Fig American RevolutionFrench RevolutionU.S. Civil War – The Origin of Species is published. Wallace sends his hypothesis to Darwin. Darwin begins his notebooks. Darwin writes essay on descent with modification. Darwin travels around the world on HMS Beagle. Malthus publishes “Essay on the Principle of Population.” Lyell publishes Principles of Geology. Lamarck publishes his hypothesis of evolution. Hutton proposes his theory of gradualism. Linnaeus (classification) Cuvier (fossils, extinction) Malthus (population limits) Lamarck (species can change) Hutton (gradual geologic change) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) Evolution Unit Lecture Part I Ch 22,23 Theory: fact based

Darwin’s proposed mechanism, natural selection, explained the observable patterns in evolution * artificial selection Observation #1: Members of a population often vary greatly in their traits (snails) Observation #2: Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than their environment can support (puffball fungus) Observation #4: Owing to the lack of food or other resources, many of these offspring do not survive. Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring that other individuals. Inference #2 This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations.

Fig

Fig Spore cloud

Natural Selection: A Summary 1. NS is a process in which individuals that have certain heritable characteristics survive and reproduce at a higher rate than other individuals 2. Over time, NS can increase the match between organisms and their environment

Fig (b) A stick mantid in Africa (a) A flower mantid in Malaysia

3. If an environment changes, or if individuals move to a new environment, NS may result in adaptation to these new conditions, sometimes giving rise to new species in the process “INDIVIDUALS DO NOT EVOLVE!” POPULATIONS EVOLVE OVER TIME

Fig Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Guppies: Adult males have brighter colors than those in “pike-cichlid pools” Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools” Source population Transplanted population Source population Transplanted population Number of colored spots Area of colored spots (mm 2 ) RESULTS EXPERIMENT

Evidence Direct observations of Evolutionary Change (predation, HIV resistance) Fossil record (transition fossils) Homology (common ancestry)embryology, vestigial structures and genetic: hox genes (gene conservation) Biogeography

Fig Bristolia insolens Bristolia bristolensis Bristolia harringtoni Bristolia mohavensis Latham Shale dig site, San Bernardino County, California Depth (meters)

Fig (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) (c) Dorudon (fully aquatic) Pelvis and hind limb Pelvis and hind limb (d) Balaena (recent whale ancestor)

Fig Humerus Radius Ulna Carpals Metacarpals Phalanges HumanWhale Cat Bat

Fig Human embryoChick embryo (LM) Pharyngeal pouches Post-anal tail

Fig Hawks and other birds Ostriches Crocodiles Lizards and snakes Amphibians Mammals Lungfishes Tetrapod limbs Amnion Feathers Homologous characteristic Branch point (common ancestor) Tetrapods Amniotes Birds

Fig Sugar glider Flying squirrel AUSTRALIA NORTH AMERICA

EVOLUTION OF POPULATIONS Adapt, Migrate or Die Genes Mutate Individuals are selected Populations Evolve

Fig XX XX Geographic variation Genetic variation

Fig Georgia Warm (21°C) Latitude (°N) Maine Cold (6°C) Ldh-B b allele frequency CLINE

How do we measure evolution? The smallest unit of measure is an allele. Variation in a population –measured at the nucleotide level or gene level Hardy Weinberg equation * can be used to test whether a population is evolving * 2 independent mathematicians

Fig Frequencies of alleles Alleles in the population Gametes produced Each egg:Each sperm: 80% chance 80% chance 20% chance 20% chance q = frequency of p = frequency of C R allele = 0.8 C W allele = 0.2

Fig Sperm C R (80%) C W (20%) 80% C R ( p = 0.8) C W (20%) 20% C W ( q = 0.2) 16% ( pq ) C R C W 4% ( q 2 ) C W C W C R (80%) 64% ( p 2 ) C R C R 16% ( qp ) C R C W Eggs

Fig Gametes of this generation: 64% C R C R, 32% C R C W, and 4% C W C W 64% C R + 16% C R = 80% C R = 0.8 = p 4% C W + 16% C W = 20% C W = 0.2 = q

Fig Gametes of this generation: 64% C R C R, 32% C R C W, and 4% C W C W 64% C R + 16% C R = 80% C R = 0.8 = p 4% C W + 16% C W = 20% C W = 0.2 = q 64% C R C R, 32% C R C W, and 4% C W C W plants Genotypes in the next generation:

Fig Gametes of this generation: 64% C R C R, 32% C R C W, and 4% C W C W 64% C R + 16% C R = 80% C R = 0.8 = p 4% C W + 16% C W = 20% C W = 0.2 = q 64% C R C R, 32% C R C W, and 4% C W C W plants Genotypes in the next generation: Sperm C R (80%) C W (20%) 80% C R ( p = 0.8) C W (20%) 20% C W ( q = 0.2) 16% ( pq ) C R C W 4% ( q 2 ) C W C W C R (80%) 64% ( p 2 ) C R C R 16% ( qp ) C R C W Eggs

HW continued Significant change = allele frequency shift = evolving population Consider PKU 1 in in the US If all assumptions hold for PKU then the frequency of individuals in the population born with PKU will correspond to q2 PKU demonstrates that harmful recessive alleles can be concealed in a pop due to heterozygotes PKU cannot breakdown phenylalanine

5 conditions for HW 1. No mutations: 2. Random mating 3. No natural selection 4. Extremely large population size 5. No gene flow

Fig Generation 1 C W C R C R C W C R C R C W p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 Generation 2 C R C W C W C R p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0 C R Natural selection, genetic drift and gene flow can alter allele frequencies in a pop

Genetic drift Chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next especially in small population

Founder’s Effect When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pools differs from the source population

Fig Original population Bottlenecking event Surviving population

Fig Number of alleles per locus Range of greater prairie chicken Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) Minnesota, 1998 (no bottleneck) Nebraska, 1998 (no bottleneck) Kansas, 1998 (no bottleneck) Illinois 1930–1960s 1993 Location Population size Percentage of eggs hatched 1,000–25,000 <50 750,000 75,000– 200,000 4, < (a) (b)

Effects of Genetic Drift 1. Significant in small populations 2. Can Cause allele frequencies to change at random 3. can lead to a loss of genetic variation within populations 4. can cause harmful alleles to become fixed

Fig

Gene Flow The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes Gene flow tends to reduce the genetic differences between populations Single population with a common gene pool