Ecological Speciation of Lake Organisms

1. Ecological Speciation of Lake Organisms Jennifer Linton

2. Outline Definitions Ecological Causes of Divergent Selection Ecological Environmental Differences Sexual Selection Examples Whitefish in the Yukon Stickleback in Northern Hemisphere Cichlids in African Rift Lakes Implications of human impacts Cichlids

3. What is a species? Biological Species Concept Related to reproductive compatibility

4. What is a species? 4. Cohesion Species Concept Focuses on mechanisms that maintain discrete phenotypic entities e.g. reproductive barriers

5. What is a species? 6. Ecological Species Concept Species defined by the unique role it plays or by a specific function or position in its environment Speciation by divergent natural selection Different members of the same species face different selective pressures Eventual reproductive isolation

6. Modes of Speciation Allopatric (allos = other, patria = homeland) Geographic barrier that physically isolates two populations blocking gene flow E.g. Mountain, river

7. Modes of Speciation 2. Sympatric Sym = together Intrinsic factors that lead to reproductive isolation among individuals living in the same geographic area E.g. mate selection in animals

8. Modes of Speciation

9. Outline Definitions Ecological Causes of Divergent Selection Ecological Environmental Differences Sexual Selection Examples Whitefish in the Yukon Stickleback in Northern Hemisphere Cichlids in African Rift Lakes Implications of human impacts Cichlids

10. Ecological Causes of Divergent Selection Ecological Divergence may arise between pop�n due to ecological interactions Similar to Sympatric Speciation � though could occur between allopatric pop�n E.g. interspecific competition

11. Ecological Causes of Divergent Selection Environmental Differences Divergence due to differences in environments Habitat structure Climate Resources Predators Competition Similar to both sympatric and allopatric speciation

12. Ecological Causes of Divergent Selection Sexual Selection Animals who seek out a mate with a particularly desirable trait e.g. distinctive plumage, colouration Animals with those traits mate at a higher rate Desirable trait becomes more common, more exaggerated Sexual advantage to have trait Facilitates mate recognition

13. Outline Definitions Ecological Causes of Divergent Selection Ecological Environmental Differences Sexual Selection Examples Whitefish in the Yukon Stickleback in British Columbia Cichlids in African Rift Lakes Implications of human impacts Cichlids

14. Speciation of Lake Whitefish (Coregonus sp.)

16. 3 Questions Are there genetic differences between ecotypes?

17. Monophyletic vs. Polyphyletic Monophyletic Descendants arising from a single common ancestor Polyphyletic Descendants arising from multiple ancestors

18. 3 Questions Are there genetic differences between ecotypes?

19. Methods Analyzed Mitochondrial DNA Analyzed Nuclear Genes Allozymes Variants of enzymes with different genetic backgrounds

20. Results > HGR whitefish in surface nets > LGR whitefish in bottom nets Little Teslin Lake ~ Different spawning seasons Dezadeash Lake Different spawning seasons Squanga Lake Similar spawning season Different spawning habitats

21. Conclusions Genetic differences between ecotypes? Yes Reproductive isolation Highly significant difference in MtDNA for Little Teslin and Dezadeash Lake Significant (but weaker) difference for Squanga Lake

22. Conclusions Monophyletic or Polyphyletic Evolutionary Events?

23. Conclusions Allopatric or Sympatric speciation? Sympatric and ~ Allopatric MtDNA data 2 monophyletic groups that evolved in allopatry during last glaciation Secondary contact in Little Teslin and Squanga

26. Outline Definitions Ecological Causes of Divergent Selection Ecological Environmental Differences Sexual Selection Examples Whitefish in the Yukon Stickleback in Northern Hemisphere Cichlids in African Rift Lakes Implications of human impacts Cichlids

27. Threespine Stickleback in B.C.(Gasterosteus sp.)

28. Hypothesis Reproductive isolation may be accounted for by non-random mating based on: Body Size = Speciation by ecological differences and divergent selection

29. Threespine Stickleback Anadromous Stickleback Geographically wide spread Persistent Larger

30. Methods 1. Collected individuals from allopatric populations

31. Results Greater success rate with same ecotype pairs

32. Results

33. Conclusion Reproductive isolation brought on by adaptations to environment

34. Outline Definitions Ecological Causes of Divergent Selection Ecological Environmental Differences Sexual Selection Examples Whitefish in the Yukon Stickleback in Northern Hemisphere Cichlids in African Rift Lakes Implications of human impacts Cichlids

35. Cichlids in African Rift Lakes 80% of 2,500 cichlid species from East Africa = Haplochromis genus (~2000 sp.) All haplochromines ultimately derived from Lake Tanganyika endemics Most have evolved in a short period of time e.g. Lake Victoria ~ 15-250,000 years e.g. Lake Malawi � dry about 200 y.a. with current endemics 4 defined lineages 3 ancestral lineages are species poor 1 �modern� lineage = 7% of world�s ~25,000 teleost species (~1750 sp.)

36. Cichlids in African Rift Lakes Allopatric or Sympatric Speciation?

38. Cichlids in African Rift Lakes Shorelines of lakes tend to be broken up into small isolated areas Rocky points Sandy beaches Swampy areas Some species reluctant to move across habitat barriers e.g mbuna cichlids

39. Cichlids in African Rift Lakes Lake level changes can also create microhabitats Sandbar separated Lake Nabugabo from Lake Victoria ~ 4,000 y.a. Lake Nabugabo formed its own endemic species

40. Cichlids in African Rift Lakes Molecular data = species flocks in each lake are monophyletic Evolved after a single colonization event Sympatric Speciation

41. Cichlids in African Rift Lakes ? prefer ? that are brightly coloured

42. Cichlids in African Rift Lakes Reproductively isolated groups form based on female mate colouration preference

43. Cichlids in African Rift Lakes Pharyngeal jaw apparatus is easily modified Phenotypically Genotypically

44. Outline Definitions Ecological Causes of Divergent Selection Ecological Environmental Differences Sexual Selection Examples Whitefish in the Yukon Stickleback in British Columbia Cichlids in African Rift Lakes Implications of human impacts Cichlids

45. Human Impacts & Implications

46. Cichlid Fish Diversity Threatened by Eutrophication

47. Species Diversity Clearer lakes have > # of species 300-2200 vs. 20-130 Considered lake size ? larger lakes were more turbid and had fewer species

48. Eutrophication & Turbidity Eutrophication increases turbidity

49. Turbidity and Light Light conditions constrain mate choice

50. Cichlid & Light Regime > part of interpopulation variation in male nuptial hue explained by aquatic light regime

52. Cichlid Diversity Turbidity is increasing due to agricultural runoff from surrounding land Decreasing effectiveness of colour signals ? cannot find appropriate ? to mate with