The hierarchical nature and processes of different levels of ecological systems: now we focus on the population

Transcription

1 Evolutionary Force

2 The hierarchical nature and processes of different levels of ecological systems: now we focus on the population

3 Population: Evolutionary Unit Population Ecology GeneticsEvolution Darwin s finches

4 Objectives Understand (micro)evolution and its relation to genetics Sources of genetic variation Forces causing change in gene frequency in pop Natural selection Small population size Assortative mating Gene flow

5 *** A pre-test on phenotypic variation, genetic variation, natural selection, fitness, evolution, adaptation (pre-adapt) Non-Cyanresistant Cyanide experienced by an insect population Cyan-resistant individuals Use these words to explain evolution of cyanide resistance. TIME

6 What is definition of (micro)evolution? Change in allele frequency in a population through time What must be present for natural selection to cause evolutionary change? Genetic (allele) variation What is the ultimate source of genetic variation? Mutation, a change in nucleotide in DNA ---> change in amino acid it specifies ---> change in phenotype of organism

7 Genetic variation is also produced by chromosome recombination during 1)meiosis and by 2) fertilization.

8 this slide show phenotypic or genotypic variation? what underlies different patterns of coloration (different phenotypes) in the population?

9 ***How much genetic variation exists? ***Why is genetic variation important? In changing environments, the reservoir of genetic variation may take on positive survival value. Rapid environmental change by humans may exceed the capacity of a population to respond by evolution --> extinction

10 ***Are most mutations beneficial? Are most mutations dominant? What happens to harmful mutations? Most mutations are harmful and recessive, natural selection weeds out most deleterious alleles, leaving those that best suit organisms to their environments. Mutations are likely to be beneficial when the relationship of the organism to its environment changes; organism is pre-adapted to change. Selection for beneficial mutations is the basis for evolutionary change, enabling organisms to exploit new environmental conditions.

11 ***What forces can cause change in genotype frequency? 1) Natural selection --> differentiates subpopulations 2) Effects of small population size a) Genetic drift b) Founder effect c) Population bottlenecks 3) Assortative (non-random) mating 4) Gene flow (= dispersal/migration) --> homogenizes subpopulations

12 1. Evolution by natural selection Finches beak size changes in response to change in seed hardness in drought years.

13 Natural selection: change in the frequency of traits in a population because of differential survival and reproduction of individuals with those traits. Individuals with the most offspring are selected and the proportion of their genes increases over time. Fitness: the genetic contribution by an individual to future generations (keberhasilan dlm meneruskan gen ke generasi selanjutnya)

14 SELEKSI TERARAH Seleksi yg menyebabkan adaptasi ke lingkungan baru. Misal ; sebelum revolusi industri, juml. Kupu-kupu Biston betularia berwarna cerah lebih banyak daripada kupu-kupu Biston betularia berwarna gelap. Sebaliknya setelah revolusi industri, Biston betularia bersayap gelap lebih banyak daripada yg berwarna cerah. SELEKSI STABILASI Adalah seleksi yg bekerja pada varian tertentu dari satu populasi ygmenghasilkan populasi adaptif dan menyisihkan varian yg tidak adaptif SELEKSI PEMUTUS Terjadi jika kondisi lingkungan berbeda, menyebabkan satu populasi terbagi menjadi dua subpopulasi.

15 2 a. Genetic drift: 5 of 10 plants 2 of 10 plants leave offspring leave offspring Generation 1 Generation 2 Generation 3p p =.7, q =.3 p =.5, q =.5 p = 1.0, q = 0 Change in allele frequency due to random variation in births and deaths.

16 2 b. Population Bottleneck: period of small pop. size. subject to genetic drift

17 Population bottlenecks often result in reduced or no genetic variation (e.g. cheetahs).

18 Small populations experience genetic drift, founder events, and population bottlenecks. Each causes a loss in genetic variation. Allele becomes fixed = no variation. + genetic drift

19 ***Summarize the results. What is the potential consequence for small populations? % polymorphic genes Population size

20 3. Assortative mating: when individuals choose mates non-randomly with respect to their own genotypes. Negative: mates differ genetically --> increases proportion of heterozygotes Most individuals do this to avoid inbreeding. Positive: like mating with like (includes inbreeding) --> increases proportion of homozygotes

21 Positive assortment increases the proportion of homozygotes unmasks deleterious recessive alleles --> inbreeding depression (decrease in fitness)

22 % homozygosity depends on level of inbreeding.

23 4. Gene flow (migration)--> mixes alleles between subpopulations and homogenizes them. Maintains genetic variation ***What represents gene flow in animals? plants? Animals: dispersal of the adult animal or gametes Plants: dispersal of pollen and seeds

24 Summary of forces Remove genetic variation: Natural selection Small population size Maintain genetic variation: Mutation Gene flow Varying selective pressures in time and space