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What is a species?
Speciation
  Biological species concept
population whose members can interbreed &
produce viable, fertile offspring
  reproductively compatible

Mom, Dad…
There s something
you need to know…
I’m a MAMMAL!
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Distinct species:
songs & behaviors are different
enough to prevent interbreeding
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How and why do new species originate?
  *EK: Speciation has occurred
throughout Earth’s history
Eastern Meadowlark Western Meadowlark
Pre-zygotic barriers
  Obstacle to mating or to fertilization if
mating occurs
  *EK: Speciation may occur when 2
populations become reproductively
isolated from each other

populations become isolated
  allopatric – geographically
isolated
geographic isolation
  sympatric – still live in same area
ecological isolation
temporal isolation
mechanical isolation
gametic isolation
but are reproductively isolated

isolated populations evolve
independently
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behavioral isolation
Ammospermophilus spp
Geographic isolation
  Species occur in different areas


different habitats so rarely encounter
each other
physical barrier
allopatric speciation
  other country
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Ecological isolation
  Species occur in same area, but occupy
Harris’s antelope
squirrel inhabits
the canyon s
south rim (L). Just
a few miles away
on the north rim
(R) lives the
closely related
white-tailed
antelope squirrel
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial
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lions & tigers could
hybridize, but they
live in different
habitats:
  lions in grasslands
  tigers in rainforest
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sympatric speciation?
Temporal isolation
Behavioral isolation
  Species that breed during different
  Unique behavioral patterns & rituals isolate species
times of day, different seasons, or
different years cannot mix gametes

sympatric speciation

ex: E and W spotted shunk


identifies members of species
attract mates of same species 
  courtship rituals, mating calls
  same country”
Eastern spotted skunk
(L) & western spotted
skunk (R) overlap in
range but eastern mates
in late winter & western
mates
in late summer
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Blue footed boobies mate
only after a courtship display
unique to their species
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sympatric speciation?
Recognizing your
own species
courtship songs of sympatric
species of lacewings
courtship display of
Gray-Crowned Cranes, Kenya
firefly
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courtship displays
Mechanical isolation
  Morphological differences can prevent
successful mating
Plants
Even in closely related
species of plants, the
flowers often have distinct
appearances that attract
different pollinators.
These 2 species of monkey
flower differ greatly in
shape & color, therefore
cross-pollination does not
happen.
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sympatric speciation?
Mechanical isolation
  For many insects, male &
Animals

Damsel fly penises
mechanisms
  biochemical barrier so sperm cannot penetrate egg
  receptor recognition: lock & key between egg & sperm
  chemical incompatibility
  sperm cannot survive in female reproductive tract
lack of fit between sexual organs:
hard to imagine for us… but a big issue for insects with
different shaped genitals!
I can’t even imagine!
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  Sperm of one species may not be able to fertilize eggs of
another species
female sex organs of
closely related species do
not fit together, preventing
sperm transfer

Gametic isolation
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
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sympatric speciation?
Post-zygotic barriers
  Prevent hybrid offspring from
developing into a viable, fertile adult
Reduced hybrid viability
  Genes of different parent species may
interact & impair the hybrid’s development
reduced hybrid viability
  reduced hybrid fertility
  hybrid breakdown

Species of salamander
genus, Ensatina, may
interbreed, but most
hybrids do not complete
development & those
that do are frail.
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zebroid
Salamander Speciation
Reduced hybrid fertility
Ensatina
salamanders in
California exhibit
subtle physical and
genetic differences
all along their
range. They all
interbreed with
their immediate
neighbors with one
exception: where
the extreme ends of
the range overlap
in Southern
California, E.
klauberi and E.
eschscholtzii do
not interbreed.
  Even if hybrids are vigorous
they may be sterile

chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64
chromosomes
(32Biology
pairs)
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Donkeys have 62
chromosomes
Mules have 63 chromosomes! (31 pairs)
sympatric speciation?
Hybrid breakdown
  Hybrids may be fertile & viable in first
A love story……
generation, but when they mate offspring
are feeble or sterile
In strains of cultivated rice,
hybrids are vigorous but
plants in next generation are
small & sterile.
On
path to
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separate species.
The female chooses to
mate with another
species only if the
environment demands it.
The hybrid is weaker
but will develop into a
tadpole faster.
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  Species can be physically separated by
Rate of Speciation
  Does speciation happen gradually or
rapidly?
geographic barriers or various pre- and
post-zygotic mechanisms can maintain
reproductive isolation and prevent gene
flow.

Gradualism
  Darwin
  Lyell

Punctuated equilibrium
  Gould
  Eldredge
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Punctuated Equilibrium
  Rate of speciation is not
Gradualism
  Gradual divergence
constant
over long spans of
time

Niles Eldredge
Curator
American Museum of Natural History

rapid bursts of change
  species undergo rapid
assume that big
changes occur as
the accumulation
of many small ones
change when they 1st bud
from parent population
  Ex: surviving organisms
evolving rapidly after mass
extinctions
long periods of little or no
change
  Speciation rates can vary,
especially when adaptive
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radiation occurs.

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Ex: punctuated equilibrium in the
fossil record
Time
  New species arise from reproductive
isolation over long periods of time or
rapidly.
  Ex: rapid speciation – plant polyploidy
polyploid – mutational change in cell division
that results in an extra set of chromosomes
  prevents interbreeding with original population
  In just one generation, these ployploid plants
can reproduce asexually or they can reproduce
with other polyploids

Foraminiferan
(unicellular
organisms)
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Extinction
Evolution is not goal-oriented
•  Species extinction rates are rapid at times of ecological stress
•  At least 5 mass extinctions have occurred throughout
history
An evolutionary trend does not mean that
evolution is goal-oriented.
•  Ex. causes: dramatic
climate changes
occurring after meteorite
collisions and/or
continents drift into new
and different
configurations
•  Today, human have a
large impact on ecosystems
and species extinction rates
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well
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Remember that for
humans as well!
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