Lecture 12: Adaptation & EvoDevo PDF

Lecture 12: From Genes to Traits BIO 4083: Evolution We’ve been talking a lot about genes and genomes. We’ve been talking a lot about genes and genomes. What about traits? This lecture: the evolution of genetic networks and development The ”Nuts and Bolts” of evolution This lecture: the evolution of...

Lecture 12: From Genes to Traits BIO 4083: Evolution We’ve been talking a lot about genes and genomes. We’ve been talking a lot about genes and genomes. What about traits? This lecture: the evolution of genetic networks and development The ”Nuts and Bolts” of evolution This lecture: the evolution of genetic networks and development “Evo-Devo” The ”Nuts and Bolts” of evolution Big idea: The process of evolution works with what’s there Today’s Lecture Genetic networks Complex adaptations How do complex traits evolve? How do new innovations evolve? Shared ancestry of complex traits Constraints on evolution Complex adaptations Coexpressed traits that experience selection for a common, often novel, function Vonk et al. 2013 Roggen. 2005 Complex adaptations are controlled by genes, proteins, RNA, control regions, repressors, and other transcription factors https://www.youtube.com/watch?v=MkUgkDLp2iE Regulatory networks are often involved in complex adaptations Hierarchical gene organization controls development of animal embryos Mutations to genes at the top of the hierarchy can have drastic effects How do new innovations (adaptations) evolve? Where does the new information come from? Horizontal gene transfer (HGT): A source of innovation in bacteria and archaea (and some eukaryotes) Geenen et al. 2010 De novo gene formation from non-coding (non-genic) regions Rice Bornberg-Bauer and Heames 2019 Gene duplication can produce novel functions Promiscuous proteins: capable of carrying out two functions; are especially likely to take on new functions if duplicated Paralog: a homologous gene that arises by gene duplication Gene recruitment: the co-option of a particular gene or network for a totally different function as a result of a mutation; the reorganization of a preexisting regulatory network can be a major evolutionary event Example: Consumption of citrate in E. coli evolved through duplication The ability to consume citrate is a complex trait Gene duplication led to the evolution of a complex trait Example: Snake venoms evolved through duplication and co-option of genes https://www.youtube.com/watch?v =cNXD10-r6QE Evolution of crotamine venome Mutations led to the production of the defensin gene in the mouth Venom genes have been recruited from genes expressed in many organs in snakes Venom evolved before snakes evolved Example: evolution of eyespots in butterflies Common buckeye Junonia coenia Native to Arkansas Beldade and Monteiro. 2021. Single evolution of eyespots Coincides with the evolution of gene expression Monteiro. 2015 Gene and regulatory architecture of butterfly eyespots Different genes active at different times Monteiro. 2015 One of these genes – Distal-less (Dll) – is involved in limb development in insects Drosophila Panganiban et al. 1994. Beldade et al. 2002 Co-option! Networks that result in complex traits are rooted in ancient genetic toolkits Homology/Homologous Homology/Homologous Similarity in traits or sequences due to inheritance from a common ancestor Directional terminology: an example in homology Hox genes are part of a conserved “genetic toolkit” among animals A common ancestor in early animal evolution passed this gene set to animals Bergstrom and Dugatkin (Norton) Dorsal-ventral patterning is conserved Flies and mice use homologous genes for dorsal-ventral patterning, though they are expressed as “mirror images” Fly and mouse leg genes reflect derivation from genes in a common ancestor Fly and mouse leg genes reflect derivation from genes in a common ancestor “Hedehog” Homologs “Sonic Hedehog” Of mice and men and fish: an example of shared ancestry The expression of HOXd13 in zebrafish and mouse embryos Same genes, but timing and location of expression are different Experimental evidence of evolution of tetrapod limbs from fins Misconception: “Ontogeny recapitulates phylogeny” Ernst Haeckel Example: complex eyes have evolved in several lineages Different forms, but a shared ancient genetic toolkit Opsins evolved in a common ancestor as long as 1 billion years ago Crystallins evolved through gene recruitment Why don’t we see more adaptations? Constraints on evolution Physics Why no insects the size of an elephant? Giant weta Constraints on evolution Physics Meganeura monyi ~300 mya Atmospheric oxygen levels and insect respiratory systems Constraints on evolution Antagonistic pleiotropy Ungewitter and Scrable. 2009 Why do we age? Why 7 cervical vertebrae? Complex adaptations are not perfect If it ain’t broke don’t fix it! Evolution does not “perfect” organisms Environment Selection acts on existing genetic variation in a population Genetic drift Assignments Paper reflection on Friday (Lowe et al. 2014) Read ”The Panda’s Thumb” (Gould)