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"Wings (Anatomy) Evolution."
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On the wing : insects, pterosaurs, birds, bats and the evolution of animal flight
On the Wing is the first book to take a comprehensive look at the evolution of flight in all four groups of powered flyers: insects, pterosaurs, birds and bats. David Alexander describes and evaluates both traditional and modern wing-origin theories in light of new fossil and genetic evidence.
eBook
Social regulation of a rudimentary organ generates complex worker-caste systems in ants
The origin of complex worker-caste systems in ants perplexed Darwin
1
and has remained an enduring problem for evolutionary and developmental biology
2
–
6
. Ants originated approximately 150 million years ago, and produce colonies with winged queen and male castes as well as a wingless worker caste
7
. In the hyperdiverse genus
Pheidole
, the wingless worker caste has evolved into two morphologically distinct subcastes—small-headed minor workers and large-headed soldiers
8
. The wings of queens and males develop from populations of cells in larvae that are called wing imaginal discs
7
. Although minor workers and soldiers are wingless, vestiges or rudiments of wing imaginal discs appear transiently during soldier development
7
,
9
–
11
. Such rudimentary traits are phylogenetically widespread and are primarily used as evidence of common descent, yet their functional importance remains equivocal
1
,
12
–
14
. Here we show that the growth of rudimentary wing discs is necessary for regulating allometry—disproportionate scaling—between head and body size to generate large-headed soldiers in the genus
Pheidole
. We also show that
Pheidole
colonies have evolved the capacity to socially regulate the growth of rudimentary wing discs to control worker subcaste determination, which allows these colonies to maintain the ratio of minor workers to soldiers. Finally, we provide comparative and experimental evidence that suggests that rudimentary wing discs have facilitated the parallel evolution of complex worker-caste systems across the ants. More generally, rudimentary organs may unexpectedly acquire novel regulatory functions during development to facilitate adaptive evolution.
In the ant genus
Pheidole
the growth of rudimentary wing discs—which influence developmental allometry to produce castes with distinct morphologies—is socially regulated to determine the worker-to-soldier ratio in
Pheidole
colonies.
Journal Article
Mutation predicts 40 million years of fly wing evolution
Mutation enables evolution, but the idea that adaptation is also shaped by mutational variation is controversial1–4. Simple evolutionary hypotheses predict such a relationship if the supply of mutations constrains evolution5,6, but it is not clear that constraints exist, and, even if they do, they may be overcome by long-term natural selection. Quantification of the relationship between mutation and phenotypic divergence among species will help to resolve these issues. Here we use precise data on over 50,000 Drosophilid fly wings to demonstrate unexpectedly strong positive relationships between variation produced by mutation, standing genetic variation, and the rate of evolution over the last 40 million years. Our results are inconsistent with simple constraint hypotheses because the rate of evolution is very low relative to what both mutational and standing variation could allow. In principle, the constraint hypothesis could be rescued if the vast majority of mutations are so deleterious that they cannot contribute to evolution, but this also requires the implausible assumption that deleterious mutations have the same pattern of effects as potentially advantageous ones. Our evidence for a strong relationship between mutation and divergence in a slowly evolving structure challenges the existing models of mutation in evolution.
Journal Article
New specimen of Archaeopteryx provides insights into the evolution of pennaceous feathers
A new specimen of
Archaeopteryx
with extensive pennaceous feather preservation.
Feathers prominent on latest
Archaeopteryx
fossil
The discovery of numerous feathered dinosaurs and early birds has set the iconic 'Urvogel' (or 'first bird')
Archaeopteryx
in a broader context. But this venerable taxon still has the capacity to surprise. A newly discovered specimen from the Solnhofen limestone in Bavaria — only the eleventh since 1861 — shows a generous covering of feathers all over the body. Of particular note is a hindlimb covering resembling feathered 'trousers'. Analysis of feather distribution on the limbs and tail strongly suggests that pennaceous feathers — the type we are familiar with on birds today — evolved for reasons other than flight, perhaps for display.
Discoveries of bird-like theropod dinosaurs and basal avialans in recent decades have helped to put the iconic ‘Urvogel’
Archaeopteryx
1
into context
2
,
3
,
4
,
5
,
6
and have yielded important new data on the origin and early evolution of feathers
7
. However, the biological context under which pennaceous feathers evolved is still debated. Here we describe a new specimen of
Archaeopteryx
with extensive feather preservation, not only on the wings and tail, but also on the body and legs. The new specimen shows that the entire body was covered in pennaceous feathers, and that the hindlimbs had long, symmetrical feathers along the tibiotarsus but short feathers on the tarsometatarsus. Furthermore, the wing plumage demonstrates that several recent interpretations
8
,
9
are problematic. An analysis of the phylogenetic distribution of pennaceous feathers on the tail, hindlimb and arms of advanced maniraptorans and basal avialans strongly indicates that these structures evolved in a functional context other than flight, most probably in relation to display, as suggested by some previous studies
10
,
11
,
12
. Pennaceous feathers thus represented an exaptation and were later, in several lineages and following different patterns, recruited for aerodynamic functions. This indicates that the origin of flight in avialans was more complex than previously thought and might have involved several convergent achievements of aerial abilities.
Journal Article
Pterosaurs evolved a muscular wing–body junction providing multifaceted flight performance benefits
Pterosaurs were the first vertebrate flyers and lived for over 160 million years. However, aspects of their flight anatomy and flight performance remain unclear. Using laser-stimulated fluorescence, we observed direct soft tissue evidence of a wing root fairing in a pterosaur, a feature that smooths out the wing–body junction, reducing associated drag, as in modern aircraft and flying animals. Unlike bats and birds, the pterosaur wing root fairing was unique in being primarily made of muscle rather than fur or feathers. As a muscular feature, pterosaurs appear to have used their fairing to access further flight performance benefits through sophisticated control of their wing root and contributions to wing elevation and/or anterior wing motion during the flight stroke. This study underscores the value of using new instrumentation to fill knowledge gaps in pterosaur flight anatomy and evolution.
Journal Article
Genomic architecture and introgression shape a butterfly radiation
We used 20 de novo genome assemblies to probe the speciation history and architecture of gene flow in rapidly radiating Heliconius butterflies. Our tests to distinguish incomplete lineage sorting from introgression indicate that gene flow has obscured several ancient phylogenetic relationships in this group over large swathes of the genome. Introgressed loci are underrepresented in low-recombination and gene-rich regions, consistent with the purging of foreign alleles more tightly linked to incompatibility loci. Here, we identify a hitherto unknown inversion that traps a color pattern switch locus. We infer that this inversion was transferred between lineages by introgression and is convergent with a similar rearrangement in another part of the genus. These multiple de novo genome sequences enable improved understanding of the importance of introgression and selective processes in adaptive radiation.
Journal Article
Enigmatic dinosaur precursors bridge the gap to the origin of Pterosauria
Pterosaurs were the first vertebrates to evolve powered flight
1
and comprised one of the main evolutionary radiations in terrestrial ecosystems of the Mesozoic era (approximately 252–66 million years ago), but their origin has remained an unresolved enigma in palaeontology since the nineteenth century
2
–
4
. These flying reptiles have been hypothesized to be the close relatives of a wide variety of reptilian clades, including dinosaur relatives
2
–
8
, and there is still a major morphological gap between those forms and the oldest, unambiguous pterosaurs from the Upper Triassic series. Here, using recent discoveries of well-preserved cranial remains, microcomputed tomography scans of fragile skull bones (jaws, skull roofs and braincases) and reliably associated postcrania, we demonstrate that lagerpetids—a group of cursorial, non-volant dinosaur precursors—are the sister group of pterosaurs, sharing numerous synapomorphies across the entire skeleton. This finding substantially shortens the temporal and morphological gap between the oldest pterosaurs and their closest relatives and simultaneously strengthens the evidence that pterosaurs belong to the avian line of archosaurs. Neuroanatomical features related to the enhanced sensory abilities of pterosaurs
9
are already present in lagerpetids, which indicates that these features evolved before flight. Our evidence illuminates the first steps of the assembly of the pterosaur body plan, whose conquest of aerial space represents a remarkable morphofunctional innovation in vertebrate evolution.
Lagerpetids, bipedal archosaurs that are thought to be related to dinosaurs, are instead a sister group to pterosaurs, and although they have no obvious flight adaptations they share numerous synapomorphies with pterosaurs across the entire skeleton.
Journal Article
optix Drives the Repeated Convergent Evolution of Butterfly Wing Pattern Mimicry
Mimicry—whereby warning signals in different species evolve to look similar—has long served as a paradigm of convergent evolution. Little is known, however, about the genes that underlie the evolution of mimetic phenotypes or to what extent the same or different genes drive such convergence. Here, we characterize one of the major genes responsible for mimetic wing pattern evolution in Heliconius butterflies. Mapping, gene expression, and population genetic work all identify a single gene, optix, that controls extreme red wing pattern variation across multiple species of Heliconius. Our results show that the cis-regulatory evolution of a single transcription factor can repeatedly drive the convergent evolution of complex color patterns in distantly related species, thus blurring the distinction between convergence and homology.
Journal Article
An integrative approach to understanding bird origins
Recent discoveries of spectacular dinosaur fossils overwhelmingly support the hypothesis that birds are descended from maniraptoran theropod dinosaurs, and furthermore, demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system originated among Mesozoic terrestrial dinosaurs. The transition from ground-living to flight-capable theropod dinosaurs now probably represents one of the best-documented major evolutionary transitions in life history. Recent studies in developmental biology and other disciplines provide additional insights into how bird characteristics originated and evolved. The iconic features of extant birds for the most part evolved in a gradual and stepwise fashion throughout archosaur evolution. However, new data also highlight occasional bursts of morphological novelty at certain stages particularly close to the origin of birds and an unavoidable complex, mosaic evolutionary distribution of major bird characteristics on the theropod tree. Research into bird origins provides a premier example of how paleontological and neontological data can interact to reveal the complexity of major innovations, to answer key evolutionary questions, and to lead to new research directions. A better understanding of bird origins requires multifaceted and integrative approaches, yet fossils necessarily provide the final test of any evolutionary model. Research on the origin and evolution of birds has gathered pace in recent years, aided by a continuous stream of new fossil finds as well as molecular phylogenies. Bird origins, in particular, are now better understood than those of mammals, for which the early fossil record is relatively poor compared with that of birds. Xu et al. review progress in tracing the origins of birds from theropod dinosaurs, focusing especially on recent fossil finds of feathered dinosaurs of northeastern China. They integrate current research on developmental biology and functional anatomy with the paleontological record, to show how key features of birds—feathers, wings, and flight—originated and evolved, and radiated from their dinosaur forebears. Science , this issue 10.1126/science.1253293
Journal Article