and 4 days off with different starting times are the worst…

Shift Work Remember the hormone and other rhythms take about 10 days to synchronise. A person working these times can have 4 shifts in 10 days They become moody and depressed. They become extremely irritable. They can’t sleep. They are more susceptible to infections. They have more accidents on the job They are not as efficient as day workers

Circamonthly (Lunar) Cycles Some animals synchronise their behaviour with the phases of the moon. The positions of the sun and moon generate our tidal patterns, so the response to these tidal changes during a 24hr period is considered to be a lunar cycle.

Circamonthly (Lunar) Cycles The ovulatory cycles of primate females is about 4 weeks long but there is no firm evidence that these are synchronised with the lunar month.

Circamonthly (Lunar) Cycles The spawning behaviour of certain marine worms is synchronised by the moon, which ensures that eggs and sperms will be released at the same time. The spawning of the palolo worm is governed by a combination of tidal, lunar and annual rhythms.

Circatidal (tidal) Rhythms The Grunion is a fish that spawns on land. From April to June, on the 3 or 4 nights that the spring tide occurs at precisely high tide, the fish squirm onto the beach. The female buries her tail in the sand. The male wraps around her to release sperm. Then they catch the outgoing tide.

Circatidal (tidal) Rhythms By the time the tide next reaches that part of the beach, 15 days later, the young grunions have hatched and catch a ride out to sea.

Circannual (Yearly) Cycles These result from the rotation of the earth around the sun over a period of 365.25 days. On top of this is the earth’s rotation on its own axis, set at an angle of 23.45º to the sun. This results in the seasonal changes which dictate many responses seen in organisms.

Circannual (Yearly) Cycles E.g. animals may migrate to and from breeding grounds twice a year, and have many annual cycles of reproduction and hibernation.

Hibernation This is the way that animals survive over winter, usually by slowing down their metabolism. Small animals are particularly susceptible to the cold as they have a large surface area to their volume and can lose heat rapidly.

Hibernation Most animals that hibernate lay down a vast quantity of fat before the onset of winter, then find a warm burrow and go into a form of suspended animation. Insects also suspend development in addition to the drop in metabolic rate; this is called diapause. Often triggered by a decrease in day length.

Aestivation This is a form of summer hibernation. When the soil gets too dry, earthworms will dig down deep and curl into a ball, secrete mucus and will aestivate until the soil becomes moist again.

Migration This is the annual movement of animals from their breeding area to another area where they do not breed, and then the return journey back again. It is usually triggered by the shortening day length or a drop in temperature.

Reproduction Animals need to produce their offspring when the conditions are most favourable. For most animals this is in the spring. Animals come into breeding condition in response to increased day length, temperature, rainfall, increasing food, etc. Animals detect environmental clues through the skin, and detect light through the eyes or the pineal gland.

Reproduction This causes secretion of various hormones which ready the sex organs and produce sex hormones. It also starts the appropriate behaviour for courtship and reproduction.