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opencc-zeroDec 2013View details →

Data from: From baby birds to feathered dinosaurs incipient wings and the evolution of flight

Reconstructing the tree of life requires deciphering major evolutionary transformations and the functional capacities of fossils with "transitional" morphologies. Some of the most iconic, well-studied fossils with transitional features are theropod dinosaurs, whose skeletons and feathered forelimbs record the origin and evolution of bird flight. However, in spite of over a century of discussion, the functions of forelimb feathers during the evolution of flight remain enigmatic. Both aerodynamic and non-aerodynamic roles have been proposed, but few of the form-function relationships assumed by these scenarios have been tested. Here, we use the developing wings of a typical extant ground bird (Chukar Partridge) as possible analogues/homologues of historical wing forms to provide the first empirical evaluation of aerodynamic potential in flapping theropod "protowings." Immature ground birds with underdeveloped, rudimentary wings generate useful aerodynamic forces for a variety of locomotor tasks. Feather development in these birds resembles feather evolution in theropod dinosaurs, and reveals a predictable relationship between wing morphology and aerodynamic performance that can be used to infer performance in extinct theropods. By spinning an ontogenetic series of spread-wing preparations on a rotating propeller apparatus across a range of flow conditions and measuring aerodynamic force, we explored how changes in wing size, feather structure, and angular velocity might have affected aerodynamic performance in dinosaurs choosing to flap their incipient wings. At slow angular velocities, wings produced aerodynamic forces similar in magnitude to those produced by immature birds during behaviors like wing-assisted incline running. At fast angular velocities, wings produced forces sufficient to support body weight during flight. These findings provide a quantitative, biologically relevant bracket for theropod performance and suggest that protowings could have provided useful aerodynamic function early in maniraptoran history, with improvements in aerodynamic performance attending the evolution of larger wings, more effective feather morphologies, and faster angular velocities.

Data from: Hummingbirds control hovering flight by stabilizing visual motion

Relatively little is known about how sensory information is used for controlling flight in birds. A powerful method is to immerse an animal in a dynamic virtual reality environment to examine behavioral responses. Here, we investigated the role of vision during free-flight hovering in hummingbirds to determine how optic flow—image movement across the retina—is used to control body position. We filmed hummingbirds hovering in front of a projection screen with the prediction that projecting moving patterns would disrupt hovering stability but stationary patterns would allow the hummingbird to stabilize position. When hovering in the presence of moving gratings and spirals, hummingbirds lost positional stability and responded to the specific orientation of the moving visual stimulus. There was no loss of stability with stationary versions of the same stimulus patterns. When exposed to a single stimulus many times or to a weakened stimulus that combined a moving spiral with a stationary checkerboard, the response to looming motion declined. However, even minimal visual motion was sufficient to cause a loss of positional stability despite prominent stationary features. Collectively, these experiments demonstrate that hummingbirds control hovering position by stabilizing motions in their visual field. The high sensitivity and persistence of this disruptive response is surprising, given that the hummingbird brain is highly specialized for sensory processing and spatial mapping, providing other potential mechanisms for controlling position.

Data from: Reanalyzing the Palaeoptera problem - the origin of insect flight remains obscure

The phylogenetic relationships of the winged insect lineages – mayflies (Ephemeroptera), damselflies and dragonflies (Odonata), and all other winged insects (Neoptera) – are still controversial with three hypotheses supported by different datasets: Palaeoptera, Metapterygota and Chiastomyaria. Here, we reanalyze available phylogenomic data with a focus on detecting confounding and alternative signal. In this context, we provide a framework to quantitatively evaluate and assess incongruent molecular phylogenetic signal inherent in phylogenomic datasets. Despite overall support for the Palaeoptera hypothesis, we also found considerable signal for Chiastomyaria, which is not easily detectable by standardized tree inference approaches. Analyses of the accumulation of signal across gene partitions showed that signal accumulates gradually. However, even in case signal only slightly supported one over the other hypothesis, topologies inferred from large datasets switch from statistically strongly supported Palaeoptera to strongly supported Chiastomyaria. From a morphological point of view, Palaeoptera currently appears to be the best-supported hypothesis; however, recent analyses were restricted to head characters. Phylogenetic approaches covering all organ systems including analyses of potential functional or developmental convergence are still pending so that the Palaeoptera problem has to be considered an open question in insect systematics.

Data from: Aerobic power and flight capacity in birds: a phylogenetic test of the heart-size hypothesis

Flight capacity is one of the most important innovations in animal evolution; it only evolved in insects, birds, mammals and the extinct pterodactyls. Given that powered flight represents a demanding aerobic activity, an efficient cardiovascular system is essential for the continuous delivery of oxygen to the pectoral muscles during flight. It is well known that the limiting step in the circulation is stroke volume (the volume of blood pumped from the ventricle to the body during each beat), which is determined by the size of the ventricle. Thus, the fresh mass of the heart represents a simple and repeatable anatomic measure of aerobic power of an animal. Although several authors have already compared heart masses across bird species, a phylogenetic comparative analysis of these comparisons is still lacking. Compiling heart sizes for 915 species and applying several statistical procedures controlling for body size and/or testing for adaptive trends in the dataset (e.g., model selection approaches, phylogenetic generalized linear models), we found that (residuals of) heart sizes are consistently associated with four categories of flight capacity. In general, our results indicate that species exhibiting continuous hovering flight (i.e., hummingbirds) have substantially larger hearts than do other groups, that species that use flapping flight and gliding show intermediate values, and that species categorized as poor flyers show the smallest values. Our study shows that at a broad scale, routine flight modes seem to have shaped the energetic requirements of birds sufficiently to be anatomically detected at the comparative level.

opencc-zeroSep 2019View details →

Data from: Reduced metabolism supports hypoxic flight in the high-flying bar-headed goose (Anser indicus)

The bar-headed goose is famed for migratory flight at extreme altitude. To better understand the physiology underlying this remarkable behavior, we imprinted and trained geese, collecting the first cardiorespiratory measurements of bar-headed geese flying at simulated altitude in a wind tunnel. Metabolic rate during flight increased 16-fold from rest, supported by an increase in the estimated amount of O2 transported per heartbeat and a modest increase in heart rate. The geese appear to have ample cardiac reserves, as heart rate during hypoxic flights was not higher than in normoxic flights. We conclude that flight in hypoxia is largely achieved via the reduction in metabolic rate compared to normoxia. Arterial was maintained throughout flights. Mixed venous PO2 decreased during the initial portion of flights in hypoxia, indicative of increased tissue O2 extraction. We also discovered that mixed venous temperature decreased during flight, which may significantly increase oxygen loading to hemoglobin.

Data from: Aerodynamics of manoeuvring flight in brown long-eared bats (Plecotus auritus)

In this study, we explicitly examine the aerodynamics of manoeuvring flight in animals. We studied brown long-eared bats flying in a wind tunnel while performing basic sideways manoeuvres. We used particle image velocimetry in combination with high-speed filming to link aerodynamics and kinematics to understand the mechanistic basis of manoeuvres. We predicted that the bats would primarily use the downstroke to generate the asymmetries for the manoeuvre since it has been shown previously that the majority of forces are generated during this phase of the wingbeat. We found instead that the bats more often used the upstroke than they used the downstroke for this. We also found that the bats used both drag/thrust-based and lift-based asymmetries to perform the manoeuvre and that they even frequently switch between these within the course of a manoeuvre. We conclude that the bats used three main modes: lift asymmetries during downstroke, thrust/drag asymmetries during downstroke and thrust/drag asymmetries during upstroke. For future studies, we hypothesize that lift asymmetries are used for fast turns and thrust/drag for slow turns and that the choice between up- and downstroke depends on the timing of when the bat needs to generate asymmetries.

Data from: Luminance-dependent visual processing enables moth flight in low light

Animals must operate under an enormous range of light intensities. Nocturnal and twilight flying insects are hypothesized to compensate for dim conditions by integrating light over longer times. This slowing of visual processing would increase light sensitivity but should also reduce movement response times. Using freely hovering moths tracking robotic moving flowers, we showed that the moth's visual processing does slow in dim light. These longer response times are consistent with models of how visual neurons enhance sensitivity at low light intensities, but they could pose a challenge for moths feeding from swaying flowers. Dusk-foraging moths avoid this sensorimotor tradeoff; their nervous systems slow down but not so much as to interfere with their ability to track the movements of real wind-blown flowers.

Data from: Allometry of wing twist and camber in a flower chafer during free flight: how do wing deformations scale with body size?

Intraspecific variation in adult body mass can be particularly high in some insect species, mandating adjustment of the wing's structural properties to support the weight of the larger body mass in air. Insect wings elastically deform during flapping, dynamically changing the twist and camber of the relatively thin and flat aerofoil. We examined how wing deformations during free flight scale with body mass within a species of rose chafers (Coleoptera: Protaetia cuprea) in which individuals varied more than threefold in body mass (0.38–1.29 g). Beetles taking off voluntarily were filmed using three high-speed cameras and the instantaneous deformation of their wings during the flapping cycle was analysed. Flapping frequency decreased in larger beetles but, otherwise, flapping kinematics remained similar in both small and large beetles. Deflection of the wing chord-wise varied along the span, with average deflections at the proximal trailing edge higher by 0.2 and 0.197 wing lengths compared to the distal trailing edge in the downstroke and the upstroke, respectively. These deflections scaled with wing chord to the power of 1.0, implying a constant twist and camber despite the variations in wing and body size. This suggests that the allometric growth in wing size includes adjustment of the flexural stiffness of the wing structure to preserve wing twist and camber during flapping.

Data from: Metabolism studies of paeoniflorin in rat liver microsomes by ultra-performance liquid chromatography coupled with hybrid quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS)

To explore metabolism mechanism of paeoniflorin in the liver and further understand intact metabolism process of paeoniflorin, a rapid, convenient and effective assay is described using ultra-performance liquid chromatography coupled with hybrid quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS). The strategy was confirmed in the following primary processes: firstly, different concentration of paeoniflorin, rat liver microsomes, coenzymes and different incubated conditions were optimized to build a biotransformation model of rat liver microsomes in vitro by high performance liquid chromatography with diode array detection (HPLC-DAD); secondly, the metabolites of paeoniflorin in rat liver microsomes were detected and screened using UPLC-Q-TOF-MS/MS by comparing the total ion chromatogram (TIC) of the experimental group with those of control groups; finally, the molecular formulae and corresponding chemical structures of paeoniflorin metabolites were identified by comparing the MS and MS/MS spectra with the self-constructed database and simulation software. Based on this analytical strategy, 20 metabolites of paeoniflorin were found and 6 metabolites (including four new compounds) were tentatively identified. It was shown that hydrolysis and oxidation were the major metabolic pathways of paeoniflorin in rat liver microsomes, and the main metabolic sites were the structures of pinane and the ester bond. These findings were significant for a better understanding of the metabolism of paeoniflorin in rat liver microsomes and the proposed metabolic pathways of paeoniflorin might provide fundamental support for the further research in the pharmacological mechanism of Paeoniae Radix Rubra (PRR).

Data from: The wake of hovering flight in bats

Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down- and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%.

Data from: A genetic signature of the evolution of loss of flight in the Galapagos cormorant

We have a limited understanding of the genetic and molecular basis of evolutionary changes in the size and proportion of limbs. We studied wing and pectoral skeleton reduction leading to flightlessness in the Galapagos cormorant (Phalacrocorax harrisi). We sequenced and de novo assembled the genomes of four cormorant species and applied a predictive and comparative genomics approach to find candidate variants that may have contributed to the evolution of flightlessness. These analyses and cross-species experiments in Caenorhabditis elegans and in chondrogenic cell lines implicated variants in genes necessary for transcriptional regulation and function of the primary cilium. Cilia are essential for Hedgehog signaling, and humans affected by skeletal ciliopathies suffer from premature bone growth arrest, mirroring skeletal features associated with loss of flight.

Data from: Flexibility and control of thorax deformation during hawkmoth flight

The interaction between neuromuscular systems and body mechanics plays an important role in the production of coordinated movements in animals. Lepidopteran insects move their wings by distortion of the thorax structure via the indirect flight muscles (IFMs), which are activated by neural signals at every stroke. However, how the action of these muscles affects thorax deformation and wing kinematics is poorly understood. We measured the deformation of the dorsal thorax (mesonotum) of tethered flying hawkmoths, Agrius convolvuli, using a high-speed laser profilometer combined with simultaneous recordings of electromyograms and wing kinematics. We observed that locally amplified mesonotum deformation near the wing hinges ensures sufficient wing movement. Furthermore, phase asymmetry in IFM activity leads to phase asymmetry in mesonotum oscillations and wingbeats. Our results revealed the flexibility and controllability of the single structure of the mesonotum by neurogenic action of the IFMs.

opencc-zeroJul 2019View details →

Data from: Orographic lift shapes flight routes of gulls in virtually flat landscapes

Interactions between landscape and atmosphere result in a dynamic flight habitat which birds may use opportunistically to save energy during flight. However, their ability to utilise these dynamic landscapes and its influence on shaping movement paths is not well understood. We investigate the degree to which gulls utilise fine scale orographic lift created by wind deflected upwards over landscape features in a virtually flat landscape. Using accelerometer measurements and GPS tracking, soaring flight is identified and analysed with respect to orographic lift, modelled using high-resolution digital elevation models and wind measurements. The relationship between orographic lift and flight routes suggests gulls have advanced knowledge of their aerial surroundings and the benefits to be gained from them, even regarding small features such as tree lines. We show that in a landscape constantly influenced by anthropogenic change, the structure of our landscape has an aerial impact on flight route connectivity and costs.

opencc-zeroDec 2015View details →

Data from: Dispersal propensity, but not flight performance, explains variation in dispersal ability

Enhanced dispersal ability may lead to accelerated range expansion and increased rates of population establishment, thereby affecting population genetic structure and evolutionary potential. Morphological, behavioural and physiological traits that characterize dispersive individuals from residents are poorly understood for many invertebrate systems, especially in non-polymorphic pterygote species. Here we examined phenotypic differences between dispersal-prone and philopatric individuals from repeated mark-release-recapture (MRR) experiments using an invasive agricultural pest, Ceratitis capitata. Comprehensive morphometric assessment and subsequent minimal adequate modelling using an information theoretic approach identified thorax mass : body mass ratio as a key predictor of disperser flies under semi-natural conditions. Performance differences in flight ability were then examined under controlled laboratory conditions to assess whether greater thorax mass : body mass ratio was associated with enhanced flight ability. The larger thorax : body mass ratio was associated with measurable differences in mean flight duration, most predominantly in males, and also by their willingness to disperse, scored as the number and duration of voluntary flights. No other measures of whole-animal flight performance (e.g. mean and peak vertical force, total or maximum flight duration) differed. Variation in voluntary behaviour may result in significant alterations of movement behaviour and realized dispersal in nature. This phenomenon may help explain intraspecific variation in the dispersal ability of insects.

Data from: Cytoskeleton structure and total methylation of mouse cardiac and lung tissue during space flight

The purpose of this work was to evaluate the protein and mRNA expression levels of multiple cytoskeletal proteins in the cardiac and lung tissue of mice that were euthanized onboard the United States Orbital Segment of the International Space Station 37 days after the start of the SpaceX-4 mission (September 2014, USA). The results showed no changes in the cytoskeletal protein content in the cardiac and lung tissue of the mice, but there were significant changes in the mRNA expression levels of the associated genes, which may be due to an increase in total genome methylation. The mRNA expression levels of DNA methylases, the cytosine demethylases Tet1 and Tet3, histone acetylase and histone deacetylase did not change, and the mRNA expression level of cytosine demethylase Tet2 was significantly decreased.

opencc-zeroDec 2015View details →

Data from: Three-dimensional simulation for fast forward flight of a calliope hummingbird

We present a computational study of flapping-wing aerodynamics of a calliope hummingbird (Selasphorus calliope) during fast forward flight. Three-dimensional wing kinematics were incorporated into the model by extracting time-dependent wing position from high-speed videos of the bird flying in a wind tunnel at 8.3 m s−1. The advance ratio, i.e. the ratio between flight speed and average wingtip speed, is around one. An immersed-boundary method was used to simulate flow around the wings and bird body. The result shows that both downstroke and upstroke in a wingbeat cycle produce significant thrust for the bird to overcome drag on the body, and such thrust production comes at price of negative lift induced during upstroke. This feature might be shared with bats, while being distinct from insects and other birds, including closely related swifts.

opencc-zeroDec 2013View details →

Data from: Evolution of thorax architecture in ant castes highlights trade-off between flight and ground behaviors

The concerted evolution of morphological and behavioral specializations has compelling examples in ant castes. Unique to ants is a marked divergence between winged queens and wingless workers, but morphological specializations for behaviors on the ground have been overlooked. We analyzed thorax morphology of queens and workers in species from 21 of the 25 ant subfamilies. We uncovered unique skeletomuscular modifications in workers that presumably increase power and flexibility of head–thorax articulation, emphasizing that workers are not simply wingless versions of queens. We also identified two distinct types of queens and showed repeated evolutionary associations with strategies of colony foundation. Solitary founding queens that hunt have a more worker-like thorax. Our results reveal that ants invest in the relative size of thorax segments according to their tasks. Versatility of head movements allows for better manipulation of food and objects, which arguably contributed to the ants' ecological and evolutionary success.

opencc-zeroDec 2013View details →

Data from: Cascading effects of host plant inbreeding on the larval growth, muscle molecular composition, and flight capacity of an adult herbivorous insect.

A primary function of adult winged insects is dispersal. Limiting larval dietary intake (partial starvation) has been shown to affect the flight muscle metabolism of adult moths reared on artificial diet, but a more ecologically relevant question is whether natural variation in host plant quality can lead to differences in the flight capacity of adult insects. Recent studies have shown that inbreeding compromises plant anti-herbivore defenses. We created inbred and outbred progeny from locally collected horsenettle (Solanum carolinense L.) and examined how host plant inbreeding affects the growth, development, and flight muscle physiology of tobacco hornworm (Manduca sexta L.), a specialist herbivore on Solanaceae. We tested the hypothesis that within population genetic variation in host plant quality, resulting from inbreeding, can create significant changes to the larval development and flight physiology of an adult insect. We found that Manduca larvae reared on inbred horsenettle plants grew faster and developed into larger pupae compared to larvae reared on outbred plants. Adult flight metabolic rate was greater in adults reared on inbred plants compared to outbred plants, and this elevation was independent of body mass when we excluded one plant family that produced small, low metabolic rate moths regardless of breeding regime. Differences in mass-specific flight metabolism were associated with changes in alternative splicing of Troponin t, a flight muscle protein that regulates muscle contraction. These results show that host plant inbreeding can create effects that cascade through larval and pupal development to affect dispersal-related traits of the adult stage. Hence, plant inbreeding may also impact herbivore population dynamics, particularly their ability to spread away from, and possibly into, isolated patches of inbred plants creating increased herbivore pressure on these plant populations. More generally, our findings reveal that changes in population biology at one trophic level can affect the metabolic physiology and flight capacity of an animal at a higher trophic level.

Data from: Simulated moult reduces flight performance but overlap with breeding does not affect breeding success in a long-distance migrant

1. Long-distance migrants are time-constrained as they need to incorporate many annual cycle stages within a year. Migratory passerines moult in the short interval between breeding and migration. To widen this interval, moult may start while still breeding, but this results in flying with moulting wings when food provisioning. 2. We experimentally simulated wing gaps in breeding male pied flycatchers by plucking 2 primary feathers from both wings. We quantified the nest visitations of both parents, proportion of high-quality food brought to the nestlings and adults and nestlings condition. Differences in oxidative damage caused by a possible reduction in flight efficiency were measured in amounts of ROMs and OXY in the blood. We also measured how flight performance was affected with recordings of the male`s escape flight using high-speed cameras. Finally, we collected data on adult survival, clutch size and laying date in the following year. 3. "Plucked" males travelled a 5% shorter distance per wingbeat, showing that our treatment reduced flight performance. In line with this, "plucked" males visited their nests less often. Females of "plucked" males, however, visited the nest more often than controls, and fully compensated their partner's reduced visitation rate. As a result, there were no differences between treatments in food quality brought to the nest, adult or chick mass or number of successfully fledged chicks. Males did not differ in their oxidative damage or local survival to the following year. In contrast, females paired with plucked males tended to return less often to breed in the next year in comparison to controls, but this difference was not significant. For the birds that did return there were no effects on breeding. 5. Our results reveal that wing gaps in male pied flycatchers reduce their flight performance, but when it occurs during breeding they prioritise their future reproduction by reducing parental care. As a result, there is no apparent detriment to their condition during breeding. Because non-moulting females are able to compensate their partner's reduced care, there is also no immediate costs to the offspring, but females may pay the cost suffering from a reduced survival.

Data from: Carrying a logger reduces escape flight speed in a passerine bird, but relative logger mass may be a misleading measure of this flight performance detriment

1. The recent boost in bird migration studies following the development of various tracking devices raised awareness of how detrimental attaching devices can be for animals. Such effects can occur during migration, but also immediately post-release if the device impairs escape flight performance and, consequently, the bird's ability to evade predators. 2. In this study, we investigated the effect of carrying a device on the escape flight speed and aerodynamic force production in a migratory passerine. We recorded upward-directed escape flights of 15 male blackcaps. Each individual was tested without a tag, and when equipped with three different leg-loop dummy tags with masses representing around 3%, 5% and 7% of their body mass. The experiment was designed such that all individuals passed through all treatments in a randomized order. 3. We found that two factors affected flight speed in roughly equal amounts: first, tagged escape flights had lower flight speeds compared to the control flights, irrespective of tag mass. Second, we found an effect of the total mass, i.e. the sum of the masses of the individual bird and of the tag, with heavier birds being slower. In contrast, flight speed was not correlated with relative tag mass in percentage of body mass, the metric commonly used in ethical guidelines for tag attachment. Aerodynamic flight force production also depended on total mass, with heavier birds producing higher forces. But these flight forces did not differ between flights with or without a tag. 4. We conclude that, when tagging birds, it is misleading to choose heavy individuals for tagging in order to minimize the tag mass as a percentage of body mass. This is particularly relevant in species for which body mass is not necessarily related to size, like migratory birds that accumulate large fat reserves. The lower escape speed in "tagged" flights could not be explained by differences in net flight force production, because these did not differ between flights with and without a tag. This suggests that the tag also affected pre-flight take-off dynamics, possibly due to a leg harness-induced reduction in leg push-off performance.