Transcript Adaptation / Speciation

Science & Society Picture Library
Natural Selection & Speciation
Journal of Researches 1836
5 – year voyage of the Beagle
On the Origin of Species by Means of
Natural Selection(1859)
Journal of Researches 1836
5 – year voyage of the Beagle
On the Origin of Species by Means of
Natural Selection(1859)
http://www.aboutdarwin.com/literature/CD_Books.html
The phenotype is the external, observable expression of an
organisms genetic make up.
The phenotype, is the expression of an organisms genotype.
The genotype is the sum of heritable information (genes) carried
by an organism
Alternative forms of a gene are called alleles.
So…phenotypic variation within a population is related to allele
frequency (the frequency of alternate forms of a gene).
-Natural Selection is the differential success of individuals within
a population such that traits are eliminated or emphasized over
(evolutionary) time. This is trait-based, acting on individuals…
but the effects accumulate in populations over generations.
(1) Heritable Variation
(2) This Variation Results in Differences in (Evolutionary) Fitness
For any given trait, there is generally a “normal” distribution…
natural selection sometimes applies pressure along this distrubution
Sexual Selection
Fitness is not specifically
related to competition and
access to resources…
…it also is related to mate
acquisition
Sometime this “sexual
selection” drives
morphological change
Sexual selection can cause the
accumulation of apparently
useless, and bizarre, traits.
Lion’s Mane Reading for Next Time!
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Speciation
What is a species
Speciation is the process of one species diverging
(evolving) into two (or more) species.
At the most basic level, the process is dictated by two
processes:
Gene flow
Selection
1) Gene flow is the movement of genetic
material within, and among, populations
of a given species
•
For (most) animals this involves the movement of
individuals (offspring, mostly) over geographic
distances. For gene flow to be accomplished that
individual would then reproduce.
Hit the road jack!!
1) Gene flow is the movement of genetic
material within, and among, populations
of a given species
•
For (most) animals this involves the movement of
individuals (offspring, mostly) over geographic
distances. For gene flow to be accomplished,
then, that individual would then reproduce.
•
In plants, gene flow is accomplished through
pollen movement, and through seed (or clone)
dispersal.
Populations of Populus nigra.
Gene flow binds together the populations that make up a species.
Speciation is the process of one species diverging
(evolving) into two (or more) species.
At the most basic level, the process is dictated by two
processes:
1) Gene flow
2) Selection
2) (Natural) Selection is the differential success of
individuals within a population such that traits are
eliminated or emphasized over (evolutionary) time.
- variation among individuals in a heritable trait.
- variation results in difference in reproductive
success/survival (i.e., evolutionary fitness).
Flowering dogwood (Cornus florida)
http://www.plantbio.ohiou.edu/trees/Cornus%20florida.htm
Role of Selection?
(eg. habitats different)
Gene flow is holding the populations together.
Selection is driving the populations apart.
what if gene flow is prevented?
Differentiation, the development of ecotypes...
maybe, later, speciation
Ok…so how do you get from here, to speciation??
Modes of speciation:
(1) Allopatric speciation (classical model).
- Founder effect speciation.
- Peripheral isolates speciation.
(2) Sympatric speciation
- Genetic hiccups.
1) Allopatric speciation (classical model).
- A species range is divide geographically by some
event, dividing the species into sub-groups and
blocking gene flow.
- Selection pressures within the sub-groups drive
them toward dissimilarity, differentiation occurs,
then eventually the two become reproductively
isolated.
Populus nigra
- Gene flow is blocked
- Gene flow is blocked
Adaptation, differentiation, ecotypes, reproductive
isolation…speciation
A Special Case of Allopatric
- Founder effect model of speciation.
- Some event leads to a very small population- or
with plants a single individual, arriving in some new
location, beyond the range of gene flow.
- Usually intense selection pressure (and inbreeding)
commence- the founder population diverges quickly
and becomes a new species.
Populus nigra.
Populus nigra.
- Gene flow is blocked (& inbreeding &
intense selection pressure)
Adaptation, differentiation, ecotypes, reproductive
isolation…speciation
- Founder effects can lead to adaptive radition
Another Special Case of Allopatric Speciation
- Peripheral isolates speciation.
- Perhaps most common (or constant)
- Individuals at the edge of a species range are
isolated from the main body of the range.
- Gene flow is restricted- Selection intense.
- Ecotypes (varieties) develop, then reproductive
isolation, then speciation.
Puma concolor
Puma concolor
Puma concolor
Puma concolor
Gene flow from the south
to the north of this range is
highly restricted
Puma concolor
Populations on the
periphery of this very large
range are differentiating
into varieties, moving
(perhaps) toward
speciation
Argentine puma
Costa Rican Cougar
Eastern South American cougar
North American Cougar (Puma concolor couguar) includes the
previous subspecies and synonyms arundivaga, aztecus, browni,
californica, coryi, floridana, hippolestes, improcera, kaibabensis,
mayensis, missoulensis, olympus, oregonensis, schorgeri,
stanleyana, vancouverensis and youngi;
Northern South American cougar
Southern South American puma
Puma concolor
Some populations are
already completely
isolated (e.g., Florida)
Sympatric Speciation
• Sympatric speciation occurs when new species
evolve from a single ancestral species while
inhabiting the same geographic region – there is no
geographic constraint to interbreeding
• Driven by multiple mechanisms:
– Genetic Hiccup: occurs when organism carries one or
more extra sets of chromosomes than parents; common
in plants, usually causes death in animals
– Differing habitats: hunt different prey or utilize different
resources
– Sexual selection: different mating calls or behavior
Genetic hiccup.
- Something goes wrong during the reproductive process.
- Some mutation occurs, or new portion of the genome is
turned on, that cause a wildly different morphology, or
other reproductive isolating mechanism. Generally does
not work with animals!
- In plants, “hiccup” involves a change in the number of
chromosomes. E.g., reproduction involving two diploid
organisms produces a triploid offspring, which then cannot
interbreed with the parent population, but being selffertile can produce offspring by itself.
Polyploidy
Behavior
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What does speciation look like…
in the field
…on human time frames
Hybrids and Ecotypes
Hybrids and Ecotypes
Hybrids and Ecotypes
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Speciation