Evolutionary Patterns, Rates, and Trends

Evolutionary Patterns, Rates, and Trends

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

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.

Morphological Divergence 2 1 3 4 5 21 3 early reptile pterosaur Change from body form of a common ancestor 4 3 2 2 1 1 chicken bat Produces homologous structures 2 3 4 5 3 1 4 5 2 3 2 3 1 4 5 porpoise penguin human

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

Morphological Convergence

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

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

Trochophore larva

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

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

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

Sequence Conservation yeast wheat primate

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

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

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

Variable Morphology grown in water grown on land

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

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

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

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

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

Mechanical Isolation Wasp and zebra orchid

Temporal Isolation Cicada

Albatrosses Behavioral Isolation

Postzygotic Mechanisms Early death Sterility Low survival rates

Models for Speciation Allopatric speciation Sympatric speciation Parapatric speciation

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

Allopatric Speciation

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

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

Speciation on an A few individuals of a species on the mainland reach isolated island 1. Speciation follows genetic divergence in a new habitat. 1 2 3 4 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. 1 2 3 4

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

Ancestral Type Housefinch (Carpodacus) Fig. 13-18d13, p.209

Speciation in Hawaiian Honeycreepers Akepa (Loxops coccineus) Fig. 13-18d1, p.209

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

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

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

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

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 299 14AA X 14BB 14AB 28AABB X 14DD 42AABBDD cross-fertilization, followed by a spontaneous chromosome doubling

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

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