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A Brief History of Time: Metamerism and the Phylotype Lecture 16 How was the basic body plan evolved? Arthropod example body segments how arise ? soft...

A Brief History of Time: Metamerism and the Phylotype Lecture 16 How was the basic body plan evolved? Arthropod example body segments how arise ? soft body - didn't Fosilize Multicellularity, leading to gut and bilateral symmetry well Ikaria from Ediacara Biota (571 to 539 Ma) pattern of Worm-like with two openings connected by a gut primitive segmentation Urbilaterian – last common ancestor of bilaterians Insects Crustacea bilateral Worms symmetry genetic set necessary to make Mammals us found Fish Hox genes Reptiles Birds etc. Australian muck ”worm” fossil 2020 https://www.pnas.org/doi/full/10.1073/pnas.2001045117  toolset body Segmenta I - locomotin a What is a Metamere generic body seg. mechanisms in build place body after part one Build a segment, copy, repeat another (Ex lego) - - - Reiterative body segment. Why? Simplicity of genetic controls to construct Flexible locomotion (undulation) Peristaltic gut action motor/process food > - Redundant function Eg; Lumbricus (earthworm) body segments - like another Segments begin to evolve specializations Segments then cluster according to function Segments begin the fuse Ex Drisophilla. acrin Types of Metamerism Homonomous Metamerism Pseudometamerism – tape worms – carry segments defined by organs. Each segment operates independently. True metamerism – Earthworms - segments carry own organs but work together in an coordinated manner Heteronomous Metamerism Ex crustaceans More evolved situation – insects - segments cluster according to specialized function – head, thorax, abdomen etc. – clusters called Tagmata ad middle-legs wings, thoracic abdomenal MORE EVOULED Ex humans. - Spine segmented - we've gone further  Prominent body What is a Tagmata? in regions arthropods, Such as head thorax , , and abdomen in insects & each ment has seg limbs / anleuna larger/ smaller legs seg no legs https://insectsexplained.files.wordpress.com/2014/09/insect-evolution.png https://en.wikipedia.org/wiki/Tagma_(biology)#/media/File:Harpacticoida_tagmata.svg  Concept of Tagmata: Trilobite Example Seg each had 2 pairs of limbs - 3 4 below above branched - structures upper form - gills https://en.wikipedia.org/wiki/Tagma_(biology)#/media/File:Trilobite_sections-en.svg https://en.wikipedia.org/wiki/Trilobite#/media/File:Cambrian_Trilobite_Olenoides_Mt._Stephen.jpg Uniramous and Biramous ancestoral feeding 2 limbs pairs small appendages each limbs out of seg each Structure posteriorly- swimming more evolved 1 pair limbs each seg  Some Arthropods Retain Biramy some limbs rem specialized https://insectsexplained.files.wordpress.com/2014/09/insect-evolution.png Ex antenna  Appendages share Common Origin for ↑ - imaginal disc all limbs , antenna , each segment Flat layer that inflates into a tube anterior/ posterior swirls of cells unique and identifiable as precursers  Homology of Arthropod Appendage Parts antennopidias posterior dominates anterior W genes MUTATED metamere thoracic Signals anterior Scroobious Pip (1872) weird creature what i am ? biramous in some sections MS Typ 55.14 (159), Houghton Library, Harvard University What Differentiates Metameres? Hox Genes are Segment Selectors Are there Others? overlapping domains  What Genes Control Segment Identity? Hox Genes are Ancient Hox genes are present and expressed developmentally in organisms as diverse as sponges to humans They are conserved and play a developmental role Are other genes similarly conserved? Phylostratigraphy - take some of genome sea data - when data expressed where Isolate and sequence transcripts (via cDNA libraries) from different developmental stages in an organism 1. developmental Use algorithms to sequences to establish comparisons to similar genes and thereby mechanics 2 evolution identify them. take MRNA 1 2 probetranscript. reverse of genes Compare across species and try to characterize how ancient the genes are.microarray entire 4 Assign an index score according to the age of gene family (how long ago the gene was gene set deployed, and indicative of how important it is. across multiple species index of Old New age vs genes - now freq , how ancient - Stratigraphy Index Score How Old Are the Genes at Play During Development? development - average age Hox genes of genes high in early dev stage The Phylotype I have two little embryos in spirits, for which I have forgotten to note the name, and I’m not quite able to determine which class they belong to. They could be lizards, small birds, or be very young mammals. The head and trunk development in these animals is so alike. The extremities are not yet present in these embryos. Even if they were present at the first stages of development, they would teach nothing since the developing feet of lizards and mammals, the wings and feet of birds, like the hands and feet of people, are the same basic shape. body built basic plan all Karl Ernst von Baer (1828) Phylotype and Genotype Phylotype: Conserved basic body plan (Bauplan) upon which all tetrapods ↓ are based ↑ appendages genes regulate Ex Hox genes Zootype: Genotypic. hourglass of conserved array of ancient genes that regulate development of the phylotype Romanes after Haeckel 1892)  Phylotypic hourglass Phylostratigraphy defines: newer genes build structures nec for the genes – zootype – that development characterize the phylotype -most conserved bauplan more ancient genes present huge array of genes