Natural Selection Topic 4.2

Introduction Review: Define adaptation: Adaptation: special feature of an organism which allows it to survive in its environment and exploit its niche. Compare evolution and natural selection. Do they mean the same thing? How are they connected? Evolution: the gradual changes in allele frequency within a population over many generations resulting in anatomical, behavioural or physiological changes. Natural Selection: the mechanism by which allele frequencies change within a population resulting in anatomical, behavioural and phyisiological adaptation.

Theory of Natural Selection- by Charles Darwin Do all organisms born live to reproduce?- part a Are all organisms of a species identical? Why or Why not? – part b Why don‘t all organisms born live to reproduce? – Part c Changes that occur to the environment result in changes in the selection pressures. - Part d So what is the result? Part e, f, g

What is meant by allele frequency as a percentage? # of that allele in a population_____________* 100% total # of alleles for that gene in same population

Survival of the fittest : the best adapted organism will be the one which survives. Organisms which are less well adapted will not survive and may eventually become extinct. Read the cartoon on crickets- du/evolibrary/article/0_0_ 0/sneakermales_01 du/evolibrary/article/0_0_ 0/sneakermales_01

Survival of the Sneakiest When it comes to crickets, what does fitness mean? Having a good strategy for surviving long enough to passing on genes to the next generation- this could mean calling, being “sneaky” and intercepting female...or whatever Is calling good or bad for a cricket's fitness? One of several good possible mating strategies- there will not always be predators around or “sneakers”

Give some examples of selection at work in this cricket story. Relevant variation- calling males, sneaker males, tough males Predation is a selection pressure – calling males have a selective disadvantage tough males (even if they are calling males) have a selective advantage Competition for a mate is a selection pressure- calling males could have a selective advantage Sneaker males could have a selective advantage How does selection favour calling? How does selection favour not calling? Calling males are more likely to attract females Calling males are more likely to attract predators

Natural selection Within any population there is variation due to different alleles and environmental pressures. Some alleles are more advantageous than others, these are selective advantages. Example: Less water available, selective advantages would be longer roots, waxy coating, hairs, needles Environmental pressures constantly change and these changes are selective pressures. Examples are water availability, sun, food source that dies out or becomes more available.

Natural selection An allele which was previously of no particular advantage now becomes favourable. Organisms with these alleles are more likely to survive to successfully reproduce. Their offspring are more likely to have the allele for the selective advantage, and therefore be well adapted to the environment. More individuals within the population will have this allele, this increases the allele frequency.

Activity 4.6 Order the cards Read pages about head lice to check your answers. What were the selection pressures? The chemicals in the shampoo. Which allele(s) had a selective advantage? Resistance to the chemicals in the shampoo What was the resulting adaptation ? Increase in the allele frequency, for the allele for chemical resistance, in the population.

Moths and pollution Peppered moths

How adaptable? What might affect how able a population is to adapt? Reproductive rate, size of the gene pool (all of the alleles of the genes present in a population), the strength of the selection pressure. Give examples of each. Q A mutation resulting in an impermeable exoskeleton or enzyme which breaks down the insecticide. They are slow breeding and have a small gene pool With a large gene pool there is a higher chance that some individuals may have the necessary alleles to help them survive the change. They also have a slow reproductive rate.

Being Perfect In a relatively stable environment, natural selection still happens. This is called stabilizing selection Extreme phenotypes are selected against What are the consequences of stabilizing selection?

Being Perfect Can a species be perfectly adapted to the environment? Why or why not? No, there are constant changes in an environment or harmful mutations that can arise. What are the advantages and disadvantages of being (nearly) perfectly adapted? Disadvantage: when the environment changes and therefore the selection pressures the species might not be able to adapt fast enough Advantage: Avoids competition