Browsing by Author "Opell, Brent D."
Now showing 1 - 20 of 32
Results Per Page
Sort Options
- Adhesive contact and protein elastic modulus tune orb weaving spider glue droplet biomechanics to habitat humidityOpell, Brent D.; Elmore, Hannah Mae; Hendricks, Mary L. (Elsevier, 2022-10)Tiny glue droplets along the viscous capture threads of spider orb webs prevent insects from escap-ing. Each droplet is formed of a protein core surrounded by a hygroscopic aqueous layer, which cause the droplet's adhesion to change with humidity. As an insect struggles to escape the web, a thread's viscoelastic core proteins extend, transferring adhesive forces to the thread's support fibers. Maximum adhesive force is achieved when absorbed atmospheric moisture allows a flattened droplet to establish sufficient adhesive contact while maintaining the core protein cohesion necessary for force transfer. We examined the relationship between these droplet properties and adhesive force and the work of extend-ing droplets at five relative humidities in twelve species that occupy habitats which have different hu-midities. A regression analysis that included both flattened droplet area and core protein elastic modulus described droplet adhesion, but the model was degraded when core protein area was substituted for droplet. Species from low humidity habitats expressed greater adhesion at lower humidities, whereas species from high humidity habitats expressed greater adhesion at high humidities. Our results suggest a general model of droplet adhesion with two adhesion peaks, one for low humidity species, which occurs when increasing droplet area and decreasing protein cohesion intersect, and another for high humidity species, which occurs when area and cohesion have diverged maximally. These dual peaks in adhesive force explain why some species from intermediate and high humidity habitats express high adhesion at several humidities.Statement of significanceWe characterized the effect of humidity on the adhesion of twelve orb weaving spider species' glue droplets and showed how humidity-mediated changes in the contact area of a droplet's outer, hygro-scopic aqueous layer and the stiffness of its protein core affect droplet performance. This revealed how droplet adhesion has been tuned to the humidity of a species' habitat and allowed us to revise a model that describes the environmental determinants of droplet biomechanics.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )
- Around the World in Eight Million Years: Historical Biogeography and Evolution of the Spray Zone Spider Amaurobioides (Araneae: Anyphaenidae)Sara Ceccarelli, F.; Opell, Brent D.; Haddad, Charles R.; Raven, Robert J.; Soto, Eduardo M.; Ramirez, Martin J. (PLOS, 2016-10-12)Closely related organisms with transoceanic distributions have long been the focus of historical biogeography, prompting the question of whether long-distance dispersal, or tectonic-driven vicariance shaped their current distribution. Regarding the Southern Hemisphere continents, this question deals with the break-up of the Gondwanan landmass, which has also affected global wind and oceanic current patterns since the Miocene. With the advent of phylogenetic node age estimation and parametric bioinformatic advances, researchers have been able to disentangle historical evolutionary processes of taxa with greater accuracy. In this study, we used the coastal spider genus Amaurobioides to investigate the historical biogeographical and evolutionary processes that shaped the modern-day distribution of species of this exceptional genus of spiders. As the only genus of the subfamily Amaurobioidinae found on three Southern Hemisphere continents, its distribution is well-suited to study in the context of Gondwanic vicariance versus long-distance, transoceanic dispersal. Ancestral species of the genus Amaurobioides appear to have undergone several long-distance dispersal events followed by successful establishments and speciation, starting from the mid-Miocene through to the Pleistocene. The most recent common ancestor of all present-day Amaurobioides species is estimated to have originated in Africa after arriving from South America during the Miocene. From Africa the subsequent dispersals are likely to have taken place predominantly in an eastward direction. The long-distance dispersal events by Amaurobioides mostly involved transoceanic crossings, which we propose occurred by rafting, aided by the Antarctic Circumpolar Current and the West Wind Drift.
- Biodiversity, conservation and mimicry rings of Appalachian millipedesMeans, Jackson C. (Virginia Tech, 2019-01-18)The Appalachian Mountains contain some of the highest millipede diversity on the planet, including many endemic and range-restricted species. Millipedes have extremely low dispersal capacity, strict environmental requirements for survival and, in the case of the family Xystodesmidae, are completely blind. Coupled with the complex topology of the Appalachians, xystodesmid millipedes have speciated in the eastern United States to a greater degree than in any other region. Many of the taxonomic relationships within the Xystodesmidae remain to be tested using modern molecular techniques, and numerous species await description. The subtribe Nannariina, for example, contains 3 genera and 19 species, yet evidence suggests the tribe may actually contain over 100 species. Traditional taxonomic work has been hindered by a paucity of researchers in the field, and a necessary reliance on morphological characters for species delimitation. The external male genitalia, known as gonopods, are the structures which have most often been used to define species boundaries. However, in many groups, including the Xystodesmidae, the gonopods are extremely simple, making it difficult to discern whether similarity between gonopods is a result of shared ancestry or morphological convergence. Further complicating matters, somatic characters are often uniform between species, and some obvious phenotypes, such as color pattern and hue, are shared between genera in aposematic mimicry rings. Leading to the formation of mimicry rings between distantly related genera, their bright coloration functions to advertise a cyanide-based defense. Some species have been recorded as having six color patterns, each a member of a different mimicry rings. The factors which drive some taxa to participate in mimicry rings, while others have a myriad of hues and patterns, unmatched by other species, are unknown. Here I investigate the phylogenetic relationships between the tribes and genera of the Xystodesmidae, with the aims of (1) understanding the role of homoplasy within the Xystodesmidae, (2) delineating tribal and generic boundaries within the family, (3) describing species in the genus Nannaria for the purposes of revising the subtribe Nannariina, and (4) investigating mimicry and color variability through a detailed color atlas for North American Xystodesmidae. I found that 95% of the morphological characters traditionally used in xystodesmid taxonomy are homoplasious (HI > 0.5), delineated the Apheloriini, Appalachioria and Sigmoria, described 34 new Nannaria species, and created a color and mimicry dataset of 956 Xystodesmidae for use in future studies of color variability.
- A biosystematic revision of the Nearctic species of the mayfly genus Isonychia (Ephemeroptera: oligoneuriidae)Kondratieff, B. C. (Virginia Polytechnic Institute and State University, 1982)The Nearctic species of the genus Isonychia Eaton are revised. Eighteen species are recognized, of which three are described as new; eleven species names are placed in synonymy. Isonychia campestris McDunough is recognized as a fully valid geographically restricted species. Two subgenera, Isonychia sensu stricto and Prionoides Kondratieff and Voshell are recognized on the basis of adult and nymphal characteristics. Isonychia s.s. includes four species groups: bicolor group with four species, arida group with one species, sicca group containing five species, and diversa group with one species. The subgenus Prionoides includes seven species. A Neotype is designated for l. arida (Say). Previously undescribed characters of the nymphal gills are described and illustrated. The male genitalia and eggs are illustrated for every species. The distribution of each species is mapped. Diagnostic keys to male adults and nymphs are presented. A discussion of the nomenclatural history of the genus and each species is included. Diagnostic characters, rearing and collecting techniques are also discussed. The life histories and life cycles of two populations of Isonychia (Isonychia) bicolor (Walker) and one population of Isonychia (Prionoides) obscura Traver are presented in detail. Many features used in the past as specific criteria, especially in the bicolor and sicca Groups are found to be related to developmental periods of given populations involving geography, elevation, water temperature and stream size. The life cycle of I. bicolor is probably bivoltine at both sites. At the trout stream site there is a large-sized spring emerging generation and a much smaller summer emerging generation with considerable overlap. Isonychia obscura Traver is univoltine with adult emergence in mid-June and with egg diapause during the summer months. Additional life history information is also presented for I. (l.) tusculanensis Berner and I. (P.) serrata Traver. The evolution of the genus Isonychia and the two subgenera l. (Isonychia) and I. (Prionoides) is hypothesized. The North American biogeography of Isonychia may have included an invasion of North America via the "asiamerican" land mass of the Cretaceous. The early Isonychia mayflies may have been adapted to low order cool streams of high elevations. This lineage was probably similar to the subgenus Prionoides. Isonychia s.s. has been successful in colonizing the upper and lower austral zones and appears to be a warm water adapted group.
- Characterizing the Role of Magnetic Cues Underlying Spatial BehaviorPainter, Michael Scott (Virginia Tech, 2017-01-09)In the 50+ years since the discovery of magnetic compass orientation by migratory songbirds, evidence for the use of magnetic cues has been obtained for a range of taxonomic groups, including several classes of vertebrate and invertebrate taxa. Surprisingly, however, the biophysical mechanisms and biological substrate that underlie magnetic sensing are still not fully understood. Moreover, while use of magnetic cues for compass orientation is intuitive, the functional significance of other forms of behavioral responses mediated by magnetic cues, such as spontaneous magnetic alignment, is less clear. The following research was carried out to investigate the mechanisms underlying magnetic orientation in vertebrates and invertebrates. This involved the modification of existing experimental systems to characterize responses to magnetic cues in laboratory animals (flies, mice) and the development of novel techniques for studying the role of magnetic cues in the spatial behavior of free-living animals (red foxes). Chapter II examines magnetic orientation in wild-type Drosophila melanogaster larvae. We show that three strains of larvae reared under non-directional ultraviolet (UV) light exhibit quadramodal spontaneous orientation along the anti-cardinal compass directions (i.e. northeast, southeast, southwest, northwest) when tested in a radially symmetrical environment under UV light. Double-blind experiments cancelling the horizontal component of the magnetic field confirmed that the response is dependent on magnetic cues rather non-magnetic features of the test environment. Furthermore, we argue that the larval quadramodal pattern of response is consistent with properties of magnetic compass orientation observed in previous studies of adult Drosophila and laboratory mice, both of which have been proposed to be mediated by a light-dependent magnetic compass mechanism. Chapter III explores the use of novel biologging techniques to collect behavioral and spatial data from free-roaming mammals. Specifically, a previous observational study of free- roaming red foxes found a 4-fold increase in the success of predatory 'mousing' attacks when foxes were facing ~north-northeast, consistent with magnetic alignment responses reported for a range of terrestrial animals. The authors propose that the magnetic field may be used to increase accuracy of mousing attacks. Using tri-axial accelerometer and magnetometer bio-loggers fitted to semi-domesticated red foxes, we created ']magnetic ethograms' from behavioral and magnetic machine learning algorithms 'trained'] to identify three discrete behaviors (i.e. foraging, trotting, and mousing-like jumps) from raw accelerometer signatures and to classify the magnetic headings of mousing-like jumps into 45° sectors from raw magnetometer data. The classifier's ability to accurately identify behaviors from a separate fox not used to train the algorithm suggests that these techniques can be used in future experiments to obtain reliable magnetic ethograms for free-roaming foxes. We also developed the first radio-frequency emitting collar that broadcasts in the low MHz frequency range shown to disrupt magnetic compass responses in a host of animals. The radio-frequency collars coupled with biologgers will provide a powerful tool to characterize magnetic alignment responses in predatory red foxes and can be adapted for use in studies of magnetic alignment and magnetic compass orientation in other free-roaming mammals. Chapter 3 discusses findings from a magnetic nest building assay involving male labratory mice. Mice trained to position nests in one of four directions relative to the magnetic field exhibited both learned magnetic compass responses and fixed magnetic nest positioning orientation consistent with northeast-southwest spontaneous magnetic alignment behavior previously reported for wild mice and bank voles. This is the first mammalian assay in which both learned magnetic compass orientation and spontaneous magnetic alignment were exhibited in the same species, and suggests that the use of magnetic cues in rodents may be more flexible that previously realized.
- Comparisons of Secondary Production, Life History, and Mouthpart Functional Morphology Between Two Populations of the Amphipod Gammarus minusHaley, Carol J. (Virginia Tech, 1997-01-21)In this study, features of ecology, behavior, and functional morphology related to feeding activity of two populations of the amphipod Gammarus minus were compared. The two populations occupied different habitats, and I attempted to determine whether differences observed between the two populations were related to habitat. Annual production and life history of the populations were compared and their relationship to factors such as temperature, water-chemistry, and quantity of available organic matter were examined. Mouthpart and foregut morphology were compared between the two populations and between immature and mature amphipods with light and scanning electron microscopy. Measurements of structure were analyzed by linear regression. A behavioral study, comparing feeding of immature and mature G. minus, was conducted in the laboratory. Annual production of G. minus occupying a habitat characterized by the presence of watercress, gravel substrate, and constant temperature (Site 1) was 3.9 g/m² (95% C.I.: 3.2- 4.5), while that in the habitat characterized by leaf detritus and fluctuating temperatures (Site 2) was 1.8 g/m² (95% C.I.: 1.6-2.1). Breeding occurred throughout the year at Site 1, but there was a yearly cycle at Site 2. The greatest numbers of the smallest size classes of amphipod were present at Site 2 when the quantity of ash-free dry mass (AFDM) of wood and bark was greater than AFDM of leaf detritus. Of nine mouthpart and foregut structures studied, three, the number of cuspidate setae on outer plates of maxillipeds, the length of the dactyl on maxilliped palps, and the number of hook setae on the foregut ampullae, were found to be correlated with body length. Of these, rates of increase in maxilliped setae numbers and hook setae numbers were greater for immature than mature animals, and the number of hook setae for a given sized animal was generally greater for animals at Site 1 than Site 2. Animals presented with ground-up leaf material in the laboratory exhibited twenty-one recognizable behaviors. The frequencies of six behaviors were found to be statistically different between immature and mature animals. The differences suggest that immatures may prefer a food type or size other than that provided in the experiment.
- Constraints on the adhesion of viscous threads spun by orb-weaving spiders: the tensile strength of glycoprotein glue exceeds its adhesionOpell, Brent D.; Schwend, Harold S.; Vito, Stephen T. (Company of Biologists Ltd., 2011-07)In this study we tested the hypothesis that a viscous thread releases its hold on a surface because its glycoprotein glue pulls from the surface and not because its elongating droplets break near their attachment to the surface. We compared the values obtained when three species' viscous threads adhered to four smooth surfaces, which differed in their total surface energy and in the proportions of their dispersion and polar energy components. Although water comprised 43-70% of the volume of these viscous droplets, only the dispersion surface energies of test materials and not their polar surface energies impacted thread adhesion. These results support the droplet pull-off hypothesis and are consistent with a previous finding that capillary force contributes little to thread adhesion. Just as a viscous thread's stickiness is constrained by the tensile strength of its supporting axial fibers, our findings suggest that glycoprotein adhesion is constrained by glycoprotein tensile strength.
- Elastic modulus and toughness of orb spider glycoprotein glueOpell, Brent D.; Clouse, Mary E.; Andrews, Sheree F. (PLOS, 2018-05-30)An orb web's prey capture thread features tiny glue droplets, each formed of an adhesive glycoprotein core surrounded by an aqueous layer. Small molecules in the aqueous layer confer droplet hygroscopicity and maintain glycoprotein viscoelasticity, causing droplet volume and glycoprotein performance to track changes in environmental humidity. Droplet extension combines with that of a thread's supporting flagelliform fibers to sum the adhesive forces of multiple droplets, creating an effective adhesive system. We combined measurements of the force on an extending droplet, as gauged by the deflection of its support line, with measurements of glycoprotein volume and droplet extension to determine the Young's modulus (E) and toughness of three species' glycoproteins. We did this at five relative humidities between 20 - 90% to assess the effect of humidity on these properties. When droplets of a thread span extend, their extensions are constrained and their glycoprotein filaments remain covered by aqueous material. This was also the case during the first extension phase of the individual droplets that we examined. However, as extension progressed, the aqueous layer was progresses disrupted, exposing the glycoprotein. During the first extension phase E ranged from 0.00003 GPa, a value similar to that of fibronectin, a glycoprotein that anchors cells in the extracellular matrix, to 0.00292 GPa, a value similar to that of resilin in insect ligaments. Second phase E increased 4.7 - 19.4-fold. When compared at the same humidity the E of each species' glycoprotein was less than 5% of the value reported for its flagelliform fibers. This difference may facilitate the coordinated extension of these two capture thread components that is responsible for summing the thread's adhesive forces.
- Environmental response and adaptation of glycoprotein glue within the droplets of viscous prey capture threads from araneoid spider orb-websOpell, Brent D.; Karinshak, Shannon E.; Sigler, Mary A. (Company of Biologists Ltd., 2013-08)Viscous threads that form the prey capture spiral of araneoid orb-webs retain insects that strike the web, giving a spider more time to locate and subdue them. The viscoelastic glycoprotein glue responsible for this adhesion forms the core of regularly spaced aqueous droplets, which are supported by protein axial fibers. Glycoprotein extensibility both facilitates the recruitment of adhesion from multiple droplets and dissipates the energy generated by insects struggling to free themselves from the web. Compounds in the aqueous material make the droplets hygroscopic, causing an increase in both droplet volume and extensibility as humidity ( RH) rises. We characterized these humidity-mediated responses at 20%, 37%, 55%, 72% and 90% RH in two large orbweavers, Argiope aurantia, which is found in exposed habitats, and Neoscona crucifera, which occupies forests and forest edges. The volume-specific extension of A. aurantia glycoprotein reached a maximum value at 55% RH and then declined, whereas that of N. crucifera increased exponentially through the RH range. As RH increased, the relative stress on droplet filaments at maximum extension, as gauged by axial line deflection, decreased in a linear fashion in A. aurantia, but in N. crucifer increased logarithmically, indicating that N. crucifera threads are better equipped to dissipate energy through droplet elongation. The greater hygroscopicity of A. aurantia threads equips them to function in lower RH environments and during the afternoon when RH drops, but their performance is diminished during the high RH of the morning hours. In contrast, the lower hygroscopicity of N. crucifera threads optimizes their performance for intermediate and high RH environments and during the night and morning. These interspecific differences support the hypothesis that viscous capture threads are adapted to the humidity regime of an orbweavers habitat.
- Evaluation of hybridization among three Laricobius species, predators of hemlock woolly adelgid, (Adelgidae)Fischer, Melissa J. (Virginia Tech, 2013-10-02)Hybridization was evaluated among three Laricobius spp. involved in the biological control of hemlock woolly adelgid (Adelges tsugae Annand). Following lab mating studies, there was no evidence that Laricobius osakensis Montgomery and Yu could produce hybrid progeny with either Laricobius nigrinus Fender or Laricobius rubidus LeConte. Interaction between L. osakensis and L. nigrinus did not result in a lower production of progeny as a result of fitness costs associated with interspecific mating attempts. Laricobius nigrinus and L. rubidus hybrids were produced in the lab and collected in the field. Hybrid progeny showed very little evidence of decreased fitness. For example, there was no significant difference in the number of days it took for hybrids and pure parental species to develop from egg hatch to the prepupal stage, there was no difference among hybrids and pure parental species in the head capsule widths and larval lengths for the first through third instar, and there was evidence of an F2 generation from field collected specimens. Hybrids produced in the lab had intermediate shaped genital paramere angles compared with parental species, and had elytra coloration similar to that of L. rubidus. Hybrids showed no host preference in the lab, but a preference for Adelges tsugae in the field. Of 12 site factors examined, only the number of years that L. nigrinus was present at the site was found to be associated with percent hybrids. Contamination of the L. osakensis colony with Laricobius naganoensis Leschen resulted in the need to develop molecular methods to differentiate L. osakensis from L. naganoensis. Three restriction enzymes were found that correctly differentiated the two species.
- Evolutionary history of the canary grasses (Phalaris, Poaceae)Voshell, Stephanie (Virginia Tech, 2014-06-12)Canary grasses (Phalaris, Poaceae) include 21 species widely distributed throughout temperate and subtropical regions of the world with centers of diversity in the Mediterranean Basin and western North America. The genus contains annual/perennial, endemic/cosmopolitan, wild, and invasive species with basic numbers of x=6 (diploid) and x=7 (diploid/tetraploid/hexaploid). The latter display vastly greater speciation and geographic distribution. These attributes make Phalaris an ideal platform to study species diversification, dispersal, historic hybridization, polyploidy events, and chromosome evolution in the grasses. This body of research presents the first molecular phylogenetic and phylogeographic reconstruction of the genus based on the nuclear ITS and plastid trnT-F DNA regions allowing species relationships and the importance of polyploidy in speciation to be assessed. Divergence dates for the genus were determined using Bayesian methods (BEAST, version 1.6.2) and historic patterns of dispersal were analyzed with RASP (version 2.1b). Self-incompatibility and the feasibility of hybridization between major groups within the genus were studied with a series of greenhouse experiments. Acetocarmine and fluorescent staining techniques were used to study the morphology of the chromosomes in a phylogenetic context and the nuclear DNA content (C values) was quantified using flow cytometry. Four major clades were revealed in the genus with cytological and geographic affinities leading to the establishment of two subgenera and four sections in the first comprehensive infrageneric treatment of Phalaris. Divergence dating revealed a Miocene emergence (20.6-8.4 MYA) for the genus which is concurrent with studies of other genera in the Aveneae tribe. The hypothesis stating that Phalaris originated in the Mediterranean Basin and dispersed to the New World via a western route leading to a secondary center of diversification in western North America was supported by phylogeographic and cytological analyses. An empirical study comparing the weight, length, and width of the florets by morphological type and cytotype revealed significant differences that support a dispersal advantage among the New World and Arundinacea species. The x=6 species displayed greater intraspecific C value variation, higher DNA content per haploid chromosome set, and a distinct karyotype compared with the x=7 species indicating a complex history of chromosome evolution.
- Genic identity and differentiation of Ilyodon (Cyprinodontoidea: goodeidae): morphological polymorphism and chromosomal divergenceGrudzien, Thaddeus A. (Virginia Polytechnic Institute and State University, 1983)Certain populations of the goodeid fish genus Ilyodon occur as bimodal assemblages of broad and narrow-mouthed individuals which have been regarded as sympatric species. Allozyme surveys of four bimodal populations indicated no significant differences in allele frequencies between the presumed species in seven to fifteen polymorphic loci, but substantial interpopulation genic differentiation. These results suggested regular gene flow between the supposed species at each of four independent localities and conspecificity of two mouth width morphs. Progeny of field inseminated females yielded some offspring with morphs opposite to those of their mother and some progeny of laboratory crosses were of morphs different from their parents. The analysis of Ilyodon broods conclusively proved that the two presumed species were conspecific and displayed a morphological polymorphism in mouth width. Variation in the number of metacentric chromosomes has been reported for populations of Ilyodon along the length of the Rio Coahuayana. Allozyme analyses of fifteen populations including three of the known cytotypes showed that the chromosomally diverse populations of the Rio Coahuayana were half as genetically diverse as chromosomally non-divergent populations from the adjacent Rio Armeria. Evolutionary events which fixed the various cytotypes did not produce detectable differences in either levels of polymorphic loci or average heterozygosity. Genetic similarity indices produced phenograms of genetic relationships which clustered different cytotypes together; chromosomal variation and allozymic differentiation are uncoupled processes in Ilyodon.
- Humidity affects the extensibility of an orb-weaving spider's viscous thread dropletsOpell, Brent D.; Karinshak, Shannon E.; Sigler, Mary A. (Company of Biologists Ltd., 2011-09)The prey-capture threads found in most spider orb webs rely on viscous droplets for their stickiness. Each droplet is formed of a central mass of viscoelastic glycoprotein glue surrounded by an aqueous covering, both of which incorporate hydrophilic components. We found that the extensibility of droplets on Larinioides cornutus threads increased as humidity increased. However, the deflection of the droplets' supporting axial lines did not change, indicating that atmospheric water uptake increases glycoprotein plasticity, but not glycoprotein adhesion. The extensibility of droplets, along with that of the thread's supporting axial fibers, is responsible for summing the adhesion of multiple thread droplets. Therefore, daily changes in humidity have the potential to significantly alter the performance of viscous threads and orb webs.
- An investigation of the stickinness mechanism and the role of nodes in cribellar spider capture threadCampbell-Hawthorn, Anya (Virginia Tech, 2002-10-04)Sticky prey capture threads are produced by many members of the spider Infraorder Araneomorphae. Cribellar threads are plesiomorphic for this clade, and adhesive threads are apomorphic. The surface of cribellar thread is formed of thousands of fine fibrils. Basal araneomorphs produce cylindrical fibrils, whereas more derived members produce fibrils with nodes. Cribellar fibrils snag and hold rough surfaces, but other forces are required to explain their adherence to smooth surfaces. Threads of Hypochilus pococki (Hypochilidae) that are formed of non-noded fibrils hold to a smooth acetate surface with the same force under low and high humidities. In contrast, threads of Hyptiotes cavatus and Uloborus glomosus (Uloboridae) that are formed of noded fibrils hold with greater forces to the same surface at intermediate and high humidities. Threads spun by eight species representing seven genera and four families with noded fibrils absorb water, while that of two families, represented by one species each with smooth fibrils, repel water, indicating increase hygroscopisity associated with the presence of nodes. Additionally, equations describing van der Waals and hygroscopic forces can predict the observed stickiness of these threads. This model supports the hypothesis that van der Waals forces allow non-noded cribellar fibrils to adhere to smooth surfaces, whereas noded fibrils employ van der Waals forces at low humidities and add hygroscopic forces at higher humidities. Thus, there appear to have been two major events in the evolution of spider prey capture thread: the addition of hydrophilic nodes to the fibrils of cribellar threads and the replacement of cribellar fibrils by glycoprotein glue.
- Morphology, Molecular Phylogeny and Genome content of Bothriochloa focusing on Australian taxaSumadijaya, Alex (Virginia Tech, 2015-06-19)The study focuses on the genus Bothriochloa (Andropogoneae, Poaceae) in Australia. Despite morphological features separating this genus from the closely related two genera Capillipedium and Dichanthium, (the three hereafter will be called BCD), De Wet and Harlan introduced the compilospecies complex to show the interbreeding phenomena that occurred among species of these genera. This study was carried out to assess species/genus relatedness of the BCD complex using different evidences from morphology, molecular information and genomic content. Nineteen morphological characters were observed, three regions (trnT-F, rps16 intron and 3'trnK) of chloroplast genome phylogenetic were used in phylogenetic reconstruction, and chromosome counting as well as flow cytometry for chromosome number and genome size were conducted during the study. Phylogenetic trees were constructed using MP with NJ for morphological data, and MP, RAxML, and BI for molecular data. Based on morphology, all three genera were separated as monophyletic units. Bothriochloa consisted of two clades. However, phylogenetic analyses based on chloroplast genomic regions reveal that Bothriochloa and Dichanthium are paraphyletic clades and only Capillipedium is resolved as a monophyletic clade. The concatenated data set has performed better than individual data sets in terms of resolution and support for clades. Flow-cytometry and chromosome counting only found diploid and tetraploid but not hexaplod species. TCS network reveals that tetraploidization followed different pathways from the ancestral diploid species. This study provided new insight onto the evolution of the chloroplast genome in the compilospecies and empirical evidence of species grouping of the compilospecies based on morphology.
- The Mouse Magnetic CompassArnold, Tessa Jean (Virginia Tech, 2015-06-26)All five classes of vertebrates use the geomagnetic field for spatial orientation. The geomagnetic field can be used to derive both 'map' and 'compass' information. There is evidence for two different mechanisms used to sense the magnetic field, the radical pair mechanism (RPM) and the magnetite based mechanism (MBM). C57BL/6 laboratory mice can rely on directional information from the magnetic field to position their nests and to solve a water maze task. The primary objective of this research was to characterize the magnetic compass of C57BL/6 laboratory mice in the plus water maze task. These experiments explored sources of variation in magnetic responses and investigated the underlying magnetic compass orientation mechanism in C57BL/6 mice. The results provide evidence that the mouse magnetic compass is sensitive to low-level radiofrequency fields, consistent with the use of the RPM for magnetic orientation. Surprisingly, the results also suggest that C57BL/6 mice have a polarity sensitive compass, consistent with the use of a MBM for magnetic orientation. These experiments confirm that mice have a specialized magnetic compass sense. Furthermore, despite the controlled environment in which these laboratory experiments were conducted, a variety of factors can increase the variability in the response. Future experiments are needed to further characterize the mouse magnetic compass, as there is a possibility of a hybrid magnetic response where both magnetoreception mechanisms could be used for spatial orientation.
- Natural history, taxonomy, and phylogenetics of Appalachian flat-backed millipedes (Diplopoda: Polydesmida)Hennen, Derek Alan (Virginia Tech, 2020-04-29)Millipedes (class Diplopoda) are ubiquitous in forests worldwide, with about 12,000 described species and an estimated 30,000 undescribed species. The most species-rich order is the Polydesmida, the flat-backed millipedes, which encompasses about 3,500 species. Appalachia has an abundance of Polydesmida, and is a biodiversity hotspot for millipedes in the family Xystodesmidae. These diplopods are chemically defended with hydrogen cyanide and benzaldehyde, and sometimes form mimicry rings based on shared color. The evolutionary dynamics of model and mimic are incompletely known in these rings, so I investigated a mimicry ring in the central Appalachian Mountains to determine if the species Apheloria polychroma functions as a model for the genus Brachoria. I measured the size of the chemical gland to assess toxicity in 15 species, and reconstructed the ancestral dimensions of the gland to determine the direction of volume change over evolutionary time. Using a molecular phylogeny, I traced the miniaturization of chemical glands in the mimic genus Brachoria and found that in areas without Apheloria, Brachoria and related xystodesmids have larger chemical glands. Non-aposematic millipedes of the genus Nannaria have significantly smaller glands, and ostensibly rely on camouflage to avoid predation. This genus is known as the twisted claw millipedes and occur throughout eastern North America, but have their center of diversity in the Appalachian Mountains. About 22 species are described, but many undescribed species are known. To determine the diversity of this group, field collection and examination of museum specimens took place from 2015-2020. Examination of morphology, combined with molecular phylogenetics, revealed two distinct clades in the genus. One is distributed throughout the eastern United States, while the other is found only in the Appalachian Mountains. This Appalachian clade contains six described species, and I describe an additional 18 species, quadrupling the diversity of the group. Additionally, the phylogenetics of the polydesmid genus Pseudopolydesmus is investigated in an integrative taxonomic framework using five genes. I find that the genus is monophyletic, contains 8 species, and are related to one another in a hierarchical way according to a molecular phylogeny. I provide complete distributional records and live photographs of each species.
- Orb weaver aggregate glue protein composition as a mechanism for rapid evolution of material propertiesAyoub, Nadia A.; DuMez, Lucas; Lazo, Cooper; Luzaran, Maria; Magoti, Jamal; Morris, Sarah A.; Baker, Richard H.; Clarke, Thomas; Correa-Garhwal, Sandra M.; Hayashi, Cheryl Y.; Friend, Kyle; Opell, Brent D. (Frontiers, 2023-04)Introduction: Orb web and cobweb weaving spiders in the superfamily Araneoidea are distinguished by their ability to make a chemically sticky aqueous glue in specialized aggregate silk glands. Aggregate glue is an environmentally responsive material that has evolved to perform optimally around the humidity at which a spider forages. Protein components and their post-translational modifications confer stickiness to the glue, but the identities of these proteins have not been described for orb web weavers. Methods: Using biomechanics, gene expression data, and proteomics, we characterized the glue's physical properties and molecular components in two congeners that live in different environments, Argiope argentata (dry southwest US) and Argiope trifasciata (humid southeast US). Results: The droplets of A. argentata are less hygroscopic than those of A. trifasciata and have proportionately smaller viscoelastic protein cores, which incorporate a smaller percentage of absorbed water as humidity increases. Argiope argentata protein cores were many times stiffer and tougher than A. trifasciata protein cores. Each species' glue included similar to 30 aggregate-expressed proteins, most of which were homologous between the two species, with high sequence identity. However, the relative contribution and number of gene family members of each homologous group differed. For instance, the aggregate spidroins (AgSp1 and AgSp2) accounted for nearly half of the detected glue composition in A. argentata, but only 38% in A. trifasciata. Additionally, AgSp1, which has highly negatively charged regions, was similar to 2X as abundant as the positively charged AgSp2 in A. argentata, but similar to 3X as abundant in A. trifasciata. As another example, A. argentata glue included 11 members of a newly discovered cysteine-rich gene family, versus 7 members in A. trifasciata. Discussion: Cysteines form disulfide bonds that, combined with the higher potential for electrostatic interactions between AgSp1 and AgSp2, could contribute to the greater stiffness of A. argentata glue. The ability to selectively express different glue protein genes and/or to extrude their products at different rates provides a faster mechanism to evolve material properties than sequence evolution alone.
- Orb weaver capture thread biomechanics and evolutionKelly, Sean D. (Virginia Tech, 2020-07-07)Orb weavers intercept insects using non-hardening bioadhesive droplets, supported by two flagelliform fibers. Droplets contain an adhesive glycoprotein core and aqueous layer that confers hygroscopicity. The first study investigates the durability of these droplets to cycling, or repeatedly adhering, extending, and pulling off. Droplets of four species proved resilient, cycling 40 times. Cycling, coupled with droplet humidity responsiveness, qualifies them as smart materials. However, thread adhesion is complex, relying on an integrated performance of multiple droplets and the flagelliform fibers. As insects struggle, the flagelliform fibers bow and the droplets extend, forming a suspension bridge configuration whose biomechanics sum the adhesion of droplets and dissipate the energy of struggling insects. Given this performance, the second study predicts that the material properties of both thread components have evolved in a complementary way. Comparative phylogenetics of 14 study species revealed that their elastic moduli are correlated, with glycoproteins being six times more elastic than flagelliform fibers. Spider mass affects the amount of each material, but not their properties. Since glycoprotein performance changes with humidity, we hypothesized that orb weavers generate greater adhesion at their foraging humidity. After delimiting low and high humidity species groups (eight and six species, respectively), bridge force was determined as total contributing droplet adhesion at three humidities. Only three spiders generated greater adhesion outside of their foraging humidity. The distribution of force along a suspension bridge differed from a previously reported pattern. We also characterize the sheet configuration, which generates force similar to suspension bridges.
- Phylogenetic Analysis of the Genus Pistacia (Anacardiaceae)AL-Saghir, Mohannad Ghazi (Virginia Tech, 2006-06-15)Pistacia is an economically important genus because it contains the pistachio crop, P. vera, which has edible seeds of considerable commercial importance. The evolutionary history of the genus and the taxonomic relationships among the species are controversial and not well understood. This study that has been conducted on this genus to refine taxonomic and evolutionary relationship utilizing different types of data (including morphology, anatomy and molecular) The studied species were the following: Pistacia aethiopica J. O. Kokwaro, P. atlantica Desf., P. chinensis Bunge, P. eurycarpa Yaltirik, P. falcata Becc. ex Martelli, P. integerrima Stew. ex Brand., P. khinjuk Stocks, P. lentiscus L., P. mexicana HBK, P. mutica Fisch. & Mey., P. palaestina Boiss., P. terebinthus L., P. texana Swingle, P. vera L., and P. weinmannifolia Poiss. ex Franch. Phylogenetic analysis based on morphological data strongly supported the monophyly of Pistacia. The genus divided into two monophyletic groups. One group (Section Pistacia) contains P. atlantica, P. chinensis, P. eurycarpa, P. falcata, P. integerrima, P. khinjuk, P. mutica, P. palaestina, P. terebinthus, and P. vera while the other group (Section Lentiscus) contains P. aethiopica, P. lentiscus, P. mexicana, P. texana, and P. weinmannifolia. In anatomical analysis, all species had anomocytic stomata. In most species, the stomata density was higher on the abaxial surface than the adaxial. The ratio of abaxial to adaxial stomatal density varied from 0.0 to 1.7. Stomatal distribution may provide insights into how Pistacia species evolve in terms of leaf anatomy and respond to different climatic changes. Stomatal distribution changed (losing stomata on either surface) as the genus moved into regions of higher rainfall. This study revealed leaflets of P. vera, which have random orientation, were isobilateral, while leaflets of the other species were dorsiventral and were oriented horizontally. RAPD analysis showed that P. khinjuk and P. vera are very close species. This study provides more insights into understanding the evolution, taxonomy and genetics of this economically important genus.