Exam 1 - Evolution & History of Life

Five major extinctions, two well studied

Permian and Cretaceous

Fossil Records

Provide solid evidence that organisms from the past are not the same as today: • shows the extinction of species • shows the origin of new groups • shows changes within groups over time • documents important transitions - land to sea & vice versa

Cyanobacteria

These gram-negative photoautotrophs are the only prokaryotes with plantlike, oxygen-generating photosynthesis. (In fact, chloroplasts are thought to have evolved from an endosymbiotic cyanobacterium.) Both solitary and filamentous cyanobacteria are abundant components of freshwater and marine phytoplankton, the collection of small photosynthetic organisms that drift near the water's surface.

Spirochetes

These helical gram-negative heterotrophs spiral through their environment by means of rotating, internal, flagellum-like filaments. Many spirochetes are free-living, but others are notorious pathogenic parasites: Treponema pallidum causes syphilis, and Borrelia burgdorferi causes Lyme disease.

Chlamydias

These parasites can survive only within animal cells depending on their hosts for resources as basic as ATP. The gram-negative walls of chlamydias are unusual in that they lack peptidoglycan. One species, Chlamydia trachomatis, is the most common cause of blindness in the world and also causes nongonococcal urethritis, the most common sexually transmitted disease in the United States.

natural selection facts

- Natural selection can ONLY take place if there is variation in a population - Natural selection occurs through interactions between individuals & their environment, but individuals do NOT evolve • only populations evolve over time - Natural selection can only increase or decrease heritable traits that vary in a population • If individuals are genetically identical for a trait, evolution via natural selection cannot occur - Environmental factors vary by place & time, therefore, adaptations vary with different environments

Molecular homologies

- Nearly universal genetic code - Shared genes inherited from a distant common ancestor

prezygotic reproductive barriers

1) Habitat Isolation 2) Behavioral Isolation (differing behaviors for attracting mates) 3) Temporal Isolation (mate at different times) 4) Mechanical Isolation 5) Gametic Isolation (unable to fertilize egg)

Natural selection is the outcome of 3 principles:

1. Characteristics are inherited from parent to offspring 2. More offspring are produced than are able to survive - so resources are limited 3. Offspring vary from each other in characteristics & these variations are inherited

mechanisms that alter allele frequency directly:

1. Natural selection 2. Genetic drift 3. Gene flow

Conditions for Hardy-Weinberg Equilibrium

1. No mutations (no big impact) 2. Random mating (no big impact) 3. No natural selection (large impact) 4. Extremely large population size (large impact) 5. No gene flow (large impact)

Postyzygotic reproductive barriers

1. Reduced hybrid viability 2. Reduced hybrid fertility 3. Hybrid breakdown

Hybrid breakdown

2nd gen. is sterile

Cambrian Explosion (535

525 MYA)-sudden appearance of many present-day animal phyla • Animals prior were only soft bodied & no predation

natural selection

Blend of chance & sorting • Chance - the creation of new genetic variations (mutation) • Sorting - favoring alleles over others. The outcome of natural selection is NOT random - it consistently increases the frequencies of alleles that provide a reproductive advantage • Leads to adaptive evolution

Sympatric

speciation occurs in populations that live in the same geographic area

Divergent evolution

species that evolve in diverse directions from a common ancestor

Reduced hybrid fertility

sterile offspring

Vestigial structures

structures from a common ancestor that no longer provide a function

Bottleneck effect

sudden change in environment that drastically reduces the size of a population and certain alleles survive by chance

adaptive evolution

traits enhance survival or reproduction tend to increase in frequency over time

Gene flow

transfer of alleles into/out of a population due to movement of fertile individuals or their gametes • If it occurs extensively, it can result in two populations combining into a single population with a common gene pool • Can increase/decrease populations from adapting to their local conditions

Behavioral isolation

unique courtship behaviors

Permian extinction (252 MYA)

volcanic eruptions that removed 96% of marine species & many terrestrial species

Ideas from the book

• Descent with modification • Artificial selection • Natural selection • Adaptations

Evolution explains origins of life

• It does NOT, it explains how populations change over time & how life diversifies the origin of species • once life existed, the organisms would be subject to pressures of natural selection

Organisms evolve on purpose

• changes in the environment results in a benefit for SOME individuals in the population & those go on to reproduce more than other phenotypes • the variation is already present in the population, it does NOT arise in response to environmental change • species do NOT become "better" over time, they are simply adapt to their changing environment to maximize reproduction

Individuals evolve

• evolution is the change in a POPULATION'S genetic composition over time (generations) resulting from various combinations of alleles during reproduction • individuals do change in their lifetime, but this is simply development which is programmed before birth

Evolution is just a theory

• remember that theory = body of thoroughly tested & verified explanations for a set of observations • other examples: theory of gravity, theory of the atom • "theory" in science is NOT a guess or suggested explanation

Endemic Species

• species found nowhere else; typically found on islands (like Australia) • may be closely related to species on the nearest mainland, but have evolved over time to look different from their ancestor

habitat isolation

Two species that occupy different habitats within the same area may encounter each other rarely, if at all. Example: These two fly species in the genus Rhagoletis occur in the same geographic areas, but the apple maggot fly (Rhagoletis pomonella) feeds and mates on hawthorns and apples while its close relative, the blueberry maggot fly (R. mendax), mates and lays its eggs only on blueberries.

Everything is derived from

a common ancestor

Speciation types

allopatric and sympatric

Homologous structures

anatomical structures that share the same overall construction due to their origin in a common ancestor

Cretaceous extinction (66 MYA)

asteroid collided with earth eliminating more than 50% of marine species, many terrestrial plants & animals (all dinosaurs, except birds)

Macroevolution

broad pattern of evolution above the species level

Genetic drift

chance event that cause allele frequencies to fluctuate unpredictably in small populations

Gradual model

change more gradually over long periods of time

Microevolution

changes over time in allele frequencies in a population

behavioral isolation

courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species Example: Blue-footed boobies inhabitants of the Galapagos, mate only after a courtship display unique to their species. Part of the script calls for the male to high step, a behavior that calls the female's attention to his bright blue feet

Radiometric dating

decay of radioactive isotopes are used to determine the age of a fossil (C14 has a half-life of 5, 730 years, Uranium-238 = 4.5B years)

Charles Darwin

developed a scientific explanation for the diversity of life; father of evolution

Temporal isolation

diff breeding times

genetic variation

does not guarantee that evolution will occur

First Prokaryotes

earliest direct evidence of single-celled organisms dates back 3.5B years (stromatolites)

Gametic isolation

fertilization can't occur

Founder effect

few individuals become isolated from a larger population, they establish a new population with a different gene pool

Early Multicellular Eukaryotes

fossil evidence dates back 1.3B years (small algae); larger eukaryotes dates back 600M years • Large rise of eukaryotes during Ediacaran period (635-541 MYA)

First Eukaryotes

fossil evidence dates back 1.8B years • Recall endosymbiont theory

Colonization of Land

fossil evidence dates back 500M years for larger forms of life (prokaryotes may have colonized land 3.2 BYA); humans date back 6-7 MYA

Allopatric

gene flow in interrupted when population is divided geographically into subpopulations

Biogeography

geographic distribution of organisms on Earth • influenced by continental drift - slow movement of continents over time

Species

group of population whose members have the potential to interbred in nature & produce viable, fertile offspring, but don't reproduce with members of other groups

Life on Earth

has been marked by the rise & fall of groups of organisms • Related to speciation & extinction rates of species • Influenced by plate tectonics, mass extinctions & adaptive radiations

plate tectonics

movement of Earth's continents over time • 3 times the landmasses have converged, then broke apart, yielding a different configuration each time

Photosynthesis & Oxygen Revolution

oxygenation of Earth's atmosphere around 2.7B years ago • Led to evolution of cellular respiration

Punctuated model

period of no change, punctuated by sudden change

adaptive radiation

periods of evolutionary change in which groups of organisms from many new species whose adaptations allow them to fill different ecological roles • Occurred after each mass extinction

Speciation

process by which one species splits into two species • Forms a bridge between micro & macroevolution

Homeotic genes (Hox genes)

provide positional information for developing structures in an embryo

artificial selection

selecting & breeding individuals that possess desired traits

descent with modification

shared ancestry, resulting in shared characteristics and accumulation of differences Has given rise to the diversity of life

Convergent evolution

similar traits evolve independently in distantly related species - analogous features

Homology

similarity resulting from common ancestry

Mechanical isolation

morphological differences

Mutation

- can produce new alleles • Error in DNA replication, exposure to UV light/radiation, exposure to chemicals• NOT always harmfulSexual reproduction:unique combinations of alleles • Shuffles existing alleles & deals at random • Due to crossing over, an independent assortment of chromosomes & fertilization

History of Life

Fossil records provide glimpses of evolution of life over billions of years

Mass extinctions

Fossil records show that the majority of species that ever lived are now extinct • takes 5-10M years for diversity to recover

Gram-positive bacteria

Gram-positive bacteria rival the proteobacteria in diversity. Species in one subgroup, the actinomycetes, form colonies containing branched chains of cells; two of these species cause tuberculosis and leprosy, but most are decomposers living in soil. Soil-dwelling species in the genus Streptomyces are cultured as a source of antibiotics, including tetracycline and erythromycin. Other subgroups of gram-positive bacteria include pathogens such as Staphylococcus aureus (see Figure 22.14), Bacillus anthracis, which causes anthrax, and Clostridium botulinum, which causes botulism.

Anatomical homologies

Homologous structures and vestigial structures

allele frequencies

If allele & genotype frequencies remain constant from generation to generation, the population is NOT evolving (Hardy-Weinberg equilibrium)

Mechanical isolation

Matting is attempted, but morphological differences prevent its successful completion Example: Snails in the genus Bradybaena approach each other headfirst when they attempt to mate. Once their heads have moved slightly past each other, the snails' genitals emerge, and if their shells spiral in the same direction, mating can occur. But if a snail attempts to mate with a snail whose shell spirals in the opposite direction (g), the two snails' genital openings (indicated by arrows) will not be aligned, and mating cannot be completed.

Direct evidence of evolutionary change

Natural selection in response to introduced species Evolution of drug-resistant bacteria

Ideas from The Origin of Species

On the Origin of Species by Means of Natural Selection - published in 1859 Within a decade, Darwin's book convinced most scientists that life's diversity is the product of evolution

Evolution of development

Slight genetic differences can produce major morphological differences in species • Genes that alter the rate, timing & spatial patterns of change in an organism's form as it develops into adult • Homeotic genes (Hox genes) • Changes in gene sequence & gene regulation can alter body form

Speciation timing

Speciation can occur rapidly or slowly & can result from changes in few/many genes

temporal isolation

Species that breed during different times of the day, different seasons, or different years cannot mix their gametes. Example: In North America, the geographic ranges of the western spotted skunk (Spilogale gracilis) and the eastern spotted skunk (Spilogale putorius) overlap, but S. gracilis mates in late summer and S. putorius mates in late winter.

Reduced hybrid viability

impairs survival of offspring

natural selection

individuals with certain inherited traits tend to survive & reproduce at higher rates than others, due to those traits

Adaptation

inherited characteristics of organisms that enhance their survival & reproduction in certain environments; darwin

Habitat isolation

limited encounters