Transcript Mechanisms of Species Diversity

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 & Archaeaprokaryotic
• 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