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