Adaptation Flashcards
What is adaptation and function ?
Adaptation - A feature produced by Natural Selection that enables an organism to survive and reproduce better than if it lacked the feature
Function - The survival benefit of an adaptation
What are the adaptations that allow birds to fly?
*Forelimbs adapted to produce lift and thrust
*Feathers shaped like aerofoil to increase lift
*Light weight skeleton with hollow bones
-different birds have different adaptations such as specific wings for diving (kinks in wing for accuracy) or hovering
Describe natural selection
*Adaptation is ‘undirected’
*Results from differential survival value of alternative alleles
*Alternatives arise from random mutations which are not necessarily advantageous
What are ‘Coadaptations’ ?
Complex adaptations involving multiple compatible changes at the same time
E.g. cornea, retina, lens and shape in the eye
Different parts could evolve independently in small steps
Illustrated by eyes in different species of living mollusc
-accumulation of adaptations in each individual steps that were useful within the complex (eye)
(Random mutations of 1% change= 2000 steps =Vertebrate eye in 400,000 years)
Each stage has to be advantageous or it would be selected against.
Preadaptation
Adaptations are not ‘designed’
Selection on mutations in genes that coded for previous adaptations.
The previous adaptation could have had the same function as the current adaptation, e.g. the ‘eye’
It could also have had a different function – ‘preadaptations’
Give an example of a preadapted organism
lobe fish have fleshy lobed fins so you could say that they were preadapted to locomote on land ( to give rise to tetrapods)
What are Exaptations?
adaptation= features still serving their original function
exaptations= Features that have changed function
A character that performs a different function to the reason it evolved
Preadaptations become exaptations
Also includes neutral features that previously had no adaptive value
A more narrow definition of ‘adaptation’
Are all traits adaptations?
Flying fish can leave the sea but must return in order to survive
No selection between alternative forms that did and did not return to the sea (gravity will always make you fall back so its not really an adaptation)
Falling back into to the sea is beneficial, but not an adaptation
Beneficial traits that did not arise from natural selection are not ‘adaptations’
Using Spandrels as an example
Side effects of adaptations
e.g. Large brain size in humans is (perhaps) an adaptation to foraging in a complex environment
The cognitive skills produce a range of side effects that are not adaptations
The function of large brain size is not to produce arts, science and commerce.
Are adaptations “perfect”?
Imperfect at different levels of organisation
Effects that are beneficial at one level may not be as beneficial at other levels
But are adaptations even perfect within the organismal level?
A perfectly adapted phenotype would….
Live forever, be totally invulnerable to predators, absolutely resistant to disease, reproduce at an infinite rate.
What prevents perfect adaptations?
Give examples of adaptations that aren’t totally advantageous
time sometimes environment changes quicker than these adaptations can arise
*Large fruits =The function of fruits is for seed dispersal via an animal vector
Large herbivores were present in central and north America until 10,000 years ago (giant sloths)
Present small herbivores eat some of the fruit but most of it rots including the seed
A very poor adaptation for seed dispersal
*Constraints on adaptation: Genetic factors
If a heterozygote has higher fitness than either homozygote the population evolves to an equilibrium
All 3 genotypes will be present e.g sickle cell anaemia where
a low-fitness homozygotes could be beneficial.
*Constraints on adaptation: Historical factors
veins in our neck taking a detour of up to1m down to our heart
In giraffes the route is much longer which may be detrimental
due to when we were all fish and it was under the gills
*Constraints on adaptation: Developmental factorsDevelopment influences likely types of mutation
e.g. Extra branches in a plant more likely than extra limbs in a vertebrate
‘Plieotropy’: single genes contribute to more than one character
Beneficial mutations can cause ‘developmental asynchrony’
‘Modifier genes’ reduce detrimental effects
e.g pesticide resistant blowflies. Allele that confers resistance leads to badly developed wings.
What are the limiting factors for adaptations?
constraints of;
temporal
genetic
historical
developmental limits.
