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Some types of evolutionary change seem to occur repeatedly Phylogenetic patterns Are genes leaders or followers Conversion of mechanisms Regulatory mechanism with switches seem to evolve easily, at least the cue type provoking switching Are there examples wit little evolutionary change over long periods? Evolutionary Constraints Evolutionary Constraints No evolutionary response – why? Mechanisms causing constraints Trade-offs – Coupling No Evolutionary Constraints Conover et al. 2009 Cold adaptation Trophy hunting Genetic Variation and Short-Term Evolution Trait two Evolutionarily Convergence Stable Traits Response Selective advantage Selection Genetic Variation Initial Population Selective disadvantage Trait one No response in the short term The breeders equation for selection response R = Gβ Two possibilities: Some variation cannot be produced (genetic variance - covariance G is degenerate) (Stabilizing) selection prevents change (selection gradient β = 0) (consensus paper Maynard Smith et al. 1985) Allen, C., Beldade, P., Zwaan, B.J., Brakefield, P.M. (2008) Differences in the selection response of serially repeated color pattern characters: Standing variation, development, and evolution. BMC Evolutionary Biology 2008, 8:94 What are causes of constraints in the more long term? Mechanical/Physical constraints produce allometric patterns Any organism has to obey the laws of physics and chemistry • Gravity pulls everything down Meganeura moryi Gigantic proto-Odonata because of different composition atmosphere during Carboniferous (Dudley 1998) • E.g. limits on body size in organisms that have access to oxygen through trachea Ecological Constraints β(E) Available options depend on the environment High (Unavoidable?) Cost of Reproduction when 1) Carrying eggs 2) Predators are present 3) Visibility is high Not structure, but cost is constrained Daphnia pulex Levels of organization Environment Genes Developmental Constraints Phenotype Performance Ecological Constraints Physical Constraints Fitness Historical or Phylogenetic Constraints Some traits evolved already in the past and not recently Organisms resemble their ancestors Species are not independent samples Problem of generalization: contingency of actual species traits Primates cannot occupy all herbivore niches Muller et al. 2011 Waved albatross Phoebastria irrorata All Procellariiformes lay a single egg per clutch Physiological constraints : The properties of physiologies are not allowing to perform certain tasks or produce some phenotypes Genetic constraints : genotypic variation cannot produce some phenotypes Classifications of Constraints: What a Mess Physical Constraints Genetic Constraints Phylogenetic Constraints Physiological Ecological Constraints (Roff 1992) Trade- Offs (Roff 2002) No response – the short term perspective does not always relate easily to the categories of constraints Species Variation Selection Albatross Absent Foraging efficiency Daphnia Absent Reproduction Dragonfly Aquatic larva known from Permian Performance Large Meganeuridae exist from the Permian with lower oxygen There are other large insects still present (stick insects) Maybe they were just selected for large size No response – the short term perspective does not always relate easily to the categories of constraints Species Variation Selection Albatross Absent Foraging mode Daphnia Absent Reproduction Dragonfly Aquatic larva known from Permian Performance -> Estimate both variation and selection on larger timescales Phylogenetic patterns One often models evolution along a tree assuming responses R = Gβ Species traits will change or not, but also the genetic variance-covariance G Steppan et al. 2002 Phylogenetic patterns One often models evolution along a tree assuming R = Gβ Species traits will change or not, but also the genetic variance-covariance G We are aware that phylogenetic patterns are there, and need models of how they appeared! → Try to reconstruct the emergence of the constraint → Try to reconstruct the patterns of selection http://cran.r-project.org/web/views/Phylogenetics.html What is the phenotype exactly which is constrained? Switches Morphologies When multiple traits are considered, beta and G can be non-zero and non-degenerate Does it matter for the detection of patterns of natural selection? Internal selection: interactions between developmental modules constrain evolution Galis et al. 2006 Phylotypic stage Developmental hourglass Prud’homme and Gompel 2010 Germband Aminoserosa Head region minus gnathal segments Fig. 1. Extended (a) and segmented (b) germband stages in Drosophila. The germband (blue) refers to the part of the embryo that will give rise to the metameric regions: gnathal segments of the head region (Md, mandible; Mx, maxilla; Lb, labium), thoracic segments (T1–3) and abdominal segments (A1–8). The amnioserosa (red) is an extra-embryonic membrane. The extended germband stage starts ~.6.5 h after fertilization and the segmented germband stage ends at ~10.5 h after fertilization. Von Dassow et al. (2000) Are phenotypes constrained because they are robust, perturbations are dampened? Not in this case. WT Null Df(2)DE NE2 Null (wg−/−), reduced [Df(2)DE] and partial (NE2) function mutations of the wg gene lead to abnormalities in the larval ectoderm. Expression of wg in the ectoderm (A–D), and cuticular pattern in the ventral (E–H) and dorsal (I–L) larval epidermis (W.T. denotes wild type). In Df(2)DE mutants, wg expression is reduced, and in NE2 mutants, wg transport is hampered (reproduced, with permission, from Ref. [27]). Galis et al. 2002 Are phenotypes constrained because they are robust? Not in this case. Hypomorphic Wg-1 mutant showing a failure in the development of antennae, wings, halteres and thorax Galis et al. 2002 Germband Aminoserosa Head region minus gnathal segments Fig. 1. Extended (a) and segmented (b) germband stages in Drosophila. The germband (blue) refers to the part of the embryo that will give rise to the metameric regions: gnathal segments of the head region (Md, mandible; Mx, maxilla; Lb, labium), thoracic segments (T1–3) and abdominal segments (A1–8). The amnioserosa (red) is an extra-embryonic membrane. The extended germband stage starts ~.6.5 h after fertilization and the segmented germband stage ends at ~10.5 h after fertilization. Internal selection due to interactions causing effects on many phenotypes Internal selection is selection due to shapes of genotypephenotype maps I will show the genotype phenotype map is both • A component of variation • A component of the selection gradient Assume smooth genotype-phenotype maps Apparent phenotype Y - Underlying trait X Barbara Stadler has worked the ingredients to do this analysis for discrete genotype spaces Apparent phenotype Y - Underlying trait X Phenotypic trait vector Y underlying traits X of a haplotype Y depends on X Y (X ) Apparent phenotype Y - Underlying trait X Phenotypic trait vector Y underlying traits X Y X Apparent phenotype Y - Underlying trait X allelic traits → organismal traits → fitness devo eco evo The map Y(X) is locally approximately linear Phenotypic trait vector Y underlying traits X of a haplotype Y . . . . X Invasion fitness fitness of the phenotype of a mutant heterozygote Y in a population with phenotype Z of the resident allele (genotype) r (Y , Z ) fitness of a mutant X' in a population of alleles with trait X ρ ( X ' , X ) = r (Y ( X '), Y ( X )) Invasion fitness gradient ∇' ρ ( X ) = ∂ r (Y ( X '), Y ( X )) ∂X ' X '= X ∇' ρ ( X ) = ∇Y ( X )∇' r (Y ( X )) devo ∇' r ( Z ) = eco fitness gradient = phenotypic effects of allele × ecological effects of phenotype ∂ r (Y , Z ) ∂Y Y =Z Evolutionary Dynamics Gradual directional evolution by new mutations occurring d 1 X (t ) = G X ( t )∇Y ( X (t ))∇' r (Y ( X (t ) )) dt 2 scaling for devo available variation d Y (t ) = dt d Y (t ) = dt eco 1 ∇Y ( X (t ))T G X ( t )∇Y ( X (t ))∇' r (Y ( X (t ) )) 2 1 GY (t )∇' r (Y ( X (t ) )) 2 Evolutionary Dynamics d 1 X (t ) = G X ( t )∇Y ( X (t ))∇' r (Y ( X (t ) )) dt 2 selection d 1 Z (t ) = ∇Y ( X (t ))T G X (t )∇Y ( X (t ))∇' r (Y ( X (t ) )) dt 2 variation Evolutionarily Stable Configuration • evolves in the same way in any environment, independent of ecology • evolution driven by internal coherence and system performance • performance is for a proper function (raison d'être) Example: iguanians use their tongue as a prehensile organ (Wagner and Schwenk 2000) One type of internal selection Evolutionarily Stable Configuration ∇Y(X*) = 0 for all loci involved performance is for a proper function (raison d'être) → Y is one-dimensional = e.g. capture rate ∇'r(y) > 0 performance y x* tongue traits Some antidote against all this smoothness Genotype network spaces The viewpoint of the underlying level is essential to understand constraints “All complex macroscopic traits comprise microscopic, submicroscopic and molecular traits, down to the level of DNA. Likewise, DNA change can percolate all the way up to macroscopic traits. Although an understanding of the full complexity of this hierarchical organization is beyond current means, important systems can be studied that are necessary to form complex traits and changes therein.” Wagner 2011 The viewpoint of the underlying level is essential to understand constraints Example Variation Selection Gene regulation networks X X Metabolic networks X X Macromolecules X X These models provide simple genotype-phenotype maps used to investigate constraints Wagner 2011 No response – Genotype networks Each colour is a phenotype Lines represent possible mutational changes Selection on robustness To study effects of: Genotype space structure G-P mapping Wagner 2011 Genotype Networks Novelties Connected genotype spaces with different accessible phenotypes promote novelties, Below are three opposites to that: Genotype networks Plasticity Simplified plasticity: Alternative phenotype If present, can mutate in a new constitutive phenotype Espinosa-Soto et al. (2011) Genotype networks and plasticity (a) Populations find a novel genotype network faster when plasticity is allowed. The symbol t*, plast refers to the number of generations that a population of circuits needs to discover a specific genotype network when we allow plasticity. The symbol t*, control refers to the same number, but for populations without plasticity. (b) Plasticity slows the accumulation of individuals in the new genotype network. The symbol t0.25,plast stands for the number of generations that a population in which we allow plasticity needs to have at least 25 percent of its circuits in the new genotype network (after its discovery by a single individual); t0.25,control corresponds to the same number but without plastic phenotypes. Release from constraints Plasticity and a new environment revealing cryptic variation Evolutionary novelty facilitated by plasticity Exploration of genotype network spaces Life history trade-offs and constraints "Detailed knowledge of the genetic, developmental, and physiological mechanisms that affect life history traits is of major importance for understanding, from first principles, how life history traits are expressed, why they vary, and how they evolve." But some relatively old ideas are still strong…. Love for Meccano? Stearns chapter: "The glass is at least half empty" "For them life history theory provided a general motivational structure" Onto the boundary of a feasibility set Fitness often increases in this direction: The more of survival and reproduction, the better LH Trait two Feasibility Set LH Trait one Rueffler et al. 2004 Options - Fitness contours Begon et al. 2005 Classification of Environments Sensitive to growth InSensitive to growth Begon et al. 2005 Begon et al. 2005 Many open questions: constraints can arise from specialization? Heteroecious aphids (Moran 1988) Specialists References Charnov, E. L. 1993. Life History Invariants. Oxford University Press Conover, D.O., S.B. Munch, and S.A. Arnott (2009) Reversal of evolutionary downsizing caused by selective harvest of large fish. Proceedings of the Royal Society of London. Series B: Biological Sciences 276:2015-2020. Dudley, R. 1998. Atmospheric oxygen, giant Paleozoic insects and the evolution o aerial locomotor performance. Journal of Experimental Biology 201: 1043-1050. Espinosa-Soto, C. Martin, O.C., Wagner, A. (2011) Phenotypic plasticity can facilitate adaptive evolution in gene regulatory circuits. BMC Evolutionary Biology 11:5, doi:10.1186/1471-2148-11-5 Galis, F. , T.J.M. van Dooren and J.A.J. Metz (2002). Conservation of the segmented germband stage: robustness or pleiotropy? Trends Genet. 18 (10), 504-509. Galis F., T.J.M. van Dooren, Feuth, H., Ruinard, S., Witkam, A., Steigenga, M.J., Metz, J.A.J., Wijnaendts, L.C.D. (2006). Extreme selection against homeotic transformations of cervical vertebrae in humans.Evolution 60 (12):2643-2654. Maynard Smith, J., R. Burian, S. Kaufman, P. Alberch, J. Campbell et al., 1985. Developmental constraints and evolution. Q. Rev. Biol. 60: 265–287. Muller et al. 2011. Phylogenetic constraints on digesta separation: Variation in fluid throughput in the digestive tract in mammalian herbivores. Comparative biochemistry and physiology. Part A, Molecular & integrative physiology. 06/2011; Nee S et al. The illusion of invariant quantities in life histories. Science. 2005 Aug 19; 309(5738):1236-9 Prud’homme and Gompel 2010 Roff, D.A. 1992. The Evolution of Life Histories: Theory and Analysis. Chapman and Hall, New York. Roff, D.A. 2002. Life History Evolution. Sinauer Associates, Sunderland, MA. G. von Dassow, E. Meir, E. M. Munro, and G. M. Odell (2000) The segment polarity network is a robust developmental module. Nature 406: 188-92. Wagner 2011. Genotype networks shed light on evolutionary constraints. Trends in Ecology & Evolution. doi:10.1016/j.tree.2011.07.001 Wagner, G. P. and K. Schwenk (2000) Evolutionarily Stable Configurations: functional integration and the evolution of phenotypic stability. Evolutionary Biology 31:155-217.