Unit 3: Macroevolution

Phylogeny

The study of evolutionary relationships among a group of organisms

Three domains

1. Bacteria

2. Eukarya

3. Archaea

Taxonomy order

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Taxonomy

Classification of organisms based on shared characteristics

Monera

The two domains of Archaea and bacteria (Prokaryotes)

Phylogenetic tree (aka Cladogram)

Construct that represents a branching structure to illustrate the true evolutionary relationship of a group of organisms

Based on:

• Morphology and fossil record

• Embryology

• DNA, RNA, and protein similarities

Branch point (Node)

Where an ancestral lineage splits into two descendant lineages

Taxon

Any group of species designated by name (categories like kingdoms, classes, etc.)

Polytomy

If more than two lineages branch from one node (temporary and future evidence will solve it)

Sister taxa

Organisms sharing an immediate common ancestor

Clade

Any taxon that consists of all the evolutionary descendants of a common ancestor

True clade (Monophyletic group)

Contains a common ancestor and all of its descendants

Paraphyletic group

Doesn’t contain all descendants from a common ancestor

Polyphyletic group

Doesn’t have a unique common ancestor for all the descendants

Anagenesis (Phyletic change)

The accumulation of change in a species that leads to speciation over time (creation of new species and og is extinct)

Cladogenesis

The budding of one or more new species from a species that continues to exist

Relative dating

Location where fossils are found is indicative of its age which can be used to recreate phylogenies

Homologous features

Any feature shared by two or more species and inherited from a common ancestor

Ancestral trait

Original shared trait

Derived trait

Trait found in newly evolved organism

Analogous structures

Structures similar in function and sometimes structure but not inherited from a common ancestor

Molecular clock hypothesis

Among closely related species, a given gene usually evolves at a reasonably constant rate

Rules to reconstructing a phylogeny

1. Maximum likelihood

2. Maximum parsimony

Maximum likelihood

When considering multiple phylogenetic hypotheses, take into account the one that reflects the most likely sequence of evolutionary events given certain rules about how DNA changes over time

Maximum parsimony

When considering multiple explanations for an oversedations, one should first investigate the simplest explanation that is consistent with the facts

Species

A group of interbreeding organisms that produce viable, fertile offspring

Asexual species

Less adapted to environmental change

Ex: Dandelions (pollen is sterile and the egg is diploid)

Ring species

Connected neighboring populations who can interbreed with closely related populations but there are at least two “end“ populations in the series

• End pops are too distant to interbreed

Ex: Ensatina escholtzi in CA

Limited breeding

Opportunities for organisms to mate and reproduce are restricted

Ex:

• Canis species w/ domestic dogs but not w/ one another

• Lion and tigers breeding in captivity but not in nature

Allopatric speciation

Speciation due to geographical isolation/separation

Why does speciation occur after geographic isolation?

1. Different allelic makeup

2. Mutations

3. Genetic drift and different selection pressures

Adaptive radiation

A species inhabiting a new area and evolving into several new species (a type of allopatric speciation)

Ex: Galapagos Island finches

Mechanisms of speciation

Prezygotic and postzygotic barriers

Prezygotic barriers

• Habitat isolation

• Behavioral isolation

• Temporal isolation

• Mechanical isolation

• Gametic isolation

Postzygotic barriers

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

Habitat isolation

Populations live in different habitats and don’t meet

Ex: Bufo woodhousei and Bufo americanus are two closely related toads. B. woodhousei reproduces in the quiet water of a stream whereas B. americanus reproduces in shallow rain pools

Behavioral isolation

Little to no sexual attraction between males and females (mating differences)

Ex: Twelve fiddler crab species live on a beach in Panama. Males of each species have distinctive mating displays including waving claws, elevating the body, and moving around the burrow

Temporal isolation

Mating or flowering occurs at different seasons or times of day

Ex: Four species of frogs from the genus, Rana, mate at different times of the year

Mechanical isolation

Structural differences in gentila or flowers prevent copulation or pollen transfer

Ex: The Bradybaena are two different species of snails because the shells spiral in opposite directions

Gametic isolation

Female and male gametes fail to attract each other or are inviable (mating occurs but gametes cannot fertilize)

Reduced hybrid viability

Hybrid zygotes fail to develop or fail to reach sexual maturity (hybrid dies)

Reduced hybrid fertility

Hybrids fail to produce functional gametes (hybrids cannot reproduce)

Hybrid breakdown

Offspring of hybrids have reduced viability or fertility (offspring of the hybrid doesn’t survive)

Ex: Mules (horse and donkey hybrid) are sterile

Sympatric speciation

Speciation even though the two groups are still living in the same area (no isolation)

Habitat differentiation

Populations of a species diverge into different ecological niches or habitats within the same environment

Ex: species of treehoppers that are host-specific (one lives on bittersweet while the other lives on butternut and both mimic thorns to avoid predation)

Physics of light

Red, green, and blue correspond to energy and different colored lights affect vision

Ex: some fish have genes that enable them to see blue light better while others have a red light advantage

Polyploidy

• Instant speciation which occurs in most often in plants

• Contain more than two paired (homologous) sets of chromosomes

• May occur due to nondisjunction (abnormal cell division) during mitosis or commonly during metaphase I in meiosis

Autopolyploidy

The number of chromosomes double in the offspring due to total non-disjunction during meiosis (all DNA going on one side during meiosis)

• Derived from a single species, naturally occurring genome doubling

Ex: Normal primroses are diploids with 14 chromosomes but a total nondisjunction event results in primroses that are tetraploid (28 chromosomes)

Allopolyploids

• Polyploids with chromosomes from different species

• Result of multiplying the chromosome number in an F1 hybrid

• Usually more vigorous than the parents

Ex: oats, potatoes, bananas, barley, plums, apples, sugar cane, coffee and wheat

Chromosomal rearrangements

Caused deletions, duplications, inversions; and translocations

Ex: pandas (panda bear chromosome is a result of a fusion between two brown bear chromosomes)

Gradualism (phyletic gradualism)

Theorizes that most speciation is slow, steady, and gradual transformation (anagenesis)

• Evolution works on large populations over a long time

• Pop slowly accumulates changes and evolves

• No clear line exists between an ancestral species and a descendant species (unless splitting occurs)

Ex: seasonal isolating mechanism?

Punctuated equilibrium

When significant evolutionary change occurs, it is restricted to rare and geologically rapid events of branching speciation (cladogenesis)

• Species splits into two distinct species, rather than one species gradually transforming into another

Half-life

Amount of time it takes for ½ of a quantity of radioactive isotope to undergo radioactive decay to form a new substance

Protobiont hypothesis

Possible origin of life (steps below:)

1. Inorganic molecules

2. Small monomers

3. Larger polymers

4. Protocells in an RNA world

5. DNA based cells

Earth’s atmosphere went from anaerobic to aerobic

Protobiont (protocell)

A grouping of abiotically produced organic molecules surrounded by a membrane or a membrane-like structure

Stanley Miller and Harold Urey’s experiment

Demonstrated abiotic synthesis of organic compounds

• They simulated Earth’s early atmosphere by creating

• H₂O, CH₄, NH₃, CO₂, and H₂ in the early atmosphere

Iron-Sulfur World Theory

Suggested life might have originated at hydrothermal vents