Chapter4Groupselectionandindividualselection

Chapter 4Group selection and individual selection 2002 by Prentice Hall,Inc.Upper Saddle River,NJ 074581 Outline Group selection vs.individual selfishnessAltruismBenefits and trade-offs of group living2 living in Groups：.Increasing Vigilance 警戒.Dilution Effect 3 Altruism 利它主義：In an evolutionary sense,enhancement of the fitness of an unrelated individual by acts that reduce the evolutionary fitness of the altruistic individual.4 Kin selection：同族選擇A form of genetic selection in which alleles life in their rate of propagation because they influence the survival of in who carry the same alleles.5 Natural selection自然選擇：只有那些具有有利變異的後代可以在生存競爭中生存下來，通過以後各代有利變異得到累積，使這樣的後代漸漸與其親代不同。6 5.Natural selection自然選擇：(1).Stabilizing selection穩定選擇：(2).Direction selection定向選擇:(3).Disruptive selection分裂選擇:7 (1).Stabilizing selection穩定選擇：環境條件有利於族群的表現型性狀常態分布線的平均值附近時，對於兩側的極端個體有較高的淘汰率。例如人的出生死亡率和出生重的關係。8 (2).Direction selection定向選擇:選擇對於一側極端的個體有利，從而使族群的平均值向這一側移動。例如大部分的人工選擇。9 (3).Disruptive selection分裂選擇:選擇對兩側極端的個體有利，而不利於中間的個體，從而使族群分成兩個部份。10 自然選擇的條件：1.任何生物單位具有複製自身（繁殖）的能力。2.子代的數目超過其替代的需要。3.子代的存活決定於某些特徵（外表型或是基因型）。）。4.這些特徵具有遺傳傳遞的機制。11 Soft selection:特定基因型的個體比族群內的其他個體，具有更強取得資源的競爭力，因此可以有較高的活存機率。12 Hard selection:一個個體的適應度（Fitness:存活率、死亡率等量化差異）和其他基因型無關，一種突發的外界環境因素可能導致高死亡率的發生。13 Gamete selection配子選擇：選擇對基因頻率的影響，可以發生在配子上，例如精子的活動力差異可以受物理的或化學的狀況所影響。14 Kin selection親屬選擇：相關個體間（親屬間）利他行為所產生的總適應度提高的一種選擇。例如土撥鼠發出警告叫聲的土撥鼠可以使其他親屬有較高的活存率，但是本身較易受攻擊而死亡。15 Sexual selection性別選擇：最強壯或最活躍的個體具有較高的交配機率，因此這種個體的特徵在後代中會不斷的強化發展。例如孔雀的尾羽、鬥魚的鰭、雄鹿的角。16 Frequency-dependent selection頻度相關的選擇：自然選擇作用在出現頻度最多的外表型個體上較高，其結果將造成其生殖程度下降，如此可以使一個群維持平衡式的多形態性。如果選擇對於某種頻度的個體最有利，則將提高這種有個體的適應度。17 The evolution of interactions among speciesMimicry擬態：Coevolution共同演化Parasitism寄生:Mutualism互利共生：Competition競爭：Predator-prey掠食者與獵物：Herbivore-plant草食性動物與植物：18 Mimicry擬態：從模仿其他物種的外表上獲得好處的現象。.Bastesian mimicry貝氏擬態：無毒害的物種藉由模擬有害物種而獲利的情形。.Mullerian mimicry木氏擬態:兩種不同物種之間的擬態。.Aggressive mimicry攻擊性擬態：有毒的種類模擬無讀得種類，以提升其偽裝效果，增加掠食成功率。19 Coevolution共同演化：例如植物和昆蟲間的共同演化。20 Group and Individual SelectionRegulation of populations early thoughtsLevels below which competition becomes importantAvoid wastefulnessDevelopment of Group SelectionTerritoriality of birds21 Group and Individual SelectionDevelopment of Group Selection(cont.).Increase in emigration correlated with increase in numbersMechanisms operate in the absence of limitationsHigh variation in reproductive ratesExamples of self-regulation22 Group and Individual SelectionExamples of self-regulation(cont.).1940,David Lack and Alexander SkutchSelf-regulation of song birdsTropics vs.temperate Clutch size based on food1962,V.C.Wynne-EdwardsAnimal Dispersion in Relation to Social Behavior23 Group and Individual SelectionGroups of individuals control their numbers to avoid extinctionTheory known as Group SelectionDevelopment of Individual SelectionSuccessful groups individuals would not act selfishlySelfish groups overexploit their environment and die out.24 Group and Individual SelectionDevelopment of Individual Selection(cont.).1966,G.C.WilliamsAdaptations and Natural SelectionArguments against Group SelectionMutationCheater scenarioClutch size based on maximizing the number of surviving chicks(Figure 4.1)25 Group and Individual SelectionArguments against Group Selection(cont.).ImmigrationIndividual selectionResource predictionSelfish individuals can migrate to new areasIndividuals die out more quickly than groupsIndividual selection a more powerful evolutionary force26 Group and Individual SelectionArguments against Group Selection(cont.).Resource prediction Self-RegulationIntraspecific competitionIndividuals strive to command as much resources as they can.Group selection needs a reliable and predictable source of foodNo evidence27 Group and Individual SelectionSelf-Regulation(cont.).Act in self-interest.Ex.Male lions that that kill existing cubs when they take over pride.Increase their own offspringEx.Male langur monkeys kill infants(Figure 4.2)28 Group and Individual SelectionAct in self-interest.Ex.Female giant water bugs kill eggs in masses being taken care of by males(Figure 4.3)29 AltruismApparent cooperationGroomingHuntingWarning signals30 AltruismCaring for copies of ones genesGenes in offspringCoefficient of relatedness=rProbability of sharing a copy of a particular gene31 AltruismProbability of sharing a copy of a particular gene(cont.).Parents to its offspring;r=0.5Brothers and sisters;r=0.5Grandparents to grandchildren;r=0.25Cousins to each other;r=0.125Figure 4.432 0.250.25grandparentsfather0.50.5mother0.250.250.250.250.250.250.50.510.125grandparentsmateselfdaughteror songranddaughter or grandsonhalf sibaunt/uncleniece ornephewcousinbrother/sister(full sib)33 AltruismCoefficient of relatedness=r(cont.).Implications of relatedness to altruism1964,W.D.HamiltonImportance of passing on ones genes through offspring as well as related individuals.34 AltruismCoefficient of relatedness=rImplications of relatedness to altruism(cont.).Inclusive fitnessTotal copies of genes passed on to all relativesKin selection Lowers individual chance of reproduction35 AltruismKin selection Raises chances of relatives reproductionQuantifying kin selection rB C 0 r=coefficient of relatedness C=number of offspring sacrificed by donor B=number of offspring gained by recipient36 AltruismKin selection(cont.).Ex.CaterpillarsAposematic contain colors to warn predators of bad taste or poisonDatana caterpillars(Figure 4.5)37 Number of caterpillar species01020304050AposematicCrypticLarge family groupsSolitary38 AltruismEx.Caterpillars(cont.).Predator must kill one to learn Advantage of animals to congregate in groups(Figure 4.6)39 AltruismAlarms from sentries Increased risk of being attacked Animals living near sentry most likely relatives Favors kin selection Alternative to kin selection Sentries that are forced to live at the fringe Alert for their own safety If sentry is successful,predator may seek new area Sentry increases chances of own survival40 AltruismAltruism between unrelated individuals“You scratch my back,Ill scratch yours”Reciprocal altruism41 AltruismAltruism between unrelated individuals(cont.).EvidenceBrooding success correlated to availability of helpersSocial huntingBenefit:Bigger prey42 AltruismSocial hunting(cont.).Cost:Sharing meatAltruism in social insectsExtreme example of altruism sterile castes in social insectsFemale workersRarely reproduce43 AltruismFemale workers(cont.).Assist queen with her offspring(eusociality)Soldier castes(Figure 4.7)44 AltruismSocial insect reproduction (Table 4.1)45 46 AltruismRelatednessFemales are diploidMales are haploidFormed without meiosisEach sperm is identicalSister relatednessEach daughter receives an identical set of genes from her father47 AltruismSister relatednessHalf of a females genes come from her diploid motherTotal relatedness of sisters:0.5 from father+0.25 from mother=0.75.Genetic system termed haplodiploidyRelatedness and the QueenSons and daughters;r=0.548 AltruismSister relatedness(cont.).Maximize reproductive potential.50:50 sex ratioAverage relatedness for sterile workers would be 0.5Relatedness and the QueenBetter for female workers to have more sisters49 AltruismRelatedness and the QueenColonies usually have more females than malesNon-haplodiploid coloniesTermitesMole rat from South Africa(Figure 4.8)50 Snake predators may venture into surface burrows5 cmBlocked off burrowLarger“non-workers”act in defense20cm40-50 cmMean burrow length=545 feetMean number of animals=6051 AltruismLifestyles that promote eusociality in mammalsIndividuals are confined to burrows or nestsFood is abundant enough to support high concentrations of individualsAdults exhibit parental care52 Altruism Lifestyles that promote eusociality in mammals Mothers can manipulate other individualsLifestyles that promote eusociality(cont.).Heroism is possible53 Group Living Dense livingPromote intense competitionSignificant advantages to compensate 54 Group Living predators(Figure 4.9)55 School cohesion765Few123456ManyPredator abundance(streams in rank order)56 Group Living“Many-eyes hypothesis”Success of predator attacksPrey alerted to attack(Figure 4.10)57 Group Living Success of predator attacks(cont.).Ex.Goshawks less successful attacking large flocks of pigeons(Columba palumbus)The bigger the flock(more eyes)the more likely the prey will be alerted to the presence of a predator(Figure 4.11)58 12-1011-5050Number of pigeons in flock020406080100Attack success(%)59 Group Living Success of predator attacks(cont.).Cheating vs.the advantages of not cheatingSelfish-herd theoryPredators usually only take one prey per attack.60 Group Living Selfish-herd theory(cont.).The bigger the herd,the lower the probability of an individual prey being takenLarger herds are attacked more,but probability of being taken would still favor individual61 Group Living Selfish-herd theory(cont.).Geometry of the selfish herd1971,W.D.HamiltonPrey prefer middle of herd to avoid predatorPredator difficulty in tracking large numbers of prey62 Group Living Geometry of the selfish herd(cont.).Peripheral prey easier to visually isolateMore difficult for predator to reach the center of herdLarge herds are better able to defend themselves63 64 Group Living Conflicting variablesCompetition for foodPresence of predator Figure 4.1265 Percentage of timePercentage of timePercentage of timeOptimal flock sizeExtra scanning in presence of hawkOptimal flock sizeOptimal flock sizeFeedingScanningFightingIncrease inaggression bydominantsat higherfood levels(c)(a)(b)66 Group Living Conflicting variables(cont.).Figure 4.1367 Percent of time spent in each activity02040608013-46-7Flock sizeScanningFightingFeeding68 Applied EcologyTragedy of the Commons1968,Garrett Hardin“Tragedy of the Commons”Humans and cattle grazingCarrying capacity of land69 Applied EcologyEx.Carrying capacity on a piece of land-1000 cattle 10 ranchers share land,each with a 100 cattleOne individual wants to add one cattle more than his/her shareMaximizes his/her profits at expense of othersAll of the cattle suffer very little.70 Applied EcologyTragedy(cont.).What would happen if all ranchers did this?OvergrazingNot sustainableBenefits of the environment often accrue to the individual71 Applied EcologyCost of using the environment is usually borne by the entire population72 Summary Group SelectionPast theoryPopulation maintained at equilibrium based on group selectionSelf-regulation of individualsPrevent overexploitation of resources73 Summary Group Selection(cont.).Several flaws mutation,immigration,and resource prediction.Individual SelectionMore likely74 SummaryExplanations for altruismKin selectionCaste systems of social insectsHaplodiploid mating systemsOccurrence of eusociality and cooperationHaplodiploid organismsNon-Haplodiploid organismsConfinement to burrows75 SummaryOccurrence of eusociality and cooperationHigh food concentrationsParental care of offspringMothers can manipulate other individualsNon-Haplodiploid organisms Cont.).Opportunity for heroism76 SummaryGroup Size-Trade offs Competition for foodProtection from predators77 Discussion Question#1If kin selection occurs in nature,how do you think animals recognize their kin?78 Discussion Question#2If it is equally valuable for a female to raise her own young or help raise sisters(both having an r=0.5),why do we see most females preferentially raising their young?79 Discussion Question#3Unrelated vampire bats that roost communally often rest next to the same neighbors every night and sometimes regurgitate meals of blood to their hungry neighbors.How can you explain this apparent act of altruism?80