Download Speciation I

Species concepts in biology
morphological species
phylogenetic species
biological species
Morphological species
• the familiar “taxonomic”
description based on
sets of distinguishing
characteristics
• often works but can be
misleading
Morphological species of horned lizards
from Futuyma (1998), p. 463
Morphological species
• these morphologically similar meadowlarks
sing different songs and do not interbreed:
they are true species
Eastern meadowlark Sternella magna
photo from Shaw Creek Bird Supply
Western meadowlark S. neglecta
photo from USFWS
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Morphological species
• these allopatric warblers were
previously classified as distinct species
• but they freely interbreed
Audubon’s warbler
Myrtle warbler
Maps from USGS
Breeding range map of myrtle warbler
Breeding range map of Audubon’s warbler
Breeding range map of myrtle warbler
Breeding range map of Audubon’s warbler
In the Rocky Mountains of
British Columbia and Alberta,
eastern boreal forest (white
and black spruce) mixes with
western montane forest
(Douglas fir, Engelman’s
spruce, and western white
spruce)
Breeding range map of myrtle warbler
Intergrades between myrtle
and Audubon’s warblers
result from interbreeding
They are now known as the
Audubon’s and myrtle races
of the yellow-rumped warbler
Breeding range map of Audubon’s warbler
The phylogenetic
species concept:
species are
monophyletic
groups
[tips of the tree are
individuals, letters are
species, numbers are
populations]
Application of the phylogenetic concept
helped uncover cryptic species in the
copepod Eurytemora affinis
And in African elephants
Biological species
• “...groups of interbreeding populations
that are reproductively isolated from
other such groups...”
– Ernst Mayr
Biological species
• the most widely accepted
and useful species concept
• problems:
– useless for asexual
organisms
– sometimes difficult to test
(e.g. allopatric species)
Biological species
• the most widely
accepted and useful
species concept
• problems:
– useless for asexual
organisms
– sometimes difficult to test
(e.g. allopatric species)
Biological species
• reproductive isolation: an
objective criterion that is
biologically significant
• application of the concept has
born a research program
Understanding speciation?
study the evolution of reproductive
isolation
Reproductive isolating
mechanisms
• prezygotic mechanisms act
prior to hybrid zygote
formation
– behavioral (mate choice)
– gamete recognition
• postzygotic mechanisms act
on hybrid zygotes
– hybrid inviability/sterility
– ecological inferiority of hybrids
Prezygotic: behavioral isolation
• courtship and mating behaviors diverge dramatically,
even between closely related species
• Hawaiian Drosophila do not interbreed: females reject
courtship of heterospecific males
Mating behaviors can evolve rapidly
• Drosophila heteroneura and D. silvestris are sister
species, sympatric on Hawaii
from Freeman and Herron 2002
D. heteroneura has dumbbellheaded males that butt heads
with other males to gain display
territories on leks
D. silvestris has roundyheaded males that fight other
males, Greco-Roman style,
for territories
Behavioral
isolation
• mating calls of frogs
and insects are
species-specific
• females recognize
conspecific calls
Prezygotic isolation by gamete
incompatibility
• marine
invertebrates and
other organisms
that lack mating
behavior: species
recognition occurs
between egg and
sperm
Sea urchin bindin: a gamete recognition
protein involved in speciation
Bindin
egg
surface
• Bindin is an adhesive
protein that binds sperm
to the egg surface.
Without this, fertilization
does not occur.
• Rapid change of bindin
proteins creates barriers
to fertilization between
species.
Postzygotic reproductive
isolation
• hybrids are
often inviable or
sterile
Postzygotic reproductive
isolation
• hybrids are sometimes ecologically inferior
bird predation on hybrids
creates abrupt boundaries
between Heliconius color
races