Evolution of Populations Raven Ch. 21 2007-2008 Doonesbury - Sunday February 8, 2004

Populations evolve Natural selection acts on individuals Variation results in: 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 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

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

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 Fitness- Survival & Reproductive success individuals with one phenotype leave more surviving offspring

Where does Variation come from? 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) 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

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 (even three in 1000). These will give rise to tolerant offspring when intercrossed (Walley et al 1974). Guppies When evolutionary biologist John Endler began studying Trinidad's wild guppies in the 1970s, he was struck by the wide variation among guppies from different streams, even among guppies living in different parts of the same stream. Males from one pool sported vivid blue and orange splotches along their sides, while those further downstream carried only modest dots of color near their tails. Endler also observed differences in the distribution of guppy predators, and in the color and size of gravel in different stream locations. In the wild, where predators are plentiful, male guppies become increasingly drab over generations, pushed by predation pressure toward greater camouflage. However, the "flashier" a male guppy is, the more likely a female guppy will choose him as a mate, giving him the opportunity to pass his genes along to the next generation. This is sexual selection at work, and it is the force that pushes guppy coloration toward conspicuousness just as hard as predation pushes coloration toward drabness. It is clear from the research of Endler and other evolutionary biologists that male guppies live in the crossfire between their enemies and their would-be mates, with the opposing forces of predation and sexual selection forever pushing the guppy coloration in opposite directions. Target site Decreased number of target sites Insecticide resistance

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 Mutation rates in individuals are low (1 in 100,000 division) But are constantly appearing in populations Mutation changes DNA sequence. As a result, may change: Protein amino acid sequence may change protein structure? may change protein 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.

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

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

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

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

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