TIMING RESPONSES IN ANIMALS

Students can….

Explain why there are environmental rhythms

Explain why plant and animal behaviours are linked to environmental rhythms.

Earth’s Rhythms

• Yearly orbit of Earth about the sun, together with the tilt of its axis, cause the seasons

• Seasonal contrast increases with increasing latitude (ie. least contrast is near the equator)

• Seasons have characteristic abiotic conditions (temp, day length, rainfall etc)

Daily Rhythms, 24 hr

• Caused by daily rotation of Earth on its axis

• Produces alternating light and dark periods

• Length of day depends on latitude and season

• Sun also affects daily rhythms in temp, humidity, wind

Effects of the moon• Moon orbits the earth once per 27.3 days

• Affects the tides: moon’s gravitational pull combined with Earth’s rotation

• Twice-daily ocean tides• Tidal levels vary during moon’s phases (spring

and neap tides)• Changes in illumination (light) at night

Environmental Rhythms and Animal Behaviour

• Most daily and annual animal rhythms are linked to cyclical environmental changes caused by Earth’s rhythms

• Includes periods of activity & sleep, feeding & drinking, breeding, migrations, fluctuations in body temp, sensitivity, hormone levels

What are the biological advantages to an animal species of synchronising its

activities to Earth’s rhythms??• Better food supply• Avoiding predators• Avoiding competitors• Finding more favourable environmental cond’ns• Avoiding harsh conditions• Finding mates or a breeding place• Raising young successfully***ENHANCED SURVIVAL & REPRODUCTION***

Biological Rhythms

• Animals and plants exhibit all kinds of regularly repeated behaviours

• eg. activity patterns, reproduction, migration, hibernation

• EXOGENOUS rhythm: A direct response to environmental cues (external)

• ENDOGENOUS rhythm: Internally controlled, will continue in absence of environmental cues (involves a biological clock)

HOMEWORK

• BIOZONE Pg 187 and 188 questions

BIOLOGICAL RHYTHMS (biozone 188)

LEARNING OUTCOMES

• Explain what BIOLOGICAL RHYTHMS are• Explain the ADVANTAGE of these rhythms• Explain what a BIOLOGICAL CLOCK is

What is the advantage of having a biological clock?

• Activity remains in sync with environment• Keeps sleep/wake cycles constant• Able to predict events (eg. winter, spring)• Synchronise breeding stages with others of

your species and the seasons• Plants: flowers when the bees are out, lose

leaves in winter when cold

BIOLOGICAL RHYTHMS

• Animals and plants exhibit all kinds of regularly repeated behaviours

• eg. activity patterns, reproduction, migration, hibernation

• EXOGENOUS rhythm: A direct response to environmental cues (external)

• ENDOGENOUS rhythm: Internally controlled, will continue in absence of environmental cues (involves a biological clock)

Remaining in sync with environment

• Biological clocks must be reset at regular intervals

• This is the purpose of the ZEITGEBER or external timekeeper

• This is the environmental cue that resets the biol clock

• ENTRAINMENT is the process of resetting the biol clock

BIOZONE activities

• Pg 189-190

The Human Biological Clock

• Runs at about a 25.5 hr day• But we need it to be synchronised with our

environment (a 24hr cycle)• Mammals including humans have a master

circadian clock in our brain• Two tiny groups of cells called the

suprachiasmatic nuclei (SCN) in hypothalamus• Located behind our eyes, 1/3mm in size

What’s involved?• Eyes• SCN• Hypothalamus• Pineal gland• Melatonin

hormone

SCN

Pineal Gland Melatonin

production

PROMOTES SLEEP

Shuts off melatonin production

AWAKE

Light stimulus Darkness stimulus

In Hypothalamus

Zeitgeber = external timekeeper

• The light/dark cycle acts as the ZEITGEBER to reset our internal clock to a 24hr cycle

• Resetting of the clock is called ENTRAINMENT

• By following the day/night cycle, animals can better exploit the seasonal changes in the environment

The Importance of Melatonin

• Is the hormone controlling our sleep/wake cycle• When produced at night it promotes sleep• May help in the timing of onset of reproductive

cycles in many species of animals• Enhances the immune system

• More is produced over 24 hrs in the short days of winter than in summer (sleepier in winter?)

Today: Circa- rhythms & Actograms

• Learn how to read and interpret Actograms• Weta as an example

Lots of human daily rhythms

• BIOZONE “Human Biorhythms”• Susceptibility to alcohol• Body temperature• Blood pressure• Cell divisions in skin• Time of labour onset

What are Actograms?

• An actogram is a special graph • Shows the activity of an animal or plant during

the day/night and over many successive days. • Gives a good picture of when the organism is

active at any time.• Can use them to monitor changes over time

under constant conditions

Actograms show us:• Light/dark regime in lab conditions • Period = length of one full cycle eg. From start

of activity to the next start of activity.• The Free-running Period = how long the cycle

runs in the absence of all environmental cues• Phase-shift = New start time for the activity

(eg. 8am start changes to 10am) How much has it shifted? 2 hours later

DAILY RHYTHMS

• Daily night/day cycle of about 24 hours• Three types of activity are seen in animals:

1. Diurnal – mostly active during the dayEg. Humans, honey bees, tui

2. Nocturnal – mostly active at nightEg. Kiwi, owls, bats, moths, kakapo

3. Crepuscular – most active at dawn and duskeg. Rabbits, mosquitos, wombats

Today: Types of Biorhythms

• Explain what is meant by circannual, circalunar, semi-lunar, circatidal and compound rhythms

• Give examples of each of the above rhythms

Environmental rhythmsvs.

Circa- rhythms

• Environmental rhythms are daily, annual, tidal, lunar etc

• Animal rhythms can only be called circadian, circannual etc if they persist under constant conditions in the lab.

Cycle length Cues• Circadian (about 24 hours)

• circatidal (about 12.5 hours)

• circalunar (about 29.5 days)

• circasemilunar (about 15 days)

• circannual (about 365 days)

• Light/dark cycle

• Incoming/outgoing tide

• Moon phases

• Moon phases / spring high tides

• Day/night length (not temperature, too variable)

NZ Example of a Circatidal Rhythm

• Chione stutchburyi cockle• exhibits clear endogenous

circatidal rhythmicity in shell gaping and siphon extension and also in adductor activity

• occurred at the times of expected high tides

Advantage of the cockle’s endogenous rhythm being in time with high tides?

* avoid dessication at low tide* increased feeding time * increased survival

Circatidal example

• Fiddler crabs forage during low tide

• If taken away from the shore, the circatidal activity can persist for 5 weeks

Tidal/lunar cycle animation

Remember: the position of the sun and moon generate our tidal

patterns each month

Circalunar rhythm example

• Young salmon migrate downstream • Soon they will migrate to the sea• At new moon, surge in output of hormone

thyroxine• Brings about changes in physiology to cope

with being in salty water

Circalunar example

• Marine worms called Palolo worm • Spawning (egg laying and sperm

releasing) is synchronised by the moon

• Advantage? Males and females will spawn at the same time= increased reproduction

Example of Semi-lunar rhythm• Californian grunion• Leaves the sea to deposit its eggs (spawning)

in the sand of several beaches, Feb-Sept• Spawning only takes place on 3-4 nights after

full or new moon (when tides are highest). • Eggs buried in sand to develop, will be washed

out again during next spring tide in 12 days

Advantages of spawning at spring tide?

• Eggs deposited high on the sand by high tide so won’t be washed away

• spawning bed is not disturbed by the tides until the next spring tide cycle

• The eggs have a safe refuge buried in moist sand in which to develop.

• Increased survival and reproduction

NZ Inanga: Galaxias maculatus

• Adult life is spent in lowland streams and rivers

• During spring high tides, ripe adults move up on to the grassy flats of river estuaries, go to areas covered by water only at the spring tides

• The eggs develop and usually hatch at the next spring tides that cover the grasses

• Advantage = reproduction and survival

• The manner in which the fish are able to perceive and respond to the lunar cycle remains a complete mystery.

Annual Rhythms eg. Reproduction, migration, hibernation• Eg. Long-tailed Bat in NZ• Hibernates 4-5 months over autumn/winter• Reproduces annually in summer months• Responding to day/night length

Advantages for the bats?

• Breeds at the warmest time of year• More food around during breeding season• Avoids the cold months

Compound Rhythms

• Animal responds to more than one environmental rhythm

• Eg. Sandhopper – uses lunar orientation at night, solar navigation during the day.

Palola marine worm

• Highly synchronised breeding• Research shows this is related to

not only the moon’s phases, but also solar, daily and tidal rhythms.

PLANT TIMING RESPONSES

• Some plants exhibit rhythmic activity

• DAILY RHYTHMS: eg. Opening/closing of some flowers such as night-scented jasmine

• Eg. Leaf movements – the prayer plant leaves move to an erect position at night, horizontal during the day.

Plant rhythms….

ANNUAL RHYTHMS:• Eg. Production of flowers, loss of leaves in

autumn, germination of seeds• Usually in response to change in light/dark hours

WHAT’S THE PURPOSE?

• Plants synchronise with animal activity

– Eg. Open flowers and secrete nectar when animal pollinators are active in daytime

– Production of flowers coincides with the life cycles and activity of animal pollinators

PHOTOPERIODISM AND FLOWERING

• PHOTOPERIODISM: the regulation of activity by the length of daylight (the photoperiod)

• Photoperiod detected by leaves

• Flowering is induced by the length of the photoperiod

Plants are in 1 of 3 groups:

• Short Day Plants need a period of long nights before they can flower (ie. They need a photoperiod of less than a certain critical day length)

• Long day plants need a period of short nights before they can flower

• Day Neutral Plants flower independently of the length of photoperiod