Control of single-joint movements with a reversal.

We studied the kinematic and electromyographic (EMG) patterns during single-joint elbow flexion movements with a reversal and tested two hypotheses. First, that the amplitude of the second phase of the movement (M(2)) will be controlled by two different means, a drop in the second flexor burst for a small M(2) and an increase in the integral of the extensor burst for larger M(2). Second, based on the muscle stretch-shortening cycle (SSC), that movements reversing without a delay will show a larger extensor burst, as compared to movements that reverse after a delay. Changes in EMG patterns with M(2) amplitude supported the first hypothesis and could be interpreted within the framework of the equilibrium-point hypothesis. The observations also corroborate a hypothesis that discrete movements represent outcomes of an oscillatory control process stopped at a particular phase. In Experiment-2, even the shortest delay at the target led to a significantly larger extensor burst. However, there were no differences in the peak velocity of M2 with and without the delay. These observations do not support a major role of stretch reflexes in the SSC effects during such movements. However, they are compatible with the idea of peripheral factors, such as peripheral muscle and tendon elasticity, playing a major potentiating role in the SSC.     

Comparison of native and recombinant chlorite dismutase from Ideonella dechloratans.

A detailed comparison between native chlorite dismutase from Ideonella dechloratans, and the recombinant version of the protein produced in Escherichia coli, suggests the presence of a covalent modification in the native enzyme. Although the native and recombinant N- and C-terminal sequences are identical, the enzymes display different electrophoretic mobilities, and produce different peptide maps upon digestion with trypsin and separation of fragments using capillary electrophoresis. Comparison of MALDI mass spectra of tryptic peptides from the native and recombinant enzymes suggests two locations for modification in the native protein. Mass spectrometric analysis of isolated peptides from a tryptic digest of the native enzyme identifies a possible cross-linked dipeptide, suggesting an intrachain cross-link in the parent protein. Spectrophotometric titration of the native enzyme in the denatured state reveals two titrating components absorbing at 295 nm, suggesting the presence of about one tyrosine residue per subunit with an anomalously low pK(a). The EPR spectrum for the recombinant enzyme is different from that of the native enzyme, and contains a substantial contribution of a low-spin species with the characteristics of bis-histidine coordination. These results are discussed in terms of a covalent cross-link between a histidine and a tyrosine sidechain, similar to those found in other heme enzymes operating under highly oxidizing conditions.     

Biological invasion by a benthivorous fish reduced the cover and species richness of aquatic plants in most lakes of a large North American ecoregion

Biological invasions are projected to be the main driver of biodiversity and ecosystem function loss in lakes in the 21st century. However, the extent of these future losses is difficult to quantify because most invasions are recent and confounded by other stressors. In this study, we quantified the outcome of a century‐old invasion, the introduction of common carp to North America, to illustrate potential consequences of introducing non‐native ecosystem engineers to lakes worldwide. We used the decline in aquatic plant richness and cover as an index of ecological impact across three ecoregions: Great Plains, Eastern Temperate Forests and Northern Forests. Using whole‐lake manipulations, we demonstrated that both submersed plant cover and richness declined exponentially as carp biomass increased such that plant cover was reduced to <10% and species richness was halved in lakes in which carp biomass exceeded 190 kg ha^?1. Using catch rates amassed from 2000+ lakes, we showed that carp exceeded this biomass level in 70.6% of Great Plains lakes and 23.3% of Eastern Temperate Forests lakes, but 0% of Northern Forests lakes. Using model selection analysis, we showed that carp was a key driver of plant species richness along with Secchi depth, lake area and human development of lake watersheds. Model parameters showed that carp reduced species richness to a similar degree across lakes of various Secchi depths and surface areas. In regions dominated by carp (e.g., Great Plains), carp had a stronger impact on plant richness than human watershed development. Overall, our analysis shows that the introduction of common carp played a key role in driving a severe reduction in plant cover and richness in a majority of Great Plains lakes and a large portion of Eastern Temperate Forests lakes in North America.     

Network analyses support the role of prey preferences in shaping resource use patterns within five animal populations

Individual variation is an inherent aspect of animal populations and understanding the mechanisms shaping resource use patterns within populations is crucial to comprehend how individuals partition resources. Theory predicts that differences in prey preferences among consumers and/or differences in the likelihood of adding new resources to their diets are key mechanisms underlying intrapopulation variation in resource use. We developed network models based on optimal diet theory that simulate how individuals consume resources under varying scenarios of individual variation in prey preferences and in the willingness of consuming alternate resources. We then investigated how the structure of individual–resource networks generated under each model compared to the structure of observed networks representing five classical examples of individual diet variation. Our results support the notion that, for the studied populations, individual variation in prey preferences is the major factor explaining patterns in individual–resource networks. In contrast, variation in the willingness of adding prey does not seem to play an important role in shaping patterns of resource use. Individual differences in prey preferences in the studied populations may be generated by complex behavioral rules related to cognitive constraints and experience. Our approach provides a pathway for mapping foraging models into network patterns, which may allow determining the possible mechanisms leading to variation in resource use within populations.     

Pathways of the Maillard reaction under physiological conditions

Initially investigated as a color formation process in thermally treated foods, nowadays, the relevance of the Maillard reaction in vivo is generally accepted. Many chronic and age-related diseases such as diabetes, uremia, atherosclerosis, cataractogenesis and Alzheimer’s disease are associated with Maillard derived advanced glycation endproducts (AGEs) and α-dicarbonyl compounds as their most important precursors in terms of reactivity and abundance. However, the situation in vivo is very challenging, because Maillard chemistry is paralleled by enzymatic reactions which can lead to both, increases and decreases in certain AGEs. In addition, mechanistic findings established under the harsh conditions of food processing might not be valid under physiological conditions. The present review critically discusses the relevant α-dicarbonyl compounds as central intermediates of AGE formation in vivo with a special focus on fragmentation pathways leading to formation of amide-AGEs.     

Over the hills and far away: New plant records for the Guayana Shield in Brazil

The Guayana Shield is one of the oldest geological formations in South America, ranging from southern Colombia, Venezuela, and the Guianas to the extreme north of the Brazilian states of Amazonas and Roraima. Because of its ancient origin and isolation from other mountain ranges in South America, it harbors a rich flora with high levels of endemism. Recent expeditions to remote areas in the Brazilian portion of the Guayana Shield generated many new herbarium collections. Through these efforts, we report the first records for Brazil of 57 species and infraspecific taxa of vascular plants. In most cases, the taxa are narrowly distributed and were previously known from nearby populations in other countries. In other cases, however, the new Brazilian records expand considerably the known geographical distributions of the taxa.     

Functional and phylogenetic structure of forest and savanna bird assemblages across spatial scales

Ecological and evolutionary mechanisms that drive community assembly vary in space and time. However, little is known about how such mechanisms act in contrasting habitats. Here, we estimated the functional and phylogenetic structure of forest and savanna bird assemblages across different spatial scales to understand: 1) the mechanisms that govern the structure of assemblages in these habitats; 2) the relationship between phylogenetic and functional structure; and 3) the influence of species richness on the functional and phylogenetic structure of assemblages. We used a null model where forest and savanna bird species were allowed to occur in the same null assemblages and other where species were separated based on their habitats. According to the first null model, forest bird assemblages were functionally and phylogenetically clustered at all spatial scales, whereas savanna bird assemblages generally showed random functional and phylogenetic structure. These results can be explained by the low dispersal rate of forest species across of the patchy habitats and the widespread distribution of savanna species. However, in the second null model, both forest and savanna bird assemblages showed random functional and phylogenetic structure at regional and local scales. This suggests that trait‐based assembly might not play an important role in both habitats and across different spatial scales. In addition, the phylogenetic and functional structure of assemblages were not correlated, evidencing that caution is necessary when using phylogenetic relationships as a surrogate to functional distances among species. Finally, the relationships between species richness and functional and phylogenetic structure indicated that an increase in the number of species can promote both clustering and overdispersion, depending on the studied habitat and scale. Our study shows that integrating different types of habitat, spatial scales and biodiversity components in a single framework can shed light on the mechanisms that determine the community assembly.