Review: Galápagos Islands plate motion subduction zone

Galápagos Islands Cocos Plate Nazca Plate Darwin Wolf Pinta Marchesa Genovesa Santiago Fernandina Santa Cruz San Cristobal Isabela Santa Fe Floreana Española

Figure 25.15 Freeman Biological Science 5th edition Pearson Medium ground finch (Geospiza fortis) Figure 25.15 Studying Evolution in Action on the Galápagos. Daphne Major 3

Darwin’s Four Postulates Evolution is a logical outcome of four postulates… populations have natural variation the organism’s features are heritable more offspring are produced than can survive some individuals produce more offspring because of the environment Modern biologists condense Darwin’s four steps into two statements: Evolution by natural selection occurs when: Heritable variation leads to Differential reproductive success 4

Figure 25.16 Freeman Biological Science 5th edition Pearson Did natural selection on ground finches occur when the environment changed? Beak characteristics changed in response to a drought. No changes in beak characteristics occurred in response to a drought. Weigh and measure all birds in the population before and after the drought. Average 1976: Before drought N  751 (all birds on island) Figure 25.16 A Natural Experiment: Changes in a Medium Ground Finch Population in Response to a Change in the Environment (a Drought). Number of finches 1978: After drought N  90 (survivors) Average beak depth in the population increased Beak depth (mm) Natural selection occurred. The characteristics of the population have changed. 5

Figure 25.18 Freeman Biological Science 5th edition Pearson Bmp4 is a gene whose expression is shown by in situ hybridization: Lower Bmp4 expression (dark area) in embryo’s beak Higher Bmp4 expression (dark area) in embryo’s beak 2 mm 2 mm Deep adult beak Figure 25.18 Changes in Bmp4 Expression Change Beak Depth and Width. Shallow adult beak Geospiza fortis Geospiza magnirostris 6

Island Development Island appears Marine/shore colonized Island colonized by plants Terrestrial biota establishes Biota stabilizes Island moves away from hot spot Waif founders lack competition Speciation: adaptive radiation to fill empty niches Endemic species evolve Sequence of islands should reflect patterns of speciation Endemics found on just one island, one volcano Humans arrive Introduced exotic species are released Endemics that may be poor competitors…go extinct

Cladistic Analysis 1960s Development of Cladistic Analysis Determines Possible Pathways of Evolution Characters and Polarized Character States Anatomy, Morphology, Behavior, Chemical, Gene Sequence Plesiomorphies-Ancestral character states Apomorphies-Derived character states Construction of Cladogram-computers! Reveal homoplasies (parallel, convergent), reversals Most-parsimonious (fewest steps) cladogram Not necessarily unique!