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Eckhart L, Holthaus KB, Sachslehner AP. Cell differentiation in the embryonic periderm and in scaffolding epithelia of skin appendages. Dev Biol 2024:S0012-1606(24)00174-X. [PMID: 38964706 DOI: 10.1016/j.ydbio.2024.07.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 05/10/2024] [Accepted: 07/02/2024] [Indexed: 07/06/2024]
Abstract
Terminal differentiation of epithelial cells is critical for the barrier function of the skin, the growth of skin appendages, such as hair and nails, and the development of the skin of amniotes. Here, we present the hypothesis that the differentiation of cells in embryonic periderm shares characteristic features with the differentiation of epithelial cells that support the morphogenesis of cornified skin appendages during postnatal life. The periderm prevents aberrant fusion of adjacent epithelial sites during early skin development. It is shed off when keratinocytes of the epidermis form the cornified layer, the stratum corneum. A similar role is played by epithelia that ensheath cornifying skin appendages until they disintegrate to allow the separation of the mature part of the skin appendage from the adjacent tissue. These epithelia, exemplified by the inner root sheath of hair follicles and the epithelia close to the free edge of nails or claws, are referred to as scaffolding epithelia. The periderm and scaffolding epithelia are similar with regard to their transient functions in separating tissues and the conserved expression of trichohyalin and trichohyalin-like genes in mammals and birds. Thus, we propose that parts of the peridermal differentiation program were coopted to a new postnatal function during the evolution of cornified skin appendages in amniotes.
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Affiliation(s)
- Leopold Eckhart
- Department of Dermatology, Medical University of Vienna, Vienna, Austria.
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2
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Schendel V, Müller CHG, Kenning M, Maxwell M, Jenner RA, Undheim EAB, Sombke A. The venom and telopodal defence systems of the centipede Lithobius forficatus are functionally convergent serial homologues. BMC Biol 2024; 22:135. [PMID: 38867210 PMCID: PMC11170834 DOI: 10.1186/s12915-024-01925-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Accepted: 05/22/2024] [Indexed: 06/14/2024] Open
Abstract
BACKGROUND Evolution of novelty is a central theme in evolutionary biology, yet studying the origins of traits with an apparently discontinuous origin remains a major challenge. Venom systems are a well-suited model for the study of this phenomenon because they capture several aspects of novelty across multiple levels of biological complexity. However, while there is some knowledge on the evolution of individual toxins, not much is known about the evolution of venom systems as a whole. One way of shedding light on the evolution of new traits is to investigate less specialised serial homologues, i.e. repeated traits in an organism that share a developmental origin. This approach can be particularly informative in animals with repetitive body segments, such as centipedes. RESULTS Here, we investigate morphological and biochemical aspects of the defensive telopodal glandular organs borne on the posterior legs of venomous stone centipedes (Lithobiomorpha), using a multimethod approach, including behavioural observations, comparative morphology, proteomics, comparative transcriptomics and molecular phylogenetics. We show that the anterior venom system and posterior telopodal defence system are functionally convergent serial homologues, where one (telopodal defence) represents a model for the putative early evolutionary state of the other (venom). Venom glands and telopodal glandular organs appear to have evolved from the same type of epidermal gland (four-cell recto-canal type) and while the telopodal defensive secretion shares a great degree of compositional overlap with centipede venoms in general, these similarities arose predominantly through convergent recruitment of distantly related toxin-like components. Both systems are composed of elements predisposed to functional innovation across levels of biological complexity that range from proteins to glands, demonstrating clear parallels between molecular and morphological traits in the properties that facilitate the evolution of novelty. CONCLUSIONS The evolution of the lithobiomorph telopodal defence system provides indirect empirical support for the plausibility of the hypothesised evolutionary origin of the centipede venom system, which occurred through functional innovation and gradual specialisation of existing epidermal glands. Our results thus exemplify how continuous transformation and functional innovation can drive the apparent discontinuous emergence of novelties on higher levels of biological complexity.
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Affiliation(s)
- Vanessa Schendel
- Centre for Advanced Imaging, The University of Queensland, St. Lucia, QLD, 4072, Australia
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD, 4072, Australia
| | - Carsten H G Müller
- Zoological Institute and Museum, University of Greifswald, Loitzer Strasse 26, Greifswald, 17489, Germany
| | - Matthes Kenning
- Zoological Institute and Museum, University of Greifswald, Loitzer Strasse 26, Greifswald, 17489, Germany
| | - Michael Maxwell
- Centre for Advanced Imaging, The University of Queensland, St. Lucia, QLD, 4072, Australia
| | | | - Eivind A B Undheim
- Centre for Advanced Imaging, The University of Queensland, St. Lucia, QLD, 4072, Australia.
- Centre for Ecological and Evolutionary Synthesis, Department of Biosciences, University of Oslo, Oslo, 0316, Norway.
| | - Andy Sombke
- Centre for Anatomy and Cell Biology, Cell and Developmental Biology, Medical University of Vienna, Schwarzspanierstrasse 17, Vienna, 1090, Austria.
- Department of Evolutionary Biology, Integrative Zoology, University of Vienna, Djerassiplatz 1, 1030, Austria.
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3
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Kates HR, O'Meara BC, LaFrance R, Stull GW, James EK, Liu SY, Tian Q, Yi TS, Conde D, Kirst M, Ané JM, Soltis DE, Guralnick RP, Soltis PS, Folk RA. Shifts in evolutionary lability underlie independent gains and losses of root-nodule symbiosis in a single clade of plants. Nat Commun 2024; 15:4262. [PMID: 38802387 PMCID: PMC11130336 DOI: 10.1038/s41467-024-48036-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Accepted: 04/16/2024] [Indexed: 05/29/2024] Open
Abstract
Root nodule symbiosis (RNS) is a complex trait that enables plants to access atmospheric nitrogen converted into usable forms through a mutualistic relationship with soil bacteria. Pinpointing the evolutionary origins of RNS is critical for understanding its genetic basis, but building this evolutionary context is complicated by data limitations and the intermittent presence of RNS in a single clade of ca. 30,000 species of flowering plants, i.e., the nitrogen-fixing clade (NFC). We developed the most extensive de novo phylogeny for the NFC and an RNS trait database to reconstruct the evolution of RNS. Our analysis identifies evolutionary rate heterogeneity associated with a two-step process: An ancestral precursor state transitioned to a more labile state from which RNS was rapidly gained at multiple points in the NFC. We illustrate how a two-step process could explain multiple independent gains and losses of RNS, contrary to recent hypotheses suggesting one gain and numerous losses, and suggest a broader phylogenetic and genetic scope may be required for genome-phenome mapping.
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Affiliation(s)
- Heather R Kates
- Florida Museum of Natural History, University of Florida, Gainesville, FL, USA.
| | - Brian C O'Meara
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, 37996-1610, USA
| | - Raphael LaFrance
- Florida Museum of Natural History, University of Florida, Gainesville, FL, USA
| | - Gregory W Stull
- Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China
| | - Euan K James
- The James Hutton Institute, Invergowrie Dundee, Scotland, UK
| | - Shui-Yin Liu
- Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China
| | - Qin Tian
- Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China
| | - Ting-Shuang Yi
- Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China
| | - Daniel Conde
- Centro de Biotecnología y Genómica de Plantas (CBGP), Universidad Politécnica de Madrid (UPM)-Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA-CSIC), Campus de Montegancedo, Pozuelo de Alarcón, Madrid, 28223, Spain
| | - Matias Kirst
- Genetics Institute, University of Florida, Gainesville, FL, USA
- School of Forest, Fisheries and Geomatic Sciences, University of Florida, Gainesville, FL, USA
| | - Jean-Michel Ané
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, 53706, USA
- Department of Agronomy, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Douglas E Soltis
- Florida Museum of Natural History, University of Florida, Gainesville, FL, USA
- Genetics Institute, University of Florida, Gainesville, FL, USA
- Biodiversity Institute, University of Florida, Gainesville, FL, USA
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Robert P Guralnick
- Florida Museum of Natural History, University of Florida, Gainesville, FL, USA
- Biodiversity Institute, University of Florida, Gainesville, FL, USA
| | - Pamela S Soltis
- Florida Museum of Natural History, University of Florida, Gainesville, FL, USA
- Genetics Institute, University of Florida, Gainesville, FL, USA
- Biodiversity Institute, University of Florida, Gainesville, FL, USA
| | - Ryan A Folk
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA.
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4
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Lau ES, Goodheart JA, Anderson NT, Liu VL, Mukherjee A, Oakley TH. Similar enzymatic functions in distinct bioluminescence systems: evolutionary recruitment of sulfotransferases in ostracod light organs. Biol Lett 2024; 20:20230585. [PMID: 38746983 DOI: 10.1098/rsbl.2023.0585] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Accepted: 04/18/2024] [Indexed: 05/28/2024] Open
Abstract
Genes from ancient families are sometimes involved in the convergent evolutionary origins of similar traits, even across vast phylogenetic distances. Sulfotransferases are an ancient family of enzymes that transfer sulfate from a donor to a wide variety of substrates, including probable roles in some bioluminescence systems. Here, we demonstrate multiple sulfotransferases, highly expressed in light organs of the bioluminescent ostracod Vargula tsujii, transfer sulfate in vitro to the luciferin substrate, vargulin. We find luciferin sulfotransferases (LSTs) of ostracods are not orthologous to known LSTs of fireflies or sea pansies; animals with distinct and convergently evolved bioluminescence systems compared to ostracods. Therefore, distantly related sulfotransferases were independently recruited at least three times, leading to parallel evolution of luciferin metabolism in three highly diverged organisms. Reuse of homologous genes is surprising in these bioluminescence systems because the other components, including luciferins and luciferases, are completely distinct. Whether convergently evolved traits incorporate ancient genes with similar functions or instead use distinct, often newer, genes may be constrained by how many genetic solutions exist for a particular function. When fewer solutions exist, as in genetic sulfation of small molecules, evolution may be more constrained to use the same genes time and again.
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Affiliation(s)
- Emily S Lau
- Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Jessica A Goodheart
- Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA
- Division of Invertebrate Zoology, American Museum of Natural History, New York, NY 10025, USA
| | - Nolan T Anderson
- Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Vannie L Liu
- Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Arnab Mukherjee
- Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
- Department of Biological Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
- Department of Chemistry, University of California Santa Barbara, Santa Barbara, CA 93106, USA
- Neuroscience Research Institute, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Todd H Oakley
- Department of Ecology, Evolution, and Marine Biology, University of California Santa Barbara, Santa Barbara, CA 93106, USA
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Longtine C, Eliason CM, Mishkind D, Lee C, Chiappone M, Goller F, Love J, Kingsley EP, Clarke JA, Tabin CJ. Homology and the evolution of vocal folds in the novel avian voice box. Curr Biol 2024; 34:461-472.e7. [PMID: 38183987 DOI: 10.1016/j.cub.2023.12.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 08/29/2023] [Accepted: 12/06/2023] [Indexed: 01/08/2024]
Abstract
The origin of novel traits, those that are not direct modifications of a pre-existing ancestral structure, remains a fundamental problem in evolutionary biology. For example, little is known about the evolutionary and developmental origins of the novel avian vocal organ, the syrinx. Located at the tracheobronchial junction, the syrinx is responsible for avian vocalization, but it is unclear whether avian vocal folds are homologous to the laryngeal vocal folds in other tetrapods or convergently evolved. Here, we identify a core developmental program involved in avian vocal fold formation and infer the morphology of the syrinx of the ancestor of modern birds. We find that this ancestral syrinx had paired sound sources induced by a conserved developmental pathway and show that shifts in these signals correlate with syringeal diversification. We show that, despite being derived from different developmental tissues, vocal folds in the syrinx and larynx have similar tissue composition and are established through a strikingly similar developmental program, indicating that co-option of an ancestral developmental program facilitated the origin of vocal folds in the avian syrinx.
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Affiliation(s)
- Charlie Longtine
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
| | - Chad M Eliason
- The Jackson School of Geosciences and Department of Integrative Biology, The University of Texas at Austin, Austin, TX 78712, USA
| | - Darcy Mishkind
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
| | - ChangHee Lee
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
| | - Michael Chiappone
- The Jackson School of Geosciences and Department of Integrative Biology, The University of Texas at Austin, Austin, TX 78712, USA
| | - Franz Goller
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA; Department of Zoophysiology, University of Münster, 48149 Münster, Germany
| | - Jay Love
- School of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
| | - Evan P Kingsley
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
| | - Julia A Clarke
- The Jackson School of Geosciences and Department of Integrative Biology, The University of Texas at Austin, Austin, TX 78712, USA.
| | - Clifford J Tabin
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
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6
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Moroz LL, Romanova DY. Homologous vs. homocratic neurons: revisiting complex evolutionary trajectories. Front Cell Dev Biol 2023; 11:1336093. [PMID: 38178869 PMCID: PMC10764524 DOI: 10.3389/fcell.2023.1336093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 12/08/2023] [Indexed: 01/06/2024] Open
Affiliation(s)
- Leonid L. Moroz
- Department of Neuroscience and McKnight Brain Institute, University of Florida, Gainesville, FL, United States
- Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL, United States
| | - Daria Y. Romanova
- Institute of Higher Nervous Activity and Neurophysiology of RAS, Moscow, Russia
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7
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Molina-Gil S, Sotillos S, Espinosa-Vázquez JM, Almudi I, Hombría JCG. Interlocking of co-opted developmental gene networks in Drosophila and the evolution of pre-adaptive novelty. Nat Commun 2023; 14:5730. [PMID: 37714829 PMCID: PMC10504328 DOI: 10.1038/s41467-023-41414-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Accepted: 08/30/2023] [Indexed: 09/17/2023] Open
Abstract
The re-use of genes in new organs forms the base of many evolutionary novelties. A well-characterised case is the recruitment of the posterior spiracle gene network to the Drosophila male genitalia. Here we find that this network has also been co-opted to the testis mesoderm where is required for sperm liberation, providing an example of sequentially repeated developmental co-options. Associated to this co-option event, an evolutionary expression novelty appeared, the activation of the posterior segment determinant Engrailed to the anterior A8 segment controlled by common testis and spiracle regulatory elements. Enhancer deletion shows that A8 anterior Engrailed activation is not required for spiracle development but only necessary in the testis. Our study presents an example of pre-adaptive developmental novelty: the activation of the Engrailed transcription factor in the anterior compartment of the A8 segment where, despite having no specific function, opens the possibility of this developmental factor acquiring one. We propose that recently co-opted networks become interlocked, so that any change to the network because of its function in one organ, will be mirrored by other organs even if it provides no selective advantage to them.
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Affiliation(s)
- Sara Molina-Gil
- Centro Andaluz de Biología del Desarrollo (CABD), CSIC-JA-UPO Ctra. de Utrera, km1, 41013, Seville, Spain
- Málaga Biomedical Research Institute and Andalusian Centre for Nanomedicine and Biotechnology Platform, Severo Ochoa, 35, 29590, Málaga, Spain
| | - Sol Sotillos
- Centro Andaluz de Biología del Desarrollo (CABD), CSIC-JA-UPO Ctra. de Utrera, km1, 41013, Seville, Spain
| | - José Manuel Espinosa-Vázquez
- Centro Andaluz de Biología del Desarrollo (CABD), CSIC-JA-UPO Ctra. de Utrera, km1, 41013, Seville, Spain
- Department of Food Biotechnology, Instituto de la Grasa. Campus de la Universidad Pablo de Olavide. Ctra. de Utrera, km. 1, 41013, Seville, Spain
| | - Isabel Almudi
- Centro Andaluz de Biología del Desarrollo (CABD), CSIC-JA-UPO Ctra. de Utrera, km1, 41013, Seville, Spain
- Department of Genetics, Microbiology and Statistics and Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona, Diagonal, 643, 08028, Barcelona, Spain
| | - James C-G Hombría
- Centro Andaluz de Biología del Desarrollo (CABD), CSIC-JA-UPO Ctra. de Utrera, km1, 41013, Seville, Spain.
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8
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Bowsher J, Jockusch EL, Nagy L. Editorial. Semin Cell Dev Biol 2023; 145:1-2. [PMID: 36702721 DOI: 10.1016/j.semcdb.2022.12.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Julia Bowsher
- Department of Biological Sciences, North Dakota State University, Fargo, North Dakota, USA
| | - Elizabeth L Jockusch
- Department of Ecology & Evolutionary Biology, University of Connecticut, Storrs, Connecticut, USA
| | - Lisa Nagy
- Molecular and Cellular Biology, University of Arizona, Tucson, Arizona USA.
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9
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Jiang M, Jian J, Zhou C, Li L, Wang Y, Zhang W, Song Z, Yang J. Does integument arise de novo or from pre-existing structures? ── Insights from the key regulatory genes controlling integument development. FRONTIERS IN PLANT SCIENCE 2023; 13:1078248. [PMID: 36714739 PMCID: PMC9880897 DOI: 10.3389/fpls.2022.1078248] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 12/29/2022] [Indexed: 06/18/2023]
Abstract
The origin of seeds is one of the key innovations in land plant evolution. Ovules are the developmental precursors of seeds. The integument is the envelope structure surrounding the nucellus within the ovule and developing into the seed coat when ovules mature upon fertilization. The question of whether the integument arise de novo or evolve from elaboration of pre-existing structures has caused much debate. By exploring the origin and evolution of the key regulatory genes controlling integument development and their functions during both individual and historical developmental processes, we showed the widespread presence of the homologs of ANT, CUC, BEL1, SPL, C3HDZ, INO, ATS, and ETT in seedless plant genomes. All of these genes have undergone duplication-divergence events in their evolutionary history, with most of the descendant paralogous suffering motif gain and/or loss in the coding regions. Expression and functional characterization have shown that these genes are key components of the genetic program that patterns leaf-like lateral organs. Serial homology can thus be postulated between integuments and other lateral organs in terms of the shared master regulatory genes. Given that the genetic program patterning leaf-like lateral organs formed in seedless plants, and was reused during seed origin, the integument is unlikely to arise de novo but evolved from the stem segment-specific modification of pre-existing serially homologous structures. The master 'switches' trigging the modification to specify the integument identity remain unclear. We propose a successive transformation model of integument origin.
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Affiliation(s)
- Min Jiang
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
- Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical Garden, Shanghai, China
| | - Jinjing Jian
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
| | - Chengchuan Zhou
- Institute of Tree Genetics Breeding and Cultivation, Jiangxi Academy of Forestry, Nanchang, China
| | - Linfeng Li
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
| | - Yuguo Wang
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
| | - Wenju Zhang
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
| | - Zhiping Song
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
| | - Ji Yang
- Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Center for Evolutionary Biology, Fudan University, Shanghai, China
- Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical Garden, Shanghai, China
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10
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DiFrisco J, Love AC, Wagner GP. The hierarchical basis of serial homology and evolutionary novelty. J Morphol 2023; 284:e21531. [PMID: 36317664 DOI: 10.1002/jmor.21531] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2022] [Revised: 10/26/2022] [Accepted: 10/29/2022] [Indexed: 11/05/2022]
Abstract
Given the pervasiveness of gene sharing in evolution and the extent of homology across the tree of life, why is everything not homologous with everything else? The continuity and overlapping genetic contributions to diverse traits across lineages seem to imply that no discrete determination of homology is possible. Although some argue that the widespread overlap in parts and processes should be acknowledged as "partial" homology, this threatens a broad base of presumed comparative morphological knowledge accepted by most biologists. Following a long scientific tradition, we advocate a strategy of "theoretical articulation" that introduces further distinctions to existing concepts to produce increased contrastive resolution among the labels used to represent biological phenomena. We pursue this strategy by drawing on successful patterns of reasoning from serial homology at the level of gene sequences to generate an enriched characterization of serial homology as a hierarchical, phylogenetic concept. Specifically, we propose that the concept of serial homology should be applied primarily to repeated but developmentally individualized body parts, such as cell types, differentiated body segments, or epidermal appendages. For these characters, a phylogenetic history can be reconstructed, similar to families of paralogous genes, endowing the notion of serial homology with a hierarchical, phylogenetic interpretation. On this basis, we propose a five-fold theoretical classification that permits a more fine-grained mapping of diverse trait-types. This facilitates answering the question of why everything is not homologous with everything else, as well as how novelty is possible given that any new character possesses evolutionary precursors. We illustrate the fecundity of our account by reference to debates over insect wing serial homologs and vertebrate paired appendages.
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Affiliation(s)
| | - Alan C Love
- Department of Philosophy, University of Minnesota, Minneapolis, Minnesota, USA.,Minnesota Center for Philosophy of Sciences, University of Minnesota, Minneapolis, Minnesota, USA
| | - Günter P Wagner
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, USA.,Yale Systems Biology Institute, Yale University, New Haven, Connecticut, USA.,Department of Obstetrics, Gynecology and Reproductive Sciences, Yale Medical School, New Haven, Connecticut, USA.,Department of Obstetrics and Gynecology, Wayne State University, Detroit, Michigan, USA
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