Biological Science 2/e

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The Origin of Species Presented supported two
hypotheses
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• Evolution as modification
• with descent,
• and
• 2) Natural selection as the
• mechanism for adaptation
• But
• Didnt really talk about the
• origin of species!

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Speciation the divergence of a single
ancestral species into two descendent
species. It is the process responsible for all
biodiversity.
http//orgs.unca.edu/tulula/images/biodiversity.jp
g
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What is a species? Do I know one when I see
one? (Morphological species concept looks
different)
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Biological species concept Reproductive
isolation between populations. Reproductive
isolation evolutionary independence.
Willow and Alder Flycatchers Look identical!
Dont interbreed.
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Phylogenetic Species Concept The PSC looks for
pattern of independent evolution.
Monophyletic group group that contains all
descendents of an ancestor.
PSC a species is the smallest monophyletic group.
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Species concepts have conservation implications
Dusky seaside VERY RARE N6 males in 1980
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Species concepts have conservation implications
Conservation managers mated these two species to
try to save the dusky seaside sparrow
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The PSC recognizes two species. Matings should
not be done between the two.
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Biological Species Concept focuses
on Reproductive Isolation. Reproductive
Isolation could be pre-or post-zygotic.
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Examples of pre-zygotic RI include Habitat
differences Many examples! Behavioral
differences Many examples!
http//www.ebertfest.com/two/grave_fireflies_blueb
at.jpg
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Examples of pre-zygotic RI include Genetic
differences among species
Bindin protein on urchin sperm is species-specific
.
http//www.luc.edu/depts/biology/dev/spersem.jpg
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In post-zygotic reproductive isolation,
offspring have Either low fitness for
example, stickleback with intermediate
morphology. Or low fertility
Horse 2N64 Donkey 2N 62. Mule has 2N 63.
Cant make balanced gametes.
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How is reproductive isolation established? In
Allopatric (different homeland)
speciation, geographic isolation leads to
reproductive isolation. Drift and selection can
cause divergence.
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Allopatric speciation can result from
dispersal. Speciation on islands is famous
example.
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Allopatric speciation can also result from
vicariance. Physical barrier divides
species. Barrier could be due to geologic
changes such as continental drift and
volcanism or to habitat changes due to climate
change.
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Ratites are flightless birds. Gondwana 150
mya, Began to split up 140 mya.
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Summary of allopatric speciation.
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Is sympatric (same homeland) speciation
possible? Gene flow can prevent divergence,
even when selection would favor
different adaptations.
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Sympatric speciation may be occurring in
soapberry bugs.
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Sympatric speciation also thought to occur in
fish Benthic and lotic forms of sticklebacks in
Alaska And in Rhagoletis flies that feed on
apples instead of hawthorne.
www.msu.edu/jimsmith/research.html
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Polyploidy in plants also leads to sympatric
speciation. Tetraploids are reproductively
isolated from diploids. Their triploid progeny
are sterile.
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What happens when recently diverged species come
into contact? Sometimes R.I. is not complete,
and fertile hybrids form.
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Townsends warbler is overtaking the hermit
warbler.
Some Townsends have mtDNA of hermits
suggesting repeated gene flow from Townsends
to hermits.
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Humans create hybridization opportunities. Lose
distinct species through hybridization.
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Humans create hybridization opportunities. Create
new invasive species through hybridization.
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Phylogenetic context, but still somewhat
typological. Notice that the degree of
resolution is far greater for non-Africans, and
also that Europe is placed farthest from the root
of the tree.
http//www.mcdonald.cam.ac.uk/genetics/images/MtDN
A_DistributionMap.gif
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Australia/New Guinea Europe Asian/Native
American African African Ingman et al.
(2000) Nature 408708.
mt DNA
50,000 ybp