High assemblage persistence in heterogeneous habitats: an experimental test with stream benthic algae

1. The persistence of biological assemblages is positively affected by spatial heterogeneity. This influence may be indirect, through increased species richness. Another possibility is the increased availability of refuges from disturbances, which would prevent local loss. 2. We conducted a field experiment to test the hypothesis that greater roughness (a form of spatial heterogeneity) on the surface of substrata allows higher persistence of assemblages of stream benthic algae and that this relationship does not depend on species richness. Samples were taken on six occasions from smooth and rough artificial substrata used for algal colonisation. We calculated the persistence of assemblages using two analytical approaches: the mean distance to group centroid and the sum of the Euclidean distances between consecutive sampling occasions, both in a multivariate space. We also subsampled the data to take into account differences in species richness between treatments and thus to evaluate the effect of species richness on persistence. 3. Assemblages on rough substrata were more persistent than assemblages on smooth substrata. The effects detected were not due to the greater species richness on rough substrata, since a higher persistence of the assemblages on rough substrata remained after the subsampling procedures. 4. Our results indicate a strong positive relationship between substratum roughness and the persistence of stream benthic algal assemblages. We suggest that this is due to the presence of physical refuges in heterogeneous habitats.     

Anatomy of extrafloral nectaries in Fabaceae from dry‐seasonal forest in Brazil

Extrafloral nectaries (EFNs) are found in many species of Fabaceae. The aim of this work is to describe the internal morphology of the EFNs from species of Fabaceae found in areas of dry‐seasonal forest in north‐eastern Brazil. All species of Fabaceae with EFNs found were collected and samples were submitted to conventional techniques for anatomical and scanning electronic microscopy analysis. EFNs were found in 35 species, of which 32 were examined anatomically. All types have epidermal cells, secretory tissues and vascular bundles in the EFNs. Sclerenchymatous cells were found between the secretory tissues and the vascular tissues, with a few exceptions. The function of these cells is not clear; however, a role in the transportation of the sap in the nectary or with the support of the secretory tissue is possible. The nectar is released through glandular trichomes, secretory pores or even by breaking the epidermal cells and cuticle. The internal patterns found in the EFNs from different species and genera can provide important information for taxonomic and evolutionary studies in the family. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 87–98.     

Spatial eigenfunction analyses in stream networks: do watercourse and overland distances produce different results?

1. The use of spatial variables is a common procedure in ecological studies. The technique is based on the definition of a connectivity/distance matrix that conceptually defines the dispersal of organisms. The shortest distance between two points is a straight line. Despite the fact that a straight line may not represent the easiest dispersal path for many kinds of organisms, straight‐line distances are often used to detect patterns. We argue that other types of connectivity/distance matrices will better represent dispersal paths, such as the watercourse distance for aquatic organisms (e.g. fish, shrimps). 2. We used empirical and simulated community data to evaluate the usefulness of spatial variables generated from watercourse and overland (straight‐line) distances. 3. Spatial variables based on watercourse distances captured patterns that straight‐line distances did not, and provided better representations of the spatial patterns generated by dispersal along a dendritic network.     

The effect of adenine nucleotides and inhibitors of ADP translocation on uncoupled electron flux in bean mitochondria

The uncoupled electron flux and the influence of adenine nucleotides on this flux in mitochondria isolated from hypocotyls of Vigna sinensis (L.) Savi cv. Seridó were examined. In order to avoid the functioning of other enzymes capable of utilizing adenine nucleotides the reaction medium was free of Mg²⁺. When an oxidizable NADH -linked substrate such as L-malate was used, a stimulatory of adenosine-5′-monophosphate (AMP) and adenosine-5′-diphosphate (ADP) on uncoupled respiration was manifested. The stimulatory effect of AMP and ADP could not be shown when succinate was the substrate. Atractyloside and carboxyatractyloside had no effect on the stimulatory role played respectively by AMP and ADP in the presence of carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP).     

Taxonomic revision and phylogenetic relationships of the bee genus Parapsaenythia Friese (Hymenoptera,Apidae, Protandrenini), with biogeographic inferences for the South American Chacoan Subregion

The bee genus Parapsaenythia Friese (Apidae, Protandrenini) is restricted to South America and characterized by the strongly punctate integument and hairy eyes. In the present work, the species of Parapsaenythia are revised, with seven species recognized, of which three are described as new: P. carinulata sp.n. (Argentina, Brazil, Paraguay), P. inornata Moure (Brazil), P. lanata sp.n. (Brazil), P. paspali (Schrottky) (Argentina, Brazil, Paraguay), P. puncticutis (Vachal) (Argentina, Bolivia), P. scutellaris sp.n. (Argentina, Bolivia, Brazil, Paraguay) and P. serripes (Ducke) (Argentina, Brazil). Lectotypes are designated for Psaenythia (Parapsaenythia) argentina Friese, Anthrenoides paspali Schrottky and Parapsaenythia paraguayae Brèthes. Floral records, distribution maps, illustrations and an identification key are provided. The cladistic analysis of 11 terminal species (all species of Parapsaenythia plus four outgroup species), based on 45 characters of external morphology and male terminalia, produced a single most parsimonious tree. Parapsaenythia was recovered as monophyletic, with the relationships among its species as follows: (P. inornata (P. carinulata sp.n. (P. lanata sp.n. (P. scutellaris sp.n. (P. serripes, P. paspali, P. puncticutis))))). Based on these relationships plus the available distributional data, a cladistic biogeographic analysis was performed, and area cladograms for the Chacoan subregion are presented and discussed.     

Environmental variability drives phytoplankton assemblage persistence in a subtropical reservoir

Temporal changes of assemblages may result from environmental variability and reflect seasonal dynamics of their ecosystem. In the subtropics, the hydrological regime is usually characterized by well‐defined wet and dry seasons, regulating discharge and influencing a series of environmental variables that affect phytoplankton persistence. Therefore, we may expect that dry seasons are environmentally more stable than wet seasons. We analysed interannual phytoplankton assemblage variability (or, inversely, persistence) in a subtropical reservoir sampled every austral summer and winter during 5 years. We tested (i) if phytoplankton assemblage structure differed between the dry (summer) and wet (winter) seasons; (ii) if assemblage persistence differed between the seasons; (iii) if assemblage persistence was related to environmental stability; and (iv) if assemblage dissimilarity increased over time. Phytoplankton assemblages differed between the summer and winter seasons. Winter indicator species were mostly Bacillariophyceae or Cryptophyceae, whereas Cyanophyceae and Chlorophyceae taxa were more frequent and abundant in summer. Assemblages in the dry season were more persistent among years than those occurring during rainy periods. Similarly, environmental variability tended to be lower among dry than among rainy seasons. The relation between the phytoplankton temporal cycle and the temporal patterns of environmental variability supports our prediction that high environmental stability results in more persistent assemblages. Assemblage dissimilarity increased as sampling years were farther apart, for both seasons. Additionally, assemblages in the rainy periods showed a more pronounced increase in dissimilarity, as their changes among years were less predictable. We found a clear temporal pattern and an increased dissimilarity over time in the phytoplankton assemblage structure. Unravelling these temporal patterns may improve our understanding of phytoplankton temporal dynamics, and may have implications for management and monitoring programs. High dissimilarity of assemblages among years, particularly among rainy periods, can obscure human impacts, and monitoring programs should take this into account.     

Revision and phylogeny of the bee genus Paratetrapedia Moure,with description of a new genus from the Andean Cordillera (Hymenoptera,Apidae, Tapinotaspidini)

The bee genus Paratetrapedia represents a commonly collected group of bees and is especially diverse in forested areas of the Neotropics. Its taxonomy has remained poorly understood because of a lack of modern revisionary work and numerous species described as Tetrapedia whose type specimens have not been re‐examined in recent times. Here, a comprehensive study was carried out to review the taxonomy of the genus Paratetrapedia and to investigate cladistically the relationships amongst its species. Eighteen new species of Paratetrapedia are described, giving a total of 32 species in the genus. A phylogenetic analysis of the species of Paratetrapedia was carried out using 61 morphological characters for 41 terminal taxa. The phylogenetic results confirmed the monophyly of Paratetrapedia and allowed the recognition of five species groups: the lugubris, moesta, bicolor, lineata, and flavipennis groups. Nasutopedia gen. nov. , recognized as the sister group of Paratetrapedia and with its distribution restricted to the western forested portions of the Andean highlands, is proposed based on distinct morphology, its placement in the phylogenetic tree, and biogeographical patterns. Species of Paratetrapedia are especially diverse in the Amazon Forest; the eastern Brazilian Atlantic Forest contains four endemic species, and one species is endemic to the Cerrado of central Brazil. Paratetrapedia shows a biogeographical pattern similar to other Neotropical groups of bees and birds, with wide distribution and high diversity in lowland forests and whose sister taxon occurs on highlands of north‐western portions of the Andean cordillera. Identification keys for males and females of all species are provided, as well as distribution maps and illustrations of general external morphology and genitalia. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 351–442.     

Peroxisomal APX knockdown triggers antioxidant mechanisms favourable for coping with high photorespiratory H2O2 induced by CAT deficiency in rice

The physiological role of peroxisomal ascorbate peroxidases (pAPX) is unknown; therefore, we utilized pAPX4 knockdown rice and catalase (CAT) inhibition to assess its role in CAT compensation under high photorespiration. pAPX4 knockdown induced co‐suppression in the expression of pAPX3. The rice mutants exhibited metabolic changes such as lower CAT and glycolate oxidase (GO) activities and reduced glyoxylate content; however, APX activity was not altered. CAT inhibition triggered different changes in the expression of CAT, APX and glutathione peroxidase (GPX) isoforms between non‐transformed (NT) and silenced plants. These responses were associated with alterations in APX, GPX and GO activities, suggesting redox homeostasis differences. The glutathione oxidation‐reduction states were modulated differently in mutants, and the ascorbate redox state was greatly affected in both genotypes. The pAPX suffered less oxidative stress and photosystem II (PSII) damage and displayed higher photosynthesis than the NT plants. The improved acclimation exhibited by the pAPX plants was indicated by lower H₂O₂ accumulation, which was associated with lower GO activity and glyoxylate content. The suppression of both pAPXs and/or its downstream metabolic and molecular effects may trigger favourable antioxidant and compensatory mechanisms to cope with CAT deficiency. This physiological acclimation may involve signalling by peroxisomal H₂O₂, which minimized the photorespiration.