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 non-adaptive • Plant height • Ligule size • Leaf texture • Flower color • Head size • Leaf cut • Floret number • 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 Allauidia – Didieriaceae western North America 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. Adaptation 2. Exaptation 3. Disaptation 4. 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” NATURE COMMUNICATIONS | DOI: 10.1038/ncomms4706 ARTICLE a Sc8 Sc7 Sc6 Sc5 Sc4 Arabidopsis lyrata Arabidopsis Sc3 Sc2 ARTICLE Received 6 Jan 2014 | AcceptedSc1 21 Mar 2014 | Published 23 Apr 2014 DOI: 10.1038/ncomms4706 OPEN The emerging biofuel crop Camelina sativa retains a highly undifferentiatedCsa1 Csa2 Csa3 Csa4 hexaploidCsa5 Csa6 Csa7 genomeCsa8 Csa9 structure Csa10 Csa11 Csa12 Csa13 Csa14 Csa15 Csa16 Csa17 Csa18Csa19 Csa20 Sateesh Kagale1,2, Chushin Koh2, John Nixon1, Venkatesh Bollina1, Wayne E. Clarke1, Reetu TutejaCamelina3, sativa Charles Spillane3, Stephen J. Robinson1, Matthew G. Links1, Carling Clarke2, Erin E. Higgins1, Terry Huebert1, Andrew G. Sharpebcd2 & Isobel A.P. Parkin1 A A 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 J A A F F reference genome sequence for C. sativa andA annotated 89,418 protein-codingJ genes, O F R O K representing a whole-genome triplication event relativeN to the crucifer model ArabidopsisF K thaliana. C. sativa represents the first crop species to be sequenced from lineage I of the B B I S S O U I G L P V Brassicaceae. The well-preservedN hexaploidU genomeJ structure of C. sativa surprisingly mirrors O D L P V D R F U G those of economically importantK amphidiploid BrassicaI crop species from lineage III as well as J K P R wheat and cotton. TheB three genomes of C. sativa show no evidence of fractionation bias Q T D U T E H M and limited expression-levelI bias, both characteristics commonlyK associatedB withD polyploid M Q C W B G C H W evolution. The highly undifferentiated polyploid genomeE of C. sativa presentsB significant E L Q Q P J I N D D L U X consequences for breeding and geneticQ manipulation of thisL industrialV oil crop. C H N X R G C T U E T G T R C D D G O I D M M H M P P W 6 C S S E AK1 AK2 AK3 AK4 AK5 AK AK7 AK8 AK1 AK3 AK5 AK6 AK7 AK8 H W Csa01 V S AK2/4 E H C E C N O O S N Csa03 D Csa10 N N D D D Csa15 W I Csa13 Csa19 R Csa12 I I Csa20 E V Csa05 Csa14 X D E J E I E X Reciprocal I E E Pericentric Csa17 Csa08 Csa18 translocation I J U inversion E D I E Paracentric Csa02 Consecutive E D Csa07 J inversion I paracentric and I D W pericentric I AK2 I Csa16 Csa04 I I Csa06 inversions E 1 Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, Saskatchewan, Canada S7N 0X2. 2 National Research Council J J J Canada, 110 Gymnasium Place, Saskatoon, Saskatchewan, Canada S7N 0W9. 3 Plant and AgriBiosciencesD Centre (PABC), School of NaturalJ Sciences, J National University of Ireland Galway, Galway, Ireland. CorrespondenceAK1 AK2 AK3AK4 andAK5 requestsAK6 AK7 AK8 for materials should be addressed to A.G.S. (email: andrew.sharpe@nrc- X Csa09 cnrc.gc.ca) or to I.A.P.P. (email: [email protected]). NATURE COMMUNICATIONSCs-G1| 5:3706 | DOI: 10.1038/ncomms4706Csa11 Cs-G2 | www.nature.com/naturecommunicationsCs-G3 1 & 2014 Macmillan Publishers Limited. All rights reserved. AK4 AK4 AK2/4 AK2/4 AK2/4 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 of C. sativa. Chromosome and ancestral genomic-block-level organization of the sub-genomes in C. sativa is shown. Based on synteny and collinearity between C. sativa and Arabidopsis species, and GB contiguity in the ancestral karyotype, pseudochromosomes were assigned to three sub-genomes in C. sativa. Each pseudochromosome was subdivided among ancestral genomic blocks (A–X), which are coloured based on their occurrence in the ACK. (c) ACK consisting of the 24 conserved genomic blocks (A–X). (d) The ancestral diploid karyotype (derivative of ACK) of C. sativa.(e) The presumed origin and reconstruction of the fusion chromosome (AK2/4) of the dACK. of chromosome number and rearrangement of ancestral respect to A. thaliana and A. lyrata stands in contrast to these chromosomal blocks.