Mechanisms of Species Diversity

Which of the following provides evidence that vertebrates evolved from a common ancestor?

A) homologous structures B) the common development of pharyngeal

pouches in an embryonic stage C) the presence of similar genes D) similarities in protein structure E) All of the choices are correct.

What is genetic drift?

A) chance changes in the gene pool of a small population

B) the entry of alleles into a population due to immigration

C) changes in the gene pool of a population that are due to differential reproductive success

D) a change in allelic frequencies due to mutation E) the loss of alleles from a population due to

emigration

All life is organized into 3 domains• 2 Domains of

prokaryotes, 1 of all eukaryotes

• Bacteria & Archaea- prokaryotic

• Eukaryota- Includes all 4 eukaryotic kingdoms: protista, animalia, plantae, fungi

• All domains have a common ancestor

Taxonomy is the science of classification

• Categories move from the general to the specific

• Species are named according to the genus and species to which they belong (Binomial nomenclature)

• e. g. Homo sapiens

Millions of species have been named

• However, the definition of species remains vague and flexible

• Yet there are unquestionably a wide variety of living things on earth

Change in allele frequencies alone cannot generate diversity

Evolution happens at the level of species

The Biological Species Concept is based on reproductive isolation

The Biological Species Concept

• “Two organisms that are able to reproduce naturally to produce fertile offspring. Organisms that can reproduce but almost always make infertile hybrids, such as a mule or hinny, are not considered to be the same species.”

Other Species concepts

• Ecological Species concept- species are define by the ecological niche which they fill

• Morphological Species concept- Species are defined and categorized by the physical structures they share

Reproductive Barriers cause reproductive isolation

Reproductive Barriers cause reproductive isolation

Behavioral Isolation can cause speciation

• Courtship rituals are a prime example of behavioral isolation

• Temporal behavior can also isolate a species

Mechanical Barriers can lead to Speciation

Postzygotic barriers

When populations are isolated from each other, genetic drift and selection ensue,

causing allopatric speciation

In plants, polyploidy is a cause of sympatric speciation

Ecological pressures and opportunities fuel adaptive radiation

• Adaptive radiation- one species becomes many, rapidly to fill vacant ecological niches

Natural selection is a driver of speciation

Directional and disruptive pressures cause species to change

Artificial selection shows the pliancy of species morphology

Can natural selection create the same diversity?

Hallmarks of Adaptive Radiation

• Common ancestry of radiants

• Rapid speciation• Phenotypes show

adaptation suited to new niche

• Where can we find evidence of adaptive radiation?

Adaptive Radiation is easily seen in island ecosystems

New islands contain vacant ecological niches

• Species which arrive are often in reproductive isolation

• Novel competition conditions

• Many available resources

• Great opportunity

The Hawaiian islands are geographically isolated from

continents• The most isolated

landmass in the world• Colonization events are

rare• When they do occur,

they are momentous

Hawaiian islands are geographically isolated from each other

• Distance from Maui Big Island: ~40 miles

• Islands are isolated from each other

• But less isolated than all are from continents

• Islands appeared in sequence (temporal isolation)

Hawaiian islands exhibit a wide diversity of habitats

• Sea level 13,000 ft.• Rainforest desert• Fertile soil barren

rock• Warm snowy

Tremendous ecological opportunity

800 Species of Drosophila are endemic to Hawaii

• Evidence points to a single colonization event, 5 million years ago

The “Silversword Alliance” shows adaptive radiation

• 28 species of Hawaiian plants

• Traced to a single Californian tarweed

Extinction events create vacant niches

• Cretaceous-Tertiary (K-T) extinction allowed radiation of mammal species

• K-T one of the five important global extinction events

Adaptive radiation in the lab

• In variable environments, varying strains of P. fluorescens are generated

• Strains are genetically distinct

• When environments are homogeneous, no such variants are generated

Speciation can occur by gradualism or by puncuated equlibrium

Exaptation is the shift in functionality of a structure

Exaptation is the shift in functionality of a structure

Evolution is not a directed process

• Evolution perfects, but never creates perfection

• Living things adapt to ever-changing environments