CH. 22 Origin of Species (Chapter 22.1-22.5)
By: Jose Solarzano (Chief), Jose Arambulo, Daniel Guevarra,Eric Galicia, and Jarod Smith.
Period 4 Biology
22.1 The Nature of species and the Biological Species Concept
Reproductive Isolating Mechanisms
Mechanism
Description
Prezygotic Isolating Mechanism
Prezygotic Isolating Mechanism
Geographic Isolation
Species occur in different areas, which ae
often separated by a physical barrier, such as
a river or mountain range.
Ecological Isolation
Species occur in the same area, but they
occupy different habitats and rarely encounter
eachother.
Behavioral Isolation
Species differ in their mating rituals
Temporal Isolation
Species reproduce in different seasons or at
different times of the day.
Mechanical Isolation
Structural differences between species
preventing mating.
Prevention of Gamete Fusion
Different species/animals cannot successfully
sexually reproduce.
Postzygotic Isolating Mechanism
Postzygotic Isolating Mechanism
Hybrid inviability or Infertility
Hybrid Embryos do not develop properly,
hybrid adults do not survive in nature, or
hybrid adults are sterile or have reduced
fertility.
22.2 Natural Selection and Reproductive Isolation
-Selection may reinforce isolating mechanisms.
Populations may evolve complete reproductive isolation allopatry. If populations that have
evolved only partial reproductive isolation come into contact, natural selection can lead to
increased reproductive isolation, a process termed “reinforcement.”
Alternatively, genetic exchange between the populations can lead to homogenization and thus
prevent speciation from occurring.
CH. 22 Origin of Species (Chapter 22.1-22.5)
By: Jose Solarzano (Chief), Jose Arambulo, Daniel Guevarra,Eric Galicia, and Jarod Smith.
Period 4 Biology
-22.3 Natural Selection and Reproductive Isolation
-The Role of Genetic Drift and Natural Selection in Speciation
● Genetic Drift: randomly generated changes in a population’s genetic
● Random changes may cause reproductive isolation- In small populations, genetic drift
may cause populations to diverge; the differences that evolve may cause the
populations to become reproductively isolated
● Adaptation can lead to speciation- Adaptation to different situations/environments may
incidentally lead to reproductive isolation. In contrast to reinforcement, these differences
are not directly favored by natural selection because they prevent hybridization
Natural Selection can directly select for traits that increase reproductive isolation
-22.4 The Geography of Speciation
Speciation: A two-part process, initially identical populations must diverge, and second,
reproductive isolation must evolve to maintain differences
Problem: Homogenizing effect of gene flow between populations is constantly acting to erase
any arising differences by genetic drift or natural selection
Gene flow occurs only between populations that are in contact, and geographical isolation
occurs in populations for many reasons
Ernst Mayr: First biologist to demonstrate that geographically separated (allopatric) populations
appear more likely to have evolved differences leading to speciation
(ex.) Little paradise kingfishers vary little throughout the wide range in New Guinea, despite
great variation in in topography and climate.
allopatric speciation: takes place when populations are geographically separated
sympatric speciation: takes place when populations are not geographically separated
Sympatric speciation can occur either instantaneously or over the course of multiple generations,
without geographic separation
Instantaneous sympatric speciation occurs when an individual is born that is reproductively
isolated from all other members of its species
CH. 22 Origin of Species (Chapter 22.1-22.5)
By: Jose Solarzano (Chief), Jose Arambulo, Daniel Guevarra,Eric Galicia, and Jarod Smith.
Period 4 Biology
Polyploidy: produces individuals that have more than two sets of chromosomes, often seen in
plants
This polyploid factor can arise in two ways; autopolyploidy or allopolyploidy
Autopolyploidy: all of the chromosomes may arise from a single species, which might happen
due to an error in cell division that causes a doubling of chromosomes, those of which that
contract autopolyploidy this way are referred to as tetraploids because they have four sets of
chromosomes
Allopolyploidy: A more common type of polyploid speciation, which may happen when two
species hybridize, resulting in offspring with one copy of the chromosomes of each species, and
are usually infertile due to incorrect chromosome pairing, but some are otherwise healthy, can
reproduce asexually, and can become fertile through certain events
About half of the approximately 260,000 species of plants have a polyploid episode in their
history, including wheat, cotton, tobacco, sugarcane, bananas, and potatoes
Speciation by polyploidy is known to occur in a variety of animals, such as insects, fish, and
salamanders, but more rarely than plants
Sympatric speciation can occur over the course of multiple generations through the process of
disruptive selection which can cause a population to contain individuals exhibiting two different
phenotypes
Before two phenotypes could become different species, they would have to evolve reproductive
isolating mechanisms
Sympatric speciation by disruptive selection is a rare event, yet a number of cases have
appeared that are difficult to perceive in any way other than sympatric speciation
-22. 5 Adaptive Radiation a Biological Diversity
Adaptive radiations- occurs when a species finds itself in a new or suddenly changed
environment with many resources and few competing species
Key innovation-the evolution of a new trait that allows individuals to use previously
inaccessible parts of the environment; may also trigger an adaptive radiation
Character displacement- A process in which natural selection favors individuals in a species
that use resources not used by other species. This results in evolutionary change leading to
species dissimilar in resource use
Ground Finches- adapted the size of their bills to the size of the seeds that they feed on/ six
species exist
CH. 22 Origin of Species (Chapter 22.1-22.5)
By: Jose Solarzano (Chief), Jose Arambulo, Daniel Guevarra,Eric Galicia, and Jarod Smith.
Period 4 Biology
Tree finches- Five species of this finch exist. Four of them have bills suitable for feeding on
insects, but one (the woodpecker) has a chisel-like beak. It usually carries a twig around so it
can probe crevices for insects.
Vegetarian finch- Have very heavy bills to wretch buds from branches
Warbler finch- Are unusual birds with slender, warblerlike beaks that continuously search the
mainland for leaves and branches for insects.