lecture 12 Biological Clocks

Question 1

How many clocks in our bodies?

Answer 1

-Aging- Epigenetic clock

-Evolution- Molecular clock

-Development- Segmentation clock

-Geophysical cycles “(Chrono)Biological clocks”

Question 2

(Chrono)Biological clock

Answer 2

• Days, seasons, tides and lunar months

-temporal cues affect biological oscillators (clocks) which affect biological rhythms

-the sun affects your circadian clock which affects your daily rhythm (this includes gene expression, metabolism and immune function)

Question 3

Circadian clock (“Day-Clock”)

Answer 3

Circa-dian= approximately one day(lat. “circa” and “diem”)

An internal clock in every cell (genetic basis)

Producing daily rhythms in biochemistry, physiology and behaviour

Used to anticipate daily environmental changes

Can signal time without environmental input

Synchronisesto environmental input (entrainment)

Question 4

Ciradianrhythms persist under constant condition

Answer 4

The Andechsbunker close to Munich, German study showed the time awake and sleep stays constant

Question 5

Ciradian rhythms in humans -examples

Answer 5

Melatonin levels

Core body temperature

Blood transcriptome

Saliva metabolome

Question 6

Adaptive fitness of circadian clock -cyanobacteria

Answer 6

The strain with a functional circadian clock outcompetes the arrhythmic strain

The strain with a clock of resonating cycle length outcompetes slower or faster strains

Question 7

Circadian rhythms in cyanobacteria

Answer 7

Rhythm is seen in

Nitrogen fixation
photosynthesis
cell division
amino acid uptake

Question 8

Circadian rhythms in plants

Answer 8

Circadian rhythms in plants:
*Leaf movement
*Germination
*Growth
*Stomatal movement
*Gas exchange
*Photosynthesis
*Flower opening
*Fragrance emission

Question 9

Adaptive fitness of circadian clocks -Arabidopsis

Answer 9

The strain with a functional circadian clock grows better than the arrhythmic strain

The strain with a clock of resonating cycle length grows better than slower/faster strains

The strain with a clock of resonating cycle length outcompetes slower/faster strains

Question 10

Adaptive fitness of circadian clocks –Mice

Answer 10

The strain with a clock of resonating cycle length outcompetes the much faster (20h) strain

Question 11

Summary 1

Answer 11

Circadian clocks …

*are endogenous 24-h oscillators that govern daily timing of endogenous processes

*are widespread across the kingdoms of life

*evolved multiple times? (convergent evolution)

*allow organisms to anticipate daily environmental changes

*appear to have adaptive value on an Earth with a 24-h day-night rhythm

Question 12

Other (Chrono)biological clocks

Answer 12

Apart from the well-studied circadian clock (day-night),

there is good evidence for other biological clocks that allow anticipation of important geophysical cycles:

-Circatidalclock (the tides)
-Circalunar clock (the lunar cycle)
-Circannual clock (the seasons)Much less is known about their molecular clockworks

Question 13

Circalunar clocks

Answer 13

Circalunar clocks allow organisms to time their reproduction with the moon

Question 14

Marine midge Cluniomarinus adult emergence rhythm depends on?

Answer 14

-Circalunar clock
-Circadian clock

Low tide
-Adult emergence

Question 15

The Western European habitat of Clunio

Answer 15

Cluniomarinus can be found

-in the intertidal zone along the European Atlantic Coast
-mainly at rocky coasts

Question 16

Genetic adaptation of circadian emergence time of Clunio

Answer 16

Circadianemergence time:
-locally adapted
-genetically determined

Question 17

Using Clunioas a research model for circalunar adaptation

Answer 17

Cluniomarinushas clearcut circadian timing adaptation

Cluniomarinus is the only known organism with circalunar timing adaptation

Question 18

The problem of geographic isolation

Answer 18

Between rocky coasts along the Atlantic: strong geographic isolation →largegenetic differences unrelated to timing

Within same rocky coasts along the Atlantic: little geographic isolation →small genetic differences unrelated to timing (gene flow)

→Study site within same rocky coast with gene flow would be better to identify lunar timing gene

Question 19

Allochrony

Answer 19

Sympatric speciation = one population evolves into 2 or more different species in same location

… may start with changes in the ecology of an organism (e.g. behaviour, food)
… requires reproductive isolation to complete speciation (species definition)

To achieve sympatric speciation despite gene flow and recombination, ecological divergence and reproductive isolation must be genetically coupled.

This could occur via
-Pleiotropy= same gene but change in allele affects multiple traits
-Genetic linkage = physicalcoupling between two genes, e.g. proximity on chromosome
-Magic traits = multiple-effect trait that affects both ecological divergence and assortative mating (any genetic architecture)

In Clunio, changes in lunar emergence timing leads directly to differences in reproductive timing

→Lunar emergence timing is a so-called magic trait explaining sympatric speciation“

Isolation by time” or “Allochrony”

Question 20

Summary II

Answer 20

Internal clocks (oscillators) can represent a multitude of external geophysical cycles

They are common across biological systems

They provide wonderful examples of ecology and evolution for research and teaching

Clunio marinus is an example of sympatric speciation by allochrony