lecture 12 Biological Clocks Flashcards
How many clocks in our bodies?
-Aging- Epigenetic clock
-Evolution- Molecular clock
-Development- Segmentation clock
-Geophysical cycles “(Chrono)Biological clocks”
(Chrono)Biological clock
- 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)
Circadian clock (“Day-Clock”)
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)
Ciradianrhythms persist under constant condition
The Andechsbunker close to Munich, German study showed the time awake and sleep stays constant
Ciradian rhythms in humans -examples
Melatonin levels
Core body temperature
Blood transcriptome
Saliva metabolome
Adaptive fitness of circadian clock -cyanobacteria
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
Circadian rhythms in cyanobacteria
Rhythm is seen in
Nitrogen fixation
photosynthesis
cell division
amino acid uptake
Circadian rhythms in plants
Circadian rhythms in plants:
*Leaf movement
*Germination
*Growth
*Stomatal movement
*Gas exchange
*Photosynthesis
*Flower opening
*Fragrance emission
Adaptive fitness of circadian clocks -Arabidopsis
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
Adaptive fitness of circadian clocks –Mice
The strain with a clock of resonating cycle length outcompetes the much faster (20h) strain
Summary 1
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
Other (Chrono)biological clocks
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
Circalunar clocks
Circalunar clocks allow organisms to time their reproduction with the moon
Marine midge Cluniomarinus adult emergence rhythm depends on?
-Circalunar clock
-Circadian clock
Low tide
-Adult emergence
The Western European habitat of Clunio
Cluniomarinus can be found
-in the intertidal zone along the European Atlantic Coast
-mainly at rocky coasts
Genetic adaptation of circadian emergence time of Clunio
Circadianemergence time:
-locally adapted
-genetically determined
Using Clunioas a research model for circalunar adaptation
Cluniomarinushas clearcut circadian timing adaptation
Cluniomarinus is the only known organism with circalunar timing adaptation
The problem of geographic isolation
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
Allochrony
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”
Summary II
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
