Nitrogen metabolism in cultured cotyledon explants of Pinus radiata during de novo organogenesis

Nitrogen metabolism was investigated under shoot-forming (SF) and non-shoot-forming (NSF) conditions in cultured cotyledon explants of Pinus radiata by following the incorporation of [¹⁴C]-l,2-acetate into various metabolites. Early in culture, the lipid fraction contained the most ¹⁴C; however, this percentage decreased in favor of increased label in the amphoteric fraction. Label in the amphoteric fraction of SF cultures decreased by day 21 but plateaued in NSF cultures at this time. Radioactive labeling of the principle nitrogen metabolites, glutamate and glutamine, which made up the majority of the amphoteric fraction, paralleled labeling patterns in the amphoteric fraction. Percentage label in glutamate remained at similar levels throughout the 21-day culture period for both SF and NSF cultures. Specific activity of glutamate (kBq mg^-1) was significantly greater during promeristemoid formation in SF compared to that in NSF tissues. Glutamine labeling increased during shoot bud initiation in SF cultures, but dropped to lower levels during shoot bud development. In contrast, in NSF cultures, there was a continual and substantial increase in glutamine labeling throughout the 21-day culture period. These trends were similar when the specific activities of glutamine were determined, as there was a continual decrease from culture initiation to the end of shoot bud differentiation in SF cultures. In NSF cultures, in contrast, specific activity of glutamine increased substantially from day 5 to 21 relative to that in SF cultures. The nitrogen assimilation enzymes glutamate synthase and glutamine synthase increased in activity from day 0 to 21 for both SF and NSF tissues. Enzyme activities for glutamate dehydrogenase were similar in both treatments to day 10 in culture but subsequently diverged, with activities in NSF cultures being substantially greater than those of SF cultures by day 21. Taken together, labeling and enzyme data indicate that nitrogen metabolism is enhanced during culture, especially in SF tissues at the time of promeristemoid formation, and in non-organ-forming tissue senescence-like metabolism was exhibited later in culture.     

Seasonally Variable Eusocially Selected Traits in the Paper Wasp, Mischocyttarus mexicanus

The expression of alternative traits that benefit eusocial individuals but are not directly involved in reproductive differences among those individuals, which I call ‘eusocially selected traits’, may vary in response to environmental changes if this increases an individual's inclusive fitness. In this study, I describe traits that separate individuals within the reproductive division of labor of Mischocyttarus mexicanus, a eusocial paper wasp, and determine whether observed eusocially selected traits vary across seasons. I examined M. mexicanus because females initiate new nests throughout most of the year where they experience different conditions depending on the season. Findings from this study suggest two main conclusions: (1) phenotypic differences among M. mexicanus females are mixed, showing specialized, generalized, and context‐dependent eusocially selected traits and (2) a female's position within the reproductive division of labor may be influenced by its state. The presence of context‐dependent traits, e.g. large females initiated solitary nests in the spring and grouped nests during the summer, suggests that the payoff for pursuing different positions within the reproductive division of labor changes across seasons. The expression of context‐dependent eusocially selected traits also suggests that, roles, instead of castes, may better reflect the reproductive division of labor among individuals of eusocial species like M. mexicanus.     

First Early Jurassic Ornithischian and theropod footprint assemblage and a new ichnotaxon Shenmuichnus wangi ichnosp. nov. from Yunnan Province,southwestern China

The new ichnospecies, Shenmuichnus wangi ichnosp. nov., is the first evidence for the presence of large ornithischians in the Early Jurassic of Yunnan Province, whereas the known skeletal record documents small species only. Until now Shenmuichnus was known from a single locality in Shaanxi Province by the ichnospecies Shenmuichnus youngteilhardorum. Compared with the latter, Shenmuichnus wangi is larger and shows a different trackway configuration, particularly in the relative position of manus and pes imprints. Palecologically, the occurrence of Shenmuichnus wangi in a red bed facies indicates the preference of distinctive environments of trackmakers of both ichnospecies, questioning former hypotheses of exclusivity of ornithischians in more humid climates. By abundance both skeletons and footprints of ornithischians suggest their role as a minor component in Early Jurassic saurischian dominated dinosaur faunas in this region.     

A Haptic Feedback Scheme to Accurately Position a Virtual Wrist Prosthesis Using a Three-Node Tactor Array

In this paper, a novel haptic feedback scheme, used for accurately positioning a 1DOF virtual wrist prosthesis through sensory substitution, is presented. The scheme employs a three-node tactor array and discretely and selectively modulates the stimulation frequency of each tactor to relay 11 discrete haptic stimuli to the user. Able-bodied participants were able to move the virtual wrist prosthesis via a surface electromyography based controller. The participants evaluated the feedback scheme without visual or audio feedback and relied solely on the haptic feedback alone to correctly position the hand. The scheme was evaluated through both normal (perpendicular) and shear (lateral) stimulations applied on the forearm. Normal stimulations were applied through a prototype device previously developed by the authors while shear stimulations were generated using an ubiquitous coin motor vibrotactor. Trials with no feedback served as a baseline to compare results within the study and to the literature. The results indicated that using normal and shear stimulations resulted in accurately positioning the virtual wrist, but were not significantly different. Using haptic feedback was substantially better than no feedback. The results found in this study are significant since the feedback scheme allows for using relatively few tactors to relay rich haptic information to the user and can be learned easily despite a relatively short amount of training. Additionally, the results are important for the haptic community since they contradict the common conception in the literature that normal stimulation is inferior to shear. From an ergonomic perspective normal stimulation has the potential to benefit upper limb amputees since it can operate at lower frequencies than shear-based vibrotactors while also generating less noise. Through further tuning of the novel haptic feedback scheme and normal stimulation device, a compact and comfortable sensory substitution device for upper limb amputees might be created.     

An analysis of the mechanisms governing species replacements in crayfish

Summary We investigated mechanisms governing replacement of the native crayfish Orconectes sanborni by an invading cryafish, Orconectes rusticus. The two species had similar life histories, habitat preferences, and feeding patterns in allopatric and sympatric stream areas. Orconectes rusticus young-of-year (YOY) grew faster than O. sanborni YOY in the field. Adult O. rusticus were larger and, hence, dominant over adult O. sanborni; YOY were non-aggressive. In laboratory experiments, adult crayfish (about 28 mm carapace length or larger) were not susceptable to predation by largemouth bass (Micropterus salmoides, 30 cm total length) and did not alter shelter use when fish were present. Orconectes rusticus YOY were less susceptible to predation than O. sanborni YOY. Orconectes rusticus YOY reduced their vulnerability to largemouth bass by occupying shelters more often than YOY O. sanborni. In mixed-species mateselection experiments, male O. rusticus and male O. sanborni preferentially mated with O. rusticus females. Inappropriate mate selection in sympatry may have caused the 90% reduction in recruitment for both species in 1982. Orconectes rusticus probably maintains greater population growth than O. sanborni, because (1) more gravid O. rusticus females occurred in sympatry, (2) O. rusticus produced more young than O. sanborni, and (3) O. rusticus young grew faster. Reproductive interference, acting synergistically with differences in aggressive dominance and young-of-year susceptibility to predation, appears to serve as the major mechanisms regulating replacement of O. sanborni by O. rusticus in Ohio streams.     

Improved gold chloride staining method for anatomical analysis of sensory nerve endings in the shoulder capsule and labrum as examples of loose and dense fibrous tissues

Consistency in gold chloride staining is essential for anatomical analysis of sensory nerve endings. The gold chloride stain for this purpose has been modified by many investigators, but often yields inconsistent staining, which makes it difficult to differentiate structures and to determine nerve ending distribution in large tissue samples. We introduce additional steps and major changes to the modified Gairns’ protocol. We controlled the temperature and mixing rate during tissue staining to achieve consistent staining and complete solution penetration. We subjected samples to sucrose dehydration to improve cutting efficiency. We then exposed samples to a solution containing lemon juice, formic acid and paraformaldehyde to produce optimal tissue transparency with minimal tissue deformity. We extended the time for gold chloride impregnation 1.5 fold. Gold chloride was reduced in the labrum using 25% formic acid in water for 18 h and in the capsule using 25% formic acid in citrate phosphate buffer for 2 h. Citrate binds gold nanoparticles, which minimizes aggregation in the tissue. We stored samples in fresh ultrapure water at 4° C to slow reduction and to maintain color contrast in the tissue. Tissue samples were embedded in Tissue Tek and sectioned at 80 and 100 μm instead of using glycerin and teasing the tissue apart as in Gairns’ modified gold chloride method. We attached sections directly to gelatin subbed slides after sectioning with a cryostat. The slides then were processed and coverslipped with Permount. Staining consistency was demonstrated throughout the tissue sections and neural structures were clearly identifiable.     

Stable isotope analysis of production and trophic relationships in a tropical marine hard-bottom community

Seagrasses produce much of the organic carbon in the shallow waters of the Caribbean and it has long been assumed that a substantial portion of this carbon is exported to nearby habitats, contributing substantially to their food webs. In the shallow coastal waters of the Florida Keys (USA), seagrass intersperses with hard-bottom habitat where bushy, red macroalgae are the most prominent primary producers. However, the relative importance of seagrass-derived carbon versus autochthonous algal production or phytoplankton in supporting higher trophic levels within hard-bottom communities has never been investigated. We compared the carbon and nitrogen isotopic values of potential primary producers and representative higher trophic level taxa from hard-bottom sites on the bay-side and ocean-side of the Florida Keys. We also included in our study a set of bay-side sites that experienced significant ecological disturbances over the past decade (e.g., cyanobacteria blooms, seagrass die-off, and sponge die-offs) that may have altered trophic relationships in those regions. We did not detect any differences among regions in the trophic status of hard-bottom taxa that might be associated with ecosystem disturbance. However, our results suggest that autochthonous production of algal detritus is an important source of secondary production in these hard-bottom communities, with seagrass and phytoplankton contributing smaller fractions.