Evolution Final Exam

What is a cryptic species?

A species that looks very similar to another one

What is the biological species definiton?

a group of actually or potentially interbreeding populations, which are reproductively isolated from other such groups

What are the problems with the biological species concept?

• Asexual organisms (protists, fungi, bananas)

• Extinct organisms

• Must revert to morphology

• Ambiguous situations in nature

What is the phylogenetic species concept?

Species are the smallest possible group descending from a common ancestor and recognizable by unique, derived traits

General Lineage Species Concept

Species are metapopulations that exchange alleles frequently enough to comprise the same gene pool

What are the barriers to gene flow?

• prezygotic barriers

• postzygotic barriers

What are the different prezygotic barriers?

• ecological isolation (timing, habitat)

• behavioral isolation (species specific signals or mating rituals)

• mechanical isolation (anatomical)

• gametic isolation (sperm survivorship in females, molecules on egg coats)

• copulatory behavioral isolation

What are the different postzygotic barriers?

• Intrinsic: hybrid fitness is low independent of environment (hybrid viability or fertility is reduced)

• Extrinsic – hybrid fitness depends on context (ecological inviability, behavioral sterility)

What is hybrid breakdown?

First generation viable and fertile, next generation is feeble or sterile

Why does genetic divergence happen in humans after the land bridge goes away?

Genetic drift, natural selection, sexual selection

What is reinforcement?

The increase in reproductive isolation between populations through selection against hybrids

Why will lions and tigers breed?

Decision rule: “ok to mate with large, chunky big cat”

• lack of reinforcement

What is Allopatric speciation?

speciation that occurs when the initial block to gene flow is a geographical barrier that physically isolates the population

What are the two types of allopatric speciation and what do they mean?

• Vicariance: divergence of two large populations

• Peripatric: divergence of a small population from a large ancestral population

What are the 2 processes that cause allopatric speciation?

• geological processes

• dispersal into a new area

impact of barriers and likelihood of long-distance dispersal are dependent on what

mobility of species

What is sympatric speciation?

Reproductive isolation evolves without geographic isolation

What are the mechanisms of sympatric speciation?

• Disruptive Selection (Ecological Speciation) w/ Sexual Selection

  • Individuals begin to mate nonrandomly, i.e,. Mate more often with those that are genetically or phenotypically closest to themselves.

• Polyploidy

  • Polyploid populations are reproductively isolated by postzygotic barriers from their diploid progenitors

What is an allopolyploid?

A polyploid derivative of a diploid hybrid between two species

What is parapatric speciation?

Evolution of new species within a spatially extended population that still has some gene flow

• Isolation by distance & ecological adaptation

How much change is required for speciation?

No generalities can be made about genetic distance, but it’s Few loci if involved in reproduction; many otherwise

Why is there huge variation in speciation?

• Drift vs. selection

• Ecological selection vs. sexual selection

• With or without reinforcement

• Underlying genetic variation

• Polyploidy & hybridization vs. gradual change

Why is the phylogenetic species concept difficult when it comes to microbes?

Some can share 99% of DNA but still be considered different species because they do different things while others are considered the same thing and are only 3% similar. Horizontal gene transfer very frequent.

What is the stable ecotype model?

When lineages of microbes adapt to a particular ecological niche – one that is distinct from the niche of other lineages, it is appropriate to call them a species

What are some macroevoltuion questions?

• How does geography relate to Evolution?

• Why do some places have more species than others?

• Why are some clades more specious than others?

• What causes species radiations?

• What causes mass extinctions?

Definition of Macroevolution

Evolution occurring above the species level, including the origination, diversification, and extinction of species over long periods of evolutionary time

What explains the current distribution of marsupials?

Extinction, dispersal, and vicariance

Population size equation

Population size (Nt+1) = Nt + (births + immigration) – (deaths + emigration)

What is the species diversity equation? locally and globally

local: Diversity (Dt+1) = Dt + (origination + immigration) – (extinction + emigration)

global: Diversity (Dt+1) = Dt + origination – extinction

What is turnover

• The disappearance of some species and their replacement by others

• Turnover rate is the number of species eliminated and replaced per unit

  time.

What is standing diversity

Number of taxonomic units present in a particular area at a given time.

Overall standing diversity can increase when

1. origination increases

2. extinction decreases

Anagenesis

wholesale transformation of a lineage from one form to another

• An alternative to splitting lineage or speciation

Punctuated equilibria

periods of stasis punctuated by brief periods of rapid change

• Often associated with speciation events

Gradualism

Slow, gradual morphological changes over time

• Can include speciation events; traditional view

What are the two possible scenarios for incomplete fossil records

1. gradual morphological change with no speciation

2. rapid speciation and morphological change

What causes alpha (origination rate) to eclipse omega (extinction rate)

• lack of competition (loss of clade, new colonization of habitat)

• key innovation (transforms how organisms interact with their environment

Overall biodiversity can decrease when

1. origination decreases

2. extinction increases

Coevolution

Reciprocal evolutionary change between ecologically intimate species, driven by natural selection

Prerequisites of coevolution

• Heritable variation in traits relevant to interactions

• Reciprocal selection

What is required for reciprocal selection?

• Variation in response between populations of the 2 species

  • Population size, mutation, genetic variation, pleiotropy

  • Type of selection (directional vs. frequency dependent)

  • Type of interactions (mutualistic vs. antagonistic)

• Variation in # of partners in the interaction

what does reciprocal selection result in

geographic variation

Geographic mosaic theory of coevolution

• Variation in type of selection

• Variation in strength of selection

• Variation in evolved response to selection

What is coevolution “Red Queen”

Lots of parasites on the common host genotype → Common host genotype becomes rare, other host genotypes get advantage due to higher fitness, parasite is selected for differently → The rare host genotype becomes common, parasites that live on the new common host genotype will have higher fitness

What is the coevolutionary arms race

Interactions in which antagonistic players get caught in an escalation of ever-increasing abilities

Prey evolves a defense against predation → Predator responds evolutionarily to counteract the defense

(Fitness costs are typically higher for prey than for predators)

What is needed for a coevolutionary arms-race to occur?

• Both predator & prey species exert strong selective pressures on each other (reciprocal selection). hot spots (matched abilities) vs. cold spots (mismatched abilities)

• Genetic variation in prey & predator traits

Why can a coevolutionary arms race not occur even when there’s genetic variation in prey and predator traits and both species exert strong selective pressures on each other?

because of interactions with other species, energetic costs of production of traits, & abiotic factors

Snakes can quickly evolve strong resistance to the newts, whereas it is harder for the newts to evolve a more potent toxin. Why?

Because there’s trade-offs for newts (like less offspring)

The myxoma virus becoming less viral to spread more easily in Australian rabbits was an example of what

Attenuated coevolution (decelerated arms race)

What reinforces mutualistic relationships

positive frequency dependent selection

Mullerian mimicry

several harmful or distasteful species resemble each other in appearance facilitating the learned avoidance by predators, mutualistic (if too many batesian mimic happen, mutualism will collapse)

Batesian mimicry

Not mutualistic, one non non harmful species mimicing a harmful one, cheating

True or false, mutualism can become antagonisms

True, if one cheats, the other will punish

What questions do you ask when comparing phylogenies of several groups to test and reconstruct coevolution

• Do the phylogenies match?

• Have the two groups evolved and speciated in parallel?

Why does HIV evolve quickly?

• short generation time

• horizontal gene transfer

• high mutation rates

What is virulence?

How sick a disease makes you, severity of symptoms averaged over time

What type of diseases (generally) have high virulence?

Vector-borne diseases (Malaria, Rabies, Plague)

What what the example given of a highly virulent disease that isn’t vector-borne and why is it highly virulent?

Ebola because it’s young, we haven’t evolved together yet

What type of diseases have medium virulence?

air-borne (COVID, Flu, SARS, Tuberculosis, leprosy)

What type of diseases have low virulence?

STDs/ fluid-borne (HIV, Chlamydia, Gonorrhea, HPV, Herpes)

What was the exception to lower virulent diseases all being spread through contact and why?

Lyme’s (not sure why but maybe because it’s been around so long so it’s been able to evolve to not kill us)

In hospitals, ___-borne diseases become ___-borne diseases

contact, vector (doctors acting like the vector)

Why do we age?

Accidents, better to have children early because the chance of survival decrease over time

How can we answer the question: Is it inevitable that we age?

• look at all organisms- they age on different timelines

• we evolved to age this way

Is aging inevitable?

No

Why are vector-borne disease more virulent?

Because they don’t need any contact between hosts to spread, for example with malaria a person stays in one spot, gets infected, and the mosquito can bring it to another host

Primate defining features

• opposable thumbs and/or big toes

• acute vision

• large, complex brain

• prolonged pre- and postnasal development

Ape defining feature

shoulder structure that allows full rotation of arm

Human defining features

• extremely large brains

• bipedalism

• long thumb that enables precision grip

• complex tool making and use

• very long lifespan, period of development

When are homo sapiens believed to have first appeared?

• Cranio-skeletal evidence from 300-200ka

• DNA estimates ~350ka at the earliest; consistent with known fossil record

Burdens of bipedalism

• Neck pain

  ● Rotator cuff injuries

  ● Vertebral fractures

  ● Spondylolysis

  ● Obstetric problems

  ● Broken hip

  ● Torn knee ligaments

  ● Shin splints

  ● Flat feet

What are the trade-offs with bipedalism and giving birth

• hips not wide enough for baby head, mother holds the baby as long as possible and gives birth before head gets too big

• baby develops for next year, high investment from mother

• lactation is most energetically demanding part of females life

First evidence for anatomically modern humans

150-190kya

Where were the deepest splits between humans

sub-saharan Africa

True or false: Non-Africans have lower diversity

true

All non-Africans have __ Neanderthal ancestry

~2%

European DNA has how many ancestry compenents

3 or more

True or false: Asia had at least 2 early waves of migration

True

When were humans first present in Oceania

47.5–55 kya

The basal American branch was geographically isolated __

early, then complex pattern of isolation, admixture varying by group

Summary of peopling of the world

• Dispersed out of Africa repeatedly before 100ka but appear to have

gone locally extinct

● First permanent dispersal out of Africa ~70 ka

● Rapid movement into Asia, Europe, and

Australasia

○ Arrival in Americas: 30-25 ka?

○ Pacific migrations: from Taiwan ~2000 BCE, reach

Hawaii 900 CE, Rapanui (Easter Island) 1000 CE,

New Zealand 1200 CE

Summary of human population growth

7500 BCE – first permanent settlements based on agriculture become common

4000-2000 BCE – ‘cities’ develop

Slow but steady population growth until...

Population explosion during industrialization

What is an example of a medical consequence of our introgression with neanderthals

• Genomic variants associated with severe COVID-19 often originate in Neandertals

• better altitude adaptation associated with Denisovan-like DNA