MECHANISMS OF EVOLUTION What changes populations? 2007-2008

Write this in the top margin of your paper: Microevolution A change in allele frequencies in a population over generations. Population = Organisms of the Same species, Living in Same place, At the Same time.

I.Forces of evolutionary change Natural selection traits that improve survival or reproduction will accumulate in the population adaptive change Genetic drift frequency of traits can change in a population due to chance events random change

Populations evolve, individuals don’t. Natural selection acts on individuals Differential survival “Survival of the fittest” Differential reproductive success Who bears more offspring Populations evolve Genetic makeup of population changes over time Favorable traits (greater fitness) become more common Presence of lactate dehydrogenase The Mummichog (Fundulus heteroclitus heteroclitus) is a small killifish found in the eastern United States. It is capable of tolerating highly variable salinity and temperatures, and is found in estuaries and saltmarshes as well as less salty waters. A year-round resident of tidal creeks and wetlands, this brownish-green saltwater minnow may reach a maximum length of 5 inches. Its Indian name means "they go in great numbers." It is also known as the common killifish. A hardy fish, the mummichog is an important food source for larger fish and is often used as bait. The mummichog also has been used as a natural method of mosquito control in marsh ponds and ditches. It has been reported that one mummichog can eat as many as 2,000 mosquito larvae ("wrigglers") a day. The mummichog also feeds on other insects, small fish, crustaceans, and plant material. Because of the extreme hardiness of the species, it is sometimes the only species found in severely polluted and oxygen-deprived streams, such as the Hackensack River and the Arthur Kill in New Jersey during the height of the water pollution problem in the United States. In 1973 the Mummichog became the first fish in space when carried on Skylab 3 as part of the biological experiments package later space missions by the U.S., such as Bion 3, have also carried Mummichog. Mummichog

Changes in populations Bent Grass on toxic mine site Pocket Mice in desert lava flows Pesticide molecule Insect cell membrane Target site Resistant target site Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field Target site Decreased number of target sites Insecticide resistance

Individuals DON’T evolve… Individuals survive or don’t survive… Individuals DON’T evolve… Individuals are selected Populations evolve Individuals reproduce or don’t… 2007-2008

II.What is “fitness”? Describes the capability of an individual of certain genotype to reproduce Usually is equal to the proportion of the individual's genes in all the genes of the next generation The capacity of an organism to survive and transmit its genotype to reproductive offspring as compared to competing organisms

Fitness Survival & Reproductive success Body size & egg laying in water striders Fitness Survival & Reproductive success Individuals with one phenotype leave more surviving offspring.

III. Variation & natural selection Variation is the raw material for natural selection. There have to be differences within population. Some individuals must be more fit than others.

What are the causes of variations? Mean beak depth of parents (mm) Medium ground finch 8 9 10 11 1977 1980 1982 1984 Dry year Wet year Beak depth Beak depth of offspring (mm)

5 Causes of variation in a population 5 Agents of evolutionary change Changes in DNA/chromosomes Gene Flow Non-random mating Genetic Drift Selection

A. Variation from changes in DNA/ chromosomes New mutations are constantly appearing Mutation changes DNA in some way Changes in amino acid sequence leads to: Changes in protein changes structure changes function Changes in protein may change phenotype & therefore change fitness Every individual has hundreds of mutations 1 in 100,000 bases copied 3 billion bases in human genome But most happen in introns, spacers, junk of various kind Not every mutation has a visible effect. Some effects on subtle. May just affect rate of expression of a gene.

Not every mutation has a visible effect. Random changes to DNA can be caused by: errors in mitosis errors in meiosis environmental damage Every individual has hundreds of mutations 1 in 100,000 bases copied 3 billion bases in human genome But most happen in introns, spacers, junk of various kind Not every mutation has a visible effect. Some effects on subtle. May just affect rate of expression of a gene.

Variation in chromosomes from sexual reproduction: Meiosis 1. Crossing over produces new genetic combinations 2. Independent assortment of chromosomes along metaphase plate Random fertilization 1. Egg with unique DNA is fertilized by sperm with unique DNA.

Mean beak depth of parents (mm) Sexual reproduction results in: Mixing of alleles recombination of alleles new arrangements in every offspring new combinations = new phenotypes Spreads variation offspring inherit traits from parent Mean beak depth of parents (mm) Medium ground finch 8 9 10 11 1977 1980 1982 1984 Dry year Wet year Beak depth Beak depth of offspring (mm)

B. Gene Flow Movement of individuals & alleles in & out of populations due to movement of fertile individuals or their gametes

Examples: seed & pollen distribution by wind & insects migration of animals sub-populations may have different allele frequencies causes genetic mixing across regions reduce differences between populations

Are we moving towards a blended world? Human evolution today Gene flow in human populations is increasing today transferring alleles between populations Are we moving towards a blended world?

C. Non-random mating Sexual selection

How sexual selection affects populations: Intrasexual selection: Selection within the same sex Ex. = Males competing for opportunity to mate with females by challenging other males

Intersexual selection: Individuals of one sex select mates of opposite sex based on appearance or behavior. Ex. = Female peahens choose to mate with male peacocks with the largest and most colorful feather display

Show peacock video from “Evolution“ series on PBS. http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html

D. Genetic drift Effect of chance events founder effect bottleneck small group splinters off & starts a new colony bottleneck some factor (disaster) reduces population to small number & then population recovers & expands again 1 family has a lot of children & grandchildren therefore has a greater impact on the genes in the population than other families Genghis Khan tracked through Y chromosome. Warbler finch Tree finches Ground finches

Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection

Founder effect When a new population is started by only a few individuals Some rare alleles may be at high frequency; others may be missing Skew the gene pool of new population Human populations that started from small group of colonists Example: Settlement of East TN by Scot and Irish immigrants Small founder group, less genetic diversity than Africans All white people around the world are descended from a small group of ancestors 100,000 years ago (Chinese are white people!)

Bottleneck effect When large population is drastically reduced by a disaster famine, natural disaster, loss of habitat… loss of variation by chance event alleles lost from gene pool not due to fitness narrows the gene pool

Cheetahs All cheetahs share a small number of alleles 2 bottlenecks less than 1% diversity as if all cheetahs are identical twins 2 bottlenecks 10,000 years ago Ice Age last 100 years poaching & loss of habitat

Peregrine Falcon Conservation issues Bottlenecking is an important concept in conservation biology of endangered species loss of alleles from gene pool reduces variation reduces adaptability Breeding programs must consciously outcross Golden Lion Tamarin

E. Natural selection Differential survival & reproduction due to changing environmental conditions climate change food source availability predators, parasites, diseases toxins combinations of alleles that provide “fitness” increase in the population adaptive evolutionary change

Natural Selection Selection acts on any trait that affects survival or reproduction predation selection physiological selection sexual selection

Predation Selection Predation selection act on both predator & prey behaviors camouflage & mimicry speed defenses (physical & chemical)

Physiological Selection Acting on body functions disease resistance physiology efficiency (using oxygen, food, water) biochemical versatility protection from injury 5.5 mya The Antarctic Ocean freezes over

Survival doesn’t matter if you don’t reproduce! Sexual Selection Acting on reproductive success attractiveness to potential mate fertility of gametes successful rearing of offspring Survival doesn’t matter if you don’t reproduce!

The lion’s mane… Females are attracted to males with larger, dark manes Correlation with higher testosterone levels better nutrition & health more muscle & aggression better sperm count / fertility longer life Even though it’s very hot to have a large mane the benefit of attracting mates and successfully producing & rearing young since you have that large mane outweighs the costs. Females who chose these males were more “successful” (more, healthier young) and therefore had a greater opportunity to pass on the trait of being attracted to longer darker manes to their daughters and the trait of having longer, darker manes to their sons.

Sexual selection Acts in all sexually reproducing species the traits that get you mates sexual dimorphism influences both morphology & behavior can act in opposition to natural selection

How does natural selection work? Organisms produce far more offspring than could ever survive. Results in higher demand for water, space, nutrients, sunlight, etc. Competition for resources results in a “struggle for survival”. Organisms with certain variations in behavior or physical traits are more easily able to survive. Survivors pass on their unique traits.

Over generations, the accumulation of changes in the heritable characteristics of a population results in evolution – the gene pool has changed.