Elena F. Boer, Hannah F. Van Hollebeke, Sungdae Park, Carlos R. Infante, Douglas B. Menke & Michael D. Shapiro (2019)
Pigeon foot feathering reveals conserved limb identity networks.
The tetrapod limb is a stunning example of evolutionary diversity, with dramatic variation not only among distantly related species, but also between the serially homologous forelimbs (FLs) and hindlimbs (HLs) within species. Despite this variation, highly conserved genetic and developmental programs underlie limb development and identity in all tetrapods, raising the question of how limb diversification is generated from a conserved toolkit. In some breeds of domestic pigeon, shifts in the _expression_ of two conserved limb identity transcription factors, PITX1 and TBX5, are associated with the formation of feathered HLs with partial FL identity. To determine how modulation of PITX1 and TBX5 _expression_ affects downstream gene _expression_, we compared the transcriptomes of embryonic limb buds from pigeons with scaled and feathered HLs. We identified a set of differentially expressed genes enriched for genes encoding transcription factors, extracellular matrix proteins, and components of developmental signaling pathways with important roles in limb development. A subset of the genes that distinguish scaled and feathered HLs are also differentially expressed between FL and scaled HL buds in pigeons, pinpointing a set of gene _expression_ changes downstream of PITX1 and TBX5 in the partial transformation from HL to FL identity. We extended our analyses by comparing pigeon limb bud transcriptomes to chicken, anole lizard, and mammalian datasets to identify deeply conserved PITX1- and TBX5-responsive components of the limb identity program. Our analyses reveal a suite of predominantly low-level gene _expression_ changes that are conserved across amniotes to regulate the identity of morphologically distinct limbs.
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Svana Rogalla , Liliana D'Alba , Ann Verdoodt Âand Matthew D. Shawkey (2019)
Hot wings: thermal impacts of wing coloration on surface temperature during bird flight
Journal of the Royal Society Interface 16(156): 20190032
doi:
https://doi.org/10.1098/rsif.2019.0032https://royalsocietypublishing.org/doi/10.1098/rsif.2019.0032Recent studies on bird flight propose that hotter wing surfaces reduce skin friction drag, thereby improving flight efficiency (lift-to-drag ratio). Darker wings may in turn heat up faster under solar radiation than lighter wings. We used three methods to test the impact of colour on wing surface temperature. First, we modelled surface temperature based on reflectance measurements. Second, we used thermal imaging on live ospreys (Pandion haliaetus) to examine surface temperature changes with increasing solar irradiance. Third, we experimentally heated differently coloured wings in a wind tunnel and measured wing surface temperature at realistic flight speeds. Even under simulated flight conditions, darker wings consistently became hotter than pale wings. In white wings with black tips, the temperature differential produced convective currents towards the darker wing tips that could lead to an increase in lift. Additionally, a temperature differential between wing-spanning warm muscles and colder flight feathers could delay the flow separation above the wing, increasing flight efficiency. Together, these results suggest that wing coloration and muscle temperature both play important roles in modulating wing surface temperature and therefore potentially flight efficiency.
Study suggests dark-colored wing feathers may help birds fly more efficiently
https://phys.org/news/2019-07-dark-colored-wing-feathers-birds-efficiently.html===
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This study is a thorough assessment on the morphology and taxonomy of Mourasuchus amazonensis, a fossil crocodylian of the Caimaninae clade from the late Miocene SolimÃes Formation of Brazil. A thorough redescription of the holotype of the species (DGM 562-R, a nearly complete skull with an associated incomplete left mandible) is performed together with the redescription of the specimen UFAC-1424, a posterior portion of the skull with associated mandibular remains, and the description of the specimen LACM-160157, also a posterior portion of the cranium. As such, this paper brings the most comprehensive osteological study of M. amazonensis to be performed to date, enabling a thorough taxonomic reassessment of the species in question. This reassessment confirmed M. amazonensis as a valid species, with two autapomorphies and two other distinctive characters. UFAC-1424 and LACM-160157 are assigned as Mourasuchus cf. M. amazonensis, pending further studies on the taxonomy of the species in order to clarify whether these specimens belong to the same species as DGM 526-R. Additionally, implications of the morphology observed in M. amazonensis for the taxonomic status of other Mourasuchus species are also discussed, especially with respect to M. nativus, which is currently a junior synonym of M. arendsi.
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Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna. The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna. Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.
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Enav Vidan, ÂMaria Novosolov, ÂAaron M. Bauer, ÂFernando Castro Herrera, Laurent Chirio, Cristiano de Campos Nogueira, ÂTiffany M. Doan, ÂAmir Lewin, ÂDanny Meirte, ÂZoltan T. Nagy, Daniel PincheiraâDonoso, ÂOliver J.S. Tallowin, ÂOmar Torres Carvajal, ÂPeter Uetz, ÂPhilipp Wagner, ÂYuezhao Wang, ÂJonathan Belmaker Â& Shai Meiri (2019)
The global biogeography of lizard functional groups.
Journal of Biogeography (advance online publication)
doi: Â
https://doi.org/10.1111/jbi.13667https://onlinelibrary.wiley.com/doi/10.1111/jbi.13667Aim
Understanding the mechanisms determining species richness is a primary goal of biogeography. Richness patterns of subâgroups within a taxon are usually assumed to be driven by similar processes. However, if richness of distinct ecological strategies respond differently to the same processes, inferences made for an entire taxon may be misleading. We deconstruct the global lizard assemblage into functional groups and examine the congruence among richness patterns between them. We further examine the species richness â functional richness relationship to elucidate the way functional diversity contributes to the overall species richness patterns.
Location
Global.
Methods
Using comprehensive biological trait databases we classified the global lizard assemblage into ecological strategies based on body size, diet, activity times and microhabitat preferences, using Archetypal Analysis. We then examined spatial gradients in the richness of each strategy at the oneâdegree grid cell, biome, and realm scales.
Results
We found that lizards can best be characterized by seven âecological strategiesâ: scansorial, terrestrial, nocturnal, herbivorous, fossorial, large, and semiâaquatic. There are large differences among the global richness patterns of these strategies. While the major richness hotspot for lizards in general is in Australia, several strategies exhibit highest richness in the Amazon Basin. Importantly, the global maximum in lizard species richness is achieved at intermediate values of functional diversity and increasing functional diversity further result in a slow decline of species richness.
Main conclusions
The deconstruction of the global lizard assemblage along multiple ecological axes offers a new way to conceive lizard diversity patterns. It suggests that local lizard richness mostly increases when species belonging to particular ecological strategies become hyperâdiverse there, and not because more ecological types are present in the most species rich localities. Thus maximum richness and maximum ecological diversity do not overlap. These results shed light on the global richness pattern of lizards, and highlight previously unidentified spatial patterns in understudied functional groups.
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Hox genes are a remarkable example of conservation in animal development and their nested _expression_ along the headâtoâtail axis orchestrates embryonic patterning. Early in vertebrate history, two duplications led to the emergence of four Hox clusters (AâD) and redundancy within paralog groups has been partially accommodated with gene losses. Here we conduct an inventory of squamate Hox genes using the genomes of 10 lizard and 7 snake species. Although the HoxC1 gene has been hypothesized to be lost in the amniote ancestor, we reveal that it is retained in lizards. In contrast, all snakes lack functional HoxC1 and âD12 genes. Varying levels of degradation suggest differences in the process of gene loss between the two genes. The vertebrate HoxC1 gene is prone to gene loss and its functional domains are more variable than those of other Hox1 genes. We describe for the first time the HoxC1 _expression_ patterns in tetrapods. HoxC1 is broadly expressed during development in the diencephalon, the neural tube, dorsal root ganglia, and limb buds in two lizard species. Our study emphasizes the value of revisiting Hox gene repertoires by densely sampling taxonomic groups and its feasibility owing to growing sequence resources in evaluating gene repertoires across taxa.
HIGHLIGHTS
Exploration of the genomes of 17 lizard and snake species revealed the presence of a Hox gene, HoxC1, that has been thought to be lost in the amniote ancestor. This finding sheds new light on the evolution of Hox gene repertoires.
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The controversial origin of extant amphibians has been studied using several sources of data and methods, including phylogenetic analyses of morphological data, molecular dating, stratigraphic data, and integration of ossification sequence data, but a consensus has failed to emerge. We have compiled five datasets to assess the relative support for six competing hypotheses about the origin of extant amphibians: a monophyletic origin among temnospondyls, a monophyletic origin among lepospondyls, a diphyletic origin among both temnospondyls and lepospondyls, a diphyletic origin among temnospondyls alone, and two variants of a triphyletic origin, in which anurans and urodeles come from different temnospondyl taxa while caecilians come from lepospondyls and are either closer to anurans and urodeles or to amniotes. Our datasets comprise ossification sequences of up to 107 terminal taxa and up to eight cranial bones, and up to 65 terminal taxa and up to seven appendicular bones, respectively. Among extinct taxa, only two or three temnospondyl can be analyzed simultaneously for cranial data, but this is not an insuperable problem because each of the six tested hypotheses implies a different position of temnospondyls and caecilians relative to other sampled taxa. For appendicular data, more extinct taxa can be analyzed, including some lepospondyls and the finned tetrapodomorph Eusthenopteron, in addition to temnospondyls. The data are analyzed through maximum likelihood, and the AICc (corrected Akaike Information Criterion) weights of the six hypotheses allow us to assess their relative support. By an unexpectedly large margin, our analyses of the cranial data support a monophyletic origin among lepospondyls; a monophyletic origin among temnospondyls, the current near-consensus, is a distant second. All other hypotheses are exceedingly unlikely according to our data. Surprisingly, analysis of the appendicular data supports triphyly of extant amphibians within a clade that unites lepospondyls and temnospondyls, contrary to all molecular and recent paleontological phylogenies, but this conclusion is not very robust.
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The tetrapodomorph ïsh, Gogonasus andrewsae is a three dimensionally well-preserved sarcopterygian from the Gogo Formation (Frasnian, early Upper Devonian, ~380 million years ago) in Western Australia. High-resolution X-ray Micro-Computed Tomography and 3D printouts were used to obtain a digital reconstruction of its shoulder girdle and opercular series. Our new findings show the opercular series in a close fit against the upper bones of the shoulder girdle only if the anocleithrum, supracleithrum and post-temporal are aligned more horizontally than in previous reconstructions. The lowermost subopercular bone also differs, in partly covering the clavicle of the shoulder girdle. The ascending process of the clavicle, and the ventral process of the anocleithrum, do not fit closely inside the cleithrum, and perhaps functioned for ligamentous attachment. A rugose area on the anocleithral process is in a similar relative position to the attachment of a muscle ligament on the shoulder girdle of various living actinopterygians. Our manipulation of 3D printouts permits testing of the morphological fit of extremely fragile acid-etched bones, and indicates a new way to investigate the constructional morphology of one or more mechanical units of the vertebrate skeleton. It is suggested that Micro-CT imaging, reconstruction, visualisation and 3D printing techniques will provide a rigorous new test leading to modification of previous reconstructions of extinct vertebrates that were based on graphical methods and 2D imaging.
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