The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Douglas L Altshuler - One of the best experts on this subject based on the ideXlab platform.

  • The Orientation of Visual Space from the Perspective of Hummingbirds
    Frontiers Media S.A., 2018
    Co-Authors: Douglas L Altshuler, Luke P. Tyrrell, Benjamin Goller, Bret A. Moore, Esteban Fernández-juricic
    Abstract:

    Vision is a key component of hummingbird behavior. Hummingbirds hover in front of flowers, guide their bills into them for foraging, and maneuver backwards to undock from them. Capturing insects is also an important foraging strategy for most Hummingbirds. However, little is known about the visual sensory specializations Hummingbirds use to guide these two foraging strategies. We characterized the hummingbird visual field configuration, degree of eye movement, and orientation of the centers of acute vision. Hummingbirds had a relatively narrow binocular field (~30°) that extended above and behind their heads. Their blind area was also relatively narrow (~23°), which increased their visual coverage (about 98% of their celestial hemisphere). Additionally, eye movement amplitude was relatively low (~9°), so their ability to converge or diverge their eyes was limited. We confirmed that Hummingbirds have two centers of acute vision: a fovea centralis, projecting laterally, and an area temporalis, projecting more frontally. This retinal configuration is similar to other predatory species, which may allow Hummingbirds to enhance their success at preying on insects. However, there is no evidence that their temporal area could visualize the bill tip or that eye movements could compensate for this constraint. Therefore, guidance of precise bill position during the process of docking occurs via indirect cues or directly with low visual acuity despite having a temporal center of acute vision. The large visual coverage may favor the detection of predators and competitors even while docking into a flower. Overall, hummingbird visual configuration does not seem specialized for flower docking

  • visual sensory signals dominate tactile cues during docked feeding in Hummingbirds
    Frontiers in Neuroscience, 2017
    Co-Authors: Benjamin Goller, Paolo S Segre, Kevin M Middleton, Michael H Dickinson, Douglas L Altshuler
    Abstract:

    Animals living in and interacting with natural environments must monitor and respond to changing conditions and unpredictable situations. Using information from multiple sensory systems allows them to modify their behavior in response to their dynamic environment but also creates the challenge of integrating different, and potentially contradictory, sources of information for behavior control. Understanding how multiple information streams are integrated to produce flexible and reliable behavior is key to understanding how behavior is controlled in natural settings. Natural settings are rarely still, which challenges animals that require precise body position control, like Hummingbirds, which hover while feeding from flowers. Tactile feedback, available only once the hummingbird is docked at the flower, could provide additional information to help maintain its position at the flower. To investigate the role of tactile information for hovering control during feeding, we first asked whether Hummingbirds physically interact with a feeder once docked. We quantified physical interactions between docked Hummingbirds and a feeder placed in front of a stationary background pattern. Force sensors on the feeder measured a complex time course of loading that reflects the wingbeat frequency and bill movement of feeding Hummingbirds, and suggests that they sometimes push against the feeder with their bill. Next, we asked whether the measured tactile interactions were used by feeding Hummingbirds to maintain position relative to the feeder. We created two experimental scenarios-one in which the feeder was stationary and the visual background moved and the other where the feeder moved laterally in front of a white background. When the visual background pattern moved, docked Hummingbirds pushed significantly harder in the direction of horizontal visual motion. When the feeder moved, and the background was stationary, Hummingbirds generated aerodynamic force in the opposite direction of the feeder motion. These results suggest that docked Hummingbirds are using visual information about the environment to maintain body position and orientation, and not actively tracking the motion of the feeder. The absence of flower tracking behavior in Hummingbirds contrasts with the behavior of hawkmoths, and provides evidence that they rely primarily on the visual background rather than flower-based cues while feeding.

  • Hummingbirds control hovering flight by stabilizing visual motion
    Proceedings of the National Academy of Sciences of the United States of America, 2014
    Co-Authors: Benjamin Goller, Douglas L Altshuler
    Abstract:

    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.

  • hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors
    Journal of the Royal Society Interface, 2014
    Co-Authors: Jan W Kruyt, Elsa M Quicazanrubio, Gertjan Van Heijst, Douglas L Altshuler, David Lentink
    Abstract:

    Hummingbirds are the only birds that can sustain hovering. This unique flight behaviour comes, however, at high energetic cost. Based on helicopter and aeroplane design theory, we expect that hummingbird wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines aerodynamic efficacy. Previous quasi-steady experiments with a wing spinner set-up provide no support for this prediction. To test this more carefully, we compare the quasi-steady hover performance of 26 wings, from 12 hummingbird taxa. We spun the wings at angular velocities and angles of attack that are representative for every species and measured lift and torque more precisely. The power (aerodynamic torque × angular velocity) required to lift weight depends on aerodynamic efficacy, which is measured by the power factor. Our comparative analysis shows that AR has a modest influence on lift and drag forces, as reported earlier, but interspecific differences in power factor are large. During the downstroke, the power required to hover decreases for larger AR wings at the angles of attack at which Hummingbirds flap their wings (p < 0.05). Quantitative flow visualization demonstrates that variation in hover power among hummingbird wings is driven by similar stable leading edge vortices that delay stall during the down- and upstroke. A side-by-side aerodynamic performance comparison of hummingbird wings and an advanced micro helicopter rotor shows that they are remarkably similar.

  • molecular phylogenetics and the diversification of Hummingbirds
    Current Biology, 2014
    Co-Authors: Jimmy A Mcguire, Douglas L Altshuler, Christopher C Witt, J V Remsen, Ammon Corl, Daniel L Rabosky, Robert Dudley
    Abstract:

    Summary The tempo of species diversification in large clades can reveal fundamental evolutionary mechanisms that operate on large temporal and spatial scales [1–4]. Hummingbirds have radiated into a diverse assemblage of specialized nectarivores comprising 338 species, but their evolutionary history has not, until now, been comprehensively explored. We studied hummingbird diversification by estimating a time-calibrated phylogeny for 284 hummingbird species, demonstrating that Hummingbirds invaded South America by ∼22 million years ago, and subsequently diversified into nine principal clades (see [5–7]). Using ancestral state reconstruction and diversification analyses, we (1) estimate the age of the crown-group hummingbird assemblage, (2) investigate the timing and patterns of lineage accumulation for Hummingbirds overall and regionally, and (3) evaluate the role of Andean uplift in hummingbird speciation. Detailed analyses reveal disparate clade-specific processes that allowed for ongoing species diversification. One factor was significant variation among clades in diversification rates. For example, the nine principal clades of Hummingbirds exhibit ∼15-fold variation in net diversification rates, with evidence for accelerated speciation of a clade that includes the Bee, Emerald, and Mountain Gem groups of Hummingbirds. A second factor was colonization of key geographic regions, which opened up new ecological niches. For example, some clades diversified in the context of the uplift of the Andes Mountains, whereas others were affected by the formation of the Panamanian land bridge. Finally, although species accumulation is slowing in all groups of Hummingbirds, several major clades maintain rapid rates of diversification on par with classical examples of rapid adaptive radiation.

Lisa A. Tell - One of the best experts on this subject based on the ideXlab platform.

  • novel hybrid finds a peri urban niche allen s Hummingbirds in southern california
    Conservation Genetics, 2020
    Co-Authors: Braden L Godwin, Melanie E F Lacava, Beth Mendelsohn, Roderick B Gagne, Kyle D Gustafson, Sierra Love M Stowell, Andrew Engilis, Lisa A. Tell
    Abstract:

    Species range expansions and contractions can have ecological and genetic consequences, and thus are important areas of study for conservation. Hybridization and introgression are not uncommon in closely related populations that experience secondary contact during a range expansion. Allen’s Hummingbird (Selasphorus sasin) in California comprises two subspecies: the migratory S. s. sasin, which winters in central Mexico and breeds in central and northern California, and the resident S. s. sedentarius, which lives and breeds year-round on several of the Channel Islands off the California coast. Within recent decades, Allen’s Hummingbirds have been found living and breeding year-round in the southern California peri-urban mainland near Los Angeles. Ornithologists assumed that the L.A. birds were an expansion of the island subspecies, S. s. sedentarius due to similar but very subtle morphological characteristics. However, the genetic relationships among the three putative populations of Allen's hummingbird—migratory, southern California mainland, and island—are unknown. We investigated these relationships by analyzing variation of single nucleotide polymorphisms from the three geographic regions where S. sasin are present. Our population genomic analyses indicate that S. sasin Hummingbirds inhabiting mainland southern California are a hybrid population resulting from admixture between S. s. sasin and S. s. sedentarius. From one perspective, these results may be interpreted as a positive development for S. s. sasin as the growing population represent an overall increase in the S. sasin population, and the expanding population contains a significant representation of S. s. sasin alleles.

  • concentrations of retinol and α tocopherol in tissue samples from anna s Hummingbirds calypte anna
    Frontiers in Veterinary Science, 2020
    Co-Authors: Stephanie M Diao, Ruta R Bandivadekar, Janet E Foley, Robert H Poppenga, Gwendolyne Gonzales Alarcio, Linda S Aston, Lisa A. Tell
    Abstract:

    Retinol (vitamin A) and α-tocopherol (vitamin E) concentrations were measured in tissue samples (liver, heart, pectoral muscle, and brain) from Anna's Hummingbirds (Calypte anna). Hummingbirds were after-hatch year birds that were sourced from various rehabilitation centers throughout California. Tissues samples were analyzed using high-performance liquid chromatography (HPLC). Minimum, maximum, mean, standard deviation (SD), and median ppm concentrations were calculated for each vitamin and tissue sample type. A novel analytical method was developed to analyze small mass tissue samples, with the smallest sample mass being 0.05 g for which analysis can be performed. Mean ± standard deviation (SD) concentrations of retinol in hummingbird livers, hearts, and pectoral muscle samples were 269.0 ± 216.9 ppm, 1.8 ± 2.2 ppm, and 0.3 ± 0.1 ppm, respectively. Mean ± SD α-tocopherol concentrations were 6.9 ± 4.6 ppm, 5.5 ± 4.0 ppm, 3.7 ± 2.2 ppm, and 9.1 ± 3.2 ppm for liver, heart, pectoral muscle, and brain samples, respectively. Vitamin concentrations from varying tissue types were compared to determine which were best associated with liver concentrations, the most commonly analyzed tissue for these vitamins. For both retinol and α-tocopherol, heart samples were most strongly associated with the liver samples. The results of this study provide baseline retinol and α-tocopherol concentrations in different tissue types from Anna's Hummingbirds. These baseline values may be utilized in conservation efforts to avoid hypervitaminosis and hypovitaminosis of rehabilitated and/or captive Hummingbirds by providing guidelines for nutritional targets which could be assessed on post-mortem examinations. Post-mortem examination of birds and measurement of vitamin concentrations in tissues may allow for dietary changes that aid captive Hummingbirds.

  • anti microbial activity of whole blood and plasma collected from anna s Hummingbirds calypte anna against three different microbes
    PLOS ONE, 2020
    Co-Authors: Andrea M Derogatis, Kirk C Klasing, Ruta R Bandivadekar, Leilani V Nguyen, Lisa A. Tell
    Abstract:

    Hummingbirds are essential pollinators in many ecosystems, making their conservation critical. As is the case with many species, Hummingbirds are now facing a variety of challenges resulting from anthropogenic changes. As populations shift and species interactions change, disease is likely to pose a significant threat. There is a basic understanding of which pathogens currently affect a variety of hummingbird species, however there is a paucity of information about their immune systems capacity to kill pathogens and what specific factors may affect immunity. The objective of this study was to gain a basic understanding of the effect of age, sex, and molt on the constitutive innate immunity of Hummingbirds. An in vitro assay was used to assess the microbiocidal capacity of the whole blood of Anna's Hummingbirds (Calypte anna) against three different microbes: Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Candida albicans (C. albicans). The effect of age, sex and molt on anti-microbial capacity varied based on the microbe type. After-hatch-year birds tended to have better anti-microbial capacity compared to hatch-year birds. Male birds had higher anti-microbial activity than female birds, although this was not observed against C. albicans. Molting birds had a weaker antimicrobial activity against E. coli and S. aureus than birds that were not molting. These results represent an important first step towards defining the parameters of constitutive innate immunity of Anna's Hummingbirds as well as providing important knowledge about factors that should be considered when evaluating the health of wild populations.

  • taqman quantitative real time pcr for detecting avipoxvirus dna in various sample types from Hummingbirds
    PLOS ONE, 2020
    Co-Authors: Hanna E Baek, Ravinder N. M. Sehgal, Pranav Pandit, Ruta R Bandivadekar, Michelle Mah, Lisa A. Tell
    Abstract:

    BACKGROUND Avian pox is a viral disease documented in a wide range of bird species. Disease-related detrimental effects can cause dyspnea and dysphagia, and birds with high metabolic requirements, such as Hummingbirds, are thus especially vulnerable to the pathogen. Hummingbirds have a strong presence in California, especially in urban environments. However, little is understood regarding the impact of pox virus on hummingbird populations. Currently, diagnosing a pox infection relies on obtaining a tissue biopsy, which poses significant risks to birds and challenges in the field. Understanding the ecology of hummingbird pox viral infections could be advanced by a minimally invasive ante-mortem diagnostic method. Our aim was to address whether pox infections can be diagnosed using integumentary system samples besides tissue biopsies. To meet this goal, we tested multiple integumentary sample types using a quantitative real-time PCR assay. A secondary study goal was to determine which sample types (ranging from minimally to highly invasive sampling) were optimal for identifying infected birds. METHODOLOGY AND PRINCIPAL FINDINGS Pox-like lesion tissue, pectoral muscle, feathers, toenail clippings, blood, and swabs (both pox-like lesion tissue and non pox-like lesion tissue) were taken from live birds and carcasses of two species of Hummingbirds found in California. To maximize successful diagnosis, especially for samples with low viral load, a real-time quantitative PCR assay was developed for detecting the hummingbird-specific Avipoxvirus 4b core protein gene. Avipoxvirus DNA was successfully amplified from all sample types obtained from 27 individuals. These results were compared to those of conventional PCR and comparisons were also made among sample types, utilizing lesion tissue samples as the gold standard. CONCLUSIONS AND SIGNIFICANCE Hummingbird avian pox can be diagnosed without relying on tissue biopsies. We identify that feather samples, of which contour feathers yielded the best results, can be used for diagnosing infected birds, thus reducing sampling risk. In sum, the real-time PCR assay detected viral DNA in various integumentary system sample types and will be useful in future studies of hummingbird disease ecology.

  • taqman quantitative real time pcr for detecting avipoxvirus dna in various sample types from Hummingbirds
    bioRxiv, 2020
    Co-Authors: Hanna E Baek, Ravinder N. M. Sehgal, Pranav Pandit, Ruta R Bandivadekar, Michelle Mah, Lisa A. Tell
    Abstract:

    Abstract Background Avian pox is a viral disease documented in a wide range of bird species. Disease related detrimental effects can cause dyspnea and dysphagia, therefore birds with high metabolic requirements, such as Hummingbirds, are especially vulnerable. Hummingbirds have a strong presence in California, especially in urban environments; however, little is understood regarding the impact of pox virus on hummingbird populations. Diagnosing pox infections relies on obtaining a tissue biopsy that poses significant bird risks and field challenges. Understanding the ecology of hummingbird pox viral infections could be advanced by a minimally invasive ante-mortem diagnostic method. This study’s goal was to address this gap in understanding if pox infections can be diagnosed using integumentary system samples besides tissue biopsies. To meet this goal, we tested multiple integumentary sample types and tested them using a quantitative real-time PCR assay. A secondary study goal was to determine which sample types (ranging from minimally to highly invasive sampling) were optimal for identifying infected birds. Methodology/Principal Findings Lesion tissue, pectoral muscle, feathers, toenail, blood, and swabs (both lesion tissue and non-lesion tissues) were taken from live birds and carcasses of two species of Hummingbirds found in California. To maximize successful diagnosis, especially for samples with low viral load, a real-time quantitative PCR assay was developed for detecting the hummingbird-specific Avipoxvirus 4b core protein gene. Avipoxvirus DNA was successfully amplified from all sample types across 27 individuals. Our results were then compared to those of conventional PCR. Comparisons were also made between sample types utilizing lesion tissue samples as the gold standard. Conclusions/Significance Hummingbird avian pox can be diagnosed without relying on tissue biopsies. Feather samples can be used for diagnosing infected birds and reduces sampling risk. A real-time PCR assay detected viral DNA in various integumentary system sample types and could be used for studying hummingbird disease ecology in the future.

Robert Dudley - One of the best experts on this subject based on the ideXlab platform.

  • shifting paradigms in the mechanics of nectar extraction and hummingbird bill morphology
    Integrative Organismal Biology, 2019
    Co-Authors: Margaret A Rubega, Alejandro Ricoguevara, K J Hurme, Robert Dudley
    Abstract:

    Author(s): Rico-Guevara, A; Rubega, M A; Hurme, K J; Dudley, R | Abstract: As functional morphologists, we aim to connect structures, mechanisms, and emergent higher-scale phenomena (e.g., behavior), with the ulterior motive of addressing evolutionary patterns. The fit between flowers and hummingbird bills has long been used as an example of impressive co-evolution, and hence Hummingbirds’ foraging behavior and ecological associations have been the subject of intense study. To date, models of hummingbird foraging have been based on the almost two-centuries-old assumption that capillary rise loads nectar into hummingbird tongue grooves. Furthermore, the role of the bill in the drinking process has been overlooked, instead considering it as the mere vehicle with which to traverse the corolla and access the nectar chamber. As a scientific community, we have been making incorrect assumptions about the basic aspects of how Hummingbirds extract nectar from flowers. In this article, we summarize recent advances on drinking biomechanics, morphological and ecological patterns, and selective forces involved in the shaping of the hummingbird feeding apparatus, and also address its modifications in a previously unexpected context, namely conspecific and heterospecific fighting. We explore questions such as: how do the mechanics of feeding define the limits and adaptive consequences of foraging behaviors? Which are the selective forces that drive bill and tongue shape, and associated sexually dimorphic traits? And finally, what are the proximate and ultimate causes of their foraging strategies, including exploitative and interference competition? Increasing our knowledge of morphology, mechanics, and diversity of hummingbird feeding structures will have implications for understanding the ecology and evolution of these remarkable animals.

  • the biomechanical origin of extreme wing allometry in Hummingbirds
    Nature Communications, 2017
    Co-Authors: Dimitri A Skandalis, Kenneth C Welch, Jimmy A Mcguire, Christopher C Witt, Paolo S Segre, Joseph W Bahlman, Derrick J E Groom, Robert Dudley
    Abstract:

    Flying animals of different masses vary widely in body proportions, but the functional implications of this variation are often unclear. We address this ambiguity by developing an integrative allometric approach, which we apply here to Hummingbirds to examine how the physical environment, wing morphology and stroke kinematics have contributed to the evolution of their highly specialised flight. Surprisingly, Hummingbirds maintain constant wing velocity despite an order of magnitude variation in body weight; increased weight is supported solely through disproportionate increases in wing area. Conversely, wing velocity increases with body weight within species, compensating for lower relative wing area in larger individuals. By comparing inter- and intraspecific allometries, we find that the extreme wing area allometry of Hummingbirds is likely an adaptation to maintain constant burst flight capacity and induced power requirements with increasing weight. Selection for relatively large wings simultaneously maximises aerial performance and minimises flight costs, which are essential elements of humming bird life history. Hummingbirds are known to defy the predicted scaling relationships between body and wing size. Here, Skandalis et al. develop a ‘force allometry’ framework to show that, regardless of wing size, hummingbird species have the same wing velocity during flight.

  • electrostatic charge on flying Hummingbirds and its potential role in pollination
    PLOS ONE, 2015
    Co-Authors: Marc A Badger, Robert Dudley, Victor Manuel Ortegajimenez, Lisa Von Rabenau, Ashley Smiley
    Abstract:

    Electrostatic phenomena are known to enhance both wind- and insect-mediated pollination, but have not yet been described for nectar-feeding vertebrates. Here we demonstrate that wild Anna's Hummingbirds (Calypte anna) can carry positive charges up to 800 pC while in flight (mean ± s.d.: 66 ± 129 pC). Triboelectric charging obtained by rubbing an isolated hummingbird wing against various plant structures generated charges up to 700 pC. A metal hummingbird model charged to 400 pC induced bending of floral stamens in four plants (Nicotiana, Hemerocallis, Penstemon, and Aloe spp.), and also attracted falling Lycopodium spores at distances of < 2 mm. Electrostatic forces may therefore influence pollen transfer onto nectar-feeding birds.

  • molecular phylogenetics and the diversification of Hummingbirds
    Current Biology, 2014
    Co-Authors: Jimmy A Mcguire, Douglas L Altshuler, Christopher C Witt, J V Remsen, Ammon Corl, Daniel L Rabosky, Robert Dudley
    Abstract:

    Summary The tempo of species diversification in large clades can reveal fundamental evolutionary mechanisms that operate on large temporal and spatial scales [1–4]. Hummingbirds have radiated into a diverse assemblage of specialized nectarivores comprising 338 species, but their evolutionary history has not, until now, been comprehensively explored. We studied hummingbird diversification by estimating a time-calibrated phylogeny for 284 hummingbird species, demonstrating that Hummingbirds invaded South America by ∼22 million years ago, and subsequently diversified into nine principal clades (see [5–7]). Using ancestral state reconstruction and diversification analyses, we (1) estimate the age of the crown-group hummingbird assemblage, (2) investigate the timing and patterns of lineage accumulation for Hummingbirds overall and regionally, and (3) evaluate the role of Andean uplift in hummingbird speciation. Detailed analyses reveal disparate clade-specific processes that allowed for ongoing species diversification. One factor was significant variation among clades in diversification rates. For example, the nine principal clades of Hummingbirds exhibit ∼15-fold variation in net diversification rates, with evidence for accelerated speciation of a clade that includes the Bee, Emerald, and Mountain Gem groups of Hummingbirds. A second factor was colonization of key geographic regions, which opened up new ecological niches. For example, some clades diversified in the context of the uplift of the Andes Mountains, whereas others were affected by the formation of the Panamanian land bridge. Finally, although species accumulation is slowing in all groups of Hummingbirds, several major clades maintain rapid rates of diversification on par with classical examples of rapid adaptive radiation.

  • implications of floral orientation for flight kinematics and metabolic expenditure of hover feeding Hummingbirds
    Functional Ecology, 2013
    Co-Authors: Nir Sapir, Robert Dudley
    Abstract:

    Summary Nectar-bearing flowers are characterized by many different shapes, sizes and orientations, which may affect the way Hummingbirds feed from them. Many hummingbird-pollinated flowers are oriented downwards, thereby requiring that trochilids feed while hovering with the bill oriented vertically upward. We measured body orientations, wingbeat kinematics and hovering metabolic rates for Anna's Hummingbirds (Calypte anna) feeding from artificial flowers that were oriented horizontally, tilted 45° downwards and pointing vertically downwards. When feeding from vertically oriented flowers, Hummingbirds employed an upright body position combined with dorsal head flexion. Additional kinematic adjustments included an increased stroke plane angle relative to the longitudinal body axis and an increased stroke amplitude deriving from increases in the minimum positional angle of the wingbeat. By contrast, wingbeat frequency, the stroke plane angle relative to horizontal, the ratio of the minimum to maximum positional angles of the wingbeat and the upstroke/downstroke ratio did not vary during feeding from different flower orientations. Metabolic rates increased by an average (±SD) of 10·8 (±8·8)% for feeding from vertically compared to horizontally oriented flowers. Feeding from pendent flowers comes with a substantial metabolic cost that may influence floral selection by Hummingbirds and thus the evolution of associated pollination syndromes.

Christopher C Witt - One of the best experts on this subject based on the ideXlab platform.

  • the biomechanical origin of extreme wing allometry in Hummingbirds
    Nature Communications, 2017
    Co-Authors: Dimitri A Skandalis, Kenneth C Welch, Jimmy A Mcguire, Christopher C Witt, Paolo S Segre, Joseph W Bahlman, Derrick J E Groom, Robert Dudley
    Abstract:

    Flying animals of different masses vary widely in body proportions, but the functional implications of this variation are often unclear. We address this ambiguity by developing an integrative allometric approach, which we apply here to Hummingbirds to examine how the physical environment, wing morphology and stroke kinematics have contributed to the evolution of their highly specialised flight. Surprisingly, Hummingbirds maintain constant wing velocity despite an order of magnitude variation in body weight; increased weight is supported solely through disproportionate increases in wing area. Conversely, wing velocity increases with body weight within species, compensating for lower relative wing area in larger individuals. By comparing inter- and intraspecific allometries, we find that the extreme wing area allometry of Hummingbirds is likely an adaptation to maintain constant burst flight capacity and induced power requirements with increasing weight. Selection for relatively large wings simultaneously maximises aerial performance and minimises flight costs, which are essential elements of humming bird life history. Hummingbirds are known to defy the predicted scaling relationships between body and wing size. Here, Skandalis et al. develop a ‘force allometry’ framework to show that, regardless of wing size, hummingbird species have the same wing velocity during flight.

  • molecular phylogenetics and the diversification of Hummingbirds
    Current Biology, 2014
    Co-Authors: Jimmy A Mcguire, Douglas L Altshuler, Christopher C Witt, J V Remsen, Ammon Corl, Daniel L Rabosky, Robert Dudley
    Abstract:

    Summary The tempo of species diversification in large clades can reveal fundamental evolutionary mechanisms that operate on large temporal and spatial scales [1–4]. Hummingbirds have radiated into a diverse assemblage of specialized nectarivores comprising 338 species, but their evolutionary history has not, until now, been comprehensively explored. We studied hummingbird diversification by estimating a time-calibrated phylogeny for 284 hummingbird species, demonstrating that Hummingbirds invaded South America by ∼22 million years ago, and subsequently diversified into nine principal clades (see [5–7]). Using ancestral state reconstruction and diversification analyses, we (1) estimate the age of the crown-group hummingbird assemblage, (2) investigate the timing and patterns of lineage accumulation for Hummingbirds overall and regionally, and (3) evaluate the role of Andean uplift in hummingbird speciation. Detailed analyses reveal disparate clade-specific processes that allowed for ongoing species diversification. One factor was significant variation among clades in diversification rates. For example, the nine principal clades of Hummingbirds exhibit ∼15-fold variation in net diversification rates, with evidence for accelerated speciation of a clade that includes the Bee, Emerald, and Mountain Gem groups of Hummingbirds. A second factor was colonization of key geographic regions, which opened up new ecological niches. For example, some clades diversified in the context of the uplift of the Andes Mountains, whereas others were affected by the formation of the Panamanian land bridge. Finally, although species accumulation is slowing in all groups of Hummingbirds, several major clades maintain rapid rates of diversification on par with classical examples of rapid adaptive radiation.

  • the smallest avian genomes are found in Hummingbirds
    Proceedings of The Royal Society B: Biological Sciences, 2009
    Co-Authors: Ryan T Gregory, Jimmy A Mcguire, Chandler B Andrews, Christopher C Witt
    Abstract:

    It has often been suggested that the genome sizes of birds are constrained relative to other tetrapods owing to the high metabolic demands of powered flight and the link between nuclear DNA content and red blood cell size. This hypothesis predicts that Hummingbirds, which engage in energy-intensive hovering flight, will display especially constrained genomes even relative to other birds. We report genome size measurements for 37 species of Hummingbirds that confirm this prediction. Our results suggest that genome size was reduced before the divergence of extant hummingbird lineages, and that only minimal additional reduction occurred during hummingbird diversification. Unlike in some other avian taxa, the small amount of variation observed within Hummingbirds is not explained by variation in respiratory and flight-related parameters. Unexpectedly, genome size appears to have increased in four unrelated hummingbird species whose distributions are centred on humid forests of the upper-tropical elevational zone on the eastern slope of the Andes. This suggests that the secondary expansion of the genome may have been mediated by biogeographical and demographic effects.

  • phylogenetic systematics and biogeography of Hummingbirds bayesian and maximum likelihood analyses of partitioned data and selection of an appropriate partitioning strategy
    Systematic Biology, 2007
    Co-Authors: Jimmy A Mcguire, Douglas L Altshuler, Christopher C Witt, J V Remsen
    Abstract:

    Hummingbirds are an important model system in avian biology, but to date the group has been the subject of remarkably few phylogenetic investigations. Here we present partitioned Bayesian and maximum likelihood phylogenetic analyses for 151 of approximately 330 species of Hummingbirds and 12 outgroup taxa based on two protein-coding mitochondrial genes (ND2 and ND4), flanking tRNAs, and two nuclear introns (AK1 and BFib). We analyzed these data under several partitioning strategies ranging between unpartitioned and a maximum of nine partitions. In order to select a statistically justified partitioning strategy following partitioned Bayesian analysis, we considered four alternative criteria including Bayes factors, modified versions of the Akaike information criterion for small sample sizes (AIC(c)), Bayesian information criterion (BIC), and a decision-theoretic methodology (DT). Following partitioned maximum likelihood analyses, we selected a best-fitting strategy using hierarchical likelihood ratio tests (hLRTS), the conventional AICc, BIC, and DT, concluding that the most stringent criterion, the performance-based DT, was the most appropriate methodology for selecting amongst partitioning strategies. In the context of our well-resolved and well-supported phylogenetic estimate, we consider the historical biogeography of Hummingbirds using ancestral state reconstructions of (1) primary geographic region of occurrence (i.e., South America, Central America, North America, Greater Antilles, Lesser Antilles), (2) Andean or non-Andean geographic distribution, and (3) minimum elevational occurrence. These analyses indicate that the basal hummingbird assemblages originated in the lowlands of South America, that most of the principle clades of Hummingbirds (all but Mountain Gems and possibly Bees) originated on this continent, and that there have been many (at least 30) independent invasions of other primary landmasses, especially Central America.

  • phylogenetic systematics and biogeography of Hummingbirds bayesian and maximum likelihood analyses of partitioned data and selection of an appropriate partitioning strategy
    Systematic Biology, 2007
    Co-Authors: Jimmy A Mcguire, Douglas L Altshuler, Christopher C Witt, J V Remsen
    Abstract:

    Hummingbirds are an important model system in avian biology, but to date the group has been the subject of remarkably few phylogenetic investigations. Here we present partitioned Bayesian and maximum likelihood phylogenetic analyses for 151 of approximately 330 species of Hummingbirds and 12 outgroup taxa based on two protein-coding mito- chondrial genes (ND2 and ND4), flanking tRNAs, and two nuclear introns (AK1 and BFib). We analyzed these data under several partitioning strategies ranging between unpartitioned and a maximum of nine partitions. In order to select a statisti- cally justified partitioning strategy following partitioned Bayesian analysis, we considered four alternative criteria including Bayes factors, modified versions of the Akaike information criterion for small sample sizes (AICc), Bayesian information cri- terion (BIC), and a decision-theoretic methodology (DT). Following partitioned maximum likelihood analyses, we selected a best-fitting strategy using hierarchical likelihood ratio tests (hLRTS), the conventional AICc, BIC, and DT, concluding that the most stringent criterion, the performance-based DT, was the most appropriate methodology for selecting amongst parti- tioning strategies. In the context of our well-resolved and well-supported phylogenetic estimate, we consider the historical biogeography of Hummingbirds using ancestral state reconstructions of (1) primary geographic region of occurrence (i.e., South America, Central America, North America, Greater Antilles, Lesser Antilles), (2) Andean or non-Andean geographic distribution, and (3) minimum elevational occurrence. These analyses indicate that the basal hummingbird assemblages originated in the lowlands of South America, that most of the principle clades of Hummingbirds (all but Mountain Gems and possibly Bees) originated on this continent, and that there have been many (at least 30) independent invasions of other primary landmasses, especially Central America. (Akaike information criterion; ancestral state reconstruction; Bayesian information criterion; Bayes factors; biogeography; branch-length priors; decision theory; hierarchical likelihood-ratio test.)

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  • trait evolution resource specialization and vulnerability to plant extinctions among antillean Hummingbirds
    Proceedings of The Royal Society B: Biological Sciences, 2018
    Co-Authors: Bo Dalsgaard, Pietro K Maruyama, Jimmy A Mcguire, Ana Martin M Gonzalez, Jonathan D Kennedy, Benno I Simmons, Andrea C Baquero, Allan Timmermann, Jeff Ollerton, William J Sutherland
    Abstract:

    Species traits are thought to predict feeding specialization and the vulnerability of a species to extinctions of interaction partners, but the context in which a species evolved and currently inhabits may also matter. Notably, the predictive power of traits may require that traits evolved to fit interaction partners. Furthermore, local abiotic and biotic conditions may be important. On islands, for instance, specialized and vulnerable species are predicted to be found mainly in mountains, whereas species in lowlands should be generalized and less vulnerable. We evaluated these predictions for Hummingbirds and their nectar-food plants on Antillean islands. Our results suggest that the rates of hummingbird trait divergence were higher among ancestral mainland forms before the colonization of the Antilles. In correspondence with the limited trait evolution that occurred within the Antilles, local abiotic and biotic conditions-not species traits-correlate with hummingbird resource specialization and the vulnerability of Hummingbirds to extinctions of their floral resources. Specifically, Hummingbirds were more specialized and vulnerable in conditions with high topographical complexity, high rainfall, low temperatures and high floral resource richness, which characterize the Antillean Mountains. These findings show that resource specialization and species vulnerability to extinctions of interaction partners are highly context-dependent.

  • the biomechanical origin of extreme wing allometry in Hummingbirds
    Nature Communications, 2017
    Co-Authors: Dimitri A Skandalis, Kenneth C Welch, Jimmy A Mcguire, Christopher C Witt, Paolo S Segre, Joseph W Bahlman, Derrick J E Groom, Robert Dudley
    Abstract:

    Flying animals of different masses vary widely in body proportions, but the functional implications of this variation are often unclear. We address this ambiguity by developing an integrative allometric approach, which we apply here to Hummingbirds to examine how the physical environment, wing morphology and stroke kinematics have contributed to the evolution of their highly specialised flight. Surprisingly, Hummingbirds maintain constant wing velocity despite an order of magnitude variation in body weight; increased weight is supported solely through disproportionate increases in wing area. Conversely, wing velocity increases with body weight within species, compensating for lower relative wing area in larger individuals. By comparing inter- and intraspecific allometries, we find that the extreme wing area allometry of Hummingbirds is likely an adaptation to maintain constant burst flight capacity and induced power requirements with increasing weight. Selection for relatively large wings simultaneously maximises aerial performance and minimises flight costs, which are essential elements of humming bird life history. Hummingbirds are known to defy the predicted scaling relationships between body and wing size. Here, Skandalis et al. develop a ‘force allometry’ framework to show that, regardless of wing size, hummingbird species have the same wing velocity during flight.

  • molecular phylogenetics and the diversification of Hummingbirds
    Current Biology, 2014
    Co-Authors: Jimmy A Mcguire, Douglas L Altshuler, Christopher C Witt, J V Remsen, Ammon Corl, Daniel L Rabosky, Robert Dudley
    Abstract:

    Summary The tempo of species diversification in large clades can reveal fundamental evolutionary mechanisms that operate on large temporal and spatial scales [1–4]. Hummingbirds have radiated into a diverse assemblage of specialized nectarivores comprising 338 species, but their evolutionary history has not, until now, been comprehensively explored. We studied hummingbird diversification by estimating a time-calibrated phylogeny for 284 hummingbird species, demonstrating that Hummingbirds invaded South America by ∼22 million years ago, and subsequently diversified into nine principal clades (see [5–7]). Using ancestral state reconstruction and diversification analyses, we (1) estimate the age of the crown-group hummingbird assemblage, (2) investigate the timing and patterns of lineage accumulation for Hummingbirds overall and regionally, and (3) evaluate the role of Andean uplift in hummingbird speciation. Detailed analyses reveal disparate clade-specific processes that allowed for ongoing species diversification. One factor was significant variation among clades in diversification rates. For example, the nine principal clades of Hummingbirds exhibit ∼15-fold variation in net diversification rates, with evidence for accelerated speciation of a clade that includes the Bee, Emerald, and Mountain Gem groups of Hummingbirds. A second factor was colonization of key geographic regions, which opened up new ecological niches. For example, some clades diversified in the context of the uplift of the Andes Mountains, whereas others were affected by the formation of the Panamanian land bridge. Finally, although species accumulation is slowing in all groups of Hummingbirds, several major clades maintain rapid rates of diversification on par with classical examples of rapid adaptive radiation.

  • projected changes in elevational distribution and flight performance of montane neotropical Hummingbirds in response to climate change
    Global Change Biology, 2011
    Co-Authors: Wolfgang Buermann, Jaime A. Chaves, Jimmy A Mcguire, Robert Dudley, Thomas B Smith, Douglas L Altshuler
    Abstract:

    The hovering flight of Hummingbirds is one of the most energetically demanding forms of animal locomotion and is influenced by both atmospheric oxygen availability and air density. Montane Neotropical Hummingbirds are expected to shift altitudinally upwards in response to climate change to track their ancestral climatic regime, which is predicted to influence their flight performance. In this study, we use the climate envelope approach to estimate upward elevational shifts for five Andean hummingbird species under two climate change scenarios. We then use field-based data on hummingbird flight mechanics to estimate the resulting impact of climate change on aerodynamic performance in hovering flight. Our results show that in addition to significant habitat loss and fragmentation, projected upwards elevational shifts vary between 300 and 700 m, depending on climate change scenario and original mean elevation of the target species. Biomechanical analysis indicates that such upwards elevational shifts would yield a � 2–51 increase in wing stroke amplitude with no substantial effect on wingbeat frequency. Overall, the physiological impact of elevational shifts of o1000 m in response to climate change is likely to be small relative to other factors such as habitat loss, changes in floristic composition, and increased interspecific competition.

  • the smallest avian genomes are found in Hummingbirds
    Proceedings of The Royal Society B: Biological Sciences, 2009
    Co-Authors: Ryan T Gregory, Jimmy A Mcguire, Chandler B Andrews, Christopher C Witt
    Abstract:

    It has often been suggested that the genome sizes of birds are constrained relative to other tetrapods owing to the high metabolic demands of powered flight and the link between nuclear DNA content and red blood cell size. This hypothesis predicts that Hummingbirds, which engage in energy-intensive hovering flight, will display especially constrained genomes even relative to other birds. We report genome size measurements for 37 species of Hummingbirds that confirm this prediction. Our results suggest that genome size was reduced before the divergence of extant hummingbird lineages, and that only minimal additional reduction occurred during hummingbird diversification. Unlike in some other avian taxa, the small amount of variation observed within Hummingbirds is not explained by variation in respiratory and flight-related parameters. Unexpectedly, genome size appears to have increased in four unrelated hummingbird species whose distributions are centred on humid forests of the upper-tropical elevational zone on the eastern slope of the Andes. This suggests that the secondary expansion of the genome may have been mediated by biogeographical and demographic effects.