Species and Speciation
Organisms
• Organisms are classified into species
• Number of species on earth: 5-100 million (only
~1.4 million species described )
• 70% of the world's species are in only 12 countries:
Australia, Brazil, China, Colombia, Ecuador, India,
Indonesia, Madagascar, Mexico, Peru, and Zaire.
Species
A
Species
B
Non-Evolutionary Approaches I
• Typological Species Concept: species are a
'type' of organism…Plato
• Existence of a limited number of universals
• No regard to variation in a species
• "Species are as many as were created in the
beginning by the Infinite." (Linnaeus, 1758)
Non-Evolutionary Approaches II
• Essentialism
• Similar to typological thinking
• Species consist of individuals sharing the same
essence
• Species are separated by sharp discontinuity
• Each species is constant through time
• Limits to variation within a species
Non-Evolutionary Approaches III
•
•
•
•
•
Nominalistic
Only Individuals exist
There are no “real” universals
Popular in France in late 1800s
Nature produces individuals and nothing
more…no species.
• Species are only mental constructs
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Evolutionarily Species Concepts
• The lineage species concept
• A single species forms an evolutionary
lineage separated from other species.
• They are not in genetic contact with other
species
• Therefore, the species concepts might be
criteria for determining the split between
species.
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Biological Species Concept
• Species are groups of actually or
potentially interbreeding natural
populations, which are reproductively
isolated from other such groups (Mayr,
1940).
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Problems with the BSC
• What do you do with asexual organisms, and
what do you do with organisms that
occasionally form hybrids with one another?
Other difficulties include:
• What is meant by “potentially interbreeding
• Fossils---for example, it is not really possible
(or very meaningful!) to figure out whether a
trilobite living 300 million years ago would
have interbred with its ancestor living 310
million years ago.
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Evolutionary species concept
• Evolutionary species concept: A species is
a single lineage of ancestor-descendant
populations which maintain its identity
from other such lineages and which has it
own evolutionary tendencies and historical
fate (Simpson, 1961; Wiley, 1981).
• Difficult to apply, so we use the following:
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Phylogenetic species concept
• A species is the smallest diagnosable
cluster of individual organisms within
which there is a parental pattern of
ancestry and descent (Cracraft 1983).
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Six Giraffe Species?
Approximate geographic ranges, pelage patterns, and phylogenetic
relationships between giraffe subspecies based on mtDNA sequences.
(From: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2254591/ )
https://www.wvup.edu/.../Biology%20461%20Species%20and%20Sp...
Other concepts
•
Cohesion species concept: A species is the most inclusive group
of organisms having the potential for genetic and/or demographic
exchangeability. (Templeton, 1989)
•
Ecological species concept: A species is a set of organisms
exploiting (or adapted to) a single niche (Ridley 1993).
•
Recognition species concept: A species is the most inclusive
population of individual biparental organisms which share a common
fertilization system. (as defined by Paterson, 1985; in Templeton,
1989).
•
Isolation species concept: Species are systems of populations:
the gene exchange between these systems is limited or prevented
by a reproductive isolating mechanism or perhaps by a combination
of several such mechanisms. (as defined by Dobzhansky 1970; in
Templeton, 1989)
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Speciation
• Formation of
new species
„
(a) Morphospecies. Viewed today, at one moment in time, species A, C, and E are
clearly distinct, demarcated by current natural discontinuities between them. (b)
Paleospecies (chronospecies). Viewed historically, through time, discovered
fossil intermediates (B and D) fill in the missing gaps above, giving us a more or
less continuous series with no obvious discontinuities between them.
https://www.wvup.edu/.../Biology%20461%20Species%20and%20Sp...
Allopatric Speciation
• The simplest and
most common
mechanism of
speciation is allopatric
speciation: 2 groups
of one species are
isolated
geographically, and
diverge into separate
species.
www.bios.niu.edu/johns/bios103/speciation.ppt
Allopatric Speciation
• Results from
populations of a single
species becoming
separated from each
other and evolving in
different ways
• 1. Geographic isolation
• 2. Adapt to different
environments
• 3. Can no longer
interbreed with each
other
Early fox
population
Northern
population
Spreads
northward
and
southward
and
separates
Arctic Fox
Adapted to cold
through heavier
fur, short ears,
short legs, short
nose. White fur
matches snow
for camouflage.
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Southern
population
Gray Fox
Adapted to
heat
through
lightweight
fur and long
ears,
legs, and
nose, which
give off
more heat.
Rocky Mountains may be
a barrier that prevents
Canada lynx from
breeding with
populations on the other
side of the mountain.
U.S. Fish & Wildlife Service
Image
PA
NG
AE
A
120° 80°
LAURASIA
40°
80°
120°
120° 80°
80°
120°
GONDWANALAND
135 million years ago
225 million years ago
Continental drift
NORTH AMERICA
EURASIA
AFRICA
120° 80°
SOUTH
AMERICA
INDIA
MADAGASCAR
120°
120°
0°
AUSTRALIA
ANTARCTICA
65 million years ago
Present
40°
120°
Reproductive
barriers
Prevent gene flow
Peripatric Speciation
•
•
•
An isolated group is
severed from the original
population
Rare genes move to
fixation
If these genes are
associated with
reproduction, sexual
selection takes over, then
speciation has occurred
as they may not mate
with the original
population
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Hawai’ian Drosophila
500 species!!!
http://dbs.umt.edu/courses/biol223/documents/speciation2232006post.ppt.
Parapatric speciation
•
In parapatric speciation
there is no specific extrinsic
barrier to gene flow.
•
The population is
continuous, but
nonetheless, the population
does not mate randomly.
•
Mating with geographic
neighbors more often.
•
In this mode, divergence
may happen because of
reduced gene flow within
the population and varying
selection pressures across
the population’s range.
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Sympatric speciation
•
Does not require large-scale
geographic distance to
reduce gene flow between
parts of a population.
•
Exploiting a new niche may
automatically reduce gene
flow with individuals
exploiting the other niche.
•
This may occasionally
happen when, for example,
herbivorous insects try out a
new host plant.
163.238.8.180/~fburbrink/Courses/.../Evolution%2017%20ppt.ppt
Species and Speciation
Sympatric Speciation
Cichlid fish in Lake Barmobi Mbo
in Cameroon, Africa—an
isolated volcanic lake.
Nine species, all more closely
related to each other (by DNA
evidence) than to similar fish in
other lakes.
Lake has no distinct geographical
zones, and the fish can easily
swim anywhere in it.
They feed in different locations,
but all breed in the same
location, close to the bottom.
An example of sympatric
speciation, but the mechanism
is not clear.
www.bios.niu.edu/johns/bios103/speciation.ppt
Sympatric Speciation
Polyploidy
July 27, 2005
Two Species Become One, Study Says
The newly discovered Lonicera fly
species arose through hybridization, a
new study says. Two other fly species
mated and formed a hybrid, a
combined form that cannot mate with
its fellow hybrids. Given a separate
niche in which to evolve—in this case,
an alien huneysuckle imported to the
U.S.—a hybrid animal can become a
full-fledged new species, according to
researchers.
Photograph by Guy Bush
Ring Species
http://dbs.umt.edu/courses/biol223/documents/speciation2232006post.ppt.
Speciation & Macroevolution
The Gradualism model
suggests that change is
gradual with the
accumulation of unique
morphological adaptation.
- The Punctuated
Equilibrium model
suggests that rapid change
occurs, with a new species
“erupting” from the
ancestral lineage and then
staying the same
thereafter.
www.eeescience.utoledo.edu/.../Lecture%207%20-%20macroevoluti...
Mesozoic
Cenozoic
Marsupials
(kangaroos, etc.)
Rabbits
Rodents
Primates
Bats
Insectivores
Carnivores
Whales
Even-toed
hoofed mammals
Odd-toed
hoofed mammals
Elephants
Monotremes
(platypus, etc.)
Extinction
•
•
Background extinction –
inability to adapt to changing
environment
Mass extinction – periodic
large-scale extinctions
resulting from asteroid
impacts or other causes
– Reshuffle life on the planet
– Winners become losers
and vice versa
• E.g. 65 mya mammals
take over from reptiles
and underwent
adaptive radiation
Cenozoic
Era
Period
Quaternary
Millions of
years ago
Today
Bar width represents relative Species and families experiencing
number of living species
mass extinction
Extinction
Tertiary
65
Extinction
Mesozoic
Cretaceous
Jurassic
180
Extinction
Cretaceous: up to 80% of ruling
reptiles (dinosaurs); many marine
species including many
foraminiferans and mollusks.
Triassic: 35% of animal families, including
many reptiles and marine mollusks.
Triassic
250
Extinction
Permian
Carboniferous
Paleozoic
Current extinction crisis caused
by human activities. Many species
are expected to become extinct
within the next 50–100 years.
345
Permian: 90% of animal families, including
over 95% of marine species; many trees,
amphibians, most bryozoans and
brachiopods, all trilobites.
Extinction
Devonian: 30% of animal families,
including agnathan and placoderm
fishes and many trilobites.
Extinction
Ordovician: 50% of
animal families,
including many
trilobites
Devonian
Silurian
Ordovician
Cambrian
500