Download The process of Speciation

The process of
Speciation
How Different Species Arise
New information has revised our
understanding of the tree of life
• Molecular data has provided insights into the
deepest branches of the tree of life
finding evidence…
Genes that regulate development are
highly conserved*.
*changed little over time
Genotype alone is not the whole story…
genetic
“switches”
HOX
gene
example
2 main ways changes in developmental genes lead to
evolutionary important morphological changes.
• Mutations in genes that
regulate developmental
processes.
Changes in time/place of
expression of developmental
regulatory genes.
Why are you
following me?
SO – according to modern evolution – how did diversity
come about?
Separation and separate reproduction of
populations causing
speciation events
What is a species?
a group of individuals capable of interbreeding
and producing fertile offspring
What must happen
in order for new
species to evolve?
Populations must be
reproductively isolated
from each other.
Introduction
• What is speciation?
• It is the formation of new species
because of
Reproductive Isolating Mechanisms
What does it mean for two species to be
reproductively isolated from each other?
• Members of the two species cannot interbreed
and produce fertile offspring.
Speciation
• 3 main types
• Allopatric Speciation
• Sympatric Speciation
• Adaptive Radiation
The process of species formation:
Four Steps:
• Single population is an interbreeding, reproductive
community.
• Development of a reproductive
allopatric populations).
barrier (formation of
• Differentiation of the separated populations.
• New species can no longer interbreed even if barrier
disappears and they become sympatric.
Reproductive barriers
prezygotic
• Barriers:
• Geographic
• Temporal
• Behavioral
• Mechanical
• Gamete compatibility
prevent fertilization
postzygotic
• fertilization occurs, but the
hybrid zygote does not
develop into a viable, fertile
adult
Prezygotic Barriers - examples
mechanical
structural differences prevents
mating
Gamete incompatibility
female and male gametes are
chemically incompatible
Postzygotic Barriers - examples
Reduced hybrid viability
frogs; zygotes fail to develop or reach sexual maturity
Reduced hybrid fertility
mule; horse x donkey; cannot backbreed
Hybrid breakdown
cotton; 2nd generation hybrids are sterile
allopatric
sympatric
Three Ways Reproductive Isolation
(barriers) occurs
• Behavioral isolation
sympatric
• Temporal isolation
• Geographic isolation
allopatric
Allopatric speciation
involves the
geographic
separation of the
parent population
into two
subpopulations.
It can occur if a
physical barrier
separates the range
of a population.
Allopatric speciation example
• The populations of Tamarin
monkeys are separated on
the sides of the Amazon
River.
• Where the river tributary is
wide and individuals on
opposite banks do not
interbreed, the populations
are diverging toward separate
species. Where the river
tributary is narrow, the
individuals still interbreed.
Geographic Isolation in action
• Speciation in action?
• In the summer of 1995, at least 15 iguanas survived
Hurricane Marilyn on a raft of uprooted trees.
• They rode the high seas for a month before colonizing
the Caribbean island, Anguilla.
• Evolutionary biologists would love to know what happens
next:
• will the colonizing iguanas die out,
• will they survive and change only
slightly, or
• will they become reproductively
isolated from other Iguana iguana
and become a new species?
Geographic isolation is
usually a prerequisite to
speciation.
However, there are
situations in which
speciation can take place
between populations that
are sympatric.
Sympatric
speciation
occurs without any
separation of the
ancestral
geographic range.
(Some evolutionary
biologists doubt this
ever happens.)
Sympatric Speciation
macro
temporal
behavioral
micro
• Balanced Polymorphism
• Polyploidy
• Hybridization
Balanced Polymorphism example:
• Suppose a population of mice
possesses a polymorphism for color.
Each color provides a camouflage to
a different substrate (rock, sand,
etc..).
• When not camouflaged, they are
eaten
• Thus, only mice with the same
color associate and mate
• Similarly colored mice are
reproductively isolated…so gene
pools can diverge.
Polyploidy example
• More than 2 sets of
chromosomes found in
diploid (2n) cells.
• Often occurs in plants
(occasionally animals)
where triploid (3n),
tetraploid (4n) and
higher chromosome
numbers exist.
• Caused by
nondisjunction in
meiosis
Tetraploid individuals will
continue to produce diploid
gametes – making them
reproductively isolated very
quickly.
Hybridization example
• Occurs when 2 different forms
of a species mate and produce
offspring along a geographic
boundary called a hybrid zone.
• The genetic variation of the
hybrids is greater than that of
either parent
• This permits hybrids to adapt
to environmental conditions
beyond the range of either
parent.
• Hybrids can eventually diverge
from parent forms when
faced with selective pressures
The Process of sympatric Speciation
temporal isolation
genetic isolation achieved due to
temporal differences in breeding.
lacewings
C. Carnea is light green in spring
and early summer, changing to
brown in the fall. They live in fields
and meadows in the summer and
move to deciduous trees in the fall.
C. downesi is a darker green year
round. C. downesi lives mainly on
conifers.
Their ranges are sympatric. The
species are separated by breeding
season as well as habitat. C. carnea
breeds in winter and again in
summer. C. downesi breeds only in
the spring.
The Process of Speciation
• When does behavioral isolation occur?
• It occurs when populations are capable
of interbreeding but have differences in
courtship rituals or other types of
behavior.
niche choice due to food
preference
A rare, but local example
"resident" and "transient" Orcas
Resident and transient orcas inhabit the same waters, but avoid each other
and do not interbreed. The two forms hunt different prey species and have
different diets, vocal behavior, and social structures.
Another example
Wolves and dogs courtship patterns are different in the wild
Behavioral Isolation example
• Difference in courtship rituals
Western and Eastern
Meadowlark
Different mating songs
graphic summary
Adaptive Radiation
• Relatively rapid evolution of many species from a single
ancestor.
• Ancestral species colonizes an area where diverse
geographic or ecological niches are available for
colonization.
• Examples: Darwin’s Finches, Australian Marsupials
Adaptive Radiation
Concept Map
Reproductive Isolation
results from
Isolating mechanisms
which include
Behavioral isolation
Geographic isolation
Temporal isolation
produced by
produced by
produced by
Behavioral differences
Physical separation
Different mating times
which result in
Independently
evolving populations
which result in
Formation of
new species
allopatric
Gene flow
sympatric
Patterns of Evolution
• Evolution can take place along the lines
of the following patterns:
• Divergent Evolution
• Convergent Evolution
• Parallel Evolution
• Coevolution
Divergent Evolution
• Describes two or more species that originate from a common
ancestor.
• This may happen as a result of allopatric or sympatric
speciation or by adaptive radiation
Convergent Evolution
• Describes two unrelated species that share similar traits.
• Similar traits arise because each species has independently
adapted to a similar niche
• These traits are called: Analogous Traits
Convergent Examples
• Sharks, porpoises, and penguins have torpedoshaped bodies with peripheral fins. These traits
arise as a result of adaptations each species has
made to aquatic life…not due to a common
ancestor.
• The eyes of squids and vertebrates are physically
and functionally similar. However they are not
from a recent common ancestor, both evolved
independently to perform similar functions.
Parallel Evolution
• Describes two related species or two related lineages that
have made similar evolutionary changes after their
divergence from a common ancestor
• Example:
• Species from two groups of mammals, the marsupial mammals and
the placental mammals, have independently evolved similar
adaptations when ancestors encountered comparable environments
Coevolution
• Describes the evolution of one species in response to new
adaptations that appear in another species
• An example: evolutionary arms race between predators and
prey…or
• Plants and plant eating insects
• Pollinators and flowering plants
• Pathogens and animal immune systems