Disruptive selection and speciation

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Disruptive selection and speciation in red
crossbills, Loxia curvirostra
highly specialized -- seeds of coniferous trees
(seeds retained in cones) use the crossed bill
to extract seeds from within the cone
extraction efficiency depends on bill shape and
palate structure bill structure and cone
structure affect feeding performance --- no
generalist crossbill nine different call types
seven are specialized on different species of
conifers
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Benkman 2003 Evolution 571176 detailed study
of one population in southern Idaho feeds on
Rocky Mountain lodgepole pine (Pinus contorta
latifolia) estimated form of selection on bill
shape (bill depth)
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Selection on bill depth is stabilizing
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Benkman 2003 Evolution 571176 detailed study
of one population in southern Idaho feeds on
Rocky Mountain lodgepole pine (Pinus contorta
latifolia) estimated form of selection on bill
shape (bill depth) relationship between bill
depth and fitness (survival)
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Benkman 2003 Evolution 571176 detailed study
of one population in southern Idaho feeds on
Rocky Mountain lodgepole pine (Pinus contorta
latifolia) estimated form of selection on bill
shape (bill depth) relationship between bill
depth and fitness (survival) fitness surface
based on feeding performance (bill depth and
palate structure) for five species
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Natural selection, sexual selection selection
and speciation in the cichlids of Lake
Victoria Verheyen et al. 2003 Science
300325
Lake Victoria -- more than 500 species of
haplochromine cichlids morphological,
ecological, and behavioral diversity
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Lake Victoria cichlids are a monophyletic
group most closely related to taxa from
Lake Kivu
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algal grazer insect eater piscivore
algal grazer
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Sexual selection drives speciation in African
great lakes cichlids
Couldridge and Alexander 2002 Behavioral Ecology
1359 Pseudotropheus zebra complex of at least
four species (Lake Malawi) differ in color
pattern similar in other morphology, ecology,
behavior Test for assortative mating female
preference with choice (conspecifics and
heterospecifics) female preference without
choice (heterospecifics only)
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C P. callainos pale blue, no bars R P.
zebra red dorsal pale blue dark
blue bars orange dorsal fin G P. zebra
gold pale orange, faint brown bars L
P. lombardoi yellow, 5 vertical black
bars
Predict 1) in choice tests, females will
prefer conspecific males 2) in no choice tests,
females will prefer the heterospecific male
whose color pattern is most similar
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Predict 1) in choice tests, females will
prefer conspecific males 2) in no choice tests,
females will prefer the heterospecific male
whose color pattern is most similar
Couldridge and Alexander 2002 Behavioral
Ecology 1359
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Allender et al. 2003 PNAS 10014074 evolution
of haplochromiine cichlids in Lake
Malawi recent, extensive adaptive radiations
--- feeding morphology closely related species
within each lake have similar morphology,
differ in color (frequent sexual
dimorphism) rapidly radiating groups have
polygynous mating system color pattern is
important in mate choice
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phylogeny from 2189 polymorphic AFLP loci
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Allender et al. 2003 PNAS 10014074 evolution
of haplochromiine cichlids in Lake
Malawi recent, extensive adaptive radiations
--- feeding morphology closely related species
within each lake have similar morphology,
differ in color (frequent sexual
dimorphism) rapidly radiating groups have
polygynous mating system color pattern is
important in mate choice repetitive pattern
of coloration -- genetic or ecological
constraints
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frequency distribution of male color patterns (n
293)
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Frequency distribution of female color patterns
(n 293)
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Allender et al. 2003 PNAS 10014074 evolution
of haplochromiine cichlids in Lake
Malawi recent, extensive adaptive radiations
--- feeding morphology closely related species
within each lake have similar morphology,
differ in color (frequent sexual
dimorphism) rapidly radiating groups have
polygynous mating system color pattern is
important in mate choice repetitive pattern
of coloration -- genetic or ecological
constraints speciation by - divergent sexual
selection (in sympatry, parapatry) - spread of
color pattern from source of origin
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colonization character displacement sexual
selection model (A) model (B)
model (C)
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Maylandia (Pseudotrophus) zebra complex
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color pattern arose repeatedly in
evolutionary history of M zebra
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tests of speciation models A
colonization r -0.06 p 0.81 B
character displacement r -0.02 p 0.93
C sexual selection r 0.39 p 0.01
D allopatric speciation on full geographic
scale r -0.32 p 0.97 E allopatric
speciation on intermediate geographic scale r
0.22 p 0.01 multiple regression C and E
explain complementary fractions of variance in
genetic distance (CE) r 0.55 for combined
model residual variance unrelated to geographic
distance---no recent hybridization
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rate of ecological diversification and
speciation may be correlated
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Genetics of speciation -- performance and
habitat preference in pea aphids Via
2002 two host races/incipient species --
alfalfa and clover known trade-off between
performance on clover and alfalfa
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reaction norms mean fitness of
clones tested on both hosts
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Genetics of speciation -- performance and
habitat preference in pea aphids Via
2002 two host races/incipient species --
alfalfa and clover known trade-off between
performance on clover and alfalfa what is the
genetic architecture of this trade-off?
are genes for performance independent of genes
for habitat choice/assortative
mating? negative genetic correlation pleiotro
py or LDE of closely linked loci vs. LDE of
unlinked loci QTL analysis
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intrinsic postmating incompatibility
Drosophila Coyne and Orr 1989 Evolution
43362 Coyne and Orr 1997 Evolution
51295 frogs Sasa et al. 1998 Evolution
521811 Lepidoptera Presgraves 2002 Evolution
561168 birds Price and Bouvier 2002
562083 hybrid sterility and inviability evolve
gradually positively correlated with the time
since divergence -- gradual accumulation
of deleterious epistatic interactions between
species hybrid sterility evolves faster than
inviability Haldanes Rule if hybrid sterility
or inviability is present in only one sex of
F1 offspring, it will be the heterogametic sex
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Haldanes Rule if hybrid sterility or
inviability is present in only one sex of F1
offspring, it will be the heterogametic sex
inviability due to lethal incompatibilities
between autosomal and X-linked loci dominance
theory hybrid incompatibilities are partially
recessive XX hybrids are heterozygous
and protected X/ hybrids express all
X-linked recessives faster-male evolution
- sexual selection drives rapid divergence of
male fertility factors --- hybrid male
sterility - spermatogenesis is inherently more
sensitive to perturbation consensus
dominance theory important for taxa possessing a
degenerate / chromosome, but faster male
evolution is responsible in male heterogametic
taxa
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Species are evolutionarily independent groups. A
species is often defined as a group of
populations that are capable of interbreeding,
but this definition applies best to
diploid, sexually reproducing taxa. Populations
which are phenotypically or ecologically
distinct, yet regularly interbreed, or species
that reproduce largely asexually may still be
valid species. The process of adaptive
divergence that leads to speciation may occur
either in allopatry or sympatry. Speciation
is a result of divergent natural (ecological) or
sexual selection. Genetic drift may
accelerate the process of divergence through
founder events. Reproductive isolation between
species may result from assortative mating
(prezygotic) or from hybrid sterility/inviability
(postzygotic). Although reinforcement may occur
during secondary contact, it is not a universal
requirement for speciation. Haldanes rule
is a general description of the early stages of
speciation. Genetic correlations for performance
in different environments and for habitat
choice may facilitate the rate at which
divergence occurs.