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

Possible hybridization

Character shifts

Variable, but distinct species where several co-occur

History and Phylogeny

• Common Ancestor, something like a grassquit

• Warbler finch earliest split

• Galapagos colonized then Cocos

• Likely 2-3my—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 large-billed 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-Evolution-Speciation

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

Differences consistent with amount that would accumulate with .8-3.2my of drift—Andes uplift was 3my

2 distinct clades on east-side suggest ancient split and secondary contact

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

Hourlay et al. 2008

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)

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.