Biological Rhythms Repeated rhythms in animals which control the body or behaviour and synchronise the organism with the environment

Biological Clocks The existence of rhythms means that animals must have a way of keeping track of time They have an internal clock which lets them predict and prepare for changes to come Synchronising mating , migration, etc Horseshoe crabs mating They would not be very successful if one turned up on the beach to mate and no-one else was there!

Biological Clocks Cont… Biological clocks are used for: Control of the daily rhythms of the body Reproduction timing Preparing for migration by eating of plenty of food Preparing for winter by storing of food, increasing thickness of coat and hibernating Navigating by the sun or stars

Biological Timing responses to the abiotic world All organisms respond to various cues The responses can be: Annual cycles – yearly changes of the season Daily – night and day Lunar – monthly, often related to the moon Tidal – related to the ebb and flow of the tides It is to an individual’s advantage to synchronise its activities to these rhythms. They are reliable!!

There are 2 words to describe where the rhythms come from Outside the body Exogenous - A rhythm that is control by the external, environmental stimuli detected by the organisms. We hear the school bell and move to a different lesson Inside the body Endogenous – A rhythm that is controlled by an internal biological clock.

How do animals tell the time? Biological clock is an internal timing system which continues without external time clues, and controls the time of activities of plants and animals Period of the rhythm the time it takes to complete one cycle of activity Our biological clocks are constantly corrected by cues in the environment. They are called zeitgebers ( German for time keepers) Our most powerful zeitgeber is light. We are programmed to be awake in the day and asleep at night.

Jet lag jet lag is when our biological clock gets out of synch. When we move to a different time zone.

Biologists use actograms to record an animals biorhythm An actogram They are often double, triple or quadruple plotted so you can see a repeating pattern. (This means repeated side by side) The dark bars represent the animal being active

In the top section zeitgebers ( time cues ) keep the rhythms synchronised at the same time each day. When the zeitgebers are absent the rhythm still continues because it is endogenous( comes from inside the animal) but it starts to wander off the time by being a bit later each day

Circa-(about) Eg. whelks that come up to feed when the tide is in and hide under rocks when the tide is out and still continue this behaviour when you keep then in a bucket and the is no tide can be said to be circa- tidal Circadian means circa- daily. It is a rhythm that continues to occur every day without any environmental cues to keep it going. Circa is a word to describe a biorhythm that is endogenous and free running. This means it continues even when there are no external cues in the environment because it originates inside of the organism. Often the rhythm wanders off slightly which is why it is circa or approximately

Definitions. Circa – because each of the rhythms is not exactly the time length stated, eg daily is not 24 hours, their names start with circa (which means ‘about’) this can only be used if the rhythm is free running. ( see later for its definition) Photoperiod – the responses of plants and animals to the lengths of day and night

Definitions cont…. Free running period this is the time when the biorhythm is running without any clues from the environment, so it ‘runs free’ Entrainment this is the resetting of the bio clock forcing it to take up the period of the environment. It requires regular zeitgebers Zeitgeber – the environmental agent that resets the biological clock regularly to keep the biorhythm in time with the environment eg light.

Definitions Phase shift- this is the period of adjustment to a new biorhythm. Eg. When you travel to a different time zone you get jet lag but over a few days your biological clock adjusts to the new time. Look at slide 15 the bottom bit is a phase shift.

Circadian Rhythms Animals are active at different times of the day Diurnal – active during the day, inactive at night Nocturnal – active at night, inactive during the day Crepuscular – active at dawn and dusk Arrhythmic – no regular pattern – tend to be found were changes in the microclimate are negligible

Examples of circadian rhythms see page 34 in biozone book Periods of activity Periods of sleep Physiological processes Endocrine system rhythms Temperature changes Heart rate rhythms Pain rhythms Alcohol metabolism rhythms Times of births and deaths, etc

Circamonthly Rhythms Some animals synchronise their behaviour with the phases of the moon Changes associated with tidal patterns are also considered circamonthly (lunar) The spawning behaviour of some marine worms is synchronised by the moon so that the egg and sperm are released at the same time Grunion fish also work on this method of spawning, using the tides

Circannual Rhythms These result from the rotation of the earth around the sun Also a factor is seasonal changes caused by the tilt of the earth and the seasons produced as it rotates around the sun Examples of circannual rhythms are: Migration to and from breeding sites Hibernation Reproduction cycles Aestivation

Circannual Rhythms cont…. Hibernation - This is the way some animals survive over winter by slowing their metabolic rate Aestivation – this is a form of hibernation over summer when the weather gets too dry or temperature gets too hot Reproduction – the method by which most animals reproduce when conditions are most favourable, ie spring