Chapter 23- Evolution of populations Origin of species Blue edged slides taken from slide shows by: Kim Foglia http://www.explorebiology.com

Individuals are selected Populations evolve 2007-2008

REZNICK & ENGLER- (1980’s) Guppy experiments IMAGE FROM Campbell and Reece AP BIOLOGY Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field Changes in populations happened within 11 years Age and size at sexual maturity change depending on predators

IMAGE FROM Campbell and Reece AP BIOLOGY Small killifish eat juvenile guppies Large pike-cichlids eat adult guppies Guppies in populations with pike-cichlid predators begin reproducing at a younger age and are smaller at maturity than guppies in populations preyed on by killifish IMAGE FROM Campbell and Reece AP BIOLOGY

IMAGE FROM Campbell and Reece AP BIOLOGY Moving guppies to pools with different predators changes size and age of maturity in population Changes are heritable IMAGE FROM Campbell and Reece AP BIOLOGY

Changes in populations Pesticide molecule Insect cell membrane Target site Resistant target site Target site Decreased number of target sites Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field Insecticide resistance 2005-2006

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

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

Where does Variation come from? Mutation random changes to DNA errors in mitosis & meiosis environmental damage Sex 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)

5 Agents of evolutionary change Mutation Gene Flow Non-random mating Genetic Drift Selection

Not every mutation has a visible effect. 1. Mutation & Variation Mutation creates variation new mutations are constantly appearing Mutation changes DNA sequence changes amino acid sequence? changes 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.

A diverse gene pool is important for the survival of a species in a changing environment Environments can more stable, less stable or fluctuating This affects evolutionary rate and direction Different genetic variations can be selected in each different generation

2. Gene Flow Movement of individuals & alleles in & out of populations seed & pollen distribution by wind & insect 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?

3. Non-random mating Sexual selection

SEXUAL SELECTION Favors traits with no advantage for survival other than fact that males/females prefer them Leads to pronounced differences between sexes =SEXUAL DIMORPHISM http://informalfotos.com/Fauna/Male%20Peacock%20displaying.JPG http://www.distinctivecruises.com/AfricanSafaris/MaleFemaleLion.jpg http://espanol.wunderground.com/data/wximagenew/i/icmoore/1013.jpg

Image from: http://www. kittens-lair. net/store/en/articles/sylvester4 KIN SELECTION Natural selection that favors altruistic behavior by enhancing reproductive success of relatives Bird that calls to warn others is in danger of being eaten, but does it anyway.

4. 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

Reduction of genetic variation within a given population can increase the differences between populations of the same species.

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: colonization of New World 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

5. 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

typical of polygenic traits POLYGENIC traits are controlled by two or more genes. A bell shaped curve is typical of polygenic traits Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006

DIRECTIONAL SELECTION Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006 DIRECTIONAL SELECTION KEY Low mortality, high fitness High mortality, low fitness Food becomes scarce. Individuals at one end of the curve have higher fitness than individuals in middle or at other end. Graph shifts as some individuals fail to survive at one end and succeed and reproduce at other

EXAMPLE OF DIRECTIONAL SELECTION Beak size varies in a population Birds with bigger beaks can feed more easily on harder, thicker shelled seeds. A food shortage causes small and medium size seeds to run low. Birds with bigger beaks would be selected for and increase in numbers in population. http://www.animalbehavior.org/ABS/Stars/ONI/Podos_-_finch_graphic.jpg

STABILIZING SELECTION Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006 STABILIZING SELECTION Individuals in center of the curve have higher fitness than individuals at either end Graph stays in same place but narrows as more organisms in middle are produced.

STABILIZING SELECTION Section 16-2 Male birds with showier, brightly colored plumage also attract predators, and are less likely to live long enough to find a mate. The most fit is male bird in the middle-- showy, but not too showy. Stabilizing Selection Male birds use their plumage to attract mates. Male birds with less brilliant and showy plumage are less likely to attract a mate Male birds with showy plumage are more likely to attract a mate. Key Low mortality, high fitness High mortality, low fitness Selection against both extremes keep curve narrow and in same place. Percentage of Population Brightness of Feather Color Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006

EXAMPLE OF STABILIZING SELECTION Human babies born with low birth weight are less likely to survive. Babies born too large have difficulty being born. Average size babies are selected for.

DISRUPTIVE SELECTION Individuals at extremes of the curve Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006 DISRUPTIVE SELECTION Individuals at extremes of the curve have higher fitness than individuals in middle. Can cause graph to split into two. Selection creates two DIFFERENT PHENOTYPES

EXAMPLE OF DISRUPTIVE SELECTION A bird population lives in area where climate change causes medium size seeds become scarce while large and small seeds are still plentiful. Birds with bigger or smaller beaks would have greater fitness and the population may split into TWO GROUPS. One that eats small seeds and one that eats large seeds. http://www.animalbehavior.org/ABS/Stars/ONI/Podos_-_finch_graphic.jpg