Macro evolution Flashcards
Change in perspective
Move to How does evolution pay out on grand time scales
- Not within popultion
- How do evolutionary porcesses scale up to long term change we see in fossil records
***Taking our understanding of mechansims of evolution to see if they explain patterns of larger change through time
Evolution as an on-going process
Evolution is an ongoing process –> see change in allele frequencey from one generation to next BUT now what happens when scale up 3 billion years
We are going to turn to how the mechansims of evolution have played out in the long run
- Is there meaningful distiction between micro and macro evolution
Micro vs. macro evolution
Micro –> evolution process within popultion
Macro –> patterns of change above species level
Micro –> macro – is this just allele frequencey change – can we look based on popultion genetics or do other factors come into play
Speciation + micro/macro evolution
Interface between micro and macro evolution (during speciation within species variation is converted to variation between species by our basic microevolutionary forces) – in this sense macroevolutionary change is just scaled up microevolutionary change BUT the vast time scale may add some important factors that are worth considering
- If Micro evolution is population genetic changes within populations and macroevolution involves patterns of change above the species level then speciation is the link between the two
Link = derived from mechanisms of evolution point of view – maybe can just extend mechanisms trhough time
Macroevolution
Large evolutionary change, usually in morphology, typically refers to the evolution of differences among populations that would warrant their placement in different higher-level taxa (beyond species)
Questions in unit
- Do we see trends NS favoring phenotypic change through time? Are certain directions of phenotypic change favored in the long run?
- Some level of predictability in process
- How might researchers see if reason is because SN is favoring rather than passive?
- What are the patterns of biological diversity through time? Consider both that diversity as a whole and the composition of that diversity by different major clades and their change through time.
- Increase or decrease diversity
- Process to drive turnover in biodiveristy
Determine trends of evolutionary change
Can extend gould’s wall of complexity –> complexity increases even if NS does not tend to favor complexity
- Just need limit on one end –> since have limit = distribution only goes one way –> means the average only goes one way because have limit
Before = discussed with complexity BUT we can apply to many phenotypes
Example - can apply to morphology or chemical reactions that are passive or NS favoring outcomes
Application of Goulds left wall
Example – body size
Apparent direction bias through time = Cope’s Rule –> body size increases through evolutionary time (larger organisms derived from smaller) = increase body size favored by NS
2 Hypothesis for increase in body size through time:
1. Conform to cope –> was small and have consistent favor in increase in body size
2, Gould –> have minimum threshold to how small –> pasisve chnage but in end increas ein trait value
Charts:
Left = NS favored
Right = Passive –> mimimum thrshold for how small can be that set wall to allow passove provess to increase trait value through time
Directions vs. Biased changes
Whether apparent directional patterns in evolution are the result of biases in directional selection or passive processes with constraint can be difficult to parse apart
- Try to parse out if apparent trend is driven by NS or passive process
Cope’s rule
Observation that body size appears to increase in lineages through time
2 hypothesis for change in body size predictions
These two hypotheses make specific predictions for how phenotypic change plays out:
- In driven trends both ends of the distribution change in the same direction through time (in passive trends the minimum remain unaltered) vs. passive where only one end of the distubution changes through time
First prediction about body size
In driven trends both ends of the distribution change in the same direction through time (in passive trends the minimum remain unaltered) vs. passive where only one end of the distribution changes through time
Left image = passive – can’t be smaller = through time trait value increases – Does so in passive manner
- Increase maximum
- Mean Trait value increase through time because max changes but the minimum stays the same
Right = Increase maximum and minimum through time –> shift on both sides = NS favoring dorection of change
- Entire distribution moves –> not only stretch ax – change both ends
Scaling Mechanisms of evolution
Some mechanisms (selection + migration) are deterministic –> can we predict across time y scaling up mechanisms or do other factors that some into play that make it more difficult
Are the dP equations enough to explain macroevolution
Body size example
Do we see NS favoring outcomes that let us infer inevitability about patterns of change
- Active vs. Increase in trait value based on passive trend
Cope = observed that large body organisms evoloved from smaller ancestors –> see tendency towards large body size
Cope could be true or could just be passive process
Inevitability of large from small
Larger organisms evolve form smaller because the largest organisms are necessarily larger than ancestors smaller than them
This observation is not sufficient to know this is a driven trend where NS favors large
Evidence for NS favoring Trait value
Change in bounds of distrubution = evidence NS favors Trait value
2nd hypothesis about passive vs. active
In Passive trends apparent driven pattern on the whole clade is built from even distributions of change within clades
- Entire phylogeny looks like decedents have larger trait value BUT how is it in the different components of the phylogeny
Looking at second hypothesis of Passive vs. Active
Image – Across phylogeny not one phylogeny does it match or is it equally likley to go both ways
Through time look at size of circle –> see large at end compared to when starts –> seems to confrom to Cope = favored by NS
BUT lookiing at subclaves across phylogeny = see increase TV BUT the increase is because of ONE change in one branch = only happened once
- Just had change once in phylogeny = Trait value chnage in the end BUT it is not favored in across lineage – just happend once
Curve showing second prediction of favored vs. passive
A and C = not chnaging and B changes –> change in one in common ancestor and then body size chnage in random way
A driven trend would have to be across subclaves
- B – larger in that subclave and A and C would also have to get larger in subclaves rather than just a chnage in one branch from smaller to larger
3rd prediction in Passive vs. Active
In driven trends individual ancestor descendents changes are biased in one directions
***Not the case in passive
Example – Diansours –> look at invidious change in body size across phylogeny and see if there is pattern change in particular direction
- Examine direction of trait evolution along indiviual lineages
See green is harger and red is snaller – see if randomly distrubuted in either driection
For driven – 8/12 lareger – trend to increase = biased in direction of evolution
For passive – trait change can be even number of increase of decrease but might have one big shift that chnages the mean across phylogeny
Null model
Passive trends are essentially the null model
Paleontologists are generally reluctant to assign patterns to driven trends without substantial corroborating evidence from multiple lines
- Are this way becasue know that paaasice can occur = high threshold to sat trait is due to favore by NS
- One prediction might not be enough = look for more lines of evidence to back hypothesis
Driven trends in fossil record
There are some definte driven trends observed in the fossil record
Example:
1. Body size being favored in horses (body size increases) – in horses have a trend in body size but other aspects of horse evolution that is driven such as specialization of digits (run on middle finger – 5 –> 3 –> 1)
- Seems to be across lineages –> driven NS favoring outcome in lineages
- Simplification of skulls in mammals
- Most mammalian reptiles Jaw joining is complex
- Through time complex reduces and some bones evolved in flexible jaw to become inner ear bones
- Process of simplification = driven change –> have many lineages favored by NS
- Solid Jaw + auditory bone for hearing = favored acriss ancestors
Seeing interactions in fossil record
Co-evolution – can’t see in fossil record to see specialized interactions (hard to see interactions)
BUT can see interactions we know today and can assume they went on in the pat
Example - long term co-evolutionary trend
Running mammals vs. Ungulates
Can understand how they interact today –> assume past interaction
Look at interactions – what dictates outciome of hunts = median term speed of predator and prey –> who wins in rates dictates outcome of interactoon
Can look at anatomy that correlates with speed and apply undersatdning to morohs in fossil and see how fast running speed over time
They went through fossils – looking at features coreelating to running speed
Reults: 3 clades of predator mammal that exists through time period
- #1 trait that correlatd with speed = metatarsal femur index
- Can see driven trend for speed in ungelates= ungelates min and max change through time – mives together –> ungelates = faster not just few are faster ALL are –> many are faster now
- Predators –> don’t show driven trend – speed is passiove - some are fatser but the minimum is not changing
Explaining co-evolutinoary. change
Overall: Outcome of capture deopends on footseed –> NS is string in prey but not in predator
3 options for why this might be the case:
1. Trophic structure and demographics
2. Stronger tradeoffs for predators
3. Selection on predators maybe weaker
Option #1 for co-evolutionary change
Overall: Trophic structure and demographics
Trophic structure – always have smaller amount of predator than prey
Looked at effective popultion size – predator smaller popultion size = weaker selection AND higher drift + get lower number of new mutations
- Prey = more indiviuals getting mutations = more mutations for faster in prey + NS is stringer in prey than the smaller predator (predator also has more dirft)
Option 2 for co-evolution outcome
Overall: Stronger tradeoffs for predators
Tradeoff is compenent of speed or can be limited on degree of how speciated fir speed
- Traits conbtrollubg limb developemnt
Tradeoff - example of Antagonistic pleitropy – gene for limb might increase soeed but might decrease other asoect of fitness
Option #3 for co-evolution
Overall: Selection on predators may be weaker
Prey killed –> predator can take advatantge of weaker in prey = this might be less consequence
Can look At functional repsinse curve
- If mean popultion fitness of prey increases = popultion density increase 00 as prey density invcreases = capture rate increases because more individuals to capture = predator might not need to adapt because more prey to begin with
Fuynctional response curve
Density of prey vs. Number of prey consumed
All explination for change in co-evolution
Pattern of evolution changes over time BUT all are explained by rooting in mechanisms of evolution in ecological context
- Same mechanisms occuring today
Constraint of NS or ecological interaction that shape strength of NS
Million years that change but by our mechanism of evolution –> Analyze large patterns and see from lense of mechanisms of evolution
Questions on Patterns of diversity through time
How has biodiversity changed over the history if life?
Are there patterns of diversity that indicative of macroevolutionary phenomama?
Potential trends of diverity
Has diversity been increasing
OR – did it saturate early (low then increase then plataue – stable through time)
Second question about diversity
Has taxonomic composition of diversity changed or did diversity stay constant?
Does the diversity stay constant or does change in composition if diversity come from moving alteration to diversity as a whole
OR were taxonomic changes associated with major changes in diversity?
What drives patterns of diversification
Patterns of diversification are driven by the balance between speciation rate (alpha) and the extiction rate of lineages
Pattern of diversification = result of two parameters acting against each other:
1. Speciation rate –> create new lineages
2. Extiction rate
Net result that drives pattern of biodiverity
Looking at patterns of biodiverity
People look at pattern of diveristy through time but looking fossilo reocord – specifcially lookung at marine organisms (mollusks) with hard shells because they fossilize a lot (good record)
Sedimentary rock form marine envirnment – have record of organisms that live there – see fossil record to see how diverity changes through time
Patterns of diversity over time
Family level diversity in marinbe invertabrete fauna through the phanerozoic era
Results: Doveristy has clearly chnaged through time + the diverity of that diverity has changed (rare groups become more abdundant and visa versa)
PLOT – shows diverity change through time
- Increase in diverity thorugh time then short decrease then increase through Parts of fossil
- Types of diverity change over time –> repaltive abundence shifts over time
- Have turnover in composition of diverity through time
Exitiction
We think about exitiction as this unnaturak thing that humans on biodiverity
Example – humans drive species to extivction through hunting
- We think about it from negeitive way that hurts the natural order
BUT doesn’t mean that how exoection operates in every case
Exiction = natural part of evolutionary processes –> understanding varaution in rate of extiction through time assumes that there is varaition in rate
- Use fossil record data to undersatnd varaition in backgroun exitction rates in ecosystems
Diverity is net result of
Diversity is net result of speciation and extinction
***Patterns of extinction are crucial to understanding macroevolutionary patterns
Background extiction
Normal rates of extinction are referred to as “Background extiction”
Plot of extcition rates through time
Shows spikes that appear at the junctions of many geologoc periods
- Plot = looks at genera –> very dramatic
- Shows 5 major mass exictions events that are statsitical anomlies
- Spikes = associated with shifts in composition of biodiverity –> see change in levels of diveristy and in what makes up the diversity
5 spikes were associated (not just identifiable shifts in fauana but ALSO have major restructuring of the biosphere)
***Have profound changes at the genus level
- 85% of gernera lost in one and 96% of genera lost in other – profound change in biodiveristy
Were people destined to take over
People think that mammals were detsined to take over the world BUT this is not the case that we would just outcompete over time
Image – Ecological competition of mamals vs. dinasours – can see what it would look like if outcompete iver time
- Can see that as mammals expand the diansours are driven to extiction
Reality = this is not what we see
Expected pattern of change
If evolution is a gradual process = we might expect to see pattern of change through time like image
IMAGE
X - Axis -= change in trait
Y - Axis = time/diverisfication
Have slanted lines –> gradual shift as linage diverge
- See Morphology changing gradually as lineages diverse
BUT this is not what we see
What do we see in the fossil record
IMAGE
1. Lineages stay the same through time and have no trends in one directions
2. Change in fossils is accompanied by speciation events
- Morphological change associated with new lineages occur very abruptly in geologic time and then remian constant within lineages for long stretches of time
What would PE look like in Fossil record
See something like image –> miss the change because it happens rapidly in a small popultion far away (in popultion that split)
Seems like population pop out of nowhere because its from peripatric speciation
