Comparative analysis of shell occupation by two southern populations of the hermit crab Loxopagurus loxochelis (Decapoda, Diogenidae)

The present study aimed to comparatively verify the relation between the hermit crabs and the shells they use in two populations of Loxopagurus loxochelis. Samples were collected monthly from July 2002 to June 2003, at Caraguatatuba and Ubatuba Bay, Sao Paulo, Brazil. The animals sampled had their sex identified, were weighed and measured; their shells were identified, measured and weighed, and their internal volume determined. To relate the hermit crab's characteristics and the shells' variables, principal component analysis (PCA) and a regression tree were used. According to the PCA analysis, the three gastropod shells most frequently used by L. loxochelis varied in size. The regression tree successfully explained the relationship between the hermit crab's characteristics and the internal volume of the inhabited shell. It can be inferred that the relationship between the morphometry of an individual hermit crab and its shell is not straightforward and it is impossible to explain only on the basis of direct correlations between the body's and the shell's attributes. Several factors (such as the morphometry and the availability of the shell, environmental conditions and inter- and intraspecific competition) interact and seem to be taken into consideration by the hermit crabs when they choose a shell, resulting in the diversified pattern of shell occupancy shown here and elsewhere.

Analysis of confinement potential fluctuation and band-gap renormalization effects on excitonic transition in GaAs/AlGaAs multiquantum wells grown on (100) and (311)A GaAs surfaces

The competition between confinement potential fluctuations and band-gap renormalization (BGR) in GaAs/AlxGa1-xAs quantum wells grown on [1 0 0] and [3 1 1]A GaAs substrates is evaluated. The results clearly demonstrate the coexistence of the band-tail states filling related to potential fluctuations and the band-gap renormalization caused by an increase in the density of photogenerated carriers during the photoluminescence (PL) experiments. Both phenomena have strong influence on temperature dependence of the PL-peak energy (E-PL(T)). As the photon density increases, the E-PL can shift to either higher or lower energies, depending on the sample temperature. The temperature at which the displacement changes from a blueshift to a redshift is governed by the magnitude of the potential fluctuations and by the variation of BGR with excitation density. A simple band-tail model with a Gaussian-like distribution of the density of state was used to describe the competition between the band-tail filling and the BGR effects on E-PL(T). (C) 2012 Elsevier B.V. All rights reserved.

Analysis of 16S rRNA and mxaF genes revealing insights into Methylobacterium niche-specific plant association

The genus Methylobacterium comprises pink-pigmented facultative methylotrophic (PPFM) bacteria, known to be an important plant-associated bacterial group. Species of this group, described as plant-nodulating, have the dual capacity of producing cytokinin and enzymes, such as pectinase and cellulase, involved in systemic resistance induction and nitrogen fixation under specific plant environmental conditions. The aim hereby was to evaluate the phylogenetic distribution of Methylobacterium spp. isolates from different host plants. Thus, a comparative analysis between sequences from structural (16S rRNA) and functional mxaF (which codifies for a subunit of the enzyme methanol dehydrogenase) ubiquitous genes, was undertaken. Notably, some Methylobacterium spp. isolates are generalists through colonizing more than one host plant, whereas others are exclusively found in certain specific plant-species. Congruency between phylogeny and specific host inhabitance was higher in the mxaF gene than in the 16S rRNA, a possible indication of function-based selection in this niche. Therefore, in a first stage, plant colonization by Methylobacterium spp. could represent generalist behavior, possibly related to microbial competition and adaptation to a plant environment. Otherwise, niche-specific colonization is apparently impelled by the host plant.

ANALYSIS OF THE BALANCE CONTROL IN SURFERS DURING THE ERECT POSTURE

Background: Surfing is a sport that has become considerably popular, which increased interest in research about the aspects that can influence on the performance of these athletes, such as injuries, aerobic fitness and reaction time. Due to the ever-changing environment and high instability required for surfing, the surfers must develop some neuromuscular skills (agility, balance, muscle strength and flexibility) to acquire better performance in this modality. Nevertheless, there are still few scientific studies concerned about the investigation of these motor skills in surfing. Objective: The aim of this study was to evaluate the balance control in surfers compared to practitioners of other physical activities. Methods: Participants remained on a force platform while performing tasks involving visual deprivation (eyes open or closed) and somatosensory disturbance (steady surface or use of foam), with covariation of experimental conditions. The following variables were analyzed: speed and root mean square (RMS) displacement of the center of pressure in the anteroposterior (AP) and mediolateral (ML) directions. Results: The results showed no difference between groups during the experimental conditions, that is to say, both surfers and the control group varied over the conditions of eyes closed and on foam. Conclusion: Although surfing requires the surfer to have great balance control, the results did not reveal a relationship between this sport and better performance in balance control. However, we must consider the small sample size and the fact that this sport requires dynamic balance, while the study evaluated static balance.

Analysis of 16S rRNA and mxaF genes reveling insights into Methylobacterium niche-specific plant association

The genus Methylobacterium comprises pink-pigmented facultative methylotrophic (PPFM) bacteria, known to be an important plant-associated bacterial group. Species of this group, described as plant-nodulating, have the dual capacity of producing cytokinin and enzymes, such as pectinase and cellulase, involved in systemic resistance induction and nitrogen fixation under specific plant environmental conditions. The aim hereby was to evaluate the phylogenetic distribution of Methylobacterium spp. isolates from different host plants. Thus, a comparative analysis between sequences from structural (16S rRNA) and functional mxaF (which codifies for a subunit of the enzyme methanol dehydrogenase) ubiquitous genes, was undertaken. Notably, some Methylobacterium spp. isolates are generalists through colonizing more than one host plant, whereas others are exclusively found in certain specific plant-species. Congruency between phylogeny and specific host inhabitance was higher in the mxaF gene than in the 16S rRNA, a possible indication of function-based selection in this niche. Therefore, in a first stage, plant colonization by Methylobacterium spp. could represent generalist behavior, possibly related to microbial competition and adaptation to a plant environment. Otherwise, niche-specific colonization is apparently impelled by the host plant.

Comparative analysis of shell occupation by two southern populations of the hermit crab Loxopagurus loxochelis (Decapoda, Diogenidae)

The present study aimed to comparatively verify the relation between the hermit crabs and the shells they use in two populations of Loxopagurus loxochelis. Samples were collected monthly from July 2002 to June 2003, at Caraguatatuba and Ubatuba Bay, São Paulo, Brazil. The animals sampled had their sex identified, were weighed and measured; their shells were identified, measured and weighed, and their internal volume determined. To relate the hermit crab's characteristics and the shells' variables, principal component analysis (PCA) and a regression tree were used. According to the PCA analysis, the three gastropod shells most frequently used by L. loxochelis varied in size. The regression tree successfully explained the relationship between the hermit crab's characteristics and the internal volume of the inhabited shell. It can be inferred that the relationship between the morphometry of an individual hermit crab and its shell is not straightforward and it is impossible to explain only on the basis of direct correlations between the body's and the shell's attributes. Several factors (such as the morphometry and the availability of the shell, environmental conditions and inter- and intraspecific competition) interact and seem to be taken into consideration by the hermit crabs when they choose a shell, resulting in the diversified pattern of shell occupancy shown here and elsewhere.