Adaptation and speciationIAEB

What is an adaptation?

A trait which increases biological fitness

What is adaptation?

A process whereby organisms become better suited to their environment

What are the types of adaptation?

Structural

Physiological

Behavioural

Why are adaptations not perfect?

Spandrels, physical constraints, historical constraints, time lag, genetic constraints, trade-offs, developmental constraints.

What are spandrels?

AKA the consequences of construction- traits that are there because they have to be due to construction, without serving a purpose nor a benefit to fitness

Outline physical constraints to adaptation

Adaptations obey the laws of physics and chemistry, thus are affected by gravity, etc

Outline historical constraints to adaptation

the changing adaptive landscape leads to different configurations of fitness across a landscape. Some organisms are unable to evolve further lest they fall into a valley of reduced fitness and this is impossible.

Outline time lag constraints to adaptation

An adaptation may not be judged within the environment in which it evolved, as the environment is always changing- a few years ago it might have been a great adaptation, but now isn’t

Outline genetic constraints to adaptation

Random mutations are the root of adaptation. If no mutation for the trait that increases fitness occurs, the population cannot evolve to have that trait.

Outline trade-off constraints to adaptation

One adaptation to increase fitness through reproductive success may be a poor adaptation to increase fitness through survival (ex: avoiding predation), or vice versa

Which things do not constitute an adaptation?

Traits which arise from chemical or physical necessity

Traits which happen to have benefits to fitness but have not been naturally selected to have such benefits

Ancestoral traits

What are some ways we can determine that a trait is an adaptation and not just a trait?

Look at the phylogeny of the organism.

Ask whether the trait has been maintained by selection against departures from the favoured design

Is natural selection perfect?

No, natural selection produces organisms only as perfect, or slightly better, than the competitors they struggle with for survival.

Outline developmental constraints to adaptation

Dynamics of an organism’s development can limit adaptation. For example, in allometric development, 2 or more body parts develop relative to each other.

Provide an example of time lags limiting adaptation

Dodo birds fed on the fruits of Calvaria major, which then adapted to germinate after passing through the dodo’s intestines (this increases seed germination). After the dodos went extinct, the tree population declined.

Give an example of a ‘perfect’ adaptation

The hexagonal shape of honeybee combs- uses building materials effectively whilst minimising dead space.

What is expatriation? Why don’t we call it pre-adaptation?

Recruiting a trait to a different function. Pre-adaptation implies that natural selection has foresight, it does not.

Provide an example of compromise limiting adaptation

Sunbird’s territorial defence. Sunbirds will aggressively chase other organisms away from flowers in their territory- this is a good adaptation in terms of increasing survival by gaining access to nectar, but detracts from other behaviours such as finding a mate.

Provide an example of physical constraints limiting adaptation

Gravity prevents land mammals from evolving to be as large as whales, as they would be crushed on land.

Provide an example of a structural adaptation

Succulents have thick, short leaves and stems to store water, an adaptation for their dry, hot desert habitat.

Provide an example of a behavioural adaptation

Seasonal migration of grey whales- migrate to the arctic ocean in summer, then off the coast of mexico in winter

Provide an example of a physiological adaptation

Populations of humans living in high altitudes have been found to have increased haemoglobin concentration

Provide an example of a ‘spandrel’

Human chin- result of jaw construction

Provide an example of historical constraints upon adaptation

Recurrent laryngeal nerve in humans- nerve going from brain to larynx, takes long route around aorta then back to larynx- evolved from fish, in their environment the nerve was the fittest phenotype. Cannot get a better configuration because cannot reduce fitness whilst reconfiguring route.

Provide an example of genetic constraints upon adaptation

Sickle cell anaemia- homozygotic individuals are unaffected by malaria, but have sickle cells or are affected by malaria but do not have sickle cells. Heterozygote is most beneficial in this instance, as provides resistance to malaria without all cells being sickle-shaped, but homozygotic genotypes will always exist

What is stabilising selection?

Average phenotype is fittest, extremes are less fit, organisms w/average phenotype reproduce more, two ends of phenotypic spectrum eroded.

What is disruptive selection?

Extremes of phenotypic spectrum favoured over the mean, organisms with extreme phenotype reproduce more, mean is eroded.

What is directional selection?

One extreme favoured over mean and other extreme, individuals with the extreme reproduce more and one end of the spectrum eroded.

Outline allopatric speciation

Populations are physically separated, causing differences between them to accumulate over time, which leads to reproductive isolation.

What are the 3 steps to speciation?

1. gene flow disrupted

2. genetic differences accumulate over time

3. reproductive isolation evolves

What is the founder effect?

The few ‘founder/s’ of a new population do not have genetic identities representing the entire population from which they came, thus the random selection of the founder’s genotypes gives a different frequency distribution. Differences in populations are accelerated.

Outline incomplete speciation

Random mating population becomes two isolated populations, but then these populations experience random mating leading to incomplete speciation.

Outline complete speciation

Random mating population becomes two isolated populations, assortive mating occurs, speciation happens

Outline cladogenesis

The splitting of two lines giving two species

Outline the biological species concept

A group of organisms that can interbreed and produce viable, fertile offspring

Outline the morphological species concept

Classification of organisms into species based on their appearances and physical similarities.

Outline the theory of sympatric speciation

Reproductive isolation occurs within the same environment- habitat and range has not changed. Random mating should even out incipient differences- thus there needs to be assortive mating occuring. Needs a stable polymorphism in which mating favoured by selection.

How does sympatric speciation occur in plants?

Polyploidy (cells having 1< pair of each chromosome). 4n individual cannot breed with a 2n individual. Thus reproductive isolation occurs acutely.

What are the two types of isolating mechanisms?

Premating mechanisms and postmating mechanisms.

Premating = prevention of the transfer of gametes

Postmating = prevention of the development of gametes

Name premating mechanisms

1. habitat isolation

2. temporal isolation

3. ethological isolation

4. mechanical isolation

5. gametic isolation

6. behavioural isolation

Name postmating mechanisms

1. reduced hybrid viability

2. reduced hybrid fertility

3. hybrid breakdown

Outline mechanical isolation

Populations occupy the same geographical area, but have the wrong structures to mate

Outline habitat isolation

Populations occupy the same geographical area, but have a different habitat

Outline ethological isolation

Populations occupy the same geographical area, but there is weak or no attraction between individuals of the opposite sexes

Outline temporal isolation

Populations occupy the same geographical area, but have different mating schedules

Outline behavioural isolation

Populations occupy the same geographical area, but have differing mating behaviours

Outline gametic isolation

The egg and sperm of two populations can come into contact, but no fertilisation occurs.

Outline reduced hybrid viability

Hybrid zygotes are formed between the individuals of two species, but they do not survive or fail to develop.

Outline reduced hybrid fertility

Hybrid offspring are formed between the individuals of two species, but are sterile or have reduced fertility

Outline hybrid breakdown

First generation hybrids are viable and fertile, but further generations are inviable or sterile.