1、BIOL 4120: Principles of Ecology Lecture 2: Adaptation and Evolution,Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhuitnstate.edu,Evolutionary Ecology2.1 Nature selection as a force of evolution 2.2 Heritability is the feature of Natural Selection 2.3 Genes are the units of inheritance
2、2.4 Genetic variation is the ingredient of NS 2.5 Evolution is the outcome of NS resulted from gene frequency change 2.6 Speciation and mechanisms,Introduction to evolutionary ecology,Major question in Ecology: What determines distribution white coated polar bear in Arctic (invisible to prey),2.1 Na
3、ture selection as a force of evolution,What is Darwins natural selection?The differential success (survival and reproduction) of individuals within the population that results from their interaction with their environment.“Survival of fitness, elimination of inferior individual”,Two conditions (assu
4、mptions): 1. There is variation in populations. Variation is heritable. 2. In every generation some organisms are more successful at surviving and reproducing than others. Survival and reproduction are not random, but are related to variation among individuals. Organisms with best characteristics ar
5、e naturally selected.If 2 conditions are met then the population will change from one generation to the next. Evolution will occur.,Evidence of natural selection,Evolution of beak shape in Finches.Peter and Rosemary Grants (and colleagues) work on Medium Ground Finches Geospiza fortis.,Natural selec
6、tion,Darwins Finches Genetic studies show all arise from a single ancestral species.,Rosemary & Peter Grant,40-ha Daphne Major island,Is there a phenotypic variation in beak size?,Is variation in beak size correlated with variation in fitness?,In 1978, there was a severe drought, small seeds decline
7、d more than large seeds. Small beak birds have difficult to find seeds, and suffered heavy mortality, especially females.,Beak size evolves,pre-drought,post-drought,Conclusion: Nature selection indeed caused evolution in beak size,Types of natural selection,black bellied seed cracker beak size,2.2 H
8、eritability is an essential feature of NS,Heritability: individuals characteristics are passed from one generation to the next. Measured as proportion of the variation in a trait in a population that is due to variation in genes.Mendels genetics and inheritance,Mendles conclusions: Flower color is a
9、 heritable trait For each inherited char, an organism has two units, one from each parent(one each from egg and sperm). The unit may be the same or different. 3. When the two units are different, one is fully expressed, another one has nonoticeable effect of the organisms outward appearance. Dominan
10、t: the unit is expressed (purple)Recessive: not expressed (white).,Mendles Pea experiment,2.3 Genes are the units of inheritance,What are genes?,Genes: discrete subunit of chromosome, carry genetic information Chromosomes: the threadlike structures where DNA is contained DNA: Deoxyribonucleric acid.
11、 All DNA is composed of the same 4 nucleotide (ATGC), differ in sequence.Alleles: alternate forms of a gene (A, a). Locus: the position of an allele occupies on a chromosomeHomozygous (AA, aa) vs heterozygous (Aa) Dominance (A vs a), incomplete dominance (Aa shows different trait to AA or aa),Genoty
12、pe: the sum of genes carried by the individual. Gene pool: total collection of genes across all individual in the population at any one time Phenotype: the observed expression of genotype (color etc),How are genes transmitted?,Phenotypic plasticity,Phenotypic plasticity: the ability of a genotype to
13、 give a range of phenotypic expressions under different environmental conditions.,Norm of reaction,The set of phenotype across a range of environmental conditions.,2.4 Genetic variation is the ingredient for Natural Selection,Genetic variation within a population is absolutely necessary for natural
14、selection to occurIf all individuals are identical within a population then their fitness will all be the same,Sources of genetic variation Mutation: inheritable changes in a gene or a chromosome Gene mutation: (point mutation) Chromosome mutation deletion, duplication, inversion, translocation Gene
15、tic recombinationSexual reproductiontwo individuals produce haploid gametes (egg or sperm) that combine to form a diploid cell or zygote. Reassortment of genes provided by two parents in the offspring Increases dramatically the variation within a population by creating new combinations of existing g
16、enes.Asexual reproduction: less variation (only mutation),What do we mean by genetic variation?,Range (variance) of phenotypes, as in Darwins Finch example Different chromosomal arrangements (cytogenetics) DNA sequence differences among individuals Electrophoresis electromorphs = allozymes Molecular
17、 marks: RFLP, RAPD, etc.,2.5 Evolution is a change in gene frequency,Evolution is a change of gene frequencies within a population (or species) over time Individuals do not evolve, populations evolve Focus on gene pool, collectiveBut why do we see populations are still the same over many generations
18、?,The Hardy-Weinberg Principle,The Hardy-Weinberg Principle: Gene frequencies will remain the same in successive generations of a sexually reproducing population if the following five conditions hold:Random mating There is no mutation The population is very large There is no selection There is no mi
19、grations (isolated from other populations),The Hardy-Weinberg Principle,Five Causes of evolution,Mutations Gene flow - Emigration and immigration of individuals (Flow of alleles) Genetic Drift Changes in the gene pool of a small population due to chance Nonrandom mating: (AA mates AA, Aa) Natural se
20、lection,One Example: Genetic drift in a small population,2.6 Speciation and mechanisms,Speciation: splitting of one species into 2 different species. Concept of species: Biological Species: a species is a group of organisms whose individual have the potential to interbreed and produce fertile offspr
21、ing. Reproductively isolated: dont produce fertile hybrids Natural conditions: artificial breeding doesnt count. For example, artificial insemination, keeping 2 species locked up together.Morphological species: members of the same species look similar to each other. Many examples of organisms that l
22、ook similar but cant produce fertile offspring.No one species concept applies to all organisms,Flickers,Genetic isolation mechanisms (reproductive barriers),Premating mechanisms Habitat selection; temporal isolation; behavior or mechanical or structure incompatibilityPostmating mechanisms Genetic ba
23、rrier such as hybrids are sterile; seed abortion; hybrid inviability.,Mechanisms of speciation,Several are well documented: Allopatric speciation (probably most vertebrates) allopatric species occupy areas separated by time or space. Sympatric speciation (especially plants and insects) Sympatric spe
24、cies occupy the same place at the same time,Allopatric Speciation Geographic isolation, Easy to understand.,Allopatric speciation: Ring species,salamander,San Joaquin Valley, CA,Speciation via geographic isolation and divergence,Sympatric speciation (e.g: Speciation by Polyploidy),About half of all
25、flowering plants are polyploid: more than 2 copies of each gene. Polyploids are the result of failure of cell division (mitosis or meiosis) to separate the chromosomes into 2 cells.,2.4 Adaptations reflect trade-offs and constraints,Adaptation: Individuals of a species have certain characteristics t
26、hat enable an organism to thrive in a given environment.Adaptations maintain or increase fitness of an organism in a given environmental conditions.,Tradeoff,Evolution is reflected in changes in gene frequencies and phenotypes However, changes in gene frequencies involve tradeoffs Giraffes do not gr
27、aze well on grass due to their long necks Snow leopards can hide in snowy mountains, ordinary leopards can hide well in green trees.,Constraint,There are many other factors that can influence species adaptation. For example, response of an organism to an environmental gradient such as temperature. A
28、ll these factors influence species adaptation.,The End,Brief history of integration of Genetics into Ecological studies,Natural SelectionDarwin (1859) The Origin of Species Particulate genetics Lewontin & Hubby 1966)-using starch gel electrophoresis molecular biology. Synthesis of Ecology with Genet
29、ics Evolutionary Ecology (starting in 1970s)!,The major factors affecting the organisms survival in the system is FitnessDarwinian fitness: ability of an organism to survive and reproduce in its environment.Adaptation is a characteristic or trait of an organism that increases its fitness relative to
30、 individuals that do not possess it. It is an inherited characteristic that increases the ability of an organism to survive and reproduce.,Evolution by Natural Selection,The traits selected for by natural selection need to be inheritable so that the next generation after selection retains the change
31、 Three types of selection Directional See finches Stabilizing Long necks in giraffes Disruptive Sexual dimorphism,Fig. 5-6 An example of microevolution directional selection,Summary,What is natural selection? Different types of NS Gene and genetic variation Evolution Hardy-Weinberg principle Concept
32、 of species. Speciation and mechanisms Adaptation and trade-offs,What is a species,Ecology is based on the idea that we can identify different groups of organisms within an ecosystem These groups are generally called species There are three specific means of defining a species Morphological species
33、concept A species is defined as a morphologically consistent group of organisms than can be distinguished from all other species Can fail. So called cryptic species Biological species concept A group of populations whose individuals can interbreed and produce fertile offspring and cannot interbreed
34、with other species Reproductive isolation Still fails. If you cannot tell the individuals apart morphologically, how can you tell if they are interbreeding or not Also, some species can interbreed and produce viable offspring Bontebok and Blesbok in South Africa Genetic species concept A group of po
35、pulations whose individuals have a distinct genetic makeup and who do not interbreed with others groups of populations for some reason Bontebok and Blesbok are genetically distinct as well as being morphologically different. Do not naturally overlap in range,Geographical isolates,Salamanders,Adaptations of Honeycreepers on the island of Hawaii,Recap,Whats Nature selection? 2 assumptions? Three types of natural selection Concept in genetics: gene, chromosome, DNA, allele, locus, genotype, phenotype, dominance, incomplete dominance etc,
