Migration Evolutionarily, this means the movement of alleles, or gene flow between populations This...
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Transcript of Migration Evolutionarily, this means the movement of alleles, or gene flow between populations This...
Migration
• Evolutionarily, this means the movement of alleles, or gene flow between populations
• This will always be less than the movement of individuals
Migration
• When populations differ in allele frequencies, migration can be a powerful force
band
ed
unba
nded
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
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)
Geographic variation in natural populations
from Futuyma (1998), p. 259
Often, morphology varies geographically
With low migration, allele frequencies vary greatly over small geographic distances
from Futuyma (1998), p. 319
As in pocket gophers...
1999 R.M. Timm
Geographic barriers to dispersal often separate
genetically different populations
Historical separations between Gulf of Mexico and SE Atlantic drainages from Avise (1994)
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
Natural selection creates patterns of geographic
variation
Clinal variation
from Volpe and Rosenbaum (2000), p. 110
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)
The frequency of AdhF decreases towards the equator on 3 continents: these are parallel clines
from Futuyma (2005)
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
Races and subspecies
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)
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
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)
Parapatric races or subspecies share common borders
from Futuyma (2005)
from Futuyma (1998), p. 258
Parapatric subspecies sometimes interbreed where their borders meet
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
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
Physiological racesVermont: embryos survive 5- 28
New Jersey: 5- 28
South Florida : 11- 33
North Florida : 9- 33
Northern leopard frog Rana pipiens
from Futuyma (1998)
Sex races