Chapter 17

1. Chapter 17 Speciation –Development of new species

2. Species • Species is a Latin word meaning “kind”. It refers to a particular kind of organism. • The biological species concept is used to define characteristics particular to one kind of animal.

3. Ernst Mayr • He phrased it this way “Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.” • Differences in phenotype do not disqualify some members

4. As long as the form is the same, the physiology and behavior allow them to interbreed and produce fertile offspring, then they are considered a species.

5. Mayr continued • The other qualification for membership is the ability to contribute to the gene pool. • Mayr’s definition does not apply to asexual creatures (as they do not have an extensive gene pool – each offspring being a clone of the parent), but it does help classify sexually reproducing organisms.

6. Gene Flow • Gene flow is the movement of alleles into and out of populations by emigration (entering) or immigration (leaving). • This helps maintain a reservoir of alleles.

7. Genetic Divergence • If a physical barrier prevents mingling of genes between populations or subpopulations, then each will become evolutionarily different. • This is referred to as genetic divergence.

8. This way, genetic differences will arise in the gene pools of separated populations; mutations, natural selection, and genetic drift will be free to operate. • Mostly, speciation occurs by divergence.

9. Reproductive Isolation • This is any heritable body form, function, or behavior that prevents breeding between one or more genetically divergent populations. • Includes behavioral, temporal, mechanical, and ecological isolation.

10. Behavioral Isolation • Differences in behavior are barriers to gene flow. • A certain species has reproductive rituals that may not be recognized by similar species, but are definitely recognized by members of the same species.

11. Temporal Isolation • Members of two closely related species could breed together, but their reproductive times are too different. • For example, “some species of insects seek mates for only a few hours of the day or night, and related species do so at different times”

12. Mechanical Isolation • Incompatibility between body parts of potential mates or pollinators.

13. Ecological Isolation • In seasonal habitats, two populations are adapted to different microenvironments of one habitat. • “Two sympatric species of ladybirds in Japan, Epilachna nipponica feed on thistles and E. yasutomii feed on blue cohosh. Each species also mates exclusively on its host plant, which acts as a microhabitat.”

14. Allopatric Speciation • Some type of barrier prevents gene flow between populations or subpopulations of a species. • Reproductive isolating methods will arise in each group after the separations. • Even if the groups are reunited, they will not breed together again.

15. Archipelagos are island chains that are a far distance from a continent. • For example – Galapagos Islands. Finches from the mainland moved to one of the islands and became separated from the group. • Later some of their descendents moved to a different island in the chain. The moves kept occurring until all of the islands were inhabited with finches.

16. Each move led to evolutionary changes among the finches of each island. Each group had to evolve to the climate changes, differing foods, etc…of the island it was inhabiting. • Therefore, each island has a different finch that came from a main group of finches.

18. Sympatric Speciation • Species within the home range of an existing species may form into new species without a physical barrier.

19. Example – cichlids are fish in African volcanic lakes. • Nine to eleven species of cichlids are coexisting in one lake. • They could not have evolved because of separation – they are all in one lake and have never been separated.

20. Cichlids

21. Polyploidy may be the answer. • It is a change in chromosome number. • Offspring will inherit three or more of each type of chromosome from their parent.

22. Changes come when the chromosomes separate improperly. • Most polyploid organisms have problems, but in rare cases it can lead to sympatric speciation.

23. Parapatric Speciation • Neighboring populations can become distinct new species while maintaining a common border. • Interbreeding between the two species will produce a new hybrid species.

24. The Baltimore Oriole (a bird) has a range that overlaps with the Bullock’s Oriole. • The two species are similar enough to reproduce and produce fertile offspring. • Their offspring is a new species.

25. Baltimore Oriole Bullock’s Oriole Orioles

26. Extinction • The irrevocable loss of one species. • Example – the loss of the dodo bird

27. Mass Extinction • Loss of several species at once due to a catastrophic event. The loss of dinosaurs could be considered mass extinction.

28. Works Cited • http://hcgs.unh.edu/cichlid/fish.jpg • perso.orange.fr/.../drax/dronte.htm • http://www.birdsasart.com/Baltimore-Oriole.jpg • http://www3.nbnet.nb.ca/maryspt/observ/oriole1.jpg • http://www.geologyrocks.co.uk/tutorials/isolation_new_species • http://evolution.berkeley.edu/evolibrary/article/history_12