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Transcript
Micro to Macro
Evolution
Birds have and continue
to be important models of
the speciation process
30 year insight into
evolution and speciation
in Darwin’s Finches
Great Adaptive
Radiation
Focus on Changes in Bill Size in
Relation to Competitors and
Environment
Variable, but
distinct species
where several
co-occur
Possible hybridization
Character shifts
History and Phylogeny
• Common
Ancestor,
something
like a
grassquit
• Warbler finch
earliest split
• Galapagos
colonized
then Cocos
• Likely 23my—during
cycles of
Pleistocene
glacial
advance and
retreat
Random Drift after
Colonization
Micro-Evolution
Natural
Selection drives
consistent
change rather
than random
variation from
drift
Drought
selected for
large billed birds
in 1977 who
produced largebilled offspring in
1978
Competition Forces
Larger Differences
When large
billed finches
of different
species
colonize an
island,
medium-billed
finches are
selected to
evolve smaller
bills by a
process known
as Character
Displacement
Macro-EvolutionSpeciation
A strong interplay
between isolation,
hybridization, natural
selection, drive
speciation which is
confirmed or negated
when populations come
back into contact
Reproductive Isolation
Mate selection is assortative for bill size/shape and song
which acts to reinforce “species boundaries”
Mountains and Glaciers
• Importance of reproductive
isolating factors and allopatric
speciation
Glacial advances and retreats in American
Redstarts (Colbeck et al. 2008)
and White-throated Dippers (Hourlay et al.
2008)
Andes Mountains and the diversification in
Wedge-billed Woodcreepers (Mila et al.
2009)
Mountains, Natural
Selection along Gradients
• Vicariant versus ecological factors
• Allopatric versus parapatric
speciation
• Woodcreeper ranges to 1500m in
Eucador, a steep and substantial
environmental gradient
• Measured morphology likely to
respond to foraging, flight, and
general climate (Bergmann’s rule
that animals are larger in colder
climates)
Support for morphology
responding to environment
• Wing and tarsus respond to relevant
environmental effects on flight and
foraging
• General increase in body size with
elevation as Bergmann would have
predicted.
And Significant Genetic Variation
attributed to Andes as Barrier
2 distinct clades on eastside suggest ancient split
and secondary contact
Differences
consistent with
amount that would
accumulate with .83.2my of drift—
Andes uplift was
3my
Natural Selection Effects
Change Despite Gene Flow
On east side, where
gene flow is substantial
there are still differences
among birds from
different (but not the
same) habitats
This microevolution may
lead to macroevolution
The importance of
lowland – foothill
transition areas in
Andes are
highlighted. They
are important
sources of
variation in a bird
and hence
important areas to
conserve.
Glaciation and Refuges
• Many studies have shown that significant
variation within a species is likely associated with
past isolation in separate glacial refuges
– 700,000 years of ebbs and expansions of glaciers
every ~100,000 years
• Pleistocene refuges
– Single refuge
• Species with narrow current range
• Widespread species with limited migratory ability
– Two or more
• Species currently widely distributed across significant
geographic barriers
Colbeck et al. 2008
European Dippers show Complex Pattern
Consistent with Multiple Refuges
Hourlay et al. 2008
European Dippers show Complex Pattern
Consistent with Multiple Refuges
Strong Genetic Differences requiring a Minimum 4 mutation
events to produce changes
Amount of variation between groups suggests longest
separation between Asian birds and others (~250000 years),
long history (120000 years) of separation between east and
west Europe, less (40-100000 years) between others
Significant difference between populations of what we
currently classify as a single subspecies (east and west
Europe)
Likely many refuges
north Italy
Sicily
Balkans
Ural Mountains (Russia)
Hourlay et al. 2008
Redstarts Show A
Different Pattern
Widespread, but no difference east vs. west
Strong difference between Newfoundland and
continental (likely arose 40,000 – 2,000,000 years ago)
Support for 1 large refuge (likely in SE US) and a
second smaller one in Newfoundland
So, all widespread continental birds were not affected
in same way by glaciation during Pleistocene
How Does Micro- become
Macro-Evolution?
• Natural Selection, Sexual Selection,
maybe chance while isolated prevents
interbreeding when reconnected
– Greenish Warbler (Irwin et al. 2001), sexual
selection and cultural evolution of song types
preclude interbreeding at either end of ring
(blue vs. red)
References
• Colbeck, G. J., Gibbs, H. L., Marra, P. P.,
Hobson, K., and M. S. Webster. 2008.
Phylogeography of a widespread North American
migratory songbird (Setophaga ruticilla). Journal
of Heredity 99:453-463.
• Grant, P. R. and B. R. Grant. 2008. How and Why
Species Multiply. Princeton Univ. Press.
• Hourlay, F., Libois, R.Damico, F., Sara, M.,
O’Halloran, J, and J. R. Michaux. 2008. Evidence
of a highly complex phylogenetic structure on a
specialist river bird species, the dipper (Cinclus
cinclus). Molecular Phylogenetics and Evolution
49:435-444.
• Irwin, D. E., Bensch, S., and T. D. Price. 2001.
Speciation in a ring. Nature 409:333-337.
• Mila, B., Wayne, R. K., Fitze, P. and T. B. Smith.
2009. Divergence with gene flow and fine-scale
phylogeographical structure in the wedge-billed
woodcreeper, Glyphorynchus spirurus, a
Neotropical rainforest bird. Molecular Ecology
18:2979-2995.