Evolution Part 1

BIOL 1407

Evolution

• Heritable genetic change in populations or groups of populations over time

• Changes in gene pool

Evolution

• Also includes populations diverging from one another over time

may lead to new species

Mechanisms of Evolution

• Genetic Drift– Population Bottlenecks– Founder Effect

• Gene Flow– Immigration– Emigration

• Mutations• Natural Selection

Genetic Drift

• Changes in gene pool of populations due to random chance

Genetic Drift

Genetic Drift Image Credit: UC Museum of Paleontology's Understanding Evolution www.evolution.berkeley.edu

Genetic Drift

• Genetic drift has a bigger effect on small populations.

Bottleneck Effect

• Changes in gene pool of populations due to some event

drastically reduces population

Bottleneck Effect

• Survival is random

• Whether an organism survives does not depend on any characteristic (allele)

Example of Bottleneck Effect

• Population of plants on a mountain side

• An avalanche wipes out all but a patch of plants behind the shelter of a large outcrop.

Example of Bottleneck Effect

• Plants behind the outcrop survived only because they were out of the path of the avalanche.

• There was nothing about the plants’ genes that influenced survival.

Example of Bottleneck Effect

• Surviving population has an allele frequency different from the original population.

Bottleneck Effect

Bottleneck Effect: Cheetahs

• 10,000 years ago, cheetah populations worldwide crashed

• Due to climate change

• Photo Credit: Courtesy of Smithsonian National Zoo @ nationalzoo.si.edu

Cheetahs

• Only cheetahs in Africa & Eurasia survived

• Location, not genes Survival

• Photo Credit: Kevin Walsh, 2006, Wikimedia Commons

Cheetahs

• Cheetahs today: Genetically identical • Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons

Bottleneck Effect:Northern Elephant Seals

• Once numerous in the northern Pacific.

• 1800s: Hunted extensively for blubber

• Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons

Northern Elephant Seals

• Only 100-1000 animals in a Mexican colony survived

• Photo Credit: Michael Baird of bairdphotos.com, courtesy of Wikimedia Commons

Northern Elephant Seals

• Today: >100,000 individuals

• Very little genetic diversity

• Photo Credit: Mila Zinkova, 2008, courtesy of Wikimedia Commons

Founder Effect

• New population established by very small number of individuals (“founders”)

• By chance, founder group has a different allele mix than original population

Example of Founder Effect

• 200 German immigrants founded the Old Order Amish of Pennsylvania

• Photo credit: : Matthew Trump, 2004, Wikimedia Commons

Old Order Amish

• One couple brought allele polydactyly Six fingers and toes

• Photo credit: G. Baujat and M LeMerrer, 2007, Wikimedia Commons

Old Order Amish

• Inbreeding has frequency of polydactyly

• Click on this link:

http://www.pbs.org/wgbh/evolution/library/06/3/l_063_03.html

• Photo credit: gadjoboy, 2006, Wikimedia Commons

Gene Flow

• Movement of alleles between populations• Immigration: movement of alleles into a

population• Emigration: movement of alleles out of

population

Example of Gene Flow

• Transfer of pollen from one population of sunflowers into another population of sunflowers

• Photo Credit: Sunflower Pollen, Courtesy of Wikimedia Commons

Example of Gene Flow

• Male juvenile Belding’s ground squirrels emigrate from their birthing population to new populations.

• 40-70% emigrate as juveniles. Remaining males leave by the end of their first year.

• Photo Credit: Courtesy of Yathin at FlickR, http://www.flickr.com/photos/yathin/807378578/in/set-72157600812861150/

Mutations

• Mutations can add new alleles to a population

• Review this BIOL 1406 concept

• Photo Credit for black Eastern Fox Squirrel: Jeffrey Pippen, Duke University

• Photo Credit for wild-type Eastern Fox Squirrel: Calibas, 2007, Wikimedia Commons

Asexual Populations

• Mutations are primary source of genetic variation in asexual populations

• Photo Credit for E. coli 0157 colonies: Centers for Disease Control, 2005, Wikimedia Commons

Natural Selection

• Environment determines which genes are passed onto the next generation

• Based on which individuals successfully survive and reproduce

Natural Selection

• Requires: – Genetic Variation– Overproduction of Offspring– Struggle for Existence– Differential Survival and Reproduction

View video at: http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html

Photo credit: Dean E. Briggins, U.S. Fish and Wildlife Service, http://www.nsf.gov/news/news_images.jsp?cntn_id=104263&org=LPA

Genetic Variation

• Organisms in the population vary in their characteristics

• Variations are heritable Passed from parents to offspring

Variation in Snail Shells

Flower Variations

Natural Selection

Flow Chart

How Natural

Selection Works

View “Pocket Mouse and Predation” at http://www.hhmi.org/biointeractive/evolution/animations.html

Photo Credit: Cheryl S. Brehme, USGS at http://soundwaves.usgs.gov/2006/02/pubs.html

View “Pocket Mouse Evolution” at http://www.hhmi.org/biointeractive/evolution/animations.html

Photo Credit: J. Harris, American Society of Mammalogy, at: http://www.mammalogy.org/mil_images/images/mid/752.jpgl

Artificial Selection

• Humans select which genes are passed onto the next generation

• Based on characteristics that humans find valuable or desirable

View “Dog Breeding” at http://www.hhmi.org/biointeractive/evolution/video.html

Photo credit: papillon.cz, courtesy of Wikimedia Commons (http://commons.wikimedia.org/wiki/Image:%21flowers.jpg)

View “Breeding Teosinte” at http://www.hhmi.org/biointeractive/evolution/video.html

Photo credit: USDA, 2005, courtesy of Wikimedia Commons

Another Example of Artificial Selection

Sexual Selection

• Some characteristics influence individual’s chance of mating

• Photo Credit: Ian Sewell, 2006, Wikimedia Commons

Sexual Selection

• Individual may have shorter life but will have better chances of mating and producing offspring

• Photo Credit: David Dennis, 2007, Wikimedia Commons

Types of Sexual Selection

• Mate Competition– One sex competes for access to the other

sex– Other sex always “chooses” winner

• Mate Choice– One sex chooses mate based on

characteristics of other sex

Example of Mate Competition

• Male bighorn sheep fight for mates

• Male with largest horns usually wins

• Photo Credit: Alan D. Wilson, naturespicsonline.com, courtesy of Wikimedia Commons

Video of Bighorn Sheep Fighting:http://www.youtube.com/watch?v=WKmGiSm3-2U

Photo Credit: Jon Sullivan, Wikimedia Commons

Example of Mate Choice

• Peacocks display their tails

• Females choose male with showiest tail

• Photo credit: Aaron Logan, www.lightmatter.net, courtesy of Wikimedia Commons

Example of Mate Choice

• Large tails decrease survival of peacocks

• Natural selection favors small tails

• Photo credit: Jörg Hempel, courtesy of Wikimedia Commons

Example of Mate Choice

• Peacocks with small tails do not mate

• Mate choice favors large tails

• Photo credit: Jyshah, 2007, courtesy of Wikimedia Commons

View the video at: http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html

Photo credit: Myukii, courtesy of Wikimedia Commons

The End

Unless otherwise specified, all images in this presentation came from:

Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.