Speciation

SJCHS

Evolution• Microevolution: Change in a

population’s gene pool from generation to generation

• Speciation: When one or more new species branch from a parent species

• Evolution does not always result in new species

Species

Definition• Species Concepts

• Biological: A group of organisms that can interbreed and produce fertile offspring

• Morphological : Classified on shape, size, other features• Phylogenic: Species who share common ancestor/ evolutionary

history

Definition• Different species are determined by considering all definitions

Phylogenic Tree• Phylogenics/Cladistics: Search for clades (group that consists of

ancestral species and all its descendants) •Branch points: New species•Common Ancestor: Not necessarily a known organism;

characteristics hypothesized based on traits of descendents•Branch: History of species

Phylogenic Trees

• Species in clades share primitive characters• Sequence of branch points are defined by derived (evolutionary

innovative) characters• Changing field

Evolution

• Convergent evolution: Characteristics shared by species because of similar environments or ecological roles- NOT due to a close common ancestor

Evolution

• Coevolution: When 2 species reciprocally affect the evolution of each other

Speciation Event• Speciation event: A series of genetic changes in a common ancestor

that produces two or more separate species

Speciation Event• Reproductive barrier: Biological features that prevents interbreeding• Prezygotic Barrier: Prevents mating or fertilization

Speciation Event• Postzygotic Barrier: Prevents the development of fertile adults

Speciation Event• Barriers occur due to changes in the gene pool of a separated part of a

population

Speciation Event• Allopatric speciation: Geographic isolation of a population

• Different environments may result in different evolutionary adaptations due to natural selection

Speciation Event• Parapatric speciation

• Species are not geographically isolated but are spread over a large, differentiated geographic area

• Natural selection can result in speciation due to different environments

Speciation Event• Sympatric speciation

• Species are geographically close and a speciation event occurs

Pace• Evidence for speciation events comes from fossil record• Can use fossils to determine how quickly speciation can occur• No one pace is correct- can differ depending on species

Pace• Punctuated Equilibria: Long periods of little change followed by abrupt

(1000’s to 10,000’s of years) episodes of speciation

Pace• Gradualism: Species diverged over large periods of time (100,000’s or

millions of years)

Pace• A major mutation can “instantaneously” result in a speciation event• Rare

Evidence• Historically: Fossil and geologic record can be used to determine when

species diverged

Evidence• Differences in

RNA/DNA/protein sequences can be used to determine evolutionary relationships

Bioinformatics

• Bioinformatics: Using math, computers, and biology to store and analyze data from sequenced genomes

Molecular Clocks• Molecular Clock: Using DNA/RNA/proteins sequences to determine when

two or more species diverged

Molecular Clocks• Assumptions- The rate of mutation in a gene is:

• similar in different species• occurs at a constant speed (graphs of mutations versus time should be a

straight line)• Not true for all genes/species fibrinopeptide

Cytochrome C

Molecular Clocks• Calibrating a molecular clock: To use molecular clocks you must use the

fossil or geologic record to determine the rate of mutation