Some recent non-dino papers:
Free pdf:
Robert M. Brownstone (2020)
Key steps in the evolution of mammalian movement: a prolegomenal essay.
Neuroscience (advance online publication)
doi: https://doi.org/10.1016/j.neuroscience.2020.05.020
https://www.sciencedirect.com/science/article/pii/S0306452220303110
Highlights
Several evolutionary steps led to the emergence of vertebrate movement needed for social behaviour.
Descending systems rely on diverse spinal cord neurons to produce a rich repertoire of movement syllables.
The notochord and ventricular zone led to this diversity of neuronal types.
The sympathetic nervous system provided the substrate for homeothermic endothermy.
Homeothermic endothermy is a necessary building block for power, speed, and endurance.
Abstract
Rich repertoires of movements underlie the complex social interactions of mammals. The building blocks, or syllables, of these movements are produced by spinal cord circuits that are comprised of diverse neuronal types that control musculoskeletal systems comprised of multi-segmented limbs. Together, these systems provide mammals with the evolutionary advantages of power, speed, and endurance. Here, I propose that the key steps in chordate evolution that led to these traits began with the development of the notochord and a proliferative ventricular zone (with associated Notch signalling). This step led to the production of diverse neuronal types that included the development of a sympathetic nervous system that could regulate the evolving cardiovascular system. And the sympathetic nervous system in turn led to the development of homeothermic endothermy, a requirement for motor systems to produce a combination of power, speed, and endurance. Furthermore, the evolution of the continuous structure of the spinal cord led not only to a structure fit for cartesian signalling molecules, but also to one with high processing power in which circuits for effecting movement syllables formed. These syllables are harnessed by higher regions of nervous systems to produce the complex movements required for interactions with others and with the surrounding environment.
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Free pdf:
Atsushi Ikemoto, ÂDaiki X. Sato, ÂTakashi Makino Â& Masakado Kawata (2020))
Genetic factors for short life span associated with evolution of the loss of flight ability.
Ecology and Evolution (advance online publication)
doi: Âhttps://doi.org/10.1002/ece3.6342
https://onlinelibrary.wiley.com/doi/10.1002/ece3.6342
Free pdf:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.6342
Acquisition or loss of flying ability is evolutionarily linked with maximum life span (MLS) in mammals and birds. Although ecological factors, such as extrinsic mortality, may lead to either shortened or extended life spans through natural selection, MLS is influenced by complex molecular and metabolic processes, and the genetic changes associated with flying ability that have led to either a longer or shorter MLS are unknown. Here, we examine the parallel evolution of flight in mammals and birds and investigate positively selected genes at branches where either the acquisition (in little brown bats and large flying foxes) or loss (in AdÃlie penguins, emperor penguins, common ostriches, emus, great spotted kiwis, little spotted kiwis, okarito brown kiwis, greater rheas, lesser rheas, and cassowaries) of flight abilities occurred. Although we found no shared genes under selection among all the branches of interest, 7 genes were found to be positively selected in 2 of the branches. Among the 7 genes, only IGF2BP2 is known to affect both life span and energy expenditure. The positively selected mutations detected in IGF2BP2 likely affected the functionality of the encoded protein. IGF2BP2 , which has been reported to simultaneously prolong life span and increase energy expenditure, could be responsible for the evolution of shortened MLS associated with the loss of flying ability.
Genetic factors for short life span associated with evolution of the loss of flight ability.
Ecology and Evolution (advance online publication)
doi: Âhttps://doi.org/10.1002/ece3.6342
https://onlinelibrary.wiley.com/doi/10.1002/ece3.6342
Free pdf:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.6342
Acquisition or loss of flying ability is evolutionarily linked with maximum life span (MLS) in mammals and birds. Although ecological factors, such as extrinsic mortality, may lead to either shortened or extended life spans through natural selection, MLS is influenced by complex molecular and metabolic processes, and the genetic changes associated with flying ability that have led to either a longer or shorter MLS are unknown. Here, we examine the parallel evolution of flight in mammals and birds and investigate positively selected genes at branches where either the acquisition (in little brown bats and large flying foxes) or loss (in AdÃlie penguins, emperor penguins, common ostriches, emus, great spotted kiwis, little spotted kiwis, okarito brown kiwis, greater rheas, lesser rheas, and cassowaries) of flight abilities occurred. Although we found no shared genes under selection among all the branches of interest, 7 genes were found to be positively selected in 2 of the branches. Among the 7 genes, only IGF2BP2 is known to affect both life span and energy expenditure. The positively selected mutations detected in IGF2BP2 likely affected the functionality of the encoded protein. IGF2BP2 , which has been reported to simultaneously prolong life span and increase energy expenditure, could be responsible for the evolution of shortened MLS associated with the loss of flying ability.
=====
Chiara Bortoluzzi, Hendrik-Jan Megens, Mirte Bosse, Martijn F. L. Derks, Bert Dibbits, Kimberly Laport, Steffen Weigend, Martien A. M. Groenen, Richard P. M. A. Crooijmans (2020)
Parallel Genetic Origin of Foot Feathering in Birds.
Molecular Biology and Evolution, msaa092,
doi: https://doi.org/10.1093/molbev/msaa092
https://academic.oup.com/mbe/advance-article/doi/10.1093/molbev/msaa092/5818884
Understanding the genetic basis of similar phenotypes shared between lineages is a long-lasting research interest. Even though animal evolution offers many examples of parallelism, for many phenotypes little is known about the underlying genes and mutations. We here use a combination of whole-genome sequencing, _expression_ analyses, and comparative genomics to study the parallel genetic origin of ptilopody (Pti) in chicken. Ptilopody (or foot feathering) is a polygenic trait that can be observed in domesticated and wild avian species and is characterized by the partial or complete development of feathers on the ankle and feet. In domesticated birds, ptilopody is easily selected to fixation, though extensive variation in the type and level of feather development is often observed. By means of a genome-wide association analysis, we identified two genomic regions associated with ptilopody. At one of the loci, we identified a 17-kb deletion affecting PITX1 _expression_, a gene known to encode a transcription regulator of hindlimb identity and development. Similarly to pigeon, at the second loci, we observed ectopic _expression_ of TBX5, a gene involved in forelimb identity and a key determinant of foot feather development. We also observed that the trait evolved only once as foot-feathered birds share the same haplotype upstream TBX5. Our findings indicate that in chicken and pigeon ptilopody is determined by the same set of genes that affect similar molecular pathways. Our study confirms that ptilopody has evolved through parallel evolution in chicken and pigeon.
====
Molecular Biology and Evolution, msaa092,
doi: https://doi.org/10.1093/molbev/msaa092
https://academic.oup.com/mbe/advance-article/doi/10.1093/molbev/msaa092/5818884
Understanding the genetic basis of similar phenotypes shared between lineages is a long-lasting research interest. Even though animal evolution offers many examples of parallelism, for many phenotypes little is known about the underlying genes and mutations. We here use a combination of whole-genome sequencing, _expression_ analyses, and comparative genomics to study the parallel genetic origin of ptilopody (Pti) in chicken. Ptilopody (or foot feathering) is a polygenic trait that can be observed in domesticated and wild avian species and is characterized by the partial or complete development of feathers on the ankle and feet. In domesticated birds, ptilopody is easily selected to fixation, though extensive variation in the type and level of feather development is often observed. By means of a genome-wide association analysis, we identified two genomic regions associated with ptilopody. At one of the loci, we identified a 17-kb deletion affecting PITX1 _expression_, a gene known to encode a transcription regulator of hindlimb identity and development. Similarly to pigeon, at the second loci, we observed ectopic _expression_ of TBX5, a gene involved in forelimb identity and a key determinant of foot feather development. We also observed that the trait evolved only once as foot-feathered birds share the same haplotype upstream TBX5. Our findings indicate that in chicken and pigeon ptilopody is determined by the same set of genes that affect similar molecular pathways. Our study confirms that ptilopody has evolved through parallel evolution in chicken and pigeon.
====
Free pdf:
Diversification of color vision followed the marine invasions of elapid snakes
Polymorphisms in the SWS1 opsin persisted in the Hydrophis sea snake radiation
Polymorphisms suggest balancing selection favoring expanded spectral sensitivity
Snakes and primates may share mechanisms of spectral sensitivity diversification
Summary
Snakes are descended from highly visual lizards but have limited (probably dichromatic) color vision attributed to a dim-light lifestyle of early snakes. The living species of front-fanged elapids, however, are ecologically very diverse, with ~300 terrestrial species (cobras, taipans, etc.) and ~60 fully marine sea snakes, plus eight independently marine, amphibious sea kraits. Here, we investigate the evolution of spectral sensitivity in elapids by analyzing their opsin genes (which are responsible for sensitivity to UV and visible light), retinal photoreceptors, and ocular lenses. We found that sea snakes underwent rapid adaptive diversification of their visual pigments when compared with their terrestrial and amphibious relatives. The three opsins present in snakes (SWS1, LWS, and RH1) have evolved under positive selection in elapids, and in sea snakes they have undergone multiple shifts in spectral sensitivity toward the longer wavelengths that dominate below the sea surface. Several relatively distantly related Hydrophis sea snakes are polymorphic for shortwave sensitive visual pigment encoded by alleles of SWS1. This spectral site polymorphism is expected to confer expanded "UV-blue" spectral sensitivity and is estimated to have persisted twice as long as the predicted survival time for selectively neutral nuclear alleles. We suggest that this polymorphism is adaptively maintained across Hydrophis species via balancing selection, similarly to the LWS polymorphism that confers allelic trichromacy in some primates. Diving sea snakes thus appear to share parallel mechanisms of color vision diversification with fruit-eating primates.
Adriana MarÃa ALBINO (2020)
The Cenozoic lizard record of the Pampean Region
GEODIVERSITAS 42 (12): 175-183
http://sciencepress.mnhn.fr/en/periodiques/geodiversitas/42/12
The Pampean Region is a geographic area involving central and eastern Argentina, Uruguay, and southern Brazil. Contrasting with the fauna of squamates that currently inhabits the Pampean ÂRegion, the paleontological record is extremely reduced. Teiidae is the best-represented lizard taxon, with its earliest record in the late Miocene. Iguania is present since the early Pliocene onwards, whereas Anguidae is known only in the middle Pleistocene and Phyllodactylidae in the late Pleistocene-early Holocene interval. Other living families present in the region (Gymnophtalmidae, Scincidae) have no fossil representatives. The unique extinct taxon is the teiid Callopistes bicuspidatus Chani, 1976. The fossil record includes some taxa presently absent in the paleontological sites; this implies that the Neogene and Quaternary climatic-environmental changes that affected dramatically the avian and mammalian faunas of the Pampean Region, also influenced the biogeographical history of the herpetofauna.
Free pdf:
=====
S. M. Buttimer, N. Stepanova & M. C. Womack (2020)
Evolution of the unique anuran pelvic and hindlimb skeleton in relation to microhabitat, locomotor mode, and jump performance.
Integrative and Comparative Biology, icaa043 (advance online publication)
doi: https://doi.org/10.1093/icb/icaa043
https://academic.oup.com/icb/advance-article-abstract/doi/10.1093/icb/icaa043/5841667
Anurans (frogs and toads) have a unique pelvic and hindlimb skeleton among tetrapods. Although their distinct body plan is primarily associated with saltation, anuran species vary in their primary locomotor mode (e.g., walkers, hoppers, jumpers, and swimmers) and are found in a wide array of microhabitats (e.g., burrowing, terrestrial, arboreal, and aquatic) with varying functional demands. Given their largely conserved body plan, morphological adaptation to these diverse niches likely results from more fine-scale morphological change. Our study determines how shape differences in Anura's unique pelvic and hindlimb skeletal structures vary with microhabitat, locomotor mode, and jumping ability. Using microCT scans of preserved specimens from museum collections, we added 3D landmarks to the pelvic and hindlimb skeleton of 230 anuran species. In addition, we compiled microhabitat and locomotor data from the literature for these species that span 52 of the 55 families of frogs and ~210 million years of anuran evolution. Using this robust dataset, we examine the relationship between pelvic and hindlimb morphology and phylogenetic history, allometry, microhabitat, and locomotor mode. We find pelvic and hindlimb changes associated with shifts in microhabitat ("ecomorphs"â) and locomotor mode ("locomorphs") and directly relate those morphological changes to the jumping ability of individual species. We also reveal how individual bones vary in evolutionary rate and their association with phylogeny, body size, microhabitat, and locomotor mode. Our findings uncover previously undocumented morphological variation related to anuran ecological and locomotor diversification and link that variation to differences in jumping ability among species.
John Herrick & Bianca Sclavi (2020)
Genome Evolution in Amphibians.
eLS
doi: Âhttps://doi.org/10.1002/9780470015902.a0028996
https://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0028996
Genome size variation in vertebrates reflects an amazing amount of genetic and genomic diversity. Câvalue (genome size) ranges from 0.4 picograms (pg) in pufferfish to 133âpg in the marbled lungfish. Most vertebrate lineages have characteristic average Câvalues with restricted ranges. Amphibia, in contrast, represent an extreme: Câvalues in salamanders range from around 13 to over 122âpg; in frogs, they range from under 1 to over 13âpg. Why would closely related lineages and species have such dramatic differences in Câvalue? A number of theories have been proposed to account for the extreme range in genome size found in all eukaryote taxa. The amphibia not only have a wide range of Câvalues, but they also have a correspondingly wide range of life history traits and other phenotypes such as neoteny and limb regeneration. This remarkable class of vertebrate thus provides a unique model system for addressing evolutionary and physiological hypotheses.
Key Concepts
Junk DNA (retroviruses and DNA transposons) infected the ancestral eukaryote cell and established, together with mitochondria, a symbiotic relationship from which all other eukaryotic life forms emerged.
The host response to the original infection was adaptive rather than purifyingly selective: junk DNA provided the conditions for the emergence of a checkpoint guardian of the genome and correspondingly enhanced genome stability.
As genome size expanded, DNA repair systems increased in efficiency, allowing for the acquisition of new genes and new adaptations.
DNA replication programs and gene transcription programs reorganised as genome size either increased or decreased over evolutionary time.
Species richness negatively correlates with genome stability and positively correlates with karyotype diversity within specific lineages.
DNA damage response and repair (DDR) programs have evolved differentially in r and Kâstrategists: large body organisms have enhanced DDRs compared to small body, shortâlived organisms, and hence they tend to have more deterministic and organised replication programs.
Junk DNA serves as a substrate for the DDR to protect the cell against âmitotic catastropheâ.
Junk DNA serves as a scaffold for the formation of facultative heterochromatin during development and speciation,and hence participates in the global tissueâspecific and speciesâdependent transcription programs.
=========
David A. Kring, Sonia M. Tikoo, Martin Schmieder, Ulrich Riller, Mario Rebolledo-Vieyra, Sarah L. Simpson, Gordon R. Osinski, JÃrÃme Gattacceca, Axel Wittmann, Christina M. Verhagen, Charles S. Cockell, Marco J. L. Coolen, Fred J. Longstaffe, Sean P. S. Gulick, Joanna V. Morgan, Timothy J. Bralower, Elise Chenot, Gail L. Christeson, Philippe Claeys, Ludovic FerriÃre, Catalina Gebhardt, Kazuhisa Goto, Sophie L. Green, Heather Jones, Johanna Lofi, Christopher M. Lowery, RubÃn Ocampo-Torres, Ligia Perez-Cruz, Annemarie E. Pickersgill, H. Poelchau, Auriol S. P. Rae, Cornelia Rasmussen, Honami Sato, Jan Smit, Naotaka Tomioka, Jaime Urrutia-Fucugauchi, T. Whalen, Long Xiao and Kosei E. Yamaguchi (2020)
Probing the hydrothermal system of the Chicxulub impact crater.
Science Advances 6(22): eaaz3053
DOI: 10.1126/sciadv.aaz3053
https://advances.sciencemag.org/content/6/22/eaaz3053
News:
A steaming cauldron follows the dinosaurs' demise
Bruno F. SimÃes, David J. Gower, Arne R. Rasmussen, Mohammad A.R. Sarker, Gary C. Fry, Nicholas R. Casewell, Robert A. Harrison, Nathan S. Hart, Julian C. Partridge, David M. Hunt, Belinda S. Chang, Davide Pisani & Kate L. Sanders (2020)
Spectral Diversification and Trans-Species Allelic Polymorphism during the Land-to-Sea Transition in Snakes.
Current Biology (advance online publication)
DOI: https://doi.org/10.1016/j.cub.2020.04.061
https://www.cell.com/current-biology/fulltext/S0960-9822(20)30577-7
Spectral Diversification and Trans-Species Allelic Polymorphism during the Land-to-Sea Transition in Snakes.
Current Biology (advance online publication)
DOI: https://doi.org/10.1016/j.cub.2020.04.061
https://www.cell.com/current-biology/fulltext/S0960-9822(20)30577-7
Highlights
Diversification of color vision followed the marine invasions of elapid snakes
Polymorphisms in the SWS1 opsin persisted in the Hydrophis sea snake radiation
Polymorphisms suggest balancing selection favoring expanded spectral sensitivity
Snakes and primates may share mechanisms of spectral sensitivity diversification
Summary
Snakes are descended from highly visual lizards but have limited (probably dichromatic) color vision attributed to a dim-light lifestyle of early snakes. The living species of front-fanged elapids, however, are ecologically very diverse, with ~300 terrestrial species (cobras, taipans, etc.) and ~60 fully marine sea snakes, plus eight independently marine, amphibious sea kraits. Here, we investigate the evolution of spectral sensitivity in elapids by analyzing their opsin genes (which are responsible for sensitivity to UV and visible light), retinal photoreceptors, and ocular lenses. We found that sea snakes underwent rapid adaptive diversification of their visual pigments when compared with their terrestrial and amphibious relatives. The three opsins present in snakes (SWS1, LWS, and RH1) have evolved under positive selection in elapids, and in sea snakes they have undergone multiple shifts in spectral sensitivity toward the longer wavelengths that dominate below the sea surface. Several relatively distantly related Hydrophis sea snakes are polymorphic for shortwave sensitive visual pigment encoded by alleles of SWS1. This spectral site polymorphism is expected to confer expanded "UV-blue" spectral sensitivity and is estimated to have persisted twice as long as the predicted survival time for selectively neutral nuclear alleles. We suggest that this polymorphism is adaptively maintained across Hydrophis species via balancing selection, similarly to the LWS polymorphism that confers allelic trichromacy in some primates. Diving sea snakes thus appear to share parallel mechanisms of color vision diversification with fruit-eating primates.
News:
====
Free pdf:
Adriana MarÃa ALBINO (2020)
The Cenozoic lizard record of the Pampean Region
GEODIVERSITAS 42 (12): 175-183
http://sciencepress.mnhn.fr/en/periodiques/geodiversitas/42/12
The Pampean Region is a geographic area involving central and eastern Argentina, Uruguay, and southern Brazil. Contrasting with the fauna of squamates that currently inhabits the Pampean ÂRegion, the paleontological record is extremely reduced. Teiidae is the best-represented lizard taxon, with its earliest record in the late Miocene. Iguania is present since the early Pliocene onwards, whereas Anguidae is known only in the middle Pleistocene and Phyllodactylidae in the late Pleistocene-early Holocene interval. Other living families present in the region (Gymnophtalmidae, Scincidae) have no fossil representatives. The unique extinct taxon is the teiid Callopistes bicuspidatus Chani, 1976. The fossil record includes some taxa presently absent in the paleontological sites; this implies that the Neogene and Quaternary climatic-environmental changes that affected dramatically the avian and mammalian faunas of the Pampean Region, also influenced the biogeographical history of the herpetofauna.
===
Free pdf:
Stephanie E Pierce, LuÃs P Lamas, Ludovic Pelligand, Nadja Schilling & John R Hutchinson (2020)
Patterns of limb and epaxial muscle activity during walking in the fire salamander, Salamandra salamandra.
Integrative Organismal Biology, obaa015 (advance online publication)
doi: https://doi.org/10.1093/iob/obaa015
https://academic.oup.com/iob/advance-article/doi/10.1093/iob/obaa015/5847597
Patterns of limb and epaxial muscle activity during walking in the fire salamander, Salamandra salamandra.
Integrative Organismal Biology, obaa015 (advance online publication)
doi: https://doi.org/10.1093/iob/obaa015
https://academic.oup.com/iob/advance-article/doi/10.1093/iob/obaa015/5847597
Salamanders and newts (urodeles) are often used as a model system to elucidate the evolution of tetrapod locomotion. Studies range from detailed descriptions of musculoskeletal anatomy and segment kinematics, to bone loading mechanics and central pattern generators. A further area of interest has been in vivo muscle activity patterns, measured through electromyography (EMG). However, most prior EMG work has primarily focused on muscles of the forelimb or hindlimb in specific species or the axial system in others. Here we present data on forelimb, hindlimb, and epaxial muscle activity patterns in one species, Salamandra salamandra, during steady state walking. The data are calibrated to limb stride cycle events (stance phase, swing phase), allowing direct comparisons to homologous muscle activation patterns recorded for other walking tetrapods (e.g. lizards, alligators, turtles, mammals). Results demonstrate that Salamandra has similar walking kinematics and muscle activity patterns to other urodele species, but that interspecies variation does exist. In the forelimb, both the m. dorsalis scapulae and m. latissimus dorsi are active for 80% of the forelimb swing phase, while the m. anconaeus humeralis lateralis is active at the swing-stance phase transition and continues through 86% of the stance phase. In the hindlimb, both the m. puboischiofemoralis internus and m. extensor iliotibialis anterior are active for 30% of the hindlimb swing phase, while the m. caudofemoralis is active 65% through the swing phase and remains active for most of the stance phase. With respect to the axial system, both the anterior and posterior m. dorsalis trunci display two activation bursts, a pattern consistent with stabilization and rotation of the pectoral and pelvic girdle. In support of previous assertions, comparison of Salamandra muscle activity timings to other walking tetrapods revealed broad-scale similarities, potentially indicating conservation of some aspects of neuromuscular function across tetrapods. Our data provides the foundation for building and testing dynamic simulations of fire salamander locomotor biomechanics to better understand musculoskeletal function. It could also be applied to future musculoskeletal simulations of extinct species to explore the evolution of tetrapod locomotion across deep-time.
=====
S. M. Buttimer, N. Stepanova & M. C. Womack (2020)
Evolution of the unique anuran pelvic and hindlimb skeleton in relation to microhabitat, locomotor mode, and jump performance.
Integrative and Comparative Biology, icaa043 (advance online publication)
doi: https://doi.org/10.1093/icb/icaa043
https://academic.oup.com/icb/advance-article-abstract/doi/10.1093/icb/icaa043/5841667
Anurans (frogs and toads) have a unique pelvic and hindlimb skeleton among tetrapods. Although their distinct body plan is primarily associated with saltation, anuran species vary in their primary locomotor mode (e.g., walkers, hoppers, jumpers, and swimmers) and are found in a wide array of microhabitats (e.g., burrowing, terrestrial, arboreal, and aquatic) with varying functional demands. Given their largely conserved body plan, morphological adaptation to these diverse niches likely results from more fine-scale morphological change. Our study determines how shape differences in Anura's unique pelvic and hindlimb skeletal structures vary with microhabitat, locomotor mode, and jumping ability. Using microCT scans of preserved specimens from museum collections, we added 3D landmarks to the pelvic and hindlimb skeleton of 230 anuran species. In addition, we compiled microhabitat and locomotor data from the literature for these species that span 52 of the 55 families of frogs and ~210 million years of anuran evolution. Using this robust dataset, we examine the relationship between pelvic and hindlimb morphology and phylogenetic history, allometry, microhabitat, and locomotor mode. We find pelvic and hindlimb changes associated with shifts in microhabitat ("ecomorphs"â) and locomotor mode ("locomorphs") and directly relate those morphological changes to the jumping ability of individual species. We also reveal how individual bones vary in evolutionary rate and their association with phylogeny, body size, microhabitat, and locomotor mode. Our findings uncover previously undocumented morphological variation related to anuran ecological and locomotor diversification and link that variation to differences in jumping ability among species.
====
John Herrick & Bianca Sclavi (2020)
Genome Evolution in Amphibians.
eLS
doi: Âhttps://doi.org/10.1002/9780470015902.a0028996
https://onlinelibrary.wiley.com/doi/10.1002/9780470015902.a0028996
Genome size variation in vertebrates reflects an amazing amount of genetic and genomic diversity. Câvalue (genome size) ranges from 0.4 picograms (pg) in pufferfish to 133âpg in the marbled lungfish. Most vertebrate lineages have characteristic average Câvalues with restricted ranges. Amphibia, in contrast, represent an extreme: Câvalues in salamanders range from around 13 to over 122âpg; in frogs, they range from under 1 to over 13âpg. Why would closely related lineages and species have such dramatic differences in Câvalue? A number of theories have been proposed to account for the extreme range in genome size found in all eukaryote taxa. The amphibia not only have a wide range of Câvalues, but they also have a correspondingly wide range of life history traits and other phenotypes such as neoteny and limb regeneration. This remarkable class of vertebrate thus provides a unique model system for addressing evolutionary and physiological hypotheses.
Key Concepts
Junk DNA (retroviruses and DNA transposons) infected the ancestral eukaryote cell and established, together with mitochondria, a symbiotic relationship from which all other eukaryotic life forms emerged.
The host response to the original infection was adaptive rather than purifyingly selective: junk DNA provided the conditions for the emergence of a checkpoint guardian of the genome and correspondingly enhanced genome stability.
As genome size expanded, DNA repair systems increased in efficiency, allowing for the acquisition of new genes and new adaptations.
DNA replication programs and gene transcription programs reorganised as genome size either increased or decreased over evolutionary time.
Species richness negatively correlates with genome stability and positively correlates with karyotype diversity within specific lineages.
DNA damage response and repair (DDR) programs have evolved differentially in r and Kâstrategists: large body organisms have enhanced DDRs compared to small body, shortâlived organisms, and hence they tend to have more deterministic and organised replication programs.
Junk DNA serves as a substrate for the DDR to protect the cell against âmitotic catastropheâ.
Junk DNA serves as a scaffold for the formation of facultative heterochromatin during development and speciation,and hence participates in the global tissueâspecific and speciesâdependent transcription programs.
=========
Free pdf:
Ilja Kogan, Andrea Tintori & Martin Licht (2020)
Locomotor function of scales and axial skeleton in Middle-Late Triassic species of Saurichthys (Actinopterygii).
Rivista Italiana di Paleontologia e Stratigrafia 126(2): 475-498
https://riviste.unimi.it/index.php/RIPS/article/view/13551
Free pdf:
https://riviste.unimi.it/index.php/RIPS/article/view/13551/12651
Starting in the Late Permian, the âTriassic osteichthyan revolutionâ gave rise to several new morphotypes of actinopterygians, including the iconic barracuda-shaped predator Saurichthys. About 50 species, from 10 cm to over 1.5 m long, are known from mainly marine deposits worldwide. Despite current interest in Saurichthys, freshwater species and those from late Middle to early Late Triassic remain understudied. We document the postcranial morphology of three small to mid-sized (15â45 cm) species from this timeframe represented by sufficiently complete individuals: Saurichthys orientalis Sytchevskaya, 1999, from lacustrine deposits of the Madygen Formation (late Ladinian/Carnian); S. striolatus (Bronn, 1858) from the fully marine Predil Limestone (early Carnian); and S. calcaratus Griffith, 1977, from the terrigenously influenced coastal environment of the Lunz Formation (middle Carnian). S. orientalis resembles early saurichthyids in having six rows of large, thick ganoid scales; fins with segmented lepidotrichia; and flank scales relating to dorsal vertebral elements as 1:2. S. calcaratus and S. striolatus share unsegmented fin rays and a reduced scale cover with well-ossified but narrow mid-dorsal and mid-ventral scales and small, thin flank scales, relating to the dorsal arcualia as 1:1. Ventral arcualia are first described for S. calcaratus and S. striolatus, where they change in shape and number at the abdominal-caudal transition. In all three species, force transmission to the tail fin is enhanced by the caudal peduncle strengthened by a stiff structure arising from interlocking or fusion of the last enlarged mid-dorsal and mid-ventral scales (scutes), while the vertebral column remains rather lightly built.
Ilja Kogan, Andrea Tintori & Martin Licht (2020)
Locomotor function of scales and axial skeleton in Middle-Late Triassic species of Saurichthys (Actinopterygii).
Rivista Italiana di Paleontologia e Stratigrafia 126(2): 475-498
https://riviste.unimi.it/index.php/RIPS/article/view/13551
Free pdf:
https://riviste.unimi.it/index.php/RIPS/article/view/13551/12651
Starting in the Late Permian, the âTriassic osteichthyan revolutionâ gave rise to several new morphotypes of actinopterygians, including the iconic barracuda-shaped predator Saurichthys. About 50 species, from 10 cm to over 1.5 m long, are known from mainly marine deposits worldwide. Despite current interest in Saurichthys, freshwater species and those from late Middle to early Late Triassic remain understudied. We document the postcranial morphology of three small to mid-sized (15â45 cm) species from this timeframe represented by sufficiently complete individuals: Saurichthys orientalis Sytchevskaya, 1999, from lacustrine deposits of the Madygen Formation (late Ladinian/Carnian); S. striolatus (Bronn, 1858) from the fully marine Predil Limestone (early Carnian); and S. calcaratus Griffith, 1977, from the terrigenously influenced coastal environment of the Lunz Formation (middle Carnian). S. orientalis resembles early saurichthyids in having six rows of large, thick ganoid scales; fins with segmented lepidotrichia; and flank scales relating to dorsal vertebral elements as 1:2. S. calcaratus and S. striolatus share unsegmented fin rays and a reduced scale cover with well-ossified but narrow mid-dorsal and mid-ventral scales and small, thin flank scales, relating to the dorsal arcualia as 1:1. Ventral arcualia are first described for S. calcaratus and S. striolatus, where they change in shape and number at the abdominal-caudal transition. In all three species, force transmission to the tail fin is enhanced by the caudal peduncle strengthened by a stiff structure arising from interlocking or fusion of the last enlarged mid-dorsal and mid-ventral scales (scutes), while the vertebral column remains rather lightly built.
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Free pdf:
David A. Kring, Sonia M. Tikoo, Martin Schmieder, Ulrich Riller, Mario Rebolledo-Vieyra, Sarah L. Simpson, Gordon R. Osinski, JÃrÃme Gattacceca, Axel Wittmann, Christina M. Verhagen, Charles S. Cockell, Marco J. L. Coolen, Fred J. Longstaffe, Sean P. S. Gulick, Joanna V. Morgan, Timothy J. Bralower, Elise Chenot, Gail L. Christeson, Philippe Claeys, Ludovic FerriÃre, Catalina Gebhardt, Kazuhisa Goto, Sophie L. Green, Heather Jones, Johanna Lofi, Christopher M. Lowery, RubÃn Ocampo-Torres, Ligia Perez-Cruz, Annemarie E. Pickersgill, H. Poelchau, Auriol S. P. Rae, Cornelia Rasmussen, Honami Sato, Jan Smit, Naotaka Tomioka, Jaime Urrutia-Fucugauchi, T. Whalen, Long Xiao and Kosei E. Yamaguchi (2020)
Probing the hydrothermal system of the Chicxulub impact crater.
Science Advances 6(22): eaaz3053
DOI: 10.1126/sciadv.aaz3053
https://advances.sciencemag.org/content/6/22/eaaz3053
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https://advances.sciencemag.org/content/6/22/eaaz3053/tab-pdf
The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earthâs crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 Ã 105 km3 of Earthâs crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300Â to 400ÂC and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.
https://advances.sciencemag.org/content/6/22/eaaz3053/tab-pdf
The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earthâs crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 Ã 105 km3 of Earthâs crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300Â to 400ÂC and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.
News:
A steaming cauldron follows the dinosaurs' demise
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Adam A. Garde, Anne Sofie SÃndergaard, Carsten Guvad, Jette Dahl-MÃller, Gernot Nehrke, Hamed Sanei, Christian Weikusat, Svend Funder, Kurt H. KjÃr & Nicolaj Krog Larsen (2020)
Pleistocene organic matter modified by the Hiawatha impact, northwest Greenland.
Geology (asvance online publication)
doi: https://doi.org/10.1130/G47432.1
https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G47432.1/586763/Pleistocene-organic-matter-modified-by-the
The 31-km-wide Hiawatha impact crater was recently discovered under the ice sheet in northwest Greenland, but its age remains uncertain. Here we investigate solid organic matter found at the tip of the Hiawatha Glacier to determine its thermal degradation, provenance, and age, and hence a maximum age of the impact. Impactite grains of microbrecchia and shock-melted glass in glaciofluvial sand contain abundant dispersed carbon, and gravel-sized charcoal particles are common on the outwash plain in front of the crater. The organic matter is depleted in the thermally sensitive, labile bio-macromolecule proto-hydrocarbons. Pebble-sized lumps of lignite collected close to the sand sample consist largely of fragments of conifers such as Pinus or Picea, with greatly expanded cork cells and desiccation cracks which suggest rapid, heat-induced expansion and contraction. Pinus and Picea are today extinct from North Greenland but are known from late Pliocene deposits in the Canadian Arctic Archipelago and early Pleistocene deposits at Kap KÃbenhavn in eastern North Greenland. The thermally degraded organic material yields a maximum age for the impact, providing the first firm evidence that the Hiawatha crater is the youngest known large impact structure on Earth.
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Ying Cui, Brian A. Schubert & A. Hope Jahren (2020)
A 23 m.y. record of low atmospheric CO2.
Geology (advance online publication)
doi: https://doi.org/10.1130/G47681.1
https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G47681.1/586769/A-23-m-y-record-of-low-atmospheric-CO-2
Current atmospheric CO2 concentration is known to be higher than it has been during the past ~800 k.y. of Earth history, based on direct measurement of CO2 within ice cores. A comparison to the more ancient past is complicated by a deficit of CO2 proxies that may be applied across very long spans of geologic time. Here, we present a new CO2 record across the past 23 m.y. of Earth history based on the Î13C value of terrestrial C3 plant remains, using a method applicable to the entire ~400 m.y. history of C3 photosynthesis on land. Across the past 23 m.y., CO2 likely ranged between ~230 ppmv and 350 ppmv (68% confidence interval: ~170â540 ppm). CO2 was found to be highest during the early and middle Miocene and likely below present-day levels during the middle Pliocene (84th percentile: ~400 ppmv). These data suggest present-day CO2 (412 ppmv) exceeds the highest levels that Earth experienced at least since the Miocene, further highlighting the present-day disruption of long-established CO2 trends within Earthâs atmosphere.
