evo bio exam 3

altruism

fitness gain for recipient, cost for actor

macaws

example of selfishness

cane toad cannibalism

evolutionary explanations for altruism

kin selection

reciprocity

mutualism

manipulation

what did William Hamilton develop?

genetic model showing how allele for altruistic behavior could persist

example of reciprocal altruism

blood sharing in vamp bats

how is mutualism diff from reciprocity

due to lack of time lag between exchange of benefits

naked mole rats

• live underground in huge nests in africa

• 70-80 member colonies

• hairless, ectothermic, digest cellulose

• eusocial

  • single queen

  • 2-3 reproductive males

  • workers are male and females

  • first they tend young

  • later excavate tunnels

  • oldest defend nest

why are naked mole rats eusocial?

highly inbred so average r for siblings is 0.81, highest coefficient of relatedness ever recorded in mammals

what is life history analysis

• branch of evo bio that tries to sort out reproductive strategies

• perfect organism would mature at birth, produce many high quality offspring, and live forever but this is impossible because tradeoffs in time, size of offspring, and parental investment

why do organisms age and die?

• senescence: late life decline of fertility and probability of survival

• aging reduces individuals fitness and should be opposed by natural selection

what is the rate of living hypothesis?

• senescence caused by accumulation of irreparable damage to cells and tissues caused by errors during replication, transcription, translation, and accumulation of poison metabolic byproducts

• populations lack genetic variation to enable more effective repair mechanisms

• 2 predictions of this hypothesis

  • aging rate should be correlated to metabolic rate

  • species shouldn’t be able to evolve longer life spans

• Austad and Fischer tested first prediction and found great variation in energy expenditure between mammals

  • bats expend 3 times energy of other mammals their size

• Luckinbill tested second prediction by artificially selecting for longevity in fruit flies and increased life span from 35 days 60 days, these fruit flies had lower metabolic rates during first 15 days of life

• both predictions not supported by examination

why doesn’t natural selection activate telomerase to add more telomeres?

• could be tradeoff between extending cell life and proliferating cancer

• p53 is gene that causes cell senescence, p53 deficiency causes cancer susceptibility, tradeoff between cancer risk and aging

evolutionary hypothesis of aging

• aging not caused by damage itself but failure to repair damage, damage not repaired bc deleterious mutations or tradeoffs between repair and reproduction

• reproduce so much early that early death not selected against

• mutation devotes less to repair and more to reproduction

natural experiment in aging

• high adult mortality rates should lead to earlier maturation

senescence

late life decline of fertility and probability of survival

David Lack’s hypothesis

• selection will favor clutch size that produces most surviving offspring

• when researchers added eggs to nests, survival of all chicks decreased

• number of surviving offspring reaches max at intermediate clutch sizes

• Boyce and Perrins tested hypotheses in long term great tit study and was not consistent w Lack’s hypothesis

• although is appears to be too simple to accurately predict clutch size, it serves as valuable null model

Assumptions of Lack’s hypothesis

1. no tradeoff between parents reproductive effort in 1 year and survival and reproduction in the future

2. the only effect of clutch size on offspring is determining whether offspring survive

3. clutch size is fixed by a particular genotype

Lack’s hypothesis and parasitoid wasps

• wasps inject eggs into host insect and larvae eat host, pupate, and emerge

• females shift behavior in response to different hosts and lay smaller clutches than predicted by Lack’s hypothesis

• larger clutches may reduce female fitness in unknown ways or may be tradeoff in current and future reproduction and survival

• parasitoids may lay 2 clutches in succession

• while females search for host her fitness is 0

principle of allocation

• states that if organisms use energy for one function the amount of energy available for other functions is reduced

  • leads to tradeoffs between functions such as number and size of offspring

  • either have many small young or few large young

Smitch and Fretwell’s analysis

2 assumptions

1. tradeoff between size and number of offspring

2. individual offspring survival correlated to size

can only test if there is high polymorphism in offspring size in population

phenotypic plasticity in beetle egg size

• seed beetle lays eggs on various seeds and larvae burrow inside, feed, and pupate

• Fox studied seed beetle grown on acacia (good host, most larvae survive) and palo verde (poor host, less than half survive)

• females lay larger eggs on palo verde

genomic imprinting

occurs during gamete production in ovaries and testes, affects transcription in embryo

cholera case study

• 1854 cholera epidemic struck london

• John Snow made map of infected people and water pumps, 1st known epidemiological study

  • epidemiology=study of incidence, frequency, distribution, and control of infectious disease in defined populations

• 2010 outbreak in haiti

germ theory

• Louis Pasteur proposed germ theory of disease 1858

• arguably most important breakthrough in development of modern medicine

  • identified numerous pathogens

  • development of antiseptic surgery

  • discovery of antibiotics

  • improvements of sanitation

flu case study

• flue strains with novel antigenic sites will have selective advantage

  • antigenic sites: specific parts of foreign protein that immune system recognizes and remembers

• more amino acid replacements in antigenic sites vs non antigenic sites in order to increase survivability

• one study (85-96) found more silent substitutions than replacements

  • though 18 codons in hemagglutinin had more replacement than silent all being in antigenic site of protein under positive selection

• 1 survivor will be ancestor of all future flu strains and have most substitutions in 18 codons

flu evolution

• 1918: worst epidemic (50-100 mill deaths)

• isolated from 1918 victim preserved in permafrost and sequenced nucleoprotein gene (indicating host specificity)

• similar to human and pig (pigs may be vector, unsure if humans can get infected directly from birds but birds can infect pigs and pigs and humans can infect eachother)

antibiotics

• chemicals that kill bacteria by disrupting particular biochemical processes

  • antibiotics are powerful selective agent for bacteria

evidence that antibiotics select for resistant bacteria

• on small scale studies of bacterial evolution within individual

• on larger scale researchers can compare incidence of susceptible versus resistant bacterial strains among patients who are newly diagnosed versus relapsed after antibiotic treatment

• on largest scale researchers can examine relationship between fraction of patients w resistant bacteria and society wide level of antibiotic use

• antibiotic resistance may be costly for bacteria

  • may revert to sensitivity in absence of antibiotics

best defense against antibiotic resistance

• avoid letting bacterial pops evolve resistance by:

  • avoiding foodborne bacteria

  • don’t take antibiotics for viral infections

  • complete full course of antibiotic treatment

  • doctors should prescribe antibiotics that target narrowest range of species

  • doctors should isolate patients that carry bacterial strains resistant to several drugs

recent entrance hypothesis (evolution to beingness)

• pathogens only virulent when newly begun using humans as host and overtime evolve to benign coexistence

• the “perfect” pathogen does not harm host very much so pathogen can continue to live, reproduce, and be transmitted

• FALSE! not supported

  • pathogens evolve to optimal levels of virulence and may select for higher or lower depending on rate of transmission

  • new pathogens least virulent bc they haven’t adapted to hosts immune system

coincidental evolution hypothesis

• some pathogens not natural to humans, may occasionally infect humans

• ex. tetanus, legionnaires disease

• “accidental” pathogens occur but are the exception not the rule

short sighted evolution hypothesis

• traits that increase short term fitness in host may be detrimental if pathogen is too virulent to be passed on

• ex. polio, normally infects digestive tract and causes few symptoms but occasionally infects cells of nervous system w tragic consequences

transmission rate hypothesis (trade off)

• pathogens evolve virulence based on rate of transmission and easily transmittable pathogens have high virulence

• pathogens difficult to transmit must have lower virulence or will kill host before being transmitted

• ex. HIV

• tested hypothesis w bacteriophage that infects E. coli and found phages artificially transmitted faster evolved higher virulence than slowly transmitted ones

tissue evolution

• cancerous cells have new mutations and can genetically diverge quicker than healthy cells due to faster generation times

• tumors have mutated DNA compared to normal cells

• natural selection may differ between healthy vs cancerous cells

covid

• SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2)

  • CO stands for corona

  • VI stands for virus

  • D stands for disease

  • 19 is 1st year of outbreak

• emerged in wuhan, china

• cause mild to moderate upper respiratory tract illnesses, like common cold

• mostly circulates among pigs, camels, bats, and cats, but occasionally humans

• 4 of 7 known coronaviruses only mild to moderate but 3 new ones have emerged from animal reservoirs over past 2 decades causing widespread illness and death

• likely transmitted from bats to humans or bats to pangolin (or other mammal) to humans

• gene for spike protein has insertion of 12 nucleotides! which may help spike protein tightly bind to human cells (ACE2 human protein in respiratory airways)

benefits and drawbacks to having larger sized offspring

• benefit: offspring more likely to survive to reproductive age due to greater resource allocation

• drawback: increase resource allocation for each offspring limits total number of offspring that can be produced

3 main mechanisms underlying apparent altruism

• reciprocal altruism

• kin selection

• mutualism

• eusociality

what is a species?

• fundamental unit of evolutionary change

• all groups of individuals that send genetic migrants back and forth

• group of interbreeding populations

• group of organisms with independent evolutionary trajectory

• fundamental unit of evolutionary change

• all groups of individuals that send genetic migrants back and forth

• group of interbreeding populations

• group of organisms with independent evolutionary trajectory

which of the following transitions in energy allocation do you expect before vs after sexual maturity?

• growth, then reproduction

• metabolism, then reproduction

• growth, then repair

• growth, then metabolism

growth, then reproduction

evolutionary game theory…

• can be used to explain the evolution of altruism

• can be used to explain how cooperation can evolve in populations

• can be used in “prisoners dilemma” game to show that ESS is always to defect, even though cooperation leads to higher average payout

• can be used to explain why unrelated vampire bats would share a blood meal

• can be used to explain the evolution of altruism

• can be used to explain how cooperation can evolve in populations

• can be used in “prisoners dilemma” game to show that ESS is always to defect, even though cooperation leads to higher average payout

• can be used to explain why unrelated vampire bats would share a blood meal

in parental villages in trinidad, flynn disovered that…

• fathers had more interaction but a higher homicide rate with genetic children

• there was no significant difference in interaction or homicide rates among genetic and non-genetic children

• there was less interaction but more of it was agonistic (negative) with non-genetic children

• there was less interaction and hence less agonistic behavior with non-genetic children

• fathers had fewer interaction with genetic children but more of it was agonistic

there was less interaction but more of it was agonistic (negative) with non-genetic children

which of the following is false?

• Homo sapiens are the sole survivors of a large human radiation.

• Multiple human species have coexisted in the past.

• Earlier human species died sequentially, leading to Homo sapiens today.

• Determining phylogenies is difficult due to ancestral polymorphisms and introgression events.

• Early hominin fossils have bone structures enabling them to walk, even when the braincase was small

Earlier human species died sequentially, leading to Homo sapiens today

what is currently the earliest known hominin?

• Australopithecus africanus

• Sahelanthropus tchadensis

• Australopithecus anamensis

• Kenyanthropus platyops

• Ardipithecus ramidus

Sahelanthropus tchadensis

Which behavior results in a cost to both actor and recipient?

• cooperative

• altruistic

• selfish

• spiteful

• Ritualistic

spiteful

If the African Replacement theory were true, allele patterns should demonstrate…

greater diversity in Africa with European and Asian alleles as subsets of African alleles

Which trait would we likely see appear around the same time that language evolved?

larynx in lower throat

lactose intolerance

• lactase: enzyme that breaks down milk sugar

• only source of milk sugar is mothers milk so there is not advantage to producing lactase after weaning

• however in humans with long history of drinking cow’s milk, many have heritable ability to continue producing lactase

breast cancer

• 1 in 8 women contract in NA

• sequence similarity between mouse mammary tumor virus (MMTV) and DNA from human tissue samples

• higher incidence of cancer in regions where more mice infected w MMTV, may be caused by virus but particular alleles and environmental factors may make ppl more susceptible

fever manipulation hypothesis

fever may represent manipulation of host by pathogen, then reducing fever would probably help host combat infection

fever adaptive defense hypothesis

• fever may be adaptive defense against pathogens, then taking drugs that alleviate fever might be counterproductive to recovery

• evidence from animals suggests this is correct, study in iguanas (ectotherms) found they develop behavioral fever in response to infection w bacterium

male reed buntings

• adjust parental care effort based on who they feed

• mark flinn (1988) observed family units in rural trinidad for 6 months

  • fathers w both step and bio children spend more time and get along better w bio children

  • there is higher risk to children being killed by stepparent vs bio parent

processes that cause both micro and macroevolution

mutation

natural selection

genetic drift

migration

species concept

theoretical definition of what constitutes a species

species criterion

practical manner in which to determine what is a species

Mayr’s biological species concept

• proposed 1st formal species concept in 1942

• defined species as freely breeding population that must have reproductive isolation from all members of other species

  • does not apply to unisexual species, hybrids, isolation by distance?

• used by endangered species act

• most biologists agree it is ideal concept, it is operationally difficult to apply

morphological species concept

• aka morphospecies or typological species concept

• morphological similarity determines species membership

• problems with this are how much difference is too much, sexual dimorphism, intraspecific variation (polymorphism), cryptic species

• non scientists have been using since beginning of time

phylogenetic species concept

• proposed by Joel Cracraft in 1983

• species is smallest diagnosable cluster of individual organisms within which there is parental pattern of ancestors and descendant

  • if group is not monophyletic it is not recognized taxon and therefore not species

• in current classification many non monophyletic species

evolutionary species concept

• defined by wiley in 1978

• developed bc biological species concept could not be applied to asexual organisms or temporal sequences of species changed over geological time

• single lineage of ancestor-descendent populations of organisms which maintains its identity from other lineages and has its own evolutionary tendencies and historical fate

• based on how lineage changes over time, if distinct and stable over time then its a distinct species

other species concepts

• ecological: defined by species occupying diff adaptive zones and evolving separately

• recognition: specific mate recognition system (SMRS)

• cohesion: focuses in mechanisms that maintain genetic and phenotypic identity

• De Queiroz (1998) attempted to synthesize all concept showing how they are not so diff from eachother

steps of speciation

• population isolation

  • migration-selection balance of water snakes in Lake Erie, populations did not diverge into banded and plain forms bc migration kept gene flow active

  • if snakes prevented from immigrating to island 2 forms might diverge into separate species by selection, mutation, drift

• divergence of phenotypes and genotypes

• reproductive isolation

allopatric speciation

• model of Ernyst Mayr

• populations separated by physical barrier and diverge

• considered most common speciation mechanism

• vicariance=new barrier to gene flow arises (mountain range or river)

• evidence- regions w many barriers typically have more species than regions w fewer

peripatric speciation

• peripheral selection of population breaks off to form distinct population

• genetic drift may cause initial changes in allele frequencies, then selection may act to further diverge colony from parent population

• hawaiian fruit flies case study

  • 850 species

  • geographic isolation through dispersal, founder hypothesis of speciation when founder flies inhabited western island and emigrates east as other islands arose

  • predicted related species will occupy adjacent islands, used mtDNA to estimate pylogeny and founder hypothesis supported

parapatric speciation

• populations diverge over environmental gradient

• evolution of reproductive isolation between populations so there is substantial movement of individuals and genes between them

• generally hybrid zone may form

sympatric speciation

• populations diverge in same area, may inhabit diff microhabitats

• amongst most controversial subjects in evo bio

• can occur via polyploidy (organism possesses more than 2 complete sets of chromosomes) or disruptive selection (extreme phenotypes favored over intermediate leading to increased diversity in population)

• natural selection may be more important than drift

• apple and hawthorn maggot flies

  • have identical body forms, eat diff foods due to natural selection, have diff seasonal activity periods

  • live in sympatry on adjacent trees, recently diverged bc apples not native to US

  • separated in time by pupating at diff times of year they maintain distinct populations even w gene flow bc strong natural selection

what causes divergence?

• mutation

• drift

• selection

• NOT inbreeding (this changes genotype frequencies not allele)

• NOT migration (populations must be isolated to evolve as independent units)

mechanisms of isolation

• changes in chromosome number

  • polyploidization can create barriers to gene flow that are not geographic

  • very important mechanism of isolation in plants, much less common in animals

mechanisms of divergence

• genetic drift and natural selection act on mutations in isolated populations

• drift most important in small populations and may occur rapidly due to bottlenecking

• sexual selection

  • major source of pre-zygotic isolation

Hawaiian drosophila

• elaborate courtship behaviors and secondary sexual chracteristics

• males meet in leks and fight to attract females with their bizarre head shapes

• D. heteroneura have hammerheads and butt heads during fight

• D. silvestris have heads just like females and grapple during fights

prezygotic vs postzygotic barriers

• prezygotic isolating mechanisms prevent fertilization

  • mate choice, time of breeding, genetic compatibility

  • geographic or ecological

• postzygotic offspring are sterile or have lower viability

reinforcement hypothesis

• formulated by Theodosius Dobzhansky ab 3rd stage of speciation

• predicts pre mating isolation (reproductive barriers that prevent different species from mating or successfully fertilizing) will evolve in species in secondary contact (previously isolated populations of species come back into contact potentially leading to gene flow, hybridization, and various evolutionary outcomes)

hybridization

hybrids should have reduced fitness by reinforcement hypothesis but some have normal or increased fitness

sagebrush case study

found that hybrids have superior fitness in transitional habitats

2 bushes like diff elevations, hybrid zone on mountain

hybrid zone outcomes

• stable persistence

  • hybrid zones may persist indefinitely w selection maintaining steep clines at some loci

• reproductive isolation

  • selection may favor alleles that enhance prezygotic isolation, resulting ultimately in full reproductive isolation

• fusion

  • alleles that improve fitness of hybrids may increase in frequency. in extreme cases the postzygotic barriers to gene exchange would break down and 2 populations would become 1 species

• new species

  • in at least part of hybrid zone the hybrids could evolve reproductive isolation from parent forms and become 3rd species

Haldane’s rule

pattern of sterility is in heterogametic sex regardless of male or female

steps of speciation

1. population isolation

2. divergence of traits and genes

3. reproductive isolation in secondary contact

who are our closest relatives?

Pongo pygmaeus (orangutan), Gorilla gorilla (gorilla), Pan troglodytes (standard chimpanzee), and Pan paniscus (bonobo)

• evidence that gorillas are closest are molecular analyses placing humans and gorillas as sister taxa

• evidence for chimps as closest based on rate of change in dozens of protein sequences human/chimp most likely

  • test of 14 independent genes, 11 showed humans and chimps together, 2 showed gorillas and chimps, 1 showed humans and gorillas

introgression

stable integration of genetic material from 1 species into another through repeated back crossing

when did humans and chimps last share common ancestor?

6-7 Mya

walked on knuckles, ate mostly fruit, lived in many habitats, had complex social groups, and made tools

hominids

• Sahelanthropus tchadensis: earliest known hominid, 6-7 million yrs old

• Australopithecines: earliest humans w 2 main body forms, robust (big jaws and teeth) and gracile(more similar to modern human), bipedal like modern humans, short w small brain cases

homo

• Homo habilis: 1st homo, large brain cases, smaller teeth, and taller

• Homo erectus: 1st to leave africa (longest reign), look like humans bodywise

• Homo neanderthalensis: may be our ancestor or sister species

• Homo sapiens: modern humans, appeared ~100,000 years ago