Evolution of Populations Microevolution Chapter 23.
Post on 04-Jan-2016
Evolution of Populations MicroevolutionChapter 23
Micro- EvolutionNatural selection typesSexual selectionMicroevolutionHardy Weinberg ConditionsGenetic driftBottle neckFounder effect
MicroevolutionSlight changes in gene frequencies between generationsPopulations change, not individualsExample:Antibiotic resistance
less than 1 in 1,6001 in 400-1,6001 in 180-4001 in 100-1801 in 64-100more than 1 in 64Distribution of malaria cases in Africa, Asia, and the Middle East in the 1920sFrequency of people with the sickle-cell trait
Hardy WeinbergUnder these conditions, populations do not change No EvolutionNo mutationsRandom MatingNo Natural SelectionNo Gene FlowLarge Population Size
G.H. Hardy 1877-1947
Wilhelm Weinberg 1862-1937
Hardy WeinbergEquation looks at individual traits, one at a time p & q are allelesProbably couldnt meet the conditions for all traits at once for long.Evolution probably always working at some level.Shows us the factors that alter a populations genepool- evolution.
PopulationAll the individuals of the same species in a given location at a given timeThe potentially interbreeding groupThe basic unit of evolutionPopulations evolve, not individuals
Fig. 23-5Porcupine herdPorcupineherd rangeBeaufort SeaNORTHWESTTERRITORIESMAPAREAALASKACANADAFortymileherd rangeFortymile herdALASKAYUKON
Gene flowAllows gene to move between populationsimmigrationAny new trait arising in one population can move to othersKeeps species together as a interbreeding unit.Blocking gene flow helps form new species.
Fig. 23-12NON-MINESOILMINESOILNON-MINESOILPrevailing wind directionIndex of copper toleranceDistance from mine edge (meters)70605040302010020020020406080100120140160
Microevolution in humans: Populations became isolated for several thousands of yearsSlight morphological changes came about by natural selection by climate:Skin tone and sunlight (uv ,vitamin D, Folic acid)Eye shape and winds, and ice etc.Height in some populations.
Gene flow and human micro- evolutionIsolated populations now coming back together sharing traits
Fig. 23-16SC male graytree frogFemale graytree frogLC male graytree frogEXPERIMENTSC sperm Eggs LC spermOffspring ofLC fatherOffspring ofSC fatherFitness of these half-sibling offspring comparedRESULTS1995Fitness Measure1996Larval growthLarval survivalTime to metamorphosisLC betterNSDLC better(shorter)LC better(shorter)NSDLC betterNSD = no significant difference; LC better = offspring of LC malessuperior to offspring of SC males.
Sexual DimorphismSexual selection results in the males and females having different morphology, at least in breeding season.Size elephant seals, primatesColor- bird plumage
Genetic DriftRandom events in a small population can alter the genepool. Does not increase fitness.
Fig. 23-8-3Generation 1CW CW CR CRCR CWCR CRCR CRCR CRCR CRCR CWCR CWCR CWp (frequency of CR) = 0.7q (frequency of CW ) = 0.3Generation 2CR CWCR CWCR CWCR CWCW CW CW CW CW CW CR CRCR CRCR CRp = 0.5q = 0.5Generation 3p = 1.0q = 0.0CR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CR
AA in five populationsallele A lostfrom fourpopulations1.00.5015051015202530354045Generation (25 stoneflies at the start of each)In small populations, random deaths influence outcome, by fixing or eliminating alleles.
allele A neitherlost nor fixed in large population1.00.5015051015202530354045Generation (500 stoneflies at the start of each)
Special cases of genetic drift:Bottleneck a large population reduced by disaster. A few survivors re-grow the population, but with much less diversity.Founder effect a small population colonizes a new area. Who is in the small population affects the genepool of the new population.
phenotypes of original populationphenotype of island populationA seabird carries a few seeds, stuck to its feathers, from the mainland to a remote oceanic island.
- Fig. 23-10Numberof allelesper locusRangeof greaterprairiechickenPre-bottleneck(Illinois, 1820)Post-bottleneck(Illinois, 1993)Minnesota, 1998(no bottleneck)Nebraska, 1998(no bottleneck)Kansas, 1998(no bottleneck)Illinois19301960s1993LocationPopulationsizePercentageof eggshatched1,00025,000
Types of Natural Selectionweeds out less fit traits. Reduces genetic diversity in population.Adaptive evolutionDirectional Selection favors one extreme traitStabilizing Selection favors the most common form of a traitDisruptive Selection favors the extremes, often forming disjunct populations.
Fig. 23-14(a) Color-changing ability in cuttlefish(b) Movable jaw bones in snakesMovable bones
Fig. 23-13Original population(c) Stabilizing selection(b) Disruptive selection(a) Directional selectionPhenotypes (fur color)Frequency of individualsOriginalpopulationEvolvedpopulation
Directional Selection modifies Beak depth during drought periods
Range of values at time 1Number of individuals Stabilizing Selection
percent of population2015105birth weight (pounds)1007050302010532percent mortalityStabilizing selection
Range of values at time 1Number of individuals Disruptive Selection
Galapagos FinchesSpecialization to different feeding sources may have diversified the species.
Diversifying selection lead to two beak depths in Cameroon finches
102030405060Number of individuals1012.815.718.5Widest part of lower bill(millimeters)nestlingsdrought survivors
Frequency Dependent SelectionRight-mouthed1981Left-mouthedFrequency ofleft-mouthed individualsSample year1.00.50828384858687888990
EcotypesLocally adapted populations.Local weather or other conditions selects for adaptations.Still one species, but distinguishable from other ecotypesWhen distributed along a gradient (elevation, north to south) form a cline.
Fig. 23-41.00.80.60.40.20464442403836343230GeorgiaWarm (21C)Latitude (N)MaineCold (6C)Ldh-B b allele frequency
All made by Artificial Selection from wild mustardArtificial Selection: human designed breeding of plants and animals for desired traits by selecting which individuals get to reproduce.
Dont confuse:PolymorphismSexual Dimorphism Ecotypes - Cline
Fig. 23-1702.5%Distribution ofmalaria caused byPlasmodium falciparum(a parasitic unicellular eukaryote)Frequencies of thesickle-cell allele2.55.0%7.510.0%5.07.5%>12.5%10.012.5%
Fig. 23-UN2Sampling sites(18 representpairs of sites)Salinity increases toward the open oceanNLong IslandSoundAllelefrequenciesAtlanticOceanOther lap alleleslap94 allelesData from R.K. Koehn and T.J. Hilbish, The adaptive importance of genetic variation,American Scientist 75:134141 (1987).ESW12345910678111111023456789