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Transcript of Migration Evolutionarily, this means the movement of alleles, or gene flow between populations This...
![Page 1: Migration Evolutionarily, this means the movement of alleles, or gene flow between populations This will always be less than the movement of individuals.](https://reader036.fdocuments.in/reader036/viewer/2022070413/5697bfd81a28abf838caef1e/html5/thumbnails/1.jpg)
Migration
• Evolutionarily, this means the movement of alleles, or gene flow between populations
• This will always be less than the movement of individuals
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Migration
• When populations differ in allele frequencies, migration can be a powerful force
band
ed
unba
nded
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Migration
• Genetic patterns due to migration tend to be temporary
• Over the longer term, migration is a homogenizing force—it makes populations more genetically similar
D.R. Robertson
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Migration
• Populations in Central and Eastern Pacific (divided by 5000 km of deep ocean) are not genetically different in these two reef fish species*
D.R. Robertson
*(and 18 out of 20 species studied: Lessios and Robertson 2006)
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Geographic variation in natural populations
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from Futuyma (1998), p. 259
Often, morphology varies geographically
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With low migration, allele frequencies vary greatly over small geographic distances
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from Futuyma (1998), p. 319
As in pocket gophers...
1999 R.M. Timm
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Geographic barriers to dispersal often separate
genetically different populations
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Historical separations between Gulf of Mexico and SE Atlantic drainages from Avise (1994)
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from Avise (1994), p. 244
The Florida peninsula is a marine biogeographic barrier
It forms a long-term historical barrier to migration and gene exchange (gene flow) within many species
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Natural selection creates patterns of geographic
variation
Clinal variation
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from Volpe and Rosenbaum (2000), p. 110
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In D. melanogaster, the alcohol dehydrogenase (Adh) locus shows a cline—a regular change in frequency of a trait across a geographic transect
from Futuyma (2005)
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The frequency of AdhF decreases towards the equator on 3 continents: these are parallel clines
from Futuyma (2005)
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Clinal variation at lactate dehydrogenase-B in the mummichog Fundulus heteroclitus: Ldh-Bb increases towards the north
This allozyme has a higher catalytic efficiency at lower temperatures
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Races and subspecies
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Races and subspecies
• A race is a geographic population with well defined, discrete differences in one or more traits
• Taxonomically, races may be recognized and named as subspecies
Red-shafted C. auratus cafer
Yellow-shafted C. auratus auratus
Subspecies of Northern flicker (Colaptes)
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Color races of Heliconius butterfliesgeographic color races of H. erato
geographic color races of H. melpomene
these races display warning (aposematic) coloration to deter bird predation
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Allopatric color races
Each color race of dart-poison frogs (Dendrobaetes) lives on a different island in Bocas del Toro in western Panamá
Most animal color races are allopatric (they occupy non-overlapping ranges)
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Parapatric races or subspecies share common borders
from Futuyma (2005)
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from Futuyma (1998), p. 258
Parapatric subspecies sometimes interbreed where their borders meet
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Hamlets: sympatric races?
• 11-12 forms of Hypoplectrus in Caribbean, Florida, Bahamas
• Morphologically identical, but strikingly different color patterns
• 6 “races” live together on the same reefs, and mate like-with-like
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Racial variation
• morphological races
• host races in insects– races feed and oviposit on different host
plants– e.g. apple and hawthorn races of
Rhagoletis
• physiological races
• sex races
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Physiological racesVermont: embryos survive 5- 28
New Jersey: 5- 28
South Florida : 11- 33
North Florida : 9- 33
Northern leopard frog Rana pipiens
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from Futuyma (1998)
Sex races