Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility...

Speciation

I. Modes

II. Mechanisms

A. Progressive Genomic Incompatibility

B. Hybrid Incompatibility

C. Differential Selection

D. Hybridization

E. Polyploidy

E. Polyploidy Autopolyploidy

Allopolyploidy

E. Polyploidy

Allopolyploidy

Spartina Spartina alternifolia, native to US, was found in southern England in late1800's. There is a European species Spartina maritima. Early in the 20th century a sterile hybrid was found and was called Spartina townsendii This went through a process of diploidization (increased ploidy) and became a new sexually reproducing species known as Spartina anglica

S. maritima

S. alterniflora

S. anglicasterile hybrid

E. Polyploidy

Allopolyploidy

Speciation

I. Modes

II. Mechanisms

III. Rates

Mark Pagel, Chris Venditti, Andrew Meade .2006. Large Punctuational Contribution of Speciation to Evolutionary Divergence at the Molecular Level . Science 314:119.A long-standing debate in evolutionary biology concerns whether species diverge gradually through time or by punctuational episodes at the time of speciation. We found that approximately 22% of substitutional changes at the DNA level can be attributed to punctuational evolution, and the remainder accumulates from background gradual divergence. Punctuational effects occur at more than twice the rate in plants and fungi than in animals, but the proportion of total divergence attributable to punctuational change does not vary among these groups. Punctuational changes cause departures from a clock-like tempo of evolution, suggesting that they should be accounted for in deriving dates from phylogenies. Punctuational episodes of evolution may play a larger role in promoting evolutionary divergence than has previously been appreciated.

Origin of Life Hypotheses

I. Earth History

I. Earth History- Earliest Atmosphere - probably of volcanic origin

Gases produced were probably similar to those created by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 and CH4

I. Earth History

Stromatolites - communities of layered 'bacteria'

I. Earth History

4.5 million to present

(1/1000th of earth history)

II. Origin of Life Hypotheses

- Oparin-Haldane Hypothesis (1924):

- in a reducing atmosphere, biomonomers would form spontaneously

Aleksandr Oparin

(1894-1980)

J.B.S. Haldane

(1892-1964)

- Miller-Urey (1953)

all biologically important monomers have been produced by these experiments, even while changing gas composition and energy sources

- Sydney Fox - 1970 - polymerized protein microspheres

- Cairns-Smith (1960-70) - clays as templates for non-random polymerization

- 1969 - Murcheson meteorite - amino acids present; some not found on Earth. To date, 74 meteoric AA's.

- 2004 - Szostak - clays could catalyze

formation of RNA's

III. Acquiring the Characteristics of Life

A. Three Primary Attributes: - Barrier (phospholipid membrane) - Metabolism (reaction pathways) - Genetic System

B. Barrier (phospholipid membrane)- form spontaneously in aqueous solutions

C. Metabolic Pathways- problem:

how can pathways with useless intermediates evolve? These represent 'maladaptive valleys', don't they?

A B C D E

How do you get from A to E, if B, C, and D are non-functional?

C. Metabolic Pathways- Solution - reverse evolution

A B C D E

Esuppose E is a useful molecule, initially available in the env.

As protocells gobble it up, the concentration drops.

Anything that can absorb something else (D) and MAKE E is at a selective advantage...

but over time, D may drop in concentration...

So, anything that can absorb C and then make D and E will be selected for...

A B C D E

and so on until a complete pathway evolves.

D. Genetic Systems- conundrum... which came first, DNA or the proteins they encode?

RNA (m, r, t)

protein

RNA (m, r, t)

protein

DNA stores info, but proteins are the metabolic catalysts...

- Ribozymes

info storage ANDcataylic ability

- Ribozymes - Self replicating molecules - three stage hypothesis

IV. Early Life

- the first cells were probably heterotrophs that simply absorbed nutrients and ATP from the environment.

- as these substances became rare, there was strong selection for cells that could manufacture their own energy storage molecules.

- the most primitive cells are methanogens, but these are NOT the oldest fossils.

IV. Early Life

- the second type of cells were probably like green-sulphur bacteria, which used H2S as an electron donor, in the presence of sunlight, to photosynthesize.

IV. Early Life

- the evolution of oxygenic photosynthesis was MAJOR. It allowed life to exploit more habitats, and it produced a powerful oxidating agent! These stromatolites, which date to > 3 bya are microbial communities.

IV. Early Life

- about 2.3-1.8 bya, the concentration of oxygen began to increase in the ocean and oxidize eroded materials minerals... deposited as 'banded iron formations'.

IV. Early Life

- 2.0-1.7 bya - evolution of eukaryotes.... endosymbiosis.

IV. Early Life

Eukaryote Characteristics

- membrane bound nucleus

- organelles

- sexual reproduction

IV. Early Life

Origins

infolding of membrane

IV. Early Life

B. Origins

endosymbiosis - mitochondria and chloroplasts (Margulis - 1970's)

IV. Early Life

Relationships among life forms - deep ancestry and the last "concestor"

IV. Early Life

Woese - r-RNA analyses reveal a deep divide within the bacteria

IV. Early Life

Curiously, the very root of life may be invisible to genetic analysis. Bacteria transfer genes by division (to 'offspring'), but they also transfer genes "laterally" to other living bacteria. This makes reconstructing bacterial phylogenies difficult.

IV. Early Life

So, reconstructing the patterns of relatedness among these ancient life forms is difficult.

Different genes give different patterns of relatedness among domains

IV. Early Life

C. Domains - "Ring of Life" hypothesis (2004)

Speciation I. Modes II. Mechanisms A. Progressive Genomic Incompatibility B. Hybrid Incompatibility...

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