Macroevolution Test 3

Describe macroevolutionary trends

Directional evolutionary changes over long periods of time

• Not single species lineages, mostly clade scale (large scale patterns)

Describe how to identify a macroevolutionary trend

• need to look at the whole distribution

• in order for it to be an actual trend, we need to see an actual change in the mean, not just the variance

What is a trend

some mean change in phenotype

Describe the island rule

• large organisms on islands tend to become smaller

• opposite happens with small organisms on islands (become bigger)

List and describe the scope macroevolutionary trends can take 

• Geographic scope

  • Many trends are based on shifts based on global scale

  • eg. mainland to island, latitude, etc.

• Phylogenetic scope

  • eg. on a clade scale

• Temporal scope

  • over a few mya, or entire periods

List and describe the two kinds of trend dynamics

• passive

  • heterogeneity, bias towards 1 direction but there are conflicting directions

• Driven

  • homogeneity, arises with similar evolutionary trajectories for every clade

True or false: the different kinds of trend dynamics ALWAYS result in different outcomes

False. They can result in the same outcome (eg. body size)

True or false: Passive trend dynamics doesn’t mean neutral

False. Trend dynamic doesn’t indicate causation

How can we distinguish passive versus driven evolutionary trends? Describe each.

• based on an increase of mode or minimum

  • take samples from different times

    • judge difference in values

  • Skewed distribution with passive; more normal distribution with driven bc the entire clade is evolving in the same direction

• Subclade test

  • driven distribution of traits for subclade will be similar to whole clade

  • passive distribution of clade will be less similar to clade

List within species causes of macroevolutionary trends

• Driven natural selection

• Driven constraints

• Passive natural selection

• Passive constraints

describe driven selection as a within species cause of macroevolutionary trends

• usually just looking at patterns; need to be wary of prescribing wrong cause to the effect

describe driven constraints as a within species cause of macroevolutionary trends

• requires a directional change in the intrinsic production of variation

  • bias in the production of variation

  • may have genetic or developmental bias! NOT just based on environmental selection

describe passive natural selection as a within species cause of macroevolutionary trends

The enforcement of a boundary on one side

describe passive constraints as a within species cause of macroevolutionary trends

• A lot of values just simply cannot be smaller than 0

  • this creates limits to production of variation > proceeds in other direction, away from hard boundary

Describe the difference between a boundary and a constraint

• if a variant cant be produced at all, its a constraint

• if the variation cant be passed to the next generation, then its a boundary

What is the key distinction between trends caused by natural selection versus constraint?

• you cant tell just by just looking at pattern alone!

  • need to know something about variation and selection

List the among species causes of macroevolutionary trends

• directional speciation

• differential speciation rate

• differential extinction rate

• selective mass extinction

Describe directional speciation as an among species cause of macroevolutionary trends

• bias in production of new species \

• branching lineage has more value

• sort of like constraint

• biased production of species

Describe differential speciation rate as an among species cause of macroevolutionary trends

• higher speciation rate in one direction, or lower extinction rate

• biased on variation being produced

List the ways we test for the phylogenetic signatures of macroevolutionary trends

• Quantify change in fossil record

• Test for phylogenetic signatures of trends

Describe how we quantify changes in macroevolutionary trends in the fossil record

• directly measure morphology in fossils from individual lineages

• plot morphology against time

• Test whether model trend explains data

  • model in which mean is changing over time

Describe how we test for the phylogenetic signatures of macroevolutionary trends

• for discrete traits, test for evidence of biased character transition rates

  • are state changes biased in one direction than the other in the character

  • Is there a trend one way or another?

    • score all species > fit model . score likelihood in all transitions

• For continuous traits:

• Collect data for living AND EXTINCT data

  • cant just collect from living species (for most part)

• Obtain phylogeny for species

• Assess the fit of trend model of trait evolution

  • Trend model is just brownian motion model in which random walk is based on direction

  • mu is directional bias per unit time

What is complexity

an increasing function of the number of types of parts or interactions a system has

What is Cope’s rule?

evolutionary lineages increase in body size over time

What might be the benefit to a lineage increasing in body size over time?

• better capture prey, avoid predators

• increased reproductive success (sexual selection)

• Increased intelligence (bigger brains)

• increased variety of available food

• decreased mortality risk

• increased longevity

• increased heat retention

Describe Dollo’s Law

• organism never returns exactly to former state, even if it finds itself in exact same conditions- always keeps some trace of intermediate evolutionary stages

• evolution doesn’t revert back along the same sequence

  • more of a probabilistic statement

  • reflects historical constraint- evolution is path dependent

  • expresses a directional trend, not absolute (can be violated sometimes)

  • often invoked to explain the failure of complex traits to “re evolve” once lost

List and describe the mechanisms behind Dollo’s Law

• Genetic decay

  • genes for lost traits accumulate disabling mutations or are deleted (eg.. enamel genes in edentulous vertebrates)

  • genes become silenced

  • “undefended target” for mutations

• Developmental rewiring

  • once pathways are dismantled, re assembly is improbable

  • developmental basis may be rewired and therefore lost

  • also “undefended target”

• Functional replacement

  • other traits evolve to take over the same role (some other solution)

Provide an example of Dollo’s Law

• loss of teeth in numerous lineages of vertebrates

  • turtles

  • birds

  • baleen whales, pangolins, anteaters

• teeth never re evolve in these lineages

Describe an exception to Dollo’s law

• a complex trait can re evolve long after it was lost if genetic potential remains

• Gastrotheca guentheri re evolved teeth after 200 mya absence

• still had teeth on upper jaw, so possible heterotrophy

  • gene for upper jaw teeth re adapted for teeth on lower jaw, too?

• Re evolution more likely if homologs are present somewhere else in body?

What obstacles might prevent organisms from finding, consuming, or defending resources?

• competition

• predation

• food defense (prey defending itself from you)

Describe tempo in evolution

the rate of evolutionary change through time

Describe mode in evolution

the model by which evolutionary processes result in evolutionary pattern

• the pattern we expect to come from a particular model

Briefly describe how we measure the rate of trait evolution, and what we need to take into account when we do this

• usually not possible to directly measure instantaneous rate of evolution, measure net rate instead

  • easy to get from fossil record

• However, net rate assumes that evolution is linear, when we want proportional measurements instead

• To account for this, we log transform measurements so that they are reflective of whats actually happening

Describe the H (haldane)