The reliability of linear position transducer and force plate measurement of explosive force-time variables during a loaded jump squat in elite athletes

The best method of assessing muscular force qualities during isoinertial stretch shorten cycle lower body movements remains a subject of much debate. This study had 2 purposes: Firstly, to calculate the interday reliability of peak force (PF) measurement and a variety of force-time measures, and, secondly, to compare the reliability of the 2 most common technologies for measuring force during loaded jump squats, the linear position transducer (PT), and the force plate (FP). Twenty-five male elite level rugby union players performed 3 rebound jump squats with a 40-kg external load on 2 occasions 1 week apart. Vertical ground reaction forces (GRFs) were directly measured via an FP, and force was differentiated from position data collected using a PT. From these data, a number of force-time variables were calculated for both the FP and PT. Intraclass correlation coefficient (ICC), coefficient of variation (CV), and percent change in the mean were used as measures of between-session reliability. Additionally, Pearson's product moment correlation coefficients were used to investigate intercorrelations between variables and technologies. Both FP and PT were found to be a reliable means of measuring PF (ICC = 0.88-0.96, CV = 2.3-4.8%), and the relationship between the 2 technologies was very high and high for days 1 and 2, respectively (r = 0.67-0.88). Force-time variables calculated from FP data tended to have greater relative and absolute consistency (ICC = 0.70-0.96, CV = 5.1-51.8%) than those calculated from differentiated PT data (ICC = 0.18-0.95, CV = 7.7-93.6%). Intercorrelations between variables ranged from trivial to practically perfect (r = 0.00-1.00). It was concluded that PF can be measured reliably with both FP and PT technologies, and these measurements are related. A number of force-time values can also be reliably calculated via the use of GRF data. Although some of these force-time variables can be reliably calculated using position data, variation of measurement is generally greater when using position data to calculate force.     

Characterization of an oxidoreductase from the arylamine N-acetyltransferase operon in Mycobacterium smegmatis

Mycobacterium?tuberculosis, the most successful bacterial pathogen, causes tuberculosis, a disease that still causes more than 2 million deaths per year. Arylamine N-acetyltransferase is an enzyme that is conserved in most Mycobacterium spp. The nat gene belongs to an operon that is important for the intracellular survival of M. tuberculosis within macrophages. The nat operon in Mycobacterium smegmatis and other fast-growing mycobacterial species has a unique organization containing genes with uncharacterized function. Here, we describe the biochemical, biophysical and structural characterization of the MSMEG_0308 gene product (MS0308) of the M. smegmatis nat operon. While characterizing the function of MS0308, we validated the oxidoreductase property; however, we found that the enzyme was not utilizing dihydrofolate as its substrate, hence we first report that MS0308 is not a dihydrofolate reductase, as annotated in the genome. The structure of this oxidoreductase was solved at 2.0 ? in complex with the cofactor NADPH and has revealed the hydrophobic pocket where the endogenous substrate binds.     

Bicycle seat interface pressure: reliability, validity, and influence of hand position and workload

Bicycle seat pressure is often examined by researchers exploring solutions for reducing seat injuries as it is thought a critical determinant; however, a reliable and valid methodology for this undertaking has not been reported. The current study was designed to address this shortcoming and to establish baseline interface pressure measurements for females and males. Participants completed two separate identical bicycle ergometer trials at 118 W in the tops and drops and at 300+/-82.4 W in top handlebar positions. Seat pressures were quantified from a pressure-sensing mat and the validity of the pressure system was examined through the relationship between known seat weights and the sum of seat pressures. Within trial intraclass correlation coefficients (ICCs) ranged between 0.90 and 0.99 and the between trial ICC values ranged between 0.02 and 0.96. The relationship (Pearson correlation coefficient) between seat weight and the sum of pressures was 0.97. Significant peak pressures were 39% greater in the 118 W top than 300 W top handlebar condition and 29% greater than the 118 W drop handlebar condition (p < 0.05). The gender comparison revealed that significant male peak pressure values were greater (24%) and that female values were less influenced by the hand position factor. Select within trial pressure measurements were found to be reliable during pedaling and valid statically. Additionally, the results indicated that workrate and hand position were factors influencing seat pressure and that males and females responded differently to adjustments of these factors.     

Variation in oxytocin is related to variation in affiliative behavior in monogamous, pairbonded tamarins

Oxytocin plays an important role in monogamous pairbonded female voles, but not in polygamous voles. Here we examined a socially monogamous cooperatively breeding primate where both sexes share in parental care and territory defense for within species variation in behavior and female and male oxytocin levels in 14 pairs of cotton-top tamarins (Saguinus oedipus). In order to obtain a stable chronic assessment of hormones and behavior, we observed behavior and collected urinary hormonal samples across the tamarins’ 3-week ovulatory cycle. We found similar levels of urinary oxytocin in both sexes. However, basal urinary oxytocin levels varied 10-fold across pairs and pair-mates displayed similar oxytocin levels. Affiliative behavior (contact, grooming, sex) also varied greatly across the sample and explained more than half the variance in pair oxytocin levels. The variables accounting for variation in oxytocin levels differed by sex. Mutual contact and grooming explained most of the variance in female oxytocin levels, whereas sexual behavior explained most of the variance in male oxytocin levels. The initiation of contact by males and solicitation of sex by females were related to increased levels of oxytocin in both. This study demonstrates within-species variation in oxytocin that is directly related to levels of affiliative and sexual behavior. However, different behavioral mechanisms influence oxytocin levels in males and females and a strong pair relationship (as indexed by high levels of oxytocin) may require the activation of appropriate mechanisms for both sexes.     

Interpatch movement and edge effects: the role of behavioral responses to the landscape matrix

Animal interpatch movement and spatial distribution are known to be influenced substantially by the composition of the landscape matrix, but little is known about the underlying mechanisms. In previous mark–recapture experiments we have found that the rates of emigration and immigration for the planthopper Prokelisia crocea are greater within a matrix composed of the introduced grass smooth brome (Bromus inermis) than a mudflat matrix. Additionally, census data indicated that individuals aggregate near the edge of host‐plant patches (prairie cordgrass; Spartina pectinata) bordered by mudflat, but not in patches bordered by nonhost grasses such as brome. Here, we investigate the mechanistic basis of these matrix effects by tracking the individual movements of planthoppers released at the edge of brome‐ and mudflat‐bordered cordgrass patches, and within homogeneous habitats of each type (cordgrass, brome, and mudflat). We found that patch edges bordered by brome were three times more permeable to emigration than mudflat‐bordered edges. Also, planthoppers exhibited no tendency to avoid edges by moving away (i.e. towards the patch interior). Within homogeneous habitats, comparison of the fractal dimension of movement paths revealed that movement was more linear in mudflat than in brome or cordgrass. In addition, planthoppers exhibited greater step lengths (distance moved per 10‐min interval), shorter residency times (duration of pauses between movements), and greater rates of net linear displacement in mudflat than brome and cordgrass. We attribute the planthopper's distributional patterns within patches to the lower permeability of mudflat than nonhost grass edges and the absence of edge–avoidance behavior. Contrary to conventional wisdom that low‐resistance matrix types (e.g. those that promote high displacement rates) enhance interpatch dispersal rates, dispersal success may be higher in brome matrix because tortuous movement through this matrix increases the planthopper's rate of encounter with cordgrass patches.     

Antagonisms, mutualisms and commensalisms affect outbreak dynamics of the southern pine beetle

Feedback from community interactions involving mutualisms are a rarely explored mechanism for generating complex population dynamics. We examined the effects of two linked mutualisms on the population dynamics of a beetle that exhibits outbreak dynamics. One mutualism involves an obligate association between the bark beetle, Dendroctonus frontalis and two mycangial fungi. The second mutualism involves Tarsonemus mites that are phoretic on D. frontalis (“commensal”), and a blue-staining fungus, Ophiostoma minus. The presence of O. minus reduces beetle larval survival (“antagonistic”) by outcompeting beetle-mutualistic fungi within trees yet supports mite populations by acting as a nutritional mutualist. These linked interactions potentially create an interaction system with the form of an endogenous negative feedback loop. We address four hypotheses: (1) Direct negative feedback: Beetles directly increase the abundance of O. minus, which reduces per capita reproduction of beetles. (2) Indirect negative feedback: Beetles indirectly increase mite abundance, which increases O. minus, which decreases beetle reproduction. (3) The effect of O. minus on beetles depends on mites, but mite abundance is independent of beetle abundance. (4) The effect of O. minus on beetles is independent of beetle and mite abundance. High Tarsonemus and O. minus abundances were strongly correlated with the decline and eventual local extinction of beetle populations. Manipulation experiments revealed strong negative effects of O. minus on beetles, but falsified the hypothesis that horizontal transmission of O. minus generates negative feedback. Surveys of beetle populations revealed that reproductive rates of Tarsonemus, O. minus, and beetles covaried in a manner consistent with strong indirect interactions between organisms. Co-occurrence of mutualisms embedded within a community may have stabilizing effects if both mutualisms limit each other. However, delays and/or non-linearities in the interaction systems may result in large population fluctuations. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Protein structure similarity from principle component correlation analysis

Background  

Owing to rapid expansion of protein structure databases in recent years, methods of structure comparison are becoming increasingly effective and important in revealing novel information on functional properties of proteins and their roles in the grand scheme of evolutionary biology. Currently, the structural similarity between two proteins is measured by the root-mean-square-deviation (RMSD) in their best-superimposed atomic coordinates. RMSD is the golden rule of measuring structural similarity when the structures are nearly identical; it, however, fails to detect the higher order topological similarities in proteins evolved into different shapes. We propose new algorithms for extracting geometrical invariants of proteins that can be effectively used to identify homologous protein structures or topologies in order to quantify both close and remote structural similarities.     

Lysozyme activity and protein concentration in the haemolymph of the flat oyster Ostrea edulis (L.)

Lysozyme activity and protein concentration in the haemolymph of the flat oyster Ostrea edulis were investigated. These biochemical constituents of the haemolymph could be an indication of the physiological condition and vitality of the defence system of an animal. Haemolymph protein and lysozyme in oysters were examined over an 18 month period to determine their relationship with the strain of oyster, the season, the site, and parasitism by Bonamia ostreae. Haemolymph protein concentration exhibited seasonal fluctuations and varied between strains. Levels of protein in oysters highly infected with B. ostreae were slightly depressed but not significantly so. Haemolymph lysozyme varied greatly between individuals but no correlation was found between lysozyme levels and infection of oysters by B. ostreae.