4C part 2 Flashcards
Speciation ->
* is the process by which new ______ ____, i.e., formation of __________
* Process is one of the most fundamental questions in _________ biology
today
* combines the study of _______, ________ & ________
* links _________& _______ processes
- is the process by which new species arise, i.e., formation of biodiversity
- Process is one of the most fundamental questions in evolutionary biology
today - combines the study of ecology, evolution & genetics
- links micro & macroevolutionary processes
Population divergence is driven by _______ _________ or _______between environments
(Schluter 2000)
Population divergence is driven by natural
selection or drift between environments
(Schluter 2000)
1)What causes the initial divergence?
2)How does Reproductive Isolation Evolve?
3)When is “the process” of speciation complete?
4)What happens when hybridization occurs
1) barriers, which separate populations and prevent gene flow.
Changes in abiotic factors, such as environmental conditions or the availability of new niches.
2)Reproductive isolation evolves mainly through three mechanisms:
Divergent natural selection.
Fixation of incompatible mutations
Random genetic drift
3)Speciation is complete when two populations can no longer interbreed to produce fertile, healthy offspring.
4)When hybridization occurs, two different species or populations mate. If hybrids are strong and fertile, it can create a new species or merge the two. If hybrids are weak or sterile, it strengthens reproductive isolation. Sometimes, hybrids survive only in a special zone.
Factors causing genetic divergence between isolated
population
- Genetic drift
- Founder effect & population bottleneck
- Mutation
- Differential selection
Reproductive isolation
Reproductive isolation by ecology and behavior
1)Prezygotic mechanisms -
2)Postzygotic mechanisms-
Mating attempt ->fertilization
1)Prezygotic mechanisms - prevent mating or fertilization
2)Postzygotic mechanisms- prevent zygote development or reproduction
Reproductive isolation: Prezygotic barrier
- Habitat isolation
- Behavioural isolation
- Temporal isolation
- Mechanical isolation
- Gametic isolation
Prezygotic Barriers
- Mechanical isolation
– Genitalia
– Pollinator isolation - Columbines (bird vs. moth)
Prezygotic Barriers
Prezygotic Barriers
* Gametic/genetic isolation: zygotes do not form
– Genetic incompatibility systems in plants
– Pollen tubes cannot grow
Reproductive isolation: Postzygotic barrier
- Reduced hybrid viability
- Reduced hybrid fertility
- Hybrid breakdown
Postzygotic Barriers
- Hybrids have reduced viability (reduced fitness) compared to parents
– Rana pipiens (leopard frog) and R. sylvatica (wood frog) - Frequently breed in same ponds
– Males “grab” females indiscriminately - Embryonic development of hybrids fails in early development
Three outcomes…
With renewed or continued contact between two populations, there are
three possible outcomes:
* Individuals can ______ ______.
* Individuals do not _______ at all.
* Individuals hybridize but offspring have ________ _________
With renewed or continued contact between two populations, there are
three possible outcomes:
* Individuals can hybridize readily.
* Individuals do not hybridize at all.
* Individuals hybridize but offspring have reduced fitness
-
-
Modes of speciation
Allopatric speciation
Sympatric speciation
“Spontaneous” speciation (special cases
Allopatric speciation
- physical barrier (e.g., new river)
divides geographic range
(vicariance event) - gene flow ceases and separate
populations evolve independently - over time, different alleles become
fixed, because of mutation + drift
and/or selection
Allopatric speciation
* provided sufficient time has elapsed for __________ _________ to have taken place
* if barrier is removed and populations come back into contact, they may ______ _______
* _________ prevented by _______ and/or _________ mechanism
Allopatric speciation
* provided sufficient time has elapsed for significant divergence to have taken place
* if barrier is removed and populations come back into contact, they may remain distinct
* interbreeding prevented by prezygotic and/or postzygotic mechanism
What is sypatric specialization?
Sympatric speciation
* In sympatric speciation, there is no
geographic barrier to gene flow.
What prevents reproduction between
individuals from different populations
living in the same area
In sympatric speciation, reproduction between individuals in the same area is prevented by things like:
Different mating behaviors (like different songs, scents, or displays)
Different breeding times (like one group breeding in spring, another in fall)
Preference for different habitats or food sources
Genetic incompatibilities (even if they mate, the offspring don’t survive or are sterile)
Course of sympatric speciation
- initial stage: polymorphism that affects fitness (e.g., two forms adapted
to eat different foods) - matings between two forms are discouraged (prezygotic) and/or
disadvantageous (postzygotic
Polyploidization
* Polyploidy can cause ______ _______
* _______ fails and organism produces __
________
* If 2n gamete is fertilized with another 2n
gamete (e.g., _______) = ___________
* Autopolyploids can only mate ____ ______
________= reproductive isolation
* Allopolyploidization is similar but involves first the mating between ___ ______-______ species
Polyploidization
* Polyploidy can cause sudden speciation
* Meiosis fails and organism produces 2n
gametes
* If 2n gamete is fertilized with another 2n
gamete (e.g., selfing) = autopolyploid
* Autopolyploids can only mate with other
autopolyploids = reproductive isolation
* Allopolyploidization is similar but involves first
the mating between two closely-related specie
Polyploidization is very common in …
Species of coffee plant with ___,__,___, and __ chromosomes are known. This suggests
ancestral coffee likely n = __
Polyploidization
▪ very common in ferns & flowering plants
* Species of coffee plant with 22, 44, 66, and
88 chromosomes are known. This suggests
ancestral coffee likely n = 22
Species concepts
* _________ to address how to organize the discrete _______ of variation in
nature
* Different concepts place __________ _______ on various factors (e.g., ____
____)
* There are over __ species concepts!
* Major categories:
* –
* -
- Others:
Species concepts
* Framework to address how to organize the discrete clusters of variation in
nature
* Different concepts place differential emphasis on various factors (e.g., gene
flow)
* There are over 20 species concepts!
* Major categories:
* Morphological – individuals that look alike
* Reproductive - ability to produce offspring
* Others: Phylogenetic/evolutionary - shared evolutionary history
Morphospecies Concept
* Species are discrete types of organisms, defined by ______ ______
__________characters
* most _______ concept
* Advantages:
* Disadvantages:
Morphospecies Concept
* Species are discrete types of organisms, defined by unique reliable
morphological characters
* most traditional concept
* Advantages: practical; simple to use
* Disadvantages: no clear genetic or evolutionary justification; choice of
characters may be arbitrary, some species cannot be diagnosed morphologically
Biological Species Concept (BSC)
“Species are groups of actually or potentially ________ natural
populations that are reproductively _______ from other such groups.”
– Ernst Mayr 1942
Most commonly used ______concept
Advantages:
Disadvantages:
Biological Species Concept (BSC)
“Species are groups of actually or potentially interbreeding natural
populations that are reproductively isolated from other such groups.”
– Ernst Mayr 1942
Most commonly used species concept
Advantages: clear criteria, clear evolutionary justification
Disadvantages: may be difficult to distinguish in the field – less of an issue
with genomics
Other species concepts
Phylogenetic/evolutionary species
- members of a species share a common ancestry
- more useful when thinking about asexual species
Species Concepts: Key Points
* ______ in nature can be hard to define
* no one species concept is ‘________’ for all groups
* BSC has proven to be extremely useful for the study of _______
* Think of species as _________……
Species Concepts: Key Points
* species in nature can be hard to define
* no one species concept is ‘correct’ for all groups
* BSC has proven to be extremely useful for the study of speciation
* Think of species as hypotheses……
