1. 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. PowerPoint to accompany CONCEPTS IN BIOLOGY TWELFTH EDITION Enger Ross Bailey CHAPTER 14

2. 2 Speciation A species is a group of organisms whose members have the potential to interbreed naturally and produce fertile and viable offspring.

3. 3 Determining if two populations belong to the same species using gene flow Gene flow is the movement of genes. – From one generation to the next as a result of reproduction – From one region to the next as a result of migration If two or more populations exhibit gene flow, – then they are considered the same species. Horses and donkeys can interbreed, but do not experience gene flow. – Their offspring, mules, are sterile.

4. 4 Hybrid sterility

5. 5 How new species originate Speciation is the process of generating new species. – Speciation has occurred continuously over the history of life on earth. – The fossil record shows that huge numbers of new species have originated. Most of these have gone extinct. There are two main mechanisms of speciation. 1. Reproductive isolation 2. Genetic isolation - Polyploidy

6. 6 Speciation by reproductive isolation Geographic isolation – Occurs when a portion of a population becomes totally isolated from the rest If it is followed by genetic divergence. – Changes in allele frequencies Then reproductive isolation can result. – The isolated population becomes a new species

7. 7 Geographically isolated populations

8. 8 Mechanisms of geographic isolation Colonization of a distant area – A few individuals emigrate and establish a population far from their original home. – The distance prohibits gene flow with the original population; the new population becomes reproductively isolated. Appearance of a geographic barrier – Uplifting of mountains, rerouting of rivers or formation of deserts can subdivide a population. – This barrier prohibits gene flow between the divided subpopulations; they can become reproductively isolated.

9. 9 Genetic diversity and reproductive isolation are necessary for speciation Environmental pressures and natural selection play an important role in speciation. – After a geographical separation, the two subpopulations will likely experience different environmental conditions. – Over time, genetic differences that accumulate may result in structural, physiological and behavioral differences. These differences may prohibit interbreeding, thus resulting in speciation.

10. 10 Speciation without geographic barriers Any process that leads to reproductive isolation can lead to speciation. – May not necessarily require geographic isolation Breeding or flowering at different times of year Differences in genetically determined courtship and mating behaviors Genetically determined incompatibility of pollen from one species and flowers of another – Polyploidy is the primary mechanism of speciation in the absence of geographical isolation.

11. 11 Polyploidy A condition of having multiple sets of chromosomes. – More than haploid or diploid – Can results from abnormal events in mitosis or meiosis Cotton, potato, sugarcane, broccoli, wheat, etc. are all species that resulted from polyploidy.

12. 12 Speciation without geographic isolation

13. 13 Maintaining reproductive isolation between species New species stay reproductively isolated from other species due to mechanisms that prevent mating between species. – reproductively isolating mechanisms

14. 14 Reproductively isolating mechanisms Ecological isolating mechanisms – Two populations don’t interbreed because they occupy different niches. Seasonal isolating mechanisms – Two populations don’t interbreed because they mate at different types of year. Behavioral isolating mechanisms – Two populations don’t interbreed because they have different courtship and mating behaviors.

15. 15 Reproductively isolating mechanisms Mechanical isolating mechanisms – Two populations don’t interbreed because they have incompatible genitalia. Biochemical isolating mechanisms – Two populations don’t interbreed because their gametes are chemically incompatible. Hybrid infertility/inviability – Two populations that can interbreed, but their offspring are sterile or die before reproductive maturity.

16. 16 Evolutionary patterns above the species level The development of new species is the smallest irreversible unit of evolution. – After a speciation event, the new species continues to diverge from the original species.

17. 17 Divergent evolution An evolutionary pattern in which individual speciation events cause successive branches in the evolution in a group of organisms. The evolution of horses.

18. Divergent Evolution 18

19. 19 Extinction The loss of a species. Most species that have ever existed are now extinct. Ever changing environments leads to the generation of new species and the elimination of others. Divergence is accompanied by a great deal of extinction. – This is the basic pattern of evolution. – Other special patterns also exist.

20. 20 Adaptive radiation A special evolutionary pattern Involves a rapid increase in the number of kinds of closely related species A kind of evolutionary explosion of new species in a short amount of time

21. 21 Adaptive radiation Thought to occur because – A particular organism invades a previously unexploited environment. Animals moving to land Galapagos finches – A particular type of organism evolves a new set of characteristics that allows it to displace previously successful organisms. Reptiles replacing amphibians

22. 22 Adaptive radiation in the Galapagos finches

23. 23 Adaptive radiation in terrestrial vertebrates

24. 24 Convergent evolution A special evolutionary pattern in which similar characteristics develop in unrelated groups of organisms – The characteristics serve a similar purpose in the particular environment, but have very different ancestors. Spines in desert plants Eating while flying in bats, dragonflies and swallows Body shape of whales, sharks and tuna

25. 25 Convergent evolution

26. 26 Homologous and analogous structures Determining if a characteristic that is similar in two different species is a result of convergent or from common ancestry is important. – Homologous structures Have different appearances and functions that arose from a common ancestor Result from divergent evolution – Analogous structures Have similar structures and functions but arose from different ancestors Result from convergent evolution

27. Convergent Evolution – Analogous structures 27

28. 28 Homologous structures

29. 29 Rates of evolution Vary greatly – From thousands to millions of years When the environment changes rapidly – Organisms change rapidly as a result of natural selection. High rate of speciation High rate of extinction When the environment is stable – Organisms change very little.

30. 30 Theories about the rate of evolution Gradualism – The fossil record shows gradual changes in physical features of organisms over time. – Darwin’s view of evolution by natural selection implied gradualism. Punctuated equilibrium – The fossil record also shows long periods of stasis. – Argues that evolution happens in spurts of change, followed by long periods of equilibrium

31. 31 Gradualism vs. punctuated equilibrium

32. 32 An evolutionary diagram

33. 33 Where are we on the tree?

34. 34 Human evolution Our understanding of human evolution is based mainly on information from the fossil record. – Humans are mammals, primates, specifically anthropoids. Hominins are humans and their human-like common ancestors.

35. 35 The course of human evolution

36. 36 An overview of human evolution Early primates were adapted to living in forests. As the climate became drier, grasslands replaced forests. Early hominins (Australopithecus) were adapted to living in grasslands. – Stood upright to allowing for more rapid movement over long distances. ability to see over longer distances. freed arms for using tools, etc. Later hominins (Homo) had larger brains and used tools. – Had larger brains and bodies – Able to use tools for a more diverse diet

37. 37 The origin of Homo sapiens- two points of view Out-of-Africa hypothesis – Modern humans originated in Africa from other hominin species. – Migrated to Asia and Europe and displaced other hominin species that had colonized those areas earlier. Multiregional hypothesis – Homo erectus migrated and then evolved into H. sapiens. – Various subgroups of H. erectus existed throughout Africa, Asia and Europe and interbred to give rise to the races we know today.

38. 38 Sociobiology Study of evolution of behaviors – Altruism – Inclusive fitness