Speciation, Reproductive Isolation, and Patterns of Evolution

1. Speciation, Reproductive Isolation, and Patterns of Evolution AP Biology Evolution IV

2. Speciation • Species: a group of individuals capable of interbreeding • Speciation: the formation of new species (3 main types) • Allopatric Speciation • Sympatric Speciation • Adaptive Radiation

3. Allopatric Speciation http://www.nodvin.net/snhu/SCI219/demos/Chapter_4/

4. Allopatric Speciation • Occurs when a population is divided by a geographic barrier • Barriers: mountains, rivers, regions excluding vital resources (water, food) areas covered with volcanic lava • Interbreeding between populations not possible (reproductive isolation) • Gene frequencies can diverge due to natural selection, mutation, and genetic drift

5. Sympatric Speciation

6. Sympatric Speciation • The formation of new species without the presence of a geographic barrier • Occurs by one of 3 ways: • Balanced Polymorphism • Polyploidy • Hybridization

7. Balanced Polymorphism • Suppose a population of insects possesses a polymorphism for color. Each color provides a camouflage to a different substrate (rock, tree stump, etc..). • When not camouflaged, they are eaten • Thus, only insects with the same color can associate and mate • Similarly colored insects are reproductively isolated…so gene pools can diverge.

8. Polyploidy • More than 2 sets of chromosomes found in diploid (2n) cells. • Often occurs in plants (occasionally animals) where triploid (3n), tetraploid (4n) and higher chromosome numbers exist. • Caused by nondisjunction in meiosis • Tetraploid individuals will continue to produce diploid gametes – making them reproductively isolated very quickly.

9. Hybridization • Occurs when 2 different forms of a species mate and produce offspring along a geographic boundary called a hybrid zone. • The genetic variation of the hybrids is greater than that of either parent • This permits hybrids to adapt to environmental conditions beyond the range of either parent. • Hybrids can eventually diverge from parent forms when faced with selective pressures

10. Adaptive Radiation

11. Adaptive Radiation • Relatively rapid evolution of many species from a single ancestor. • Ancestral species colonizes an area where diverse geographic or ecological conditions are available for colonization. • i.e. many available ecological niches for a population to spread into. • Examples: Darwin’s Finches, Australian Marsupials

12. Patterns of Evolution • Evolution can take place along the lines of the following patterns: • Divergent Evolution • Convergent Evolution • Parallel Evolution • Coevolution

13. Divergent Evolution • Describes two or more species that originate from a common ancestor. • This may happen as a result of allopatric or sympatric speciation or by adaptive radiation

14. Convergent Evolution • Describes two unrelated species that share similar traits. • Similar traits arise because each species has independently adapted to a similar niche • These traits are called: Analogous Traits

15. Convergent Examples • Sharks, porpoises, and penguins have torpedo-shaped bodies with peripheral fins. These traits arise as a result of adaptations each species has made to aquatic life…not due to a common ancestor. • The eyes of squids and vertebrates are physically and functionally similar. However they are not from a recent common ancestor, both evolved independently to perform similar functions.

16. Parallel Evolution • Describes two related species or two related lineages that have made similar evolutionary changes after their divergence from a common ancestor • Example: • Species from two groups of mammals, the marsupial mammals and the placental mammals, have independently evolved similar adaptations when ancestors encountered comparable environments

17. Coevolution • Describes the evolution of one species in response to new adaptations that appear in another species • An example: evolutionary arms race between predators and prey…or • Plants and plant eating insects • Pollinators and flowering plants • Pathogens and animal immune systems