What is Evolution Changing?

Evolution acts on populations not individuals Individual organisms do not improve themselves Nature selects the best of the members of a population to survive and produce the next generation

Mutations may produce such unique features but selection enhances them Evolution does not produce new adaptations! It amplifies (increases) or diminishes (decreases) variations that are already present Mutations may produce such unique features but selection enhances them

Gene Pools All of the alleles for all of the traits for all of the members of a population Only organisms that can mate together can share alleles and produce offspring So only members of the same species are found in a gene pool

Evolution Changes the Alleles in a Gene Pool All of the alleles for all of the traits for all of the members of a population

More long ear alleles (LL) in the next generation If natural selection chooses certain traits in an organism, in reality it is really choosing particular alleles that code for the trait long ear alleles (LL) survives Babies with L short ear alleles (ll) dies No Babies  More long ear alleles (LL) in the next generation LL LL LL LL ll LL LL

So What Changed in the Population? The proportion of certain alleles! more long ear alleles (LL) in the next generation When natural selection occurs, the number of certain alleles in a population changes

This is the smiley face bug of the great paisley forest There are four variations in color, due to four alleles: R = red allele B = blue allele Y = yellow allele G = green allele Which color do you think would survive the best? What allele will increase in proportion in the next generation?

A New Definition for Evolution: Evolution is any change in the proportion (frequency) of alleles in a population, from one generation to the next It’s all about Passing on your awesome alleles!

Mechanisms for Evolution Mutations Non-random mating Migration Small population size Natural Selection

Mutations Tadpoles go through metamorphosis changing into frogs caused by a particular hormone

Axolotl injected with missing hormone Axolotl external gills External gills due to a mutation Lost the ability to make the hormone that causes metamorphosis So he lives his whole life in the water! Axolotl injected with missing hormone Completes the metamorphosis into a salamander Clearly, a mutation can cause alleles to change and even create a new organism

Such sorting out in mating affects the proportion of certain alleles Nonrandom Mating Blister beetles sort themselves out for mating by size Snow geese tend to mate by color. Such sorting out in mating affects the proportion of certain alleles

Nonrandom mating in humans

Migration allows alleles to move into or out of a gene pool

(The Bottleneck Effect) Small Population Size (The Bottleneck Effect) If some event caused most of the members of species to die, the surviving population will now have a different proportion of alleles

Different allele frequency! Event which nearly wipes out the population. Different allele frequency!

Limited alleles within a gene pool leaves an unhealthy population The Cheetah Two species whose numbers got so low that many alleles were lost from the gene pool Hey Baby! Wanta come over to my place and see my sea shell collection? Limited alleles within a gene pool leaves an unhealthy population Northern Elephant Seals

Small Population (The Founder Effect) Ellis-Van Creveld Syndrome Shortened limbs 6 fingers Lancaster Pennsylvania Amish Community

But the biggest, baddest, meanest factor in changing the alleles in a population (evolution) is: drum roll please Natural Selection

More long ear alleles (LL) in the next generation If natural selection selects against certain traits in an organism, in reality it is really selecting against particular alleles that code for the trait long ear alleles (LL) survives Babies with L short ear alleles (ll) dies No Babies  More long ear alleles (LL) in the next generation LL LL LL LL ll LL LL

Natural Selection Changes the Proportion of Certain Alleles more long ear alleles (LL) in the next generation

More Fit Population Less Fit Natural Selection More Fit More Fit More Fit More Fit The better adapted organism (with better set of alleles) passes those on to the next generation – more of them so become more popular! BETTER TRAITHIGHER REPRODUCTIVE RATECHANGE IN ALLELE FREQUENCY OF THE POPULATION More Fit More Fit More Fit More Fit Positive Trait More Fit Population More Fit Negative Trait Less Fit Less Fit Less Fit Less Fit

Types of (Natural) Selection

Disruptive Selection Favors the extremes in population at the expense of the intermediate (middle) phenotypes original population evolved population

Disruptive selection results in two very different types of males in the coho salmon coho hooknose male coho jack male coho female

Directional Selection Favors one extreme of the range of phenotypes original population original population evolved population

Directional Selection in Galapagos Finches In a drought the larger beak size is where it’s at!

Stabilizing Selection Favors the intermediate (middle) individuals in a range of phenotypes original population evolved population

An example of stabilizing selection is clutch size in birds A clutch of eggs An example of stabilizing selection is clutch size in birds Few eggs (1-2) = fewer offspring  Many eggs (6-8) = too many mouths to feed  Intermediate number (3-5) = just right to have the most surviving offspring

Sexual Selection Intersexual Selection Intrasexual Selection one sex exerts selective pressures on the other sex by selecting mates based on a specific trait members of the same sex compete for the chance of mating Long-tailed widow bird Rams!

So What is Evolution Changing? Allele Frequencies in the Gene Pool of the Population!