: The Forces of Evolutionary Change Part 2

Lecture 23 Outline

● Conditions that cause evolutionary change ● Natural vs artificial selection

● Nonrandom mating and ● The role of chance events – – Bottlenecks – Founder effects – flow

Conditions that Cause Evolutionary Change in Natural is an important, but not the only, force that results in biological ● Micro­evolution occurs when the of an in a changes – Natural selection – Artificial selection – Sexual selection, , and nonrandom mating –

– Genetic drift Review of Natural Selection

● The differential survival and of whose genetic traits better adapt them to a particular environment

● Change in the number of in a population that carry copies of a specific allele

● Determined by an 's

Evolution and Mutation

● Mutation is the source of new

● Evolution is the change in over time

● Some other evolutionary required for new alleles to become more common

● The genetic makeup of populations, and ultimately , changes as natural selection permits differential survival of genetic variants () that are better adapted to a particular environment.

Disease Evolution

● All evolve – One is not “more evolved” than another

● In most examples of evolution we are looking at the evolution of the disease rather than of the host: flu, HIV, resistant , , tuberculosis, etc. (exception: balanced )

● Our and the drugs we take are

part of the disease's environment natural =variation differential  selection reproduction

● Change in allele frequency in a population is called microevolution.

● Can take place over relatively short time period

● Some are better adapted to particular environment. ● Natural selection removes some alleles from the population ● Allele frequencies will change in response to

environmental change Role of the Environment

● Two fundamental forces are operating: and environmental change. ● Those with more adaptive traits survive in a new or changing environment.

● Environment includes – Climate – Abiotic conditions/resources: water, soils, – Parasites, predators, and competitors

● Parasites, predators, and competitors also evolve Role of the Environment

● Natural selection reflects to a prevailing environmental condition. ● The direction of natural selection can change. ● A phenotype that is adaptive in one set of circumstances may be a liability in another. ● Broad­ranging species often show local adaption among sub­populations – Affects management, conservation, and climate change

Reproductive Isolation

● Over time, an isolated sub­population could change so that it can no longer with the original group. ● Eventually, a new species would arise.

● Macro­evolution represents accumulated changes in allele frequency in two populations that preclude their interbreeding, leading to the formation of new species (or their ).

● Macro­evolutionary changes tend to span many

generations, but in some instances can occur in only a few generations. Drivers of Microevolution

● Mutation ● Natural selection

● Artificial selection ● Sexual selection, mate choice, and nonrandom mating

● Genetic drift

Artificial Selection: Proof of the Power of Selection

● Also called or ● Process of intentional or unintentional modification of a species through actions which encourage the breeding of certain inherited traits over others ● The breeding potential of individuals who possessed desirable characteristics is intentionally encouraged, whereas the breeding of individuals with less desirable characteristics is discouraged.

Artificial Selection

● “Selection was the keystone of man's in making useful races of animals and plants” ­, 1837

● No real difference in genetic processes underlying artificial and natural selection

● Underscores the power of selection in generating evolutionary change

Non­random Mating

● A variation of Natural Selection ● Completely random matings (where each individual has as equal chance of mating with every other member of the population) are nearly impossible to achieve

Sexual Selection & Mate Choice

● Sexual selection: the "natural selection of traits that increase an individual's ." ● These traits contribute to attraction, courtship, or mating. ● Most species exhibit some sort of preferences in mate choice ● The alleles for these desired traits will become more common in future generations.



Bower Bird Sexual selection: male­male

Genetic Drift

● Changes in allele frequency in a population that result from RANDOM survival or reproduction of individuals with certain characteristics. ● Survival or reproduction of an organism is sometimes just a matter of LUCK or CHANCE, not because of their phenotype or . ● Example: if a Florida Panther is killed by a truck on a highway, that is bad luck. The panther did not get hit because of some allele it carried.

● Genetic Drift contrasts with natural selection.

● In selection the environmental events that affect a population may be random, but the survival or reproduction of the individuals depends on their phenotypes. ● Example of selection: If the panther population is infected with FIV (feline AIDS), individuals

with alleles that give them resistance to the disease will survive. Types of random effects

/Migration ● Founder Effects ● Population Bottlenecks ● Genetic drift

Gene Flow / Migration ● Gene Flow is the movement of alleles from population to population. ● Immigrating individuals introduce new alleles by mating with members of the population they join. ● Any advantage given to individuals with new alleles will change the population due to subsequent natural selection. ● Because geographic barriers greatly influence migration patterns, allele frequencies may differ between adjacent but separated geographic regions.

Founder Effect

● Establishment of a new population (geographically isolated) from a single or very few individuals. ● The of a founding population only contains a subset of the total of the original population ● Different from gene flow because the migrating individuals are establishing a new population where none existed before.

Population Bottleneck

● Occurs when is drastically reduced ● The new population has lost much of the genetic diversity that was present in the larger ancestral population as a result of .

Bottlenecks and Conservation

● Common problem among endangered species ● Florida Panther – Hybrids with Texas pop'n have greater lifespan and fewer genetic problems. – Pop'n has tripled ● Greater Prairie

[Dr. Paige, Animal Bio] Genetic Drift

● Chance events affect which individuals survive and reproduce in a population. ● Small, random changes in allele frequency can "build up" over generations and result in a significant change in allele frequency.

Population Size

● Chance changes in allele frequency tend to have small effects on large populations ● Small populations (e.g. endangered species) are much more susceptible ● Tend to be inbred and have little genetic variation anyway. Micro­evolution Recap

● Microevolution (a change in allele frequency in a population) can occur as a result of several factors that fall into two broad categories. ● Factors in which an individual's chance of survival and reproduction depend on the individual's phenotype.

• Natural Selection • Artificial Selection • Mate Selection, Sexual Selection, Nonrandom Mating

– Mutation Micro­evolution Recap

2. Factors in which an individual's chance of survival and reproduction, are just that, a matter of CHANCE. An individual's phenotype and genotype has nothing to do with it. – Gene Flow – Founder Effect – Population bottle neck – Genetic Drift