History of Evolution. Biol 490 Evolution

Transcription

1 Biol 490 Evolution History of Evolution On November 24, 1859, Charles Darwin published On the Origin of Species by Means of Natural Selection. Darwin made two points: (1) Today s organisms descended from ancestral species. (2)Natural selection provided a mechanism for evolutionary change in populations. 1

2 Central to Darwin s view of the evolution of life is descent with modification. All present day organisms are related through descent from unknown ancestors. Descendents of these ancestors accumulated diverse modifications/adaptations that fit them to specific ways of life and habitats. Darwin s Main Ideas: A Summary 1. Natural selection is differential success in reproduction (unequal ability of individuals to survive and reproduce). 2. Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population. 3. The product of natural selection is the adaptation of populations of organisms to their environment. 2

3 Some Definitions Evolution - change of population over time Microevolution - change in the gene pool of a population across generations (species level) Macroevolution - formation of new species and new designs; evolutionary change above the level of species. Artificial Selection: The blue and green dots and lines represent control populations living on normal food; the red and orange dots and lines represent experimental populations living on food spiked with ethanol. From Cavener and Clegg (1981). 3

4 Battling malaria: natural selection is fast! DDT developed in 1942 for use in the Pacific during WWII 95% effective initially but 16 months later only 20% effective The effect of selection on a variable characteristic/trait Natural selection can affect the frequency of a heritable trait in a population, leading to (1) directional selection (2) diversifying selection (3) stabilizing selection 4

5 Industrial Melanism Classic example of natural selection Kettlewell (1959) conducted experiments to measure the survival of different genotypes Calculated change in frequency of dark and light individuals Industrial Melanism Increase of melanic forms from 1848 to

6 Predator-prey and parasite-host relationships often evoke evolutionary responses in each other (adaptations) Studying Adaptation Zonosemata vittegera When disturbed fly holds wings perpendicular to body and waves them up and down. Green et al. (1987): behavior seems to mimic territorial threat display of jumping spiders Why mimic display? Jumping spider is a major predator of fly 6

7 Hypotheses 1. The flies do not mimic jumping spiders 2. The flies mimic jumping spiders, but the flies behave like spiders to deter other, nonspider predators 3. The flies mimic jumping spiders, and this mimicry functions specifically to deter predation by the jumping spiders themselves Pedicted Outcomes of Experiments N=20 spiders 7

8 Speciation: the link between microevolution and macroevolution Cladogenesis, branching evolution, is the budding of one or more new species from a parent species. Cladogenesis promotes biological diversity by increasing the number of species. What is a species? 8

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10 Vicariance 10

11 Cryptocercus Speciation in Cryptocercus 11

12 Speciation in Progress: Sexual Selection A form of natural selection Acts on characters involved in mate choice. Changes in sexual selection can cause reproductive isolation and trigger rapid divergence E.g., Drosophila - many species court and copulate in aggregations called leks 12

13 Evidence for sexual selection on head width in Drosophila heteroneura Co-evolution 13

14 Sickle Cell Anemia Sickle Cell Homozygotes 80% fatal before adulthood High incidence in Africa. Why? What s Going On? AA = normal RBC s, but susceptible to malaria Aa = intermediate RBC s, protects against malaria aa = sickle-shaped RBC s - fatal 14