phylogenies and the history of life

phylogeny

the evolutionary history of a group of organisms

who is related to who?

what is a branch in a phylogenic tree

represents a population through time (length may or may not be arbitary)

what is a root in a phylogenic tree

oldest ancestor (ancestral group)

what is a tip in a phylogenic tree

end point of a branch, represents an extinct group or a living group as they currently are

what is a node/fork in a phylogenic tree

ancestral group splits into 2 or more distinct groups

phylogenic tree goes from ancestral group to

derived group

monophyletic

contains a common ancestor and all its descendants

paraphyletic

contains a common ancestor but not all its descendants

polyphyletic

contains groups of species with different common ancestors

when is branch length important

when there is a scale that explains the time

define character/trait

any genetic, morphological, physiological, developmental, pr behavioral characteristic to be studied

similar traits between species=

closer on the tree

distinguish between ancestral and derived traits

ancestral trait- characteristic that exists in an ancestor

derived trait- modified form of ancestral trait; found in descendant

*every species has both

what is the cladistic approach? why is it powerful?

relationships are reconstructed by identifying synapomorphies; tells us where to put things on the tree

define synapomorphy

shared derived characteristic

(derived from traits found in a common ancestor)

how can phenetics be used to strengthen cladistics

phenetic approach follows-

-uses statistics to summarize overall similarity among organisms

-compare stats for different populations and build a tree

similar populations= clustered

divergent populations= dispersed

distinguish between homology and homoplasy

are they similar because of common ancestor or another reason?

homology- species having similar traits due to shared ancestry (the same structure must be present in the most recent common ancestor)

homoplasy- species have similar traits for other reasons (similar traits evolve independently)

example: dolphins and ichthyosaurs bodies look like they would be related but different CA (one reptile, one mammal)

what is convergent evolution

natural selection favors similar solutions to problems posed by similar ways of making a living

example: streamlined bodies, elongated jaws help aquatic predators hunt— could look the same but do not belong close together on the tree

what is an artiodactyls?

what are some animals?

a group of animals with an astralagus (pully shaped ankle bone) and even toes, hooves

hippos, cows, deer, pigs

what is an out group

a species that has similar, but not the same structure so it is close on the tree even though it doesn’t share the exact structure

what did dna testing show in the whale case study

dna testing was used to examine short interspersed nuclear elements (SINEs) which showed that whales and hippos share several SINE genes not shared by other— moved whales to the in group

do whales belong in the in group or out group?

hypothesis: ancestor of whales and hippos fed on plants in shallow water, in 2001 evidence was found that whales “moved” to the sea

found the CA: Indohyus- unusual ear bone (astralagus bone)

this connects hippos and whales (filling in the gaps)

it is hard to determine homologous or homoplastic

-genetic info helps

-compare 2 groups of organisms, more similar the sequence, closer the relationship

what are hox genes

family of genes found in many organisms

-organized similar on chromosomes

-share a 180 base pair sequence= homeobox

-products function similar (hox genes tell our body to make muscles etc.)

how do hox genes relate to phylogeny

insects and vertebrates share a CA (branched off 600-700 MYA)

similar genes are found in both insects and vertebrates finding lineages between them, all lineages inherited these traits from a CA

*hox genes help track lineages and CA

describe the principle of parsimony

most likely explanation or pattern is the one that implies the least amount of change, simple path from point A to B

*derived trees are compared, the fewest overall evolutionary changes=most accurate

what is a fossil

physical evidence of organisms that lived in the past

what is the fossil record

the total collection of fossils found throughout the world

how do we date fossils

using the material around it

describe one way via which fossilization may occur

1. body ends up in shallow or swampy water or mud or clay (have to be buried quickly before eaten)

2. body is covered as it rots and disintegrates

3. flooding and sediment movement bury the body over time

4. sand, gravel, and damp material further bury and compress fossil

5. rediscovery (if lucky and revealed)

burial=

decomposition=

quick

slow

intact fossil

buried so quickly it does not decompose

compression fossil

buried rapidly, decomposed slowly, but compressed to paper thin or thinner (VERY DELICATE)

cast fossil

organism buried, decomposed slowly and leaves an impression of the organism which is filled by water (tells us what the outside of the organism looks like)

per mineralized fossil

decomposition happens so slowly that crystals are deposited by water over time

trace fossil

evidence of life- tracks, egg nest, poop, etc.

how common is fossilization

rare

will not fossilize unless in an environment where decomposition is slow and burial is rapid

example: Archaeopteryx

only 10 fossils all at the same sight, around 2 billion existed

limitations of the fossil record

1. Habitat Bias- beaches, mudflats, swamps (“pre-buried”)

2. Taxonomic and Tissue Bias- harder parts more likely to fossilize, exoskeleton, outer coats, heavily armored (hard for mammals)

3. Temporal Bias (Time)- recent are more common than ancient

4. Abundance Bias- common, long existing species fossilize more often

*not random, have to meet these critia to be fossilized and added to the fossil record

how do geologists date fossils

half lives

• dated fossils are used to create a timeline of “evolutionary firsts”

significant events of the precambrian

• 4.6 BYA- 542 MYA

• first life (single cell bacteria and archea)

• most life is unicellular

• photosynthesis begins: O2 is absent until after first life, changes the amount of O2 in atmosphere

significant events of the Paleozoic

• “ancient life”

• appearance of most animal lineages

• marked by mass extinctions (start, middle, end)

• massive die off of multicellular organisms

significant events of the mesozoic

• “middle life”

• begins and ends with extinction events

• dinosaurs peaked and died off

• mammals

• gymnosperms dominate (ferns etc.)

• lots of diversity in insects

significant events of the Cenozoic

• “recent life”

• angiosperms flourish (flowering plants)

• first humans

• first aquatic whales

• current era

how has the earths surface changed over time

earth is not just a stage

-continents move

-oceans move

what is the supercontinent called

Pangea

what is adaptive radiation

1 lineage produces descendants that live in a wide variety of habitats and utilize a variety of resources

3 characteristics of organisms that undergo adaptive radiation

• monophyletic group

• rapid speciation

• ecological diversification in resources/habitats (ex. what they eat)

what is ecological opportunity

ability of new or novel resources drives a lineage to diversify

example: Hawaiian silverswords

california (1 species) to Hawaii (many species because there was little life so lots of opportunity)

what is morphological innovation

evolution of new morphological traits (new alleles added due to mutation)

-new ways to exploit resources (example: wings, flight, etc.)

because of ecological opportunity and morphological innovation what developed on insects, flowering plants, and fish

Insects

• 3 pairs of legs

• complex mouthparts

• exoskeleton

• wings

Flowering Plants

• unique reproduction

• pollination

• species rich lineage

Fish

• jaws in throat

• scale shedding

what conditions/circumstances are thought to be responsible for the Cambrian explosion

-first cells appear in Precambrian (3 BYA all unicellular)
-565 MYA- primitive organisms

-515 MYA- all major animal lineages appeared

What caused it?
1. Higher O2 levels- O2 levels rose gradually over time, supported larger organisms, increased efficiency of respiration

2. Evolution of predation- from filtering sea floors to eating other organisms (led to diversity because predators got better at catching prey and prey got better at hiding)

3. New niches- movement allowed escape from benthic substrate

4. New genes- hox genes were absent in early organisms, increased through mutations

what does the fossil record tell us about the Cambrian explosion

there are 3 distinct intervals in the fossil record

1. poushantuo microfossils (China)- 570 MYA

• tiny sponges, filter feeders— morphological change

2. Ediacaran fossils (Australia)- 565-542 MYA

• small organisms; lacking shells, limbs, head mouths

• burrow and tracks

• organisms that move

3. Burgess Shale (Canada)- 525-515 MYA

• increase in size, morphology, movement, habitat

• sponges, jellyfish, arthropods

define mass extinction

• rapid

• many lineages gone

• random with respect to fitness

how many mass extinctions have occurred in history

5

describe the mother of all mass extinctions

*End Permian extinction

• biggest mass extinction in history

• 90% of all species

hypothesis as to what caused the mother of all mass extinctions

1. Siberian Traps (flood basalts) added a large amount of heat, CO2, and SO2 to the atmosphere- global warming, and formation of H2SO4 (acidic rain)

2. Oceans became largely anoxic- aerobic organisms die

3. Dramatic dropping of the sea level led to the loss of habitat- marine organisms dominated

*Low O2 levels and high CO2 levels in the atmosphere restricted the habitats of terrestrial animals to small patches

what is the impact hypothesis

an asteroid struck earth causing 60-80% of all multicellular life to go extinct (KP boundary)

when would the impact hypothesis have occurred

End Cretaceous extinction (65 MYA)

How do we know?

• Iridium is rare on Earth, abundant in asteroids and meteors

• Shocked quartz found

• Microtektites form only under high temp and pressure from molten rock splashes

where was the crater found and what was the size

Yucatan Peninsula

180 km (112 miles) wide

Who remained and why

not all life was destroyed

we can ask the questions

was the process size selective?

did those organisms capable of dormancy survive?