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Evolution occurs at the population level, evolutionary impact of natural selection is seen in how a population changes over time.
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evolution
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changes in allele frequency
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allele frequency
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(all add up to 1)
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population
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group individuals of the same species that live in the same area & interbreed to produce fertile offspring
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genetic variation
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differences in genen composition
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sources of genetic variation
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sexual reproduction
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mutation (change in nucleotide sequence)
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point mutations (single nucleotide change) ex. sickle-cell
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delete, disrupt, duplicate, rearrange loci
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effect on allele frequency
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causes
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genetic drift
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unpredictable fluctuation of alleles, reduces genetic variation, can limit natural selection
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founder effect, pop. bottleneck
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founder effect
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few individuals isolated, diff. allele frequencies in small founder pop.
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chance
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bottleneck effect
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reduced genetic variation and increased frequency of harmful alleles
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sudden environmental change
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what is it?
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individuals w certain characteristics are more likely to find mates
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sexual dimorphism
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marked differences between sexes (ex. pavo real)
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intrasexual selection
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selection within same sex for mates
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intersexual selection
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one sex is choosy with mates
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directional
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conditions favor individuals at one end of the phenotypic range
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disruptive
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conditions favor individuals at both extremes of phenotypic range
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stabilizing
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conditions favor intermediate variants
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condition
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consequence if condition is not kept
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1. no mutations
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gene pool is modified
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2. **random mating
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inbreeding = no random mixing of gametes, genotype frequencies change
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3. no natural selection
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allele frequencies change
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4. very large pop. size
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in small pop. allele frequencies change by chance (genetic drift)
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5. no gene flow
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gene flow can alter allele frequencies
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concept
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defines species by
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biological
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reproductive compatability
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reproductive isolation → new species
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gene flow between populations holds gene pool together, species pop. resemble each other
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limitations
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gene flow between morphologically & ecologically distinct species (ex. grolar bear)
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morphological
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structural features
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ecological
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ecological niche, interactions w nonliving and living environment
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speciation
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one species splits into two or more species
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speciation rates
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range from 4,000 y to 40 million y (avg. 6.5 my)
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allopatric
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geographically isolated populations
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population -gene flow interrupted→ subpopulation
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mutation, genetic drift, natural selection, reproductive isolation
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reproductive isolation
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can't breed bc of differences
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behavioral isolation
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prezygotic barrier, specific mates
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sympatric
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population (no geographic barrier)→ new species
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reproductive barrier, reduced gene flow
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polyploidy, habitat differentiation, sexual selection
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polyploidy
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extra chromosomes
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auto: same species allo: diff species
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habitat differentiation
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new ecological niches
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sexual selection
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female selecting mates
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microevolution (speciation)
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many speciations, extinctions → macroevolution
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reproductive barriers
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depend on environmental & genetic factors
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Prezygotic Barriers
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prevent mating between species
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geographical
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physical barrier (rivers, mountains)
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habitat/ecological
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same area, diff habitats
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temporal
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diff breeding times
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behavioral
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unique courtship rituals
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mechanical
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morphological diff
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gametic
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cannot fertilize
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Postzygotic Barriers
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prevent a viable, fertile hybrid
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reduced hybrid viability
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poor development/survival
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reduced hybrid fertility
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fertile hybrid
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hybrid breakdown
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infertile 2nd gen
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Hybrid Zones
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diff species mate, incomplete reproductive barriers
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novel genetic variation outcomes = *
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reinforcement
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hybrids cease
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← hybrids less fit
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fusion
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two species fuse
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← weakened rep. barriers
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stability
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continued hybrids
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← hybrids equally fit
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fossils are the traces of ancient life, naturally preserved, but an incomplete chronicle of evolution
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macroevolution
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evolution above the species level, interspecific variation
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microevolution
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evolutionary change in allele frequencies in a population over generations, intraspecific variation
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favor species that existed for a long time, were abundant/widespread, had hard shells, skeletons
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relative age determined by rock strata sequence
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younger stratum has more recent fossils
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older stratum has older fossils
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absolute age determine through radiometric dating
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radioactive "parent" isotope decays to "daughter" isotope at a constant rate
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half-life
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known time required for half parent isotope to decay
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earliest prokaryote fossils
(ARCHAEAN EON) |
form stromatolites dating back 3.5 BYA,
sole inhabitants for 1.5 BY |
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increase in atmospheric oxygen
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2.7 BYA
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cyanobacteria, other photosynthesizers
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led to extinction of many
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earliest eukaryote fossils
(PROTEROZOIC EON) |
1.8 BYA, gave rise to multicellular organisms
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jawed vertebrates
(PHANEROZOIC EON) |
440 MYA
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Cambrain explosion (535-525 mya)
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+diversity, unique mammalian features
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tetrapods
(PALOZOIC ERA) |
375 MYA colonized land
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mammals
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120 MYA, from synapsids
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can be caused by:
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Habitat destruction and/or unfavorable environmental change
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Biological causes (factors)-Origin of one new species can spell doom for another
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Permian Mass Extinction (252mya)
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96% marine life when extinct due to intense volcanisms
Paleozoic to Mesozoic era |
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Cretaceous Mass Extinction (66mya)
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+50% of all marine animals, many terrestrial plants and animals, dinosaurs (except birds) due to meteorite
Mesozoic to Cenozoic era |
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5–10 million years for diversity to recover
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the evolution of many diversely adapted species from a common ancestor that allows new species to occupy different habitats
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may follow:
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mass extinctions
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ex. mammals after extinction of dinosaurs
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evolution of novel characteristics
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ex. rise of photosynthetic organisms
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colonization of new regions
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organisms colonize new environments with little competition
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developmental genes
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program development, influence rate, timing, spatial patterns
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heterochrony
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evolutionary change in the rate or timing of developmental events
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ex. human vs chimpanzee jaw
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homeotic genes
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determine the organization of basic features
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hox genes
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a class of homeotic genes, provide positional information during animal development
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evolutionary novelties
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changes at the genetic level lead to developmental changes at the phenotypic level
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exaptations
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structures that originally played one role but gradually acquired a different role
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ex. bird feathers
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is any eukaryotic organism that is not an animal, plant, or fungus
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first eukaryote was a unicellular protist and most eukaryotes are protists
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structural and functional diversity, most are aquatic, most are unicellular
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complex at the cellular level, though simple when compared to eukaryotes
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nutritional diversity:
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photoautotroph = producers (photosynthetic)
use energy from light (or inorganic chemicals) to convert CO2 to organic compounds |
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heterotroph = consumers
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parasites =
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mixotroph =
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photosynthetic protists
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main producers in aquatic community
biomass of photosynthetic protists is limited by the availability of nitrogen, phosphorus, or iron diatoms, dinoflagelletes, multicellular algae, others blooms dramatic increase in abundance |
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symbiotic protists
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some are parasites that harm their hosts
ex. photosynthetic dinoflagellets provide food for coral reefs ex. wood-digesting protists break down cellulose in the guts of termites |
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effect on human health
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trypanosoma = excavate that causes sleeping sickness
apicomplexans = alveolate parasites ex. plasmodium - causes malaria |
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multicellular colonies
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collections of connected cells, little to no differentiation, can be simple or complex
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Multicellular organisms with differentiated cells likely originated from multiple different ancestors
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1. origin of cyanobacteria
2. origin of mitochondria 3. origin of plastid (chloroplast) 4. origin of multicellular eukaryotes 5. origin of fungal-plant symbioses |
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Excavata (unicellular protists)
‣diplomonads;parabasalids —
lack plastids, cannot do photosynthesis, reduced mitochondria, mostly anaerobic ‣euglenozoans— most have 2 flagella, diverse, inclue predatory heterotrphs, photoautotrophs, parasites ex. trypanosoma - parasitic infection that causes sleeping sickness |
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SAR (Stramenopiles, Alveolates, Rhizarians)
includes most important photosynthetic organisms)
‣diatoms — diverse photosynthetic unicellular algae
can affect ‣brown algae (seaweed) — largest & most complex, multicellular, mostly marine brown due to carotenoids in plastid anchored by holdfast, stem-like stipe supporting leaflike blades |
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Archaeplastids
‣red algae — 2nd largest, mostly multicellular, can absorb green & blue light
red due to phycoerythrin pigment ‣green algae— very similar to land plants, some are unicellular ➥chlorophytes — marine, terrestrial, mostly freshwater, multicellular, unicellular (free or symbiotic) ➥charophytes — most closely related to land plants ‣ plants chloroplasts of land plants cyanobacteria ➟ green algae ➟ land plants |
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eukaryotes
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a) plants
b) animals c) fungi, molds, mushrooms, yeast d) protists |
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early eukaryotes
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date back 2.7 billion years ago
unicellular, with nucleus, membrane, cytoskeleton, varied size & shape |
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diverse eukaryotes
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1.8 billion years ago
novel biological features evolved: multicellularity, sexual life cycles, eukaryotic photosynthesis |
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large eukaryotes
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635-541 million years ago (Ediacaran period) soft-bodied organisms
hard-bodied organisms 535-525 mya (Cambrian explosion) |
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plastid
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membrane-bound organelle (plants, algae, others)
ex. chloroplast |
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endosymbiont theory
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mitochondria and plastids were formerly small bacteria that began living within larger cells
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key evidence
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•inner membranes are similar (transport proteins) to bacteria plasma membrane
•replication is similar to bacteria cell division •have circular DNA like bacteria •transcribe/translate own DNA into proteins •ribosomes more similar to bacterial than eukaryotic |
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mitochondria come from a single proteobacterium ancestor which could do aerobic respiration using O2 to make ATP
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plastids come from a single cyanobacterium ancestor that could do photsynthesis
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ALL eukaryotes have mitochondria, not many have plastids
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anaerobic host cells may have benefited from aerobic endosymbionts as oxygen increased in the atmosphere
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+4 billion years ago
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Earth was created, lifeless for the first 2 billion years
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1.2 billion years ago
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cyanobacteria & protists
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+470 million years ago
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plants colonized land
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500 million years ago
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plants, fungi, & animals moved to land
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385 million years ago
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first forests
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ancestors
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red, green, & brown algae
multicellular eukaryotes photsynthetic autotrophs cellulose cell walls chlorplasts (chlorophyll a & b) modernly only charophytes share most traits w plants |
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chloroplasts of land plants
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cyanobacteria ➙ green algae (charophytes) ➙ land plants
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moving to land...
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🅐 evolution of:
sporopollenin — protective polymer surrounding charophyte zygotes ➙ dry land 🅑 BENEFITs: unfiltered sunlight, plenty CO2, nutrient-rich soil 🅒 CHALLENGES: scarcity of water, lack of support against gravity |
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key traits in plants not found in charophytes
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•alternation of generations
•multicellular, dependent embryos •walled spores produced in sporangia •apical meristems |
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apical meristems
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— localized regions of cell division @ tips of roots & shoots, mitotic division = +mineral & nutrients
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derived traits
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•cuticle — waxy coating, prevents water loss
•stomata — specialized pores, CO2-O2 exchange |
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vascular plants
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vascular tissue for H2O/nutrient transport
‣xylem- conducts most H2O/minerals (tracheids have lignin = water-conducting cells, provide structural support) ‣phloem - tubes of cells, distribute sugars, amino acids, other org. prod ‣lignin = polymer that makes plants rigid, allowing them to grow tall |
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nonvascular plants
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bryophytes lack vascular tissue
‣rhizoids - root-like anchor ‣gametophytes = larger, live longer than sporophytes ‣mature sporophyte fully depends on gametophyte for nutrition ‣limited to moist habitats •liverworts •mosses •hornworts |
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seedless vascular
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❋early vascular plants
‣ sporophytes = large/more complex gen. ‣ gametophyte & sporophyte are independent ‣sperm swims through water to egg (like bryophytes) •lycophytes (club mosses) •monilophytes (ferns) |
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seed plants
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❋reduced gametophytes, ovules, pollen
‣ seed= embryo + food supply + protective coat •gymnosperms = naked seeds •angiosperms = enclosed seeds in ovaries (flowers & fruits) |
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oldest fossils
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460 million years ago, terrestrial
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heterotrophs that feed by absorption
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FEED BY ABSORPTION secrete hydrolytic enzymes to break down complex molecules → small org. comp
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chitin cell walls
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diversification
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•mold (multicellular)
•yeast (unicellular) |
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life cycles & reproduction
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‣most propagate by producing many spores, sexually or asexually
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key role in land plant colonization
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symbiotic interactions...
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mutualism
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benefits BOTH
plant + fungi (endophytes) inside leaves/other •plant provide nutrition, some endophytes make toxins that deter herbivores/pathogens |
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parasitism
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benefits one, harms other
fungi absorb nutrients from host cells |
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lichen
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photosynthetic microorganism(algae/cyanobacteria)-fungus
•fungi benefit from carbs produced by algae/cyanobacteria •microorganism is protected by fungal filaments, gather moisture/nutrients |
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lichens break down surface & promote soil formation so plants can grow, on land 420 mya
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mycorrhizae
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plant-fungal — fungal hyphae transfer nutrients (phosphate/others) to plant
earliest land plants lacked true roots/leaves |
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sponges & cnidarians diverged from all other animals early on
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sponges (PORIFERA)
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•basal animals
•lack true tissues •filter feeders: capture small particles in water water is drawn through pores into central cavity and flows out through an opening at the top |
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eumetazoans
include cnidarians and all others |
"true animals" = tissues
have symmetrical bodies (radial or bilateral) |
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•radial symmetry
cnidarians (jellyfish, anemones) |
- single, central axis
most animals are sessile{nl}}➢2 embryonic tissue layers →endoderm →ectoderm |
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•bilateral symmetry
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- 2 axes
animals that move actively ➢3 germ layers →endoderm →ectoderm →mesoderm |
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cnidarians
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tissues + radial symmetry, blind digestive system, carnivores, lack brain/muscles, nerve net (simplest)
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chordata
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bilaterians, vertebrates, complete digestive tract
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bilateral invertebrates
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95% animals
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most bilaterians posses a a body cavity (coelom)
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- fluid/air filled space between digestive tract & outer body wall
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cushions organs, acts as hydrostatic skeleton, organs move independently of body wall
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