Download Allopatric Speciation*Drift

Allopatric Speciation—Drift
• Drift is important in evolution
• Just because an allele is common doesn’t
mean selection favored it
Speciation via drift?
Probably not.
• Flies in allopatry,
same environment
never  RIM
• Drift may facilitate
speciation, but
probably cannot
often cause
speciation on its
own
Ecological Speciation
• Sister species in the same lake
• Big is benthic, small is limnetic
• No interbreeding in nature– habitat isolation or premating RIM?
No-choice
mating trials in
the lab
Low probability of spawning between different ecomorphs, even when closely related (A).
Ecology is important in RIM.
C = control (same species, same population, high probability of spawning)
D = same ecotype, distantly related (act like same species)
A = sympatric, closely related, different ecotype (act like different Biological species)
B = allopatric, distantly related, different ecotype
Reproductive compatibility determined more by ecotype than by genetic relatedness
• RIM appears to be body size—did divergent
natural selection on body size  speciation?
Speciation via Sexual Selection
• Many sister lineages with same ecological
niche, but different secondary sexual
characters
Greater species diversity in lineages with greater
promiscuity. Due to stronger sexual selection?
Fig. 24-12
Speciation by Sexual Selection
EXPERIMENT
Normal light
Monochromatic
orange light
P.
pundamilia
P. nyererei
Under manipulated lighting, females made “wrong” mate choice
Genetics and Timing of Speciation
Time to Speciation
Varies
Fig. 24-19
One-gene speciation
RIM’s can be
generated by
simple
differences in
genetics
Ancestral species:
Speciation may
involve
hybridization, so it
can be quick for
many species
AA
Triticum
monococcum
(2n = 14)
BB
Wild
Triticum
(2n = 14)
Product:
AA BB DD
T. aestivum
(bread wheat)
(2n = 42)
DD
Wild
T. tauschii
(2n = 14)
Speciation involves a stochastic
element…
• Medium ground finches on Daphne major
(Gallapagos Island)
Immigrant
Immigrant Geospiza fortis:
large body,
wide beak,
unusual song (bad mimicry)
F1
F5
Top to bottom: A to F show successive generations of the hybrids, which now mate only with each other.
Grant and Grant, PNAS, doi/10.1073/pnas.0911761106
F6
• The Grants followed the fate of the immigrant over 7
generations (28 years)
• The immigrant imitated (imperfectly) the local song
and mated with a large female
• In generation 4, severe drought, lineage reduced to a
single brother and sister, which mated
• From then on, this lineage was reproductively
isolated—premating RIM
• RIM due to song
– culturally transmitted to sons (learned)?
– sound may also be a consequence of bill shape