Evolution Final Fall24

How old is the universe?

13.7 - 13.8 billion years

How old is the Earth?

4.6 billion years old

When did life first evolve?

3.8 BYA

When was the Cambrian explosion?

540 MYA

When was the KT mass extinction?

65 MYA

When was the Permian mass extinction?

250 MYA

What is adaptation (process)?

process by which animals become more fit for their environment

What causes adaptations?

selection

• directional

• stabilizing

• disruptive

• sexual

• artificial

What is adaptation (trait)?

a trait evolved for a current role through natural selection

What are the 2 ways of testing hypotheses of adaptation?

1. examine current utility

2. use historical inference

examine current utility

to assess how a trait functions in the present environment thru observation and experimentation

historical inference

look at 1. concentrated changes and 2. phenotypic convergence

concentrated changes

changes and fns on the same branch, they occur around the same time

phenotypic convergence

analogous solutions to similar problems

adaptationist programme

a flawed theory that all traits are made for a certain purpose and optimally designed

what are the flaws with the adaptationist programme?

1. doesn’t account for neutral traits

2. a trait may not be optimal in every situation

what are the 2 types of tradeoff?

1. ecological

2. functional

ecological tradeoffs

organism has to give up 1 lifestyle for another

functional tradeoffs

organism has a trait thats really good at 1 thing but can’t be used for another

speciation

process of creating new species by branching off from old species. happens via selection, mutation, gene flow, drift

microevolution

variation within and btwn species

species

1. groups of indivs that evolved independently

2. contribute to the same gene pool

3. interbreeding populatoins

4. smallest evolutionary unit

how many species concepts do we care abt?

three

1. morphological

2. phylogenetic

3. biological

morphological concept

defines a species by the physical features/traits it has

advantages to morphological

1. can use for fossils

2. simple

disadvantages

1. can’t deal w intraspecific polymorphism (like telling males and females apart)

2. doesn’t account for behavioral differences

Phylogenetic species concept

a species is the smallest group of populations that are recognized by shared derived traits (synapomorphy) which indicate ancestry

phylogenetic advantages

1. products of evolutionary descent

2. species are monophyletic like other taxa

3. shared derived traits is most important thing to consider

phylogenetic disadvantages

1. problems w local adaptations

2. hybridization issues

biological species concept

based on what organisms can reproduce with what organism

biological concept advantages

1. emphasis on gene flow

2. clear grouping principle

biological disadvantages

1. sometimes 2 species can hybridize

2. ring species + circular overlap (loops around and the 2 ends can’t interbreed)

3. asexual organisms

4. compatible populations that are geographically seperated

barriers to gene flow

1. extrinsic = geographic isolation

2. intrinsic = reproductive isolation

types of reproductive isolation

1. prezygotic - prevents a zygote from forming

2. postzygotic - prevents a zygote from developing and reproducing in the future

prezygotic

1. ecological differences = differences in physical features and behaviors

2. temporal = differences in breeding times

3. sexual behaviors = differences in courtship behaviors

4. Gametic incompatibility = fertilization cant happen

postzygotic

1. zygote mortality

2. hybrid inviability - hybrid dies later in life

3. hybrid is sterile

4. other problems

what is life?

1. carry encoded info

2. metabolize

3. replicate

RNA world hypothesis

Life began with RNA material, which underwent selection, and formed life as we know it today

LUCA, cenancestor

cyanobacteria that is the predecessor of all life

how do we know abt different diversification events?

fossil records

1. Walcott found lots of fossils in the mountains

Cambrian explosion

most animal phyla appeared

and basal lineages are older

diploblastic animals

2 embryo tissue types

triplobasts

have 3 embryonic tissue layers

1. protostomes = forms at mouth first

2. deuterostomes = form at anal region first

Background extinction

normal extinction rates bc of natural avg lifespan

mass extinction

unusually high extinction rates (greater than 60% in 1 Million years)

what causes extinction rates to increase?

1. less geographic range

2. less larval dispersal distance

basically more spread out = better survival

K-T extinction

killed the dinosaurs, allowed for adaptive radiation of mammals

2 hypotheses of evolution and development

1. species have many different genes

2. same genes among species but they are used/regulated differently

developmental genes

control rate, timing, and location of gene expression as organism develops

4 themes of evo-devo

1. redeployment of existing genes

2. evolutionary changes in time and place of gene expression

3. rapid evolution in regulatory regions

What does changing regulatory genes do?

1. changing genes in the embryo causes new features to develop

2. can change cell specialization (i.e. function)

3. ex: distal-less in butterflies was used for limb growth and then became used for eye spots

hox genes

genes that provide positional info during development

• hox genes can arise from gene duplication or deletion

• spatial pattern of expression (the clusters of expression in embryo will resemble the clusters in adult)

heterochrony

change in timing of developmental events

• ex: chimpanzee and human skulls look similar as infants but then differ as they mature

heterotopy

change in location of developmental events

• ex: rodent cheek pouches can be found internally or externally depending on species

Rapid evolution of regulatory genes

Rockman and Wray

1. observed many cis-regulatory regions in humans

2. found a lot of variation btw individuals

3. conclusions: if there is so much variation in the essential genes everyone has to function, then there must be even more variation in the non-essential genes

hierarchical control

changing 1 gene will have a cascade effect on the others

modularity of gene expression

all cells have the same DNA but different genes of DNA are actually expressed depending on location and timing

• gene expression is bound by the other genes around it

Principles of development

1. activators or repressors create thresholds/gradients of gene expression

2. coactivity causes spatial expression

3. many genes regulated by 2+ activators/repressors

4. hierarchy of gene expression assures proper temporal deployment of developmental genes

5. tissue interactions coordinate development

6. genetic variation in regulatory regions and protein coding regions

Hox Genes in flies

• bicoid triggers hunchback

• Nanos triggers caudal

• at first no cell specialization, then chemical signals told them to activate in specific locations (front or back)

Regulation of pair rule

inhibitors and promotors tell things to turn on or off

Hierarchy of development

early gene products can inhibit or activate genes later on

• spatial differentiation

• development proceeds in sequential compartmentation

hierarchy + combinatorial control of genes

evolvability + flexibility =

• resistance

• self regulation

• ability to respond to environmental cues

cis regulatory and morphology variations

source of morphological evolution

neutral variation

evolved by genetic drift and correlated w other traits under selection

coat color in beach mice

1 gene can impact morphology a lot

• 1 gene can explain 10-36% of variation in coat color

• agouti and McR1

microevolution

within populations

systematic and comparative biology

species