Download Natural Selection and Variation in Populations

Natural Selection and
Variation in Populations
Chapter 4
– from Stebbin’s 1950 Variation and Evolution in Plants
“Natural Selection”
•  Cornerstone of evolution –
1860-1900
“Natural Selection”
•  Cornerstone of evolution –
1860-1900
•  “Mutation theory” supplants n.s. –
1900-1920s
Wilhelm Johannsen William Bateson
Hugo DeVries
The early geneticist Hugo de Vries observed an act of
speciation while studying the evening primrose plant.
The original species, Oenothera lamarckiana, had 14
chromosomes, while the new species had 28. The new
species was unable to breed with Oenothera lamarckiana,
and thus he named it Oenothera gigas (De Vires, 1905)
“Natural Selection”
•  Cornerstone of evolution –
1860-1900
•  “Mutation theory” supplants n.s. –
1900-1920s
•  Resurgence of natural selection
(NeoDarwinism) 1930s-
Decline of Natural Selection
•  Mutation theory of DeVries –
evolution comes about with sudden
new mutations with large effects
rare; most mutations have small
effects
•  Artificial selection ineffective only
in choice of plants studied
Resurgence of Natural Selection
We can no longer think of mutation as the primary source
of directive tendencies in evolution and of selection in the
purely negative role of eliminating unfavorable
tendencies. On the contrary, the direction of evolution is
determined largely by selection acting on the gene fund
already present in the population, the component genes
of which represent mutations that have occurred many
generations ago. New mutations are important chiefly as
a means of replenishing the store of variability which is
continuously being depleted by selection.
Resurgence of Natural Selection
•  Mutations with large effects rare; most
mutations have small effects
but . . .
Goldschmidt, Richard. 1940.
The Material Basis of Evolution.
Yale Univ. Press.
"biologists seem inclined to think that because they have
not themselves seen a 'large' mutation, such a thing
cannot be possible. But such a mutation need only be an
event of the most extraordinary rarity to provide the
world with the important material for evolution"
Resurgence of Natural Selection
•  Mutations with large effects rare; most
mutations have small effects
but . . .
Gottlieb LD. 1984. Genetics and
morphological evolution in
plants. Am. Nat. 123: 681–709
Resurgence of Natural Selection
•  Mutations with large effects rare; most
mutations have small effects
but . . .
Theissen, G. 2006. The proper place of
hopeful monsters in evolutionary biology.
Theory Biosci 124: 349-369.
Theissen, G. 2010. Homeosis of the
angiosperm flower: Studies on three
candidate cases of saltational evolution.
Palaeodiversity 3, Supplement: 131-139.
Resurgence of Natural Selection
•  Mutations with large effects rare; most
mutations have small effects
•  Pure homozygous individuals rare in nature
•  Differences among populations/races are not
simple Mendelian but polygenic
•  Analogy between breeders (artificial selection)
and nature (natural selection) – heritability
Need for Experimental Evidence for
Natural Selection (esp. outcrossers)
•  Trifolium repens
•  Potentilla glandulosa
•  Taraxacum
•  Hordeum vulgare
Need for Experimental Evidence for
Natural Selection (esp. outcrossers)
H. V. Harlan
Plant Breeding Symposium: Who will train plant breeders?
H.V. Harlan (1957)
"The field of plant breeding actually suffered in a way from the greater knowledge we had acquired.
Mendel's work was quickly accepted as an enormous advantage in plant science. It was a definite,
tangible thing that seemed to take plant breeding from the arts and place it as a science overnight. It
captured the imagination of all workers, and genetics at once became a field offering prestige that
both soothed and satisfied."
"A genetic paper gave new dignity to the author. We boys began to get our hair cut and our shoes
shined. The effect on plant breeding was calamitous. Good varieties were still produced, but
explorations in the field of practical plant breeding were wholly neglected."
"A few of us eventually realized that there would come a day when the world would recognize the
difference between a good geneticist and a poor one, so we went back to thinking about plant
breeding. We have undoubtedly lost the resources of many good minds from this field for a time, but
they will be back."
Need for Historical Evidence for
Natural Selection
•  Many animal studies, especially Drosophila
•  Pasture grasses and forbs in Maryland (Kemp,
1937)
Fast forward 2015 – what plant or
animal examples usually cited now?
Adaptive Value of Character?
“the determination of the adaptive character of
many types of differences between organisms
is one of the most difficult problems in biology”
Adaptive Value of Character?
Achillea:
adaptive
• 
• 
• 
• 
Plant height
Leaf texture
Head size
Floret number
non-adaptive
• 
• 
• 
• 
Ligule size
Flower color
Leaf cut
Branching patter
Adaptive Value of Character?
“the determination of the adaptive character of
many types of differences between organisms
is one of the most difficult problems in biology”
Other ways to claim “adaptive” nature of a
character – not really mentioned by Stebbins
1.  Homology – “unity of type”
2.  Convergence
3.  Phylogenetic
Adaptive Value of Character? - convergence
Foquieria – Foquieriaceae
western North America
Allauidia – Didieriaceae
Madagascar
Adaptive Value of Character? - phylogenetic
“the determination of the adaptive character of
many types of differences between organisms
is one of the most difficult problems in biology”
adaptationism
Adaptive Value of Character? - phylogenetic
Adaptive Value of Character? - phylogenetic
1. 
2. 
3. 
4. 
Adaptation
Exaptation
Disaptation
Nonaptation
Indirect Action of Natural Selection
1.  Developmental
correlation (Darwin)
2.  Adaptive compensation
(C.K.H.)
3.  Selective correlation
“Developmental correlation brings about adaptive compensation
which results in selective correlation”
Arabidopsis l
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Camelina
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Sateesh Kagale1,2, Chushin Koh2, John Nixon1, Venkatesh Bollina1, Wayne E. Clarke1, Reetu Tuteja
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Charles Spillane , Stephen J. Robinson , Matthew G. Links , Carling Clarke , Erin E. Higgins , Terry Huebert1,
Andrew G. Sharpe2 & Isobel A.P. Parkin1
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Camelina sativa is an oilseed with desirable agronomic and oil-quality attributes for a viable
industrial oil platform
crop. Here we generate the first chromosome-scale
high-quality
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reference genome sequence for C. sativa and
genes,
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representing a whole-genome triplication event relative to the crucifer model Arabidopsis
thaliana. C. sativa represents the first crop species to be sequenced from lineage I of the
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wheat and cotton. The
three genomes of C. sativa show no evidence
of fractionation bias
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and limited expression-level bias, both characteristics
commonly associated with polyploid
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evolution. The highly undifferentiated polyploid genome
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The emerging biofuel crop Camelina sativa retains a
highly undifferentiated hexaploid genome structure
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OPEN
DOI: 10.1038/ncomms4706
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Received 6 Jan 2014 | Sc1
Accepted 21 Mar 2014 | Published 23 Apr 2014
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& 2014 Macmillan Publishers Limited. All rights reserved.
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NATURE COMMUNICATIONS | 5:3706 | DOI: 10.1038/ncomms4706
| www.nature.com/naturecommunications
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1 Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2. 2 National Research Council
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Canada, 110 Gymnasium Place, Saskatoon, Saskatchewan, Canada S7N 0W9. 3 Plant and AgriBiosciences D
Centre (PABC), School of Natural
Sciences,
National University of Ireland Galway, Galway, Ireland. Correspondence and requests for materials should be addressed to A.G.S. (email: andrew.sharpe@nrcX
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cnrc.gc.ca) or to I.A.P.P. (email: [email protected]).
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Figure 3 | Comparative analysis and evolution of the C. sativa genome. (a) MUMer plot comparing the C. sativa and A. lyrata genomes. Syntenic
and collinear regions making the three complete sub-genomes in C. sativa are circled in red, blue and green. (b) Reconstruction of the three sub-genomes
Indirect Action of Natural Selection
Selective correlation –
Plantago maritima
Indirect Action of Natural Selection
Selective correlation – fleshy
fruits in closed forest
Smith, J. 2001. High species diversity in
fleshy-fruited tropical understory plants.
American Naturalist 157: 646-53
Indirect Action of Natural Selection
Selective correlation – fleshy
fruits in closed forest
Givnish et al. 2005.
Repeated evolution of net
venation and fleshy fruits
among monocots in
shaded habitats confirms
a priori predictions:
evidence from an ndhF
phylogeny. Proceedings
of the Royal Society of
London, Biological
Sciences 272: 1481-1490
Indirect Action of Natural Selection
Selective correlation –
Asteraceae and Poaceae in
California
Summary Action of Natural Selection
1.  Works immediately via adaptive value of the
visible changes
2.  Works on non-adaptive traits developmentally
correlated with adaptive traits
3.  Traits not directly adaptive may acquire
selective value due to compensatory system of
adaptation
4.  Non-adaptive characters may become fixed due
to chance
Random or Drift Evolution
1.  Gives three examples: Papaver, Hutchinsia,
Linanthus
Modern Research on Natural Selection
and Drift in Plants?
1.  Anderson JT, Willis JH, Mitchell-Olds T. 2011.
Evolutionary genetics of plant adaptation.
Trends Genet. 27: 258-66.
2.  Savolainen O, Lascoux M, Merilä J. 2013.
Ecological genomics of local adaptation. Nat
Rev Genet. 14: 807-20.
3.  Others? Arabidopsis, Mimulus, Populus,
Eucalyptus, island plant lineages, Cakile