Evolution and Biodiversity Evolution the change in organisms

Evolution and Biodiversity

Evolution, the change in organisms seen over time, is a fundamental concept in Biology. This unit focuses on biodiveristy, measuring biodiversity, and loss of said biodiversity. The foundation of understanding biodiversity is learning the mechanics of how Earth has come to have such a diversity of species, and how these species interact and change.

• I. Populations and Variations • Population - a group of individuals belonging to the same species that occupy a given area.

• *In most natural populations, the manifestations of traits are not the same from one individual to the next. (variations)

• Variations in traits are inherited. • Information about traits resides in hundreds of genes. • The genetic variation results in different phenotypes within a population.

• more than 10600 combinations of genes are possible in human gametes. • Far more genetic variation is possible than can ever be expressed in the individuals of any population.

• II. Allele Frequencies and Gene Pools • Gene pool - all the genotypes that exist in a population

• Remember that the different forms of a gene are called alleles. • Allele Frequencies - The relative abundance of each kind of allele in a population.

INDEX CARD TIME! FRONT: Allele BACK: Definition of allele

INDEX CARD TIME! FRONT: Allele Frequency BACK: Definition of allele frequency

• The number and type of alleles in a population is constantly changing. • Evolution occurs when there is a change in the allele frequency of a population

• Changes in allele frequencies can occur in a number of different ways: • 1) Mutation 3) Gene Flow • 2) Genetic Drift 4) Natural Selection

• III. Mutation • Mutation - a heritable change in the genetic code (DNA) • Mutations are random events, they may be helpful, harmful, or neutral.

• Harmful Mutations: • Many mutations are harmful. Why? • Each individual inherits a combination of many genes that are already fine tuned by selection. • Therefore, the product of a mutant gene is likely to be less functional not more so.

• Helpful and Neutral Mutations • (mutations that survive in the population) • Every once in a great while a helpful mutation may arise and be beneficial to the organisms.

• Some mutations have neutral effects or sometimes the effect of the mutant gene is masked by a dominant allele. • These genes are passed on by chance.

• IV. Genetic Drift • Allele frequencies can change randomly through generations because of chance. This process is called genetic drift

GENETIC DRIFT Start with five different alleles Due to random events, only two different alleles are left after several generations.

• *Genetic drift is most rapid when population size is small. • During extreme cases of genetic drift, a population is originates or is rebuilt from very few individuals.

• Founder Effect - a few individuals leave a population and establish a new one. By chance the allele frequencies for many traits may not be the same as in the original population.

• Bottlenecks - disease, starvation, or some other disaster can nearly wipe out large populations. Even though the population recovers, the relative abundance of alleles has been altered at random

• V. Gene Flow • Allele frequencies change when individuals leave a population (migration) or enter a population. • This movement of individuals is called gene flow.

• *”Evolution” was already being discussed in 1831, when Darwin was just a college graduate of 22. His degree was in theology. *Darwin’s true interests were in natural history and so he took a a job as the ship’s naturalist on the H. M. S. Beagle and recorded all of the natural flora and fauna encountered on the ship’s voyage. The ship was destined to map the S. American coastline.

After careful study, Darwin came to suspect that geographic isolation is related to evolution and species diversity.

• His Observations: • 1) the Galapagos Islands are near Ecuador • 2) Every island or cluster has it’s distinct species of finch

• 3. All finch species closely resemble a finch living on the coast of S. America (and nowhere else) • 4. Each species had a distinct beak suited to obtaining the type of food available on it’s island

• His Hypothesis: • Perhaps all of the species descended from the mainland finch, then changed slightly after becoming isolated on different islands.

• *Darwin wondered how such changes in organisms could occur • *Thomas Malthus, a clergy man and economist provided the clue:

• Malthus’ View: • Any human population tends to outgrow it’s resources, and it’s members must compete for what is available.

• V. Darwin Develops the Theory of Natural Selection as a Mechanism of Evolution • • *Darwin hypothesized that the same principle might apply in nature - beak size or shape could lead to differences in the ability to get resources.

• *If there were “competition” for resources in a population then individuals with favorable traits might have an advantage in survival and reproduction.

• *favored individuals would pass their traits on to their offspring , their offspring would do the same, and so on. Eventually descendants of favored individuals would make up most of the population.

• VI. Presenting the Information • *Darwin did not announce his theory right away, he wanted to sift through the evidence and look for flaws in his reasoning. • *In 1858 he received a paper for another naturalist, Alfred Wallace who had reached the exact same conclusion.

• *The next year, Darwin published his theory in book form (On the Origin of Species, 1859)

Natural Selection: 1) There are variation in organisms, and some of this variation is genetic (can be passed on) 2) More offspring are produced than survive 3) These organisms compete for limited resources 4) Individuals more suited for the environment have more success living and producing offspring 5) Change in species is seen over time

• VII. Specifics of Natural Selection • Natural Selection - the differential survival and reproduction of individuals in a population based on the traits they posses

• Natural selection may have a directional, stabilizing, or disruptive effects on the range of traits (phenotypes) in a population

• a)Directional selection - shifts allele frequencies in a constant direction in response to the environment

• Peccaries are eating those plants with low-spine-number causing their alleles to vanish from the gene pool

• b) Stabilizing selection - favors the most common phenotype in a population

• STABILIZING SELECTION • Preferring densely spined cacti, egg-laying parasites more often destroy varieties of plants with larger numbers of spines. An infested cactus rarely survives.

• c)Disruptive Selection- favors characteristics at both ends of the range of traits in the population and operates against intermediate forms.

• DISRUPTIVE SELECTION • Low-spine-number plants are not picked because they don't "look right", and highspine-number varieties are left alone because they are too hard to pick.

• To maintain genetic equilibrium, individuals in a population must mate at random. • Do you think this happens in reality? Do humans choose their mates at random?

• Most animal species have some way that they choose mates- colors, behaviors, mating dances, and other factors help females decide which male is the best. • This is a special type of selection called sexual selection, where the best males pass on their genes with greater frequency than other males.

• Peacock tails are an excellent example of a trait that results from non-random mating. • Why do you think these traits evolve?

• Another type of non-random mating occurs when closely-related individuals mate more often than distantly-related ones. • This promotes inbreeding- mating with individuals closely related to you. • This tends to increase the number of homozygotes, and decrease the number of heterozygotes.

• VII. Speciation • Speciation - the process by which species originate • How does speciation occur?

• Sometimes barriers arise between the parts of the population and create local breeding units. Then, two or more gene pools exist when there was only one.

• If over time there is no gene flow between the two populations then selection, mutation, and genetic drift can operate differently in each population.

• This can cause different traits to arise in each population. This is called divergence

• When the divergence is great enough that the two populations will no longer interbreed, the two population have become different species.

• Geographic Isolation -Populations can be separated by geographic barriers ex. mountains, rivers • Ex. The Blue-headed wrasse was separated from the Rainbow wrasse when the Isthmus of Panama was created.

• Reproductive Isolation - any aspect of structure or behavior that prevents interbreeding • ex. the development of different breeding seasons or different mating behaviors

• Over time, two species of frog have developed different mating calls through isolation. • Females respond only to the calls of their species.