lecture 11: macroevolution

what is macroevolution

the study of evolutionary process and patterns among species

How macroevolutionary biologists are able to make inferences about large scale evolution processes

1. Fossil record (for orgs that fossilize well). Direct info about past life (paleontology). Age of fossil = can tell time period/what the past is like

2. Phylogenies (for orgs that don't fossilize well/live in areas where fossils don't form well). Indirect record of past evolutionary change. Inference is best for LIVING orgs (doesn't work for completely extinct groups)

history of the earth?

• Earth is 4.5 billion years old

• 1:00 (3.5-4.14 Ga (billion years ago)) first life came. Carbon signatures from crystallized rock/fossilized bacterial mats (stromatolites)

• 3.2-3.5 Ga: photosynthesis evolved

• 1.8-2.2 Ga: evolution of eukaryotic/complex cells (have organelles). Likely due to merging of 2 evolutionary lineages; archaea and bacteria (endosymbiosis). Origin of human lineage. The first meiotic sexual reproduction evolved in early eukaryotes

• 1.7 Ga: multicellular life evolved

• 540 Ma: Cambrian period: the Cambrian explosion. Sudden rapid complex animal life appeared (sudden proliferation) over a short time (20-30 million yrs)

  • Before explosion: had multicellular life but wasn't diverse. Sessile organisms

  • During: rapid proliferation of new organisms. Most animal phyla today left their first fossil evidence. Fist appearance of diverse body plans, skeletons, sensory organs, burrowing, predation

  • After: rapid diversification. Global scale biodiversity

• 470 Ma: land plants evolved

Phanerozoic biodiversity dynamics (what are the top 3 most successful)

Looking at the organisms doing the evolving. Diff orgs were successful at diff times within Phanerozoic. (like organisms in the Phanerozoic were most successful in that time periods than others)

First: Most successful during the initial Cambrian radiation: called the Cambrian fauna (ex: trilobites, anomalocarids), slowly lost diversity

Second successful: Paleozoic fauna. (ex: starfish). Most successful during the Paleozoic period. Declined over time, but increased in modern fauna

Third successful: Modern fauna. (modern orgs) 200 MYA

how does diversification occur (2 ways)

• Biodiversity increases through speciation and decreases through extinction

what is extinction

 process when all the individuals in a species die. Permanent.

What is the equation for net diversification

Speciation rate (λ): rate of formation of new species

Extinction rate (μ): rate of extinction of species

Net diversification (r): rate of biodiversity change

r = λ - μ

Positive ( λ >  μ): positive net diversification. Gaining new species

Negative: negative net diversification. Losing species

Rates are equal ( λ =  μ): no net change, no diversification

what does this represent

the diversification.

top orange: Negative diversification

blue: No diversification. The GAIN of species is equal to the LOSS of species

green: Positive diversification

Causes of changes in biodiversity (all species will eventually go extinct)

Mass extinction events: when 75% of earth's species go extinct in a very short time period (5 major events have happened) entire clades are eliminated

1. Trigger (a factor that causes a change in the environment). Ex: asteriod, volcano, human pop. Growth

a. Asteriod impact. Causes massive ecological disturbance. Blocks sun, global cooling. Caused cretacian mass extinction

b. Volcanic eruptions. Releases magma, CO2, sulfur, changes light lvls, changes ocean acidity. Ended Permian and Triassic

c. Climate system change. (earth's ocean is responsible for the climate) ocean current systems become reorganized and changes climate. Ended Ordovician

d. Changes in biological communities. Species spreading widely causes the environment to change which then causes mass extinction. Ended Later Devonian.

2. Environmental crisis (causes the environment to change)

3. Biological consequence (causes habitat loss, food web loss, widespread extinction)

what is adaptive radiation and what are factors that lead to rapid increases in net diversification

Adaptive radiation: a clade of organisms rapidly diversifies in species number (phenotypic diversity)and ecological diversity.

Factors that lead to adaptive radiation:

1. Need a single common ancestor that created a lot of different ecologically diverse species

2. The phenotypic diversity in the group is strongly related to some sort of use of ecological resources (need a correlation between organisms’ phenotype and their use of ecological resources)

3. Trait utility

4. Rapid speciation early in their history

what does adaptive radiation predict about ecological resources. (what is ecological opportunity)

• Ecological opportunity: the absence or reduction of competition for resources

• Competition free resources, selection favors for the lineage to take advantage of the resources

  • Many kinds of resources, then you get divergent evolution that produces many new species
    
    

3 types

1. Colonization: lineage colonizes an area that is competition free
   
   

2. Extinction: Competitors go extinct (survivors get the benefits)
   
   

3. Key innovation: organisms evolve an adaptive trait that allow them to access new resources that weren't available to them before (ex: bacteria evolving to eat citrate)

   • Ex: Plant evolved a reproductive feature in plants to be pollinated. Put nectar in long tube

• Any of these 3 triggers, you increase diversification

what are other factors that cause adaptive radiation

• Herbivory

• Sexual selection

• Animal pollination of plants

• Increased range size

what are the units of selection

Selection can happen at different levels of organization, not just individuals

DNA/genes -> cells -> individual organisms -> species -> larger clades

ONLY if they meet the 3 criteria (variation, the variation is heritable, and differential fitness)

can species evolve at the species level

yes.
Species can "reproduce" (through speciation)

• Species vary in fitness (variation in speciation, extinction rates)

• Speciation/extinction rates are heritable

Does selection favor outcrossing species over selfers

Selfers:

• Better colonizers (they don't need others to reproduce)

• Increase the relative fitness (pass on twice as many genes)

• BUT it leads to inbreeding depression

Experiment if it's favored or not at the species level

Speciation rate:

• Selfers: 5 species per million yrs

• Outcrossers: 2.8 species per million yrs
  
  

Extinction rate:

• Selfers have a higher extinction rate than outcrossers (5.2 vs 2.2), probs due to inbreeding depression

 

Overall net diversification:

• Selfers have nergative (more likely to go extinct) and outcrossers are positive

• Selfers are favored at the INDIVIDUAL level but unfavored at the species level

• Outcrossers have an advantage over long periods of time

units of selection at the cellular level (ex. cancer)

• Cells replicate through mitosis that produces genetic clones

• Some mutations can occur during mitosis that creates some genetic variation

• The mutations that increase cell division and decrease cell death (apoptosis) has higher fitness levels

unit of selection at the gene lvl. what are Transposable Elements (TEs), transposons

genes that can make copies of themselves (self-replicating segments of DNA/transposons)

• Can do this within a single generation

Transposons are the jumping genes that can make copies of themselves within an individuals lifetime and insert themselves into other chromosomes

• Have high gene level fitness, but it doesn't mean it's good for the organism who has the genes

  • Trash DNA. If they insert themselves into another gene that's important, can be bad

  • Fit at gene level, but unfit at the individual/cellular level

• Gene copying can go up in non-Mendelian ways (break Mendel's laws)

2 main issues of transposons/TEs

1. Costs us energy to make junk DNA

2. Junk DNA can insert themselves in the middle of other genes and cause those genes to be read incorrectly (major phenotypic effects)

What happens when transposable elements become common. How do orgs prevent their genomes from becoming full of transposable elements

2 main things that can happen:

1. Selection at the individual level can help silence transposable elements

   • Attach a methyl group to the transposable element that prevents it from being transcribed.

     • piRNA + RNA interference evolved as a silencing mechanism
       
       

2. Transposition-selection balance: Over long periods of time, selection at higher levels at the individual level will conteract selection at the gene level which leads to balance

   • When transposable elements fill up a genome, those individuals will die and the transposable elements die with them

   • Lower level selectionchecked by higher level selection