The role of delayed excitation in the co-ordination of some metathoracic flight motoneurons of a locust

Summary Intracellular recordings have been made from the somata of two metathoracic flight motoneurons, one innervating an elevator muscle of the hindwing, the tergosternal muscle 113 and the other a depressor, the first basalar muscle 127. The locust,Ghortoicetes terminifera was mounted ventral side uppermost with the thorax restrained and opened for access to the thoracic ganglia. Patterns of electrical activity recorded from the thoracic muscles were similar to those shown by a locust during flight when tethered in a more normal posture. In flight the left and right 113 motoneurons each receive a single impulse together at every stroke of the wing, with the 127 muscles active in approximate antiphase. A spike in a 113 motoneuron causes a delayed wave of excitation simultaneously upon itself and its contralateral partner (Fig. 2). The epsp's which form these waves summate and may cause a spike which follows the original one with a delay equal to the wingbeat period. The delayed excitation of the contralateral motoneuron is of larger amplitude than the ipsilateral one so that spikes in either motoneuron must activate separate but symmetrical pathways. A single spike may cause multiple waves in either motoneuron, each separated by intervals equal to the wingbeat period (Fig. 3). In the pathway must be neurons capable of reverberation.A spike in a 113 motoneuron causes a delayed excitation of the ipsilateral 127 motoneuron so that its membrane potential is lowered antiphasically to that of 113 (Fig. 17). A spike in a 127 motoneuron has no effect on the 113 motoneurons. In flight these pathways causing delayed excitation may co-ordinate the motoneurons.The left and right 113 motoneurons receive common synaptic inputs from at least two sources (Fig. 8). These occur as bursts of epsp's at intervals approximately equal to or multiples of the wingbeat period and in the absence of flight. Epsp's of sufficient amplitude cause a spike in the motoneuron which is in the correct phase in the flight pattern relative to any other active motoneurons (Fig. 9). During sustained flight epsp's contribute to the wave of depolarization that the motoneuron undergoes at each wingbeat (Fig. 11). In the absence of the epsp's the motoneuron does not oscillate on its own. At the end of flight bursts of epsp's may continue at the flight frequency long after all activity in the muscles has ceased.Beit Memorial Research Fellow.     

Three-dimensional analysis of mandibular morphology in Otolemur

Euclidean distance matrix analysis (EDMA) of three-dimensional data is used here to examine mandibular morphology between two species of galagos. Otolemur crassicaudatus consumes primarily exudates, while O. garnettii is more frugivorous. Acquisition of exudates involves either gouging or scraping tree bark, and may involve different forces at the mandible than incising fruits. Previous studies of mandibular morphology in exudate-feeding primates produced mixed results, some suggesting that morphological specializations reflect adaptations for greater force at the anterior dentition, while others suggest specializations for producing a large gape. This study addresses these controversies by testing predictions associated with O. crassicaudatus generating greater force at the anterior dentition or producing a larger gape relative to O. garnettii. In addition, this study tests predictions associated with specializations of the anterior dentition in O. crassicaudatus as related to exudate-feeding. Crania and mandibles from 28 O. crassicaudatus and 17 O. garnettii were digitized in three dimensions, using 18 landmarks that summarize the shape of the jaw. Two-dimensional measurements were taken to assess incisor robusticity. All three-dimensional data were analyzed using EDMA, and bootstrap tests were executed to identify specific interlandmark differences that were driving any significant (P < 0.05) overall shape differences. Two-dimensional data were analyzed using Student's t-test for independent measures. Results revealed that there was a significant shape difference in mandibles between species, and that mandibles of O. crassicaudatus showed higher condyles, longer mandibles, decreased incisor procumbency, and greater incisor robusticity relative to O. garnettii. It is suggested that the results of the present study reflect adaptations for scraping in O. crassicaudatus rather than gouging.     

Selection pressure-driven evolution of the Epstein-Barr virus-encoded oncogene LMP1 in virus isolates from Southeast Asia

The geographically constrained distribution of Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) in southeast Asian populations suggests that both viral and host genetics may influence disease risk. Although susceptibility loci have been mapped within the human genome, the role of viral genetics in the focal distribution of NPC remains an enigma. Here we report a molecular phylogenetic analysis of an NPC-associated viral oncogene, LMP1, in a large panel of EBV isolates from southeast Asia and from Papua New Guinea, Africa, and Australia, regions of the world where NPC is and is not endemic, respectively. This analysis revealed that LMP1 sequences show a distinct geographic structure, indicating that the southeast Asian isolates have evolved as a lineage distinct from those of Papua New Guinea, African, and Australian isolates. Furthermore, a likelihood ratio test revealed that the C termini of the LMP1 sequences of the southeast Asian lineage are under significant positive selection pressure, particularly at some sites within the C-terminal activator regions. We also present evidence that although the N terminus and transmembrane region of LMP1 have undergone recombination, the C-terminal region of the gene has evolved without any history of recombination. Based on these observations, we speculate that selection pressure may be driving the LMP1 sequences in virus isolates from southeast Asia towards a more malignant phenotype, thereby influencing the endemic distribution of NPC in this region.     

Movements and burrowing activity in the Antarctic bivalve molluscs<Emphasis Type="Italic"> Laternula elliptica</Emphasis> and<Emphasis Type="Italic"> Yoldia eightsi</Emphasis>

Burrowing was investigated in two Antarctic infaunal bivalve molluscs, Laternula elliptica and Yoldia eightsi, representing amongst the least and most active members of the class Bivalvia in the Southern Ocean. Burrowing rate was expressed via the Burrowing Rate Index (BRI=[³wet weight/time to bury]×10⁴), and produced values of 0.1–10.6 for L. elliptica and 8.8–49.8 for Y. eightsi. These compare with values ranging from 3 to 2,000 for N. American bivalves (mean=222, SE=42.6, n=81), and 200 to 2,200 for Hong Kong bivalves (mean=1,140, SE=346, n=6). Values for the Antarctic species are, therefore, low compared to warmer-water bivalves, and the values below 1 for large L. elliptica are the lowest on record by around ×5. There is no compensation of burrowing activity for low temperature in these species. The relative BRI values for L. elliptica and Y. eightsi reflect the differences in their mode of life, with the former being large, sedentary and suspension-feeding, and the latter being smaller, mobile, ploughing through the sediment and feeding on sediment-surface organic matter. Burrowing in L. elliptica is unexpected, because other members of the Laternulidae do not burrow. This ability is most probably a response to the regular disturbance of sediments in Antarctica by ice, and the strong selective advantage to being able to resume a protected position after disturbance. The burrowing cycle in L. elliptica is composed of three main phases: (1) foot extension and sediment penetration; (2) foot dilation to form an anchor; (3) the drawing down of the shell by contraction of the pedal retractor muscles. Burrowing in Y. eightsi also has three phases: (1) foot extension and penetration of the sediment (digging); (2) rocking movements in the upright position; (3) shell anchorage. In excess of burrowing activity, L. elliptica exhibits a unique suite of movements when exposed at the surface. These comprise levering, where the tips of the siphons are pressed against the sediment to lift the shell from the substratum, looping, where the siphons are extended and rotated and, in the process, translocate the whole animal across the sediment, and jetting, where water is ejected forcibly through the siphons while their tips are directed towards the sediment, lifting part or all of the animal clear of the substratum. In the field, following exhumation by icebergs, these activities serve to place the animal in a favourable position for reburial, which is a clear advantage in disturbed polar environments where predatory nemerteans and asteroids are abundant.     

Symposium report: Inaugural Australian Coastal Restoration Symposium

Summary

Globally, coastal habitat restoration is growing in recognition as a viable management tool to repair and reinstate valuable coastal habitats and species, such as mangrove and macroalgae forests, salt marshes, seagrass meadows, shellfish and coral reefs (Aronson & Alexander ( 2013 ), Restoration Ecology, 293; Anthony et al. ( 2017 ) Nature Ecology and Evolution, 1420; TNC ( 2017 ) Caribbean: A revolution to save coral reefs in the Caribbean and beyond). In Australia, there is increasing interest and investment in coastal restoration and habitat conservation, particularly with respect to growing national concerns around habitat loss, coastal inundation and erosion, loss of fisheries and climate change (Maggini et al. ( 2013 ) Protecting and restoring habitat to help Australia's threatened species adapt to climate change; GBRMPA ( 2017 ) Reef summit sets new course of action for the Great Barrier Reef). This has led to new community of practices being formed for shellfish reef restoration (Shellfish Reef Restoration Network shellfishrestoration.org.au), seagrass restoration (Seagrass Restoration Network seagrassrestoration.net), and saltmarsh and mangrove (Saltmarsh and Mangrove Network, amsn.net.au) conservation. However, despite this interest, there has been no national coordination, network or society with coastal restoration as a primary focus. The inaugural Australian Coastal Restoration Symposium brought together 60 Australian restoration practitioners, researchers and managers at James Cook University, Townsville for three days from the 31st of August 2017. The symposium goals were to enhance collaboration and national coordination amongst coastal restoration projects and practitioners, as well as to connect researchers and practitioners working in the restoration space with one another. Three international keynote speakers shared their experiences and advice. Delegates were enthusiastic about continuing to meet at future symposiu, meetings and workshops, and noted the value of being able to connect, share project experiences and learnings, and collaborate. The Australian Coastal Restoration Network has been formed with the goal of meeting annually to continue to share knowledge and improve collaboration. View a video about the symposium by following this link – https://www.youtube.com/watch?v=lukSpo3mM-4     

Persistent nitrogen limitation of stream biofilm communities along climate gradients in the Arctic

Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll‐a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.     

Molecular evolution of a multigene family in group A streptococci

The emm genes are members of a gene family in group A streptococci (GAS) that encode for antiphagocytic cell-surface proteins and/or immunoglobulin-binding proteins. Previously sequenced genes in this family have been named "emm," "fcrA," "enn," "arp," "protH," and "mrp"; herein they will be referred to as the "emm gene family." The genes in the emm family are located in a cluster occupying 3-6 kb between the genes mry and scpA on the chromosome of Streptococcus pyogenes. Most GAS strains contain one to three tandemly arranged copies of emm-family genes in the cluster, but the alleles within the cluster vary among different strains. Phylogenetic analysis of the conserved sequences at the 3' end of these genes differentiates all known members of this family into four evolutionarily distinct emm subfamilies. As a starting point to analyze how the different subfamilies are related evolutionarily, the structure of the emm chromosomal region was mapped in a number of diverse GAS strains by using subfamily-specific primers in the polymerase chain reaction. Nine distinct chromosomal patterns of the genes in the emm gene cluster were found. These nine chromosomal patterns support a model for the evolution of the emm gene family in which gene duplication followed by sequence divergence resulted in the generation of four major-gene subfamilies in this locus.      

Effects of endogenous rhythms and light conditions on foraging and predator-avoidance in juvenile plaice

The influences of a light: dark cycle and a persistent endogenous rhythm of activity on foraging (on the bivalve Donax vittatus ) and avoiding a predator (juvenile cod, Gadus morhua ) were investigated in freshly-caught juvenile plaice, Pleuronectes plalessa . Time lapse video recordings were made of fish in the presence and absence of prey and predators in laboratory tanks over 24-hour periods between the times of successive daytime low waters. Endogenous rhythms of activity were seen in all experimental treatments. Swimming both close to the bottom and in the water column showed a strong circatidal rhythm, with most activity 2 to 3 h after the predicted time of high water. Swimming in the water column was more frequent at night than by day. In the presence of a population of Donax , whose siphon tips could be eaten as food, swimming close to the bottom became more frequent. This increase in benthic swimming was independent of the endogenous cycle of activity and was correlated with the frequency of attacks on siphons. The presence of the cod predator delayed the onset of foraging activity, producing a foraging/predator avoidance trade-off. The independence of foraging from light and endogenous rhythms suggests that this trade-off may be similarly independent. The cod also greatly reduced swimming in the water column in darkness, behaviour apparently unrelated to foraging.     

Improved Preparation of Polyvinyl Alcohol-HgCl2 Fixative Used for Fecal Smears

Rather than dissolve polyvinyl alcohol (PVA) powder in a modified Schaudinn's fixative (containing glycerol) by prolonged heating and stirring, it was found better to coat the particles of PVA with glycerol first. PVA powder (Delkote brand), 5 gm, mixed with 1.5 ml of glycerol and added to 62.5 ml of distilled water, is allowed to soak 3-16 hr in a stoppered flask, then heated to 70-75 C in a water bath (with swirling) for about 10 min or until solution is complete. A separate solution of the other ingredients: 95% ethanol, 31 ml; HgCl₂ 4.5 gm; and glacial acetic acid, 5 ml, is then added to the heated PVA solution, and swirled in the stoppered flask until the mixture becomes clear. This fixative is easy to make, produces little or no sediment, does not thicken with age, and has a long shelf life. It is strongly adhesive and fixes protozoa as well or better than that made by the older method or purchased ready made.