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Egawa S, Griffin CT, Bishop PJ, Pintore R, Tsai HP, Botelho JF, Smith-Paredes D, Kuratani S, Norell MA, Nesbitt SJ, Hutchinson JR, Bhullar BAS. The dinosaurian femoral head experienced a morphogenetic shift from torsion to growth along the avian stem. Proc Biol Sci 2022; 289:20220740. [PMID: 36196539 PMCID: PMC9532989 DOI: 10.1098/rspb.2022.0740] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
Significant evolutionary shifts in locomotor behaviour often involve comparatively subtle anatomical transitions. For dinosaurian and avian evolution, medial overhang of the proximal femur has been central to discussions. However, there is an apparent conflict with regard to the evolutionary origin of the dinosaurian femoral head, with neontological and palaeontological data suggesting seemingly incongruent hypotheses. To reconcile this, we reconstructed the evolutionary history of morphogenesis of the proximal end of the femur from early archosaurs to crown birds. Embryological comparison of living archosaurs (crocodylians and birds) suggests the acquisition of the greater overhang of the femoral head in dinosaurs results from additional growth of the proximal end in the medial-ward direction. On the other hand, the fossil record suggests that this overhang was acquired by torsion of the proximal end, which projected in a more rostral direction ancestrally. We reconcile this apparent conflict by inferring that the medial overhang of the dinosaur femoral head was initially acquired by torsion, which was then superseded by mediad growth. Details of anatomical shifts in fossil forms support this hypothesis, and their biomechanical implications are congruent with the general consensus regarding broader morpho-functional evolution on the avian stem.
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Affiliation(s)
- Shiro Egawa
- Department of Earth & Planetary Sciences and Peabody Museum of Natural History, Yale University, New Haven, CT 06520, USA.,Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan.,Department of Neurophysiology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| | - Christopher T Griffin
- Department of Earth & Planetary Sciences and Peabody Museum of Natural History, Yale University, New Haven, CT 06520, USA
| | - Peter J Bishop
- Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms AL9 7TA, UK.,Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.,Geosciences Program, Queensland Museum, Brisbane, Australia
| | - Romain Pintore
- Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms AL9 7TA, UK.,Mécanismes adaptatifs et évolution (MECADEV)/UMR 7179, CNRS/Muséum National d'Histoire Naturelle, Paris, France
| | - Henry P Tsai
- Department of Biomedical Sciences, Missouri State University, Springfield, MO 65897, USA
| | - João F Botelho
- Department of Earth & Planetary Sciences and Peabody Museum of Natural History, Yale University, New Haven, CT 06520, USA.,Department of Biology, Southern Connecticut State University, New Haven, CT 06515, USA.,Escuela de Medicina Veterinaria, Facultad de Agronomía e Ingeniería Forestal, Facultad de Ciencias Biológicas y Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Daniel Smith-Paredes
- Department of Earth & Planetary Sciences and Peabody Museum of Natural History, Yale University, New Haven, CT 06520, USA
| | - Shigeru Kuratani
- Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), Kobe, Japan
| | - Mark A Norell
- Division of Vertebrate Paleontology, American Museum of Natural History, New York, NY, USA
| | | | - John R Hutchinson
- Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms AL9 7TA, UK
| | - Bhart-Anjan S Bhullar
- Department of Earth & Planetary Sciences and Peabody Museum of Natural History, Yale University, New Haven, CT 06520, USA
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2
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Mead ME, Borowsky AT, Joehnk B, Steenwyk JL, Shen XX, Sil A, Rokas A. Recurrent Loss of abaA, a Master Regulator of Asexual Development in Filamentous Fungi, Correlates with Changes in Genomic and Morphological Traits. Genome Biol Evol 2021; 12:1119-1130. [PMID: 32442273 PMCID: PMC7531577 DOI: 10.1093/gbe/evaa107] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/19/2020] [Indexed: 12/11/2022] Open
Abstract
Gene regulatory networks (GRNs) drive developmental and cellular differentiation, and variation in their architectures gives rise to morphological diversity. Pioneering studies in Aspergillus fungi, coupled with subsequent work in other filamentous fungi, have shown that the GRN governed by the BrlA, AbaA, and WetA proteins controls the development of the asexual fruiting body or conidiophore. A specific aspect of conidiophore development is the production of phialides, conidiophore structures that are under the developmental control of AbaA and function to repetitively generate spores. Fungal genome sequencing has revealed that some filamentous fungi lack abaA, and also produce asexual structures that lack phialides, raising the hypothesis that abaA loss is functionally linked to diversity in asexual fruiting body morphology. To examine this hypothesis, we carried out an extensive search for the abaA gene across 241 genomes of species from the fungal subphylum Pezizomycotina. We found that abaA was independently lost in four lineages of Eurotiomycetes, including from all sequenced species within the order Onygenales, and that all four lineages that have lost abaA also lack the ability to form phialides. Genetic restoration of abaA from Aspergillus nidulans into Histoplasma capsulatum, a pathogenic species from the order Onygenales that lacks an endogenous copy of abaA, did not alter Histoplasma conidiation morphology but resulted in a marked increase in spore viability. We also discovered that species lacking abaA contain fewer AbaA binding motifs in the regulatory regions of orthologs of some AbaA target genes, suggesting that the asexual fruiting body GRN of organisms that have lost abaA has likely been rewired. Our results provide an illustration of how repeated losses of a key regulatory transcription factor have contributed to the diversity of an iconic fungal morphological trait.
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Affiliation(s)
- Matthew E Mead
- Department of Biological Sciences, Vanderbilt University
| | | | - Bastian Joehnk
- Department of Microbiology and Immunology, University of California San Francisco
| | | | - Xing-Xing Shen
- Department of Biological Sciences, Vanderbilt University
| | - Anita Sil
- Department of Microbiology and Immunology, University of California San Francisco
| | - Antonis Rokas
- Department of Biological Sciences, Vanderbilt University
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3
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Chamberlin HM, Jain IM, Corchado-Sonera M, Kelley LH, Sharanya D, Jama A, Pabla R, Dawes AT, Gupta BP. Evolution of Transcriptional Repressors Impacts Caenorhabditis Vulval Development. Mol Biol Evol 2021; 37:1350-1361. [PMID: 31960924 DOI: 10.1093/molbev/msaa009] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Comparative genomic sequence analysis has found that the genes for many chromatin-associated proteins are poorly conserved, but the biological consequences of these sequence changes are not understood. Here, we show that four genes identified for an Inappropriate Vulval cell Proliferation (ivp) phenotype in the nematode Caenorhabditis briggsae exhibit distinct functions and genetic interactions when compared with their orthologs in C. elegans. Specifically, we show that the four C. briggsae ivp genes encode the noncanonical histone HTZ-1/H2A.z and three nematode-specific proteins predicted to function in the nucleus. The mutants exhibit ectopic vulval precursor cell proliferation (the multivulva [Muv] phenotype) due to inappropriate expression of the lin-3/EGF gene, and RNAseq analysis suggests a broad role for these ivp genes in transcriptional repression. Importantly, although the C. briggsae phenotypes have parallels with those seen in the C. elegans synMuv system, except for the highly conserved HTZ-1/H2A.z, comparable mutations in C. elegans ivp orthologs do not exhibit synMuv gene interactions or phenotypes. These results demonstrate the evolutionary changes that can underlie conserved biological outputs and argue that proteins critical to repress inappropriate expression from the genome participate in a rapidly evolving functional landscape.
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Affiliation(s)
| | - Ish M Jain
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | | | - Leanne H Kelley
- Department of Molecular Genetics, Ohio State University, Columbus, OH
| | - Devika Sharanya
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Abdulrahman Jama
- Department of Molecular Genetics, Ohio State University, Columbus, OH
| | - Romy Pabla
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Adriana T Dawes
- Department of Molecular Genetics, Ohio State University, Columbus, OH.,Department of Mathematics, Ohio State University, Columbus, OH
| | - Bhagwati P Gupta
- Department of Biology, McMaster University, Hamilton, ON, Canada
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4
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Phillips HR, Landis JB, Specht CD. Revisiting floral fusion: the evolution and molecular basis of a developmental innovation. J Exp Bot 2020; 71:3390-3404. [PMID: 32152629 DOI: 10.1093/jxb/eraa125] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 03/02/2020] [Indexed: 05/18/2023]
Abstract
Throughout the evolution of the angiosperm flower, developmental innovations have enabled the modification or elaboration of novel floral organs enabling subsequent diversification and expansion into new niches, for example the formation of novel pollinator relationships. One such developmental innovation is the fusion of various floral organs to form complex structures. Multiple types of floral fusion exist; each type may be the result of different developmental processes and is likely to have evolved multiple times independently across the angiosperm tree of life. The development of fused organs is thought to be mediated by the NAM/CUC3 subfamily of NAC transcription factors, which mediate boundary formation during meristematic development. The goal of this review is to (i) introduce the development of fused floral organs as a key 'developmental innovation', facilitated by a change in the expression of NAM/CUC3 transcription factors; (ii) provide a comprehensive overview of floral fusion phenotypes amongst the angiosperms, defining well-known fusion phenotypes and applying them to a systematic context; and (iii) summarize the current molecular knowledge of this phenomenon, highlighting the evolution of the NAM/CUC3 subfamily of transcription factors implicated in the development of fused organs. The need for a network-based analysis of fusion is discussed, and a gene regulatory network responsible for directing fusion is proposed to guide future research in this area.
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Affiliation(s)
- Heather R Phillips
- School of Integrative Plant Science, Section of Plant Biology and the L.H. Bailey Hortorium, Cornell University, Ithaca NY, USA
| | - Jacob B Landis
- School of Integrative Plant Science, Section of Plant Biology and the L.H. Bailey Hortorium, Cornell University, Ithaca NY, USA
| | - Chelsea D Specht
- School of Integrative Plant Science, Section of Plant Biology and the L.H. Bailey Hortorium, Cornell University, Ithaca NY, USA
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5
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McDonald JA, Tomoyasu Y. Sculpting new structures. eLife 2020; 9:57668. [PMID: 32463359 PMCID: PMC7255797 DOI: 10.7554/elife.57668] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 05/21/2020] [Indexed: 12/03/2022] Open
Abstract
The origins of the posterior lobe, a recently evolved structure in some species of Drosophila, have become clearer.
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6
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Smith SJ, Davidson LA, Rebeiz M. Evolutionary expansion of apical extracellular matrix is required for the elongation of cells in a novel structure. eLife 2020; 9:55965. [PMID: 32338602 PMCID: PMC7266619 DOI: 10.7554/elife.55965] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 04/06/2020] [Indexed: 12/13/2022] Open
Abstract
One of the fundamental gaps in our knowledge of how novel anatomical structures evolve is understanding the origins of the morphogenetic processes that form these features. Here, we traced the cellular development of a recently evolved morphological novelty, the posterior lobe of D. melanogaster. We found that this genital outgrowth forms through extreme increases in epithelial cell height. By examining the apical extracellular matrix (aECM), we also uncovered a vast matrix associated with the developing genitalia of lobed and non-lobed species. Expression of the aECM protein Dumpy is spatially expanded in lobe-forming species, connecting the posterior lobe to the ancestrally derived aECM network. Further analysis demonstrated that Dumpy attachments are necessary for cell height increases during posterior lobe development. We propose that the aECM presents a rich reservoir for generating morphological novelty and highlights a yet unseen role for aECM in regulating extreme cell height.
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Affiliation(s)
- Sarah Jacquelyn Smith
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, United States
| | - Lance A Davidson
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, United States
| | - Mark Rebeiz
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, United States
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7
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Torres-Paz J, Leclercq J, Rétaux S. Maternally regulated gastrulation as a source of variation contributing to cavefish forebrain evolution. eLife 2019; 8:50160. [PMID: 31670659 PMCID: PMC6874477 DOI: 10.7554/elife.50160] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2019] [Accepted: 10/30/2019] [Indexed: 11/24/2022] Open
Abstract
Sequential developmental events, starting from the moment of fertilization, are crucial for the acquisition of animal body plan. Subtle modifications in such early events are likely to have major impacts in later morphogenesis, bringing along morphological diversification. Here, comparing the blind cave and the surface morphotypes of Astyanax mexicanus fish, we found heterochronies during gastrulation that produce organizer and axial mesoderm tissues with different properties (including differences in the expression of dkk1b) that may have contributed to cavefish brain evolution. These variations observed during gastrulation depend fully on maternal factors. The developmental evolution of retinal morphogenesis and hypothalamic patterning are among those traits that retained significant maternal influence at larval stages. Transcriptomic analysis of fertilized eggs from both morphotypes and reciprocal F1 hybrids showed a strong and specific maternal signature. Our work strongly suggests that maternal effect genes and developmental heterochronies that occur during gastrulation have impacted morphological brain change during cavefish evolution.
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Affiliation(s)
- Jorge Torres-Paz
- Paris-Saclay Institute of Neuroscience, CNRS UMR9197, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Julien Leclercq
- Paris-Saclay Institute of Neuroscience, CNRS UMR9197, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Sylvie Rétaux
- Paris-Saclay Institute of Neuroscience, CNRS UMR9197, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
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8
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Jiménez-Guri E, Wotton KR, Jaeger J. tarsal-less is expressed as a gap gene but has no gap gene phenotype in the moth midge Clogmia albipunctata. R Soc Open Sci 2018; 5:180458. [PMID: 30225035 PMCID: PMC6124123 DOI: 10.1098/rsos.180458] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 07/18/2018] [Indexed: 06/08/2023]
Abstract
Gap genes are involved in segment determination during early development of the vinegar fly Drosophila melanogaster and other dipteran insects (flies, midges and mosquitoes). They are expressed in overlapping domains along the antero-posterior (A-P) axis of the blastoderm embryo. While gap domains cover the entire length of the A-P axis in Drosophila, there is a region in the blastoderm of the moth midge Clogmia albipunctata, which lacks canonical gap gene expression. Is a non-canonical gap gene functioning in this area? Here, we characterize tarsal-less (tal) in C. albipunctata. The homologue of tal in the flour beetle Tribolium castaneum (called milles-pattes, mlpt) is a bona fide gap gene. We find that Ca-tal is expressed in the region previously reported as lacking gap gene expression. Using RNA interference, we study the interaction of Ca-tal with gap genes. We show that Ca-tal is regulated by gap genes, but only has a very subtle effect on tailless (Ca-tll), while not affecting other gap genes at all. Moreover, cuticle phenotypes of Ca-tal depleted embryos do not show any gap phenotype. We conclude that Ca-tal is expressed and regulated like a gap gene, but does not function as a gap gene in C. albipunctata.
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Affiliation(s)
- Eva Jiménez-Guri
- EMBL/CRG Research Unit in Systems Biology, Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology (BIST), Dr. Aiguader 88, 08003 Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Barcelona, Spain
- Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn, Cornwall TR10 9EZ, UK
| | - Karl R. Wotton
- EMBL/CRG Research Unit in Systems Biology, Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology (BIST), Dr. Aiguader 88, 08003 Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Barcelona, Spain
| | - Johannes Jaeger
- EMBL/CRG Research Unit in Systems Biology, Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology (BIST), Dr. Aiguader 88, 08003 Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Barcelona, Spain
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9
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Vielle A, Callemeyn-Torre N, Gimond C, Poullet N, Gray JC, Cutter AD, Braendle C. Convergent evolution of sperm gigantism and the developmental origins of sperm size variability in Caenorhabditis nematodes. Evolution 2016; 70:2485-2503. [PMID: 27565121 DOI: 10.1111/evo.13043] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 08/08/2016] [Accepted: 08/08/2016] [Indexed: 01/01/2023]
Abstract
Sperm cells provide essential, if usually diminutive, ingredients to successful sexual reproduction. Despite this conserved function, sperm competition and coevolution with female traits can drive spectacular morphological change in these cells. Here, we characterize four repeated instances of convergent evolution of sperm gigantism in Caenorhabditis nematodes using phylogenetic comparative methods on 26 species. Species at the extreme end of the 50-fold range of sperm-cell volumes across the genus have sperm capable of comprising up to 5% of egg-cell volume, representing severe attenuation of the magnitude of anisogamy. Furthermore, we uncover significant differences in mean and variance of sperm size among genotypes, between sexes, and within and between individuals of identical genotypes. We demonstrate that the developmental basis of sperm size variation, both within and between species, becomes established during an early stage of sperm development at the formation of primary spermatocytes, while subsequent meiotic divisions contribute little further sperm size variability. These findings provide first insights into the developmental determinants of inter- and intraspecific sperm size differences in Caenorhabditis. We hypothesize that life history and ecological differences among species favored the evolution of alternative sperm competition strategies toward either many smaller sperm or fewer larger sperm.
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Affiliation(s)
- Anne Vielle
- University Nice Sophia Antipolis, CNRS, Inserm, IBV, Parc Valrose, 06100, Nice, France
| | | | - Clotilde Gimond
- University Nice Sophia Antipolis, CNRS, Inserm, IBV, Parc Valrose, 06100, Nice, France
| | - Nausicaa Poullet
- University Nice Sophia Antipolis, CNRS, Inserm, IBV, Parc Valrose, 06100, Nice, France
| | - Jeremy C Gray
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Asher D Cutter
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada
| | - Christian Braendle
- University Nice Sophia Antipolis, CNRS, Inserm, IBV, Parc Valrose, 06100, Nice, France.
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10
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Leimar O, Hartfelder K, Laubichler MD, Page RE. Development and evolution of caste dimorphism in honeybees - a modeling approach. Ecol Evol 2012; 2:3098-109. [PMID: 23301175 PMCID: PMC3539003 DOI: 10.1002/ece3.414] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 10/01/2012] [Accepted: 10/03/2012] [Indexed: 12/29/2022] Open
Abstract
The difference in phenotypes of queens and workers is a hallmark of the highly eusocial insects. The caste dimorphism is often described as a switch-controlled polyphenism, in which environmental conditions decide an individual's caste. Using theoretical modeling and empirical data from honeybees, we show that there is no discrete larval developmental switch. Instead, a combination of larval developmental plasticity and nurse worker feeding behavior make up a colony-level social and physiological system that regulates development and produces the caste dimorphism. Discrete queen and worker phenotypes are the result of discrete feeding regimes imposed by nurses, whereas a range of experimental feeding regimes produces a continuous range of phenotypes. Worker ovariole numbers are reduced through feeding-regime-mediated reduction in juvenile hormone titers, involving reduced sugar in the larval food. Based on the mechanisms identified in our analysis, we propose a scenario of the evolutionary history of honeybee development and feeding regimes.
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Affiliation(s)
- Olof Leimar
- Department of Zoology, Stockholm University Stockholm, Sweden ; Wissenschaftskolleg zu Berlin Wallotstrasse 19, Berlin, Germany
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11
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Gaume L, Di Giusto B. Adaptive significance and ontogenetic variability of the waxy zone in Nepenthes rafflesiana. Ann Bot 2009; 104:1281-91. [PMID: 19805403 PMCID: PMC2778386 DOI: 10.1093/aob/mcp238] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2009] [Revised: 06/05/2009] [Accepted: 08/11/2009] [Indexed: 05/04/2023]
Abstract
BACKGROUND AND AIMS The slippery waxy zone in the upper part of pitchers has long been considered the key trapping structure of the Nepenthes carnivorous plants; however, the presence of wax is reported to be variable within and between species of this species-rich genus. This study raises the question of the adaptive significance of the waxy zone and investigates the basis for an ontogenetic cause of its variability and correlation with pitcher shape. METHODS In Brunei (Borneo) the expression of the waxy zone throughout plant ontogeny was studied in two taxa of the Nepenthes rafflesiana complex, typica and elongata, which differ in pitcher shape and size. We also tested the adaptive significance of this zone by comparing the trapping efficiency and the number of prey captured of wax-bearing and wax-lacking plants. KEY RESULTS In elongata, the waxy zone is always well expanded and the elongated pitchers change little in form during plant development. Wax efficiently traps experimental ants but the number of captured prey in pitchers is low. In contrast, in typica, the waxy zone is reduced in successively produced pitchers until it is lost at the end of the plant's juvenile stage. The form of pitchers thus changes continuously throughout plant ontogeny, from elongated to ovoid. In typica, the number of captured prey is greater, but the role of wax in trapping is minor compared with that of the digestive liquid, and waxy plants do not show a higher insect retention and prey abundance as compared with non-waxy plants. CONCLUSIONS The waxy zone is not always a key trapping structure in Nepenthes and can be lost when supplanted by more efficient features. This study points out how pitcher structure is submitted to selection, and that evolutionary changes in developmental mechanisms could play a role in the morphological diversity of Nepenthes.
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Affiliation(s)
- Laurence Gaume
- UMR CNRS 5120 AMAP: botAnique et bioinforMatique de l'Architecture des Plantes, CIRAD-TA A51/PS2 Boulevard de la Lironde, F-34398 Montpellier cedex 5, France.
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