1. Examples of Selective Pressure and Evolution through Natural Selection How species change over time

2. Learning objectives: 1.Learn major examples of speciation and change in organisms due to natural selection or genetic drift Darwin’s Finches Apple maggot fly Madeira house mouse Domestic dog 2. Identify three major species concepts. a. biological species concept b. species recognition concept c. evolutionary species concept 3. Observe how small changes in species can accumulate into bigger changes over time.

3. Steps of Evolution Variation (mutation): genetic variation. Selection: preferential survival or reproductive advantages for a gene in a given environment. Time: continual selection over time, accumulating change that results in new types of organisms. This process results in either: Adaptation: functional traits of genes or species that allow them to continue to live. Or… Extinction: the death of all members of a gene, population or taxonomic grouping.

4. The Grant Family Studies Darwin’s Finches The Grant family began traveling to the Galapagos Islands in 1973 to study Darwin’s finches and test the hypothesis that the beaks of Darwin’s Finches had evolved to match their diets. By collecting data over more than 3 decades (and having their children work with the along with graduate students and other colleagues) the Grants observed and recorded the three requirements for natural selection in action. Variation = differences in beak size Heritability = data showing that beak size is a trait passed down from parents to offspring Selection = different survival based on beak size

5. Darwin’s Finches on the Galapagos Islands

6. Examples of Selective Pressure and Evolution During Darwin’s voyage on the Beagle, he discovered finches on the Galapagos Islands 1,000 miles from Ecuador, South America – About 14 different species of finches on different islands had different shaped beaks – Darwin’s colleagues studied his collections of finches and hypothesized that the beak size of the finches helped them obtain different diets on the islands where they lived – This became a famous example of how natural selection can operate

7. The Medium Ground Finch has a wide range of beak sizes. Heavy beaks are better for crushing large, heavy seeds more abundant in dry years. Smaller beaks are better for picking up smaller seeds.

8. 1976 All Daphne Birds N = 751 1978 Survivors N = 90 Number of Finches Beak (mm) Depth Variation: The Grants found that the distribution of medium ground finch beak depth differed from year to year on Daphne Island. Average beak depth in 1976 was about 9.5mm. In 1978 it was 10.1mm, an increase of 6.3% in two years.

9. Population Size Seed Abundance (g/m2) Selective Pressure: Why did the population of medium ground finches decline so strongly between 1976 and 1978? A strong drought was underway during this time, resulting in reduced seed production. Most of the seeds that were left on the island were the large, heavy variety that were difficult to crush. Natural selection favored the medium ground finches with heavier beaks during this time.

10. Parent Mid-Bill Depth (mm) Offspring Bill Depth (mm) Heritability: By monitoring the beak depth of parent and offspring birds, the Grants were able to show that offspring beak depth strongly resembled parental beak depth, strong evidence of a polygenic genetic trait.

11. What the Grants found Different bill sizes in Darwin’s finches gave different birds a selective advantage depending on environmental conditions (thick crushing bills had an advantage in dry years, thin narrow bills had an advantage in wet years). Those advantages were passed down to offspring. Natural selection acted on bill size Variation in the population helps the species survive hard times when natural selection is strong.

12. More recent research findings from the Grants on Darwin’s Finches Big beaked birds migrated to the Galapagos island Daphne Major in 1983. This island that previously only had small beaked birds. Since then on Daphne Major, beaks of small beaked birds are getting even smaller because they cannot compete for heavy-beaked birds for thick seeds. These examples from the Grant’s work shows changes due to natural selection. Longer time periods would be required to show the emergence of new species.

13. Examples of new species New species typically take thousands of years to emerge. Examples in the fossil record are common, but we also have some observed examples of new species emerging in newly colonized areas.

14. Feder, J. L. (1998) The apple maggot fly, Rhagoletis pomonella: flies in the face of conventional wisdom about speciation? In Howard, D. J. & Berlocher, S. H. (Eds.) Endless Forms: Species and Speciation. New York, Oxford University Press. Apple Maggot Fly

15. Apple maggot fly Two types – One type feeds only on hawthorne apples (native to North America) – One type only feeds on domestic apples (brought over from Europe No interbreeding occurs between types Each type is genetically distinct Apples were only available as a diet source in North America for the last 500 years. Therefore the apple maggot fly must have evolved in that time frame. This is an example of evolution where natural selection is likely to have played a strong role.

16. Madeira House Mouse Environmental genetics: Rapid chromosomal evolution in island mice Janice Britton-Davidian 1, Josette Catalan 1, Maria da Graça Ramalhinho 2, Guila Ganem 1, Jean-Christophe Auffray 1, Ruben Capela 3, Manuel Biscoito 4, Jeremy B. Searle 5 & Maria da Luz Mathias 6 Nature 403, 158 (13 January 2000) 1 2 1 3 4 5 6

17. Madiera was uninhabited by humans until 500 years ago. House mice must live in human-created environments to survive. The different populations are isolated in different valleys leading down to the sea. There are 6 distinct genetically distinct populations of house mouse on Madeira (each with different chromosome numbers. This species of mouse could have have only been on Madeira 500 years or less. This is an example of evolution probably due to non-disjunction during meiosis. Therefore, natural selection probably did not play a strong role in the evolution of these species.

18. Over time selection can result in BIG changes in organism types as well as small ones. For instance, all modern dogs are descendants of the dire wolf.

19. Artificial selection, intentional selection for preferred traits by humans, has resulted in major changes in dogs that descended from a single ancestor. Some dog breeds have reached the point that they can’t easily reproduce together without significant danger of harm to the animal. These differences meets some of the technical definitions of “speciation,” the evolution of new species.

20. Even larger changes are apparent in the fossil record. Major transitions become possible as changes occur over longer periods of time. Reduced size of bones in the neck of early amphibians allowed transitions from lobed fishes to early walking four legged animals (tetrapods). Small changes accumulate into much longer changes over very, very long periods of time.

22. Whale evolution as understood from the current fossil record: Similarly, whale evolution has resulted in major morphological changes from generalist terrestrial predators. All the organisms in this lineage have a sigmoid bone, a structure only found in whales. From 50 million years onward, species have gradually lost their hind legs, and grown strong muscular tails for swimming.

23. If organisms are constantly changing, what are the “types” of organisms? Species concepts are still debated by biologists Some groups of organisms are obvious and clear Others groups of organisms are very similar and it is difficult to know where one species ends and another begins. – Sub species – Genetic lines – Variants – Clades

24. Recent speciation in sticklebacks Large bottom dwelling types and smaller open water types Large bottom dwelling types and smaller open water types Closely related within lakes but don’t interbreed Closely related within lakes but don’t interbreed Lakes where they lived formed <10,000 years ago. Lakes where they lived formed <10,000 years ago. Observed in other systems such as the African Rift lakes species flocks Observed in other systems such as the African Rift lakes species flocks

25. Recognition species concept Any identifiable difference between two groups of organisms constitutes a species – DNA – Body shape or size (morphology) – Behavior This is the least conservative and least frequently used definition of a species.

26. The biological species concept 1.Biological Species concept: types of animals that can interbreed and produce fertile offspring in nature 2.This is the most commonly accepted and most conservative definition of a species. However, it does have some practical limitations. It is not possible to cross every organism with every other to see if they produce fertile offspring, also, hybridization is common and the degree of hybrid fertility varies.

27. Some hybrids are fertile and can interbreed with “pure” species types. Green sunfish and bluegill sunfish produce 10% fertile offspring. However, the F1 and F2 hybrids of these fertile offspring cannot produce enough offspring to keep the hybrid populations alive in the wild.

28. Florida Largemouth Bass vs. Northern Largemouth Bass Florida largemouth bass can interbreed with Northern largemouth bass, but their young suffer a loss of fitness (ability to reproduce) in some environments. These are considered “subspecies”.

29. The Evolutionary Species Concept Any group of animals that does not exchange genetic material with other groups of organisms Used by the Endangered Species Act to identify Evolutionary Significant Units (ESUs) Important to understand and conserve natural resources; allows for the conservation of local adaptations within and across species (for instance, big beaks and small beaks).