Evolutionary Patterns, Rates, and Trends

Transcription

1 Evolutionary Patterns, Rates, and Trends

2 Macroevolution Major patterns and trends among lineages Rates of change in geologic time

3 Comparative Morphology Comparing body forms and structures of major lineages Guiding principle: When it comes to introducing change in morphology, evolution tends to follow the path of least resistance: embryonic development.

4 Morphological Divergence early reptile pterosaur Change from body form of a common ancestor chicken bat Produces homologous structures porpoise penguin human

5 Morphological Convergence Individuals of different lineages evolve in similar ways under similar environmental pressures Produces analogous structures that serve similar functions

6 Morphological Convergence

7 Comparative Development Each animal or plant proceeds through a series of changes in form Similarities in these stages may be clues to evolutionary relationships Mutations that disrupt a key stage of development are selected against

8 Altering Developmental Programs Some mutations shift a step in a way that natural selection favors Small changes at key steps may bring about major differences

9

10 Trochophore larva

11

12 Molecular Evidence Biochemical traits shared by species show how closely they are related Can compare DNA, RNA, or proteins

13 Comparing Proteins Compare amino acid sequence of proteins produced by the same gene Human cytochrome c (a protein) Identical amino acids in chimpanzee protein Chicken protein differs by 18 amino acids Yeast protein differs by 56

14 Sequence Conservation Cytochrome c functions in electron transport Some sequences are identical in wheat, yeast, and primates

15 Sequence Conservation yeast wheat primate

16 Nucleic Acid Comparison Use single-stranded DNA or RNA Hybrid molecules are created, then heated The more heat required to break hybrid, the more closely related the species

17 Molecular Clock Assumption: Ticks (neutral mutations) occur at a constant rate Count the number of differences to estimate time of divergence

18 Biological Species Concept Species are groups of interbreeding natural populations that are reproductively isolated from other such groups. Ernst Mayr

19 Variable Morphology grown in water grown on land

20 Genetic Divergence Gradual accumulation of differences in the gene pools of populations Natural selection, genetic drift, and mutation can contribute to divergence Gene flow counters divergence

21 Genetic Divergence parent species time A time B time C time D daughter species

22 Reproductive Isolation Cornerstone of the biological species concept Speciation is the attainment of reproductive isolation Reproductive isolation arises as a by-product of genetic change

23 Reproductive Isolating Mechanisms Prevent pollination or mating Block fertilization or embryonic development Cause offspring to be weak or sterile

24 Prezygotic Isolation Mechanical isolation Temporal isolation Behavioral isolation Ecological isolation Gametic mortality

25 Mechanical Isolation Wasp and zebra orchid

26 Temporal Isolation Cicada

27 Albatrosses Behavioral Isolation

28 Postzygotic Mechanisms Early death Sterility Low survival rates

29 Models for Speciation Allopatric speciation Sympatric speciation Parapatric speciation

30 Allopatric Speciation Speciation in geographically isolated populations Some sort of barrier arises and prevents gene flow Effectiveness of barrier varies with species

31 Allopatric Speciation

32 Extensive Divergence Prevents Inbreeding Species separated by geographic barriers will diverge genetically If divergence is great enough it will prevent inbreeding even if the barrier later disappears

33 Archipelagos Island chains some distance from continents Galapagos Islands Hawaiian Islands Colonization of islands followed by genetic divergence sets the stage for speciation

34 Speciation on an A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat Archipelago Later in time, a few individuals of the new species colonize nearby island 2. In this new habitat, speciation follows genetic divergence. 1 2 Speciation may also follow colonization of islands 3 and 4. And it may follow invasion of island 1 by genetically different descendents of the ancestral species

35 Hawaiian Islands Volcanic origins, variety of habitats Adaptive radiations: Honeycreepers: in absence of other bird species, they radiated to fill numerous niches

36 Ancestral Type Housefinch (Carpodacus) Fig d13, p.209

37 Speciation in Hawaiian Honeycreepers Akepa (Loxops coccineus) Fig d1, p.209

38 Speciation without a Barrier Sympatric speciation Species forms within the home range of the parent species Parapatric speciation Neighboring populations become distinct species while maintaining contact along a common border

39 Sympatric Speciation in African Cichlids Studied fish species in two lakes Species in each lake are most likely descended from single ancestor No barriers within either lake

40 Sympatric Speciation in African Cichlids Feeding preferences localize species in different parts of lake

41 Speciation by Polyploidy Change in chromosome number (3n, 4n, etc.) Offspring with altered chromosome number cannot breed with parent population Common mechanism of speciation in flowering plants

42 Possible Evolution of Wheat Triticum monococcum (einkorn) Unknown species of wild wheat T. turgidum (wild emmer) T. aestivum (one of the common bread wheats) T. tauschii (a wild relative) Figure 18.9 Page AA X 14BB 14AB 28AABB X 14DD 42AABBDD cross-fertilization, followed by a spontaneous chromosome doubling

43 Parapatric Speciation Populations in contact along a common border giant velvet worm blind velvet worm

44 Evolutionary Trees species 1 species 2 species 3 ancestral stock Summarize information about relationships among groups