Diversity patterns of stygobiotic crustaceans across multiple spatial scales in Europe

1. Using species distribution data from 111 aquifers distributed in nine European regions, we examined the pairwise relationships between local species richness (LSR), dissimilarity in species composition among localities, and regional species richness (RSR). In addition, we quantified the relative contribution of three nested spatial units – aquifers, catchments and regions – to the overall richness of groundwater crustaceans.
2. The average number of species in karst and porous aquifers (LSR) varied significantly among regions and was dependent upon the richness of the regional species pool (RSR). LSR–RSR relationships differed between habitats: species richness in karstic local communities increased linearly with richness of the surrounding region, whereas that of porous local communities levelled off beyond a certain value of RSR.
3. Dissimilarity in species composition among aquifers of a region increased significantly with increasing regional richness because of stronger habitat specialisation and a decrease in the geographic range of species among karst aquifers. Species turnover among karst aquifers was positively related to RSR, whereas this relationship was not significant for porous aquifers.
4. The contribution of a given spatial unit to total richness increased as size of the spatial unit increased, although 72% of the overall richness was attributed to among-region diversity. Differences in community composition between similar habitats in different regions were typically more pronounced than between nearby communities from different habitats.
5. We conclude by calling for biodiversity assessment methods and conservation strategies that explicitly integrate the importance of turnover in community composition and habitat dissimilarity at multiple spatial scales.     

A Space-time Model of Carbon Translocation along a Shoot Bearing Fruits

A carbon-based model is described of the source-sink relationshipsof a stem bearing fruits in space and time and focusing on growthvariability along the branch. The novelty of the model comesfrom the aggregation of physiological processes taking intoaccount spatial aspects. The stem is represented as a set ofcompartments (metamers) connected to source (leafy shoots) andsink (fruits) compartments. Each leafy shoot forms one compartment.The fruit consists of three compartments involved in translocation(cytoplasm), structure (cell wall) and storage (vacuole). Physiologicalprocesses considered are photosynthesis, respiration of fruitsand leaves, translocation of assimilates and fruit growth. Assimilateproduction is regulated by sink strength. Carbon translocationbetween two compartments depends on the gradient of assimilateconcentration. The gradient induces carbon translocation fromthe most to the least concentrated compartment, except for thevacuole compartment into which translocation is possible whateverthe concentration gradient. Fruit growth, in terms of freshweight, results from the phloem water supplied to the fruitaccording to the concentration gradient between the fruit andthe stem. The model is calibrated for peach trees by comparingobserved and simulated fruit dry and fresh weights for a shootwith normal fruit load. The model simulates variability betweenpeach fruits and the effect of contrasting fruit loads. Accordingto this model, photosynthesis increases and assimilate concentrationsin leaves and phloem decrease with decreasing leaf:fruit ratioas reported in the literature. Simulated concentrations of assimilatesin the phloem range from 2 to 14%. Simulated concentration gradientsand specific mass transfer for peach trees range from 0.05 to0.17 g cm^-3m^-1and from 0 to 3 g cm^-2h^-1, respectively, and areof the same order of magnitude as those reported for variousother tree species. The model is used to analyse the effectof fruit position relative to the leaves. Copyright 1999 Annalsof Botany Company Peach tree, Prunus persica (L.) Batsch, model, carbohydrates, translocation, source-sink, fruit.     

Orthophosphate Relations of Root: NO-3 Effects on Orthophosphate Influx, Accumulation and Secretion into the Xylem

Lamaze, T., Sentenac, H. and Grignon, C. 1987. Orthophosphaterelations of root: NO^–₃effects on orthophosphate influx,accumulation and secretion into the xylem.—J. exp. Bot.38: 923–934. Orthophosphate (Pi) accumulation by barley (Hordeum vulgareL.) roots was specifically inhibited by NO^–₃ as comparedto Cl^– and SO₄^{2 –}, and Pi secretion into the xylemwas stimulated. The inhibition of Pi accumulation by NO^–₃was also observed in roots of intact photosynthesizing horsebean(Vicia faba L.), rice (Oryza sativa L.) and soybean (Glycinemax L.) plants. NO^–₃ effects on Pi transport by rootswere more thoroughly investigated with corn (Zea mays L.). Theywere due to intracellular NO^–₃. Pi secretion was stillstimulated by NO^–₃ after Pi withdrawal from the absorptionsolution. ³²Pi influx decreased during Pi accumulation, supportingthe hypothesis that this ion allosterically regulated its owntransport system by feedback control. This control was modulatedby other anions: the decrease was more pronounced in the presenceof nitrate. Chronologically, the depressive effect of NO^–₃on ³²Pi influx appeared after the inhibition of Pi accumulation.Furthermore, under conditions where Pi accumulation was notaffected by NO^–₃, ³²Pi influx and Pi secretion into thexylem became insensitive to the presence of nitrate. Our hypothesisis that the stimulative effect of NO^–₃ on Pi secretionand the depressive one on ³²Pi influx are the repercussionsof an increase in the Pi cytosolic concentration due to an NO^–₃-induced decrease in Pi uptake by the vacuoles. Key words: Root, orthophosphate fluxes, orthophosphate accumulation, nitrate, ionic interaction     

Does the M-Phase Promoting Factor (MPF) Activate a Major Ca2+-and Cyclic Nucleotide-Independent Protein Kinase in Starfish Ocytes?

In starfish, the activity of a major Ca²⁺-and cyclic nuleotide-independent protein kinase has been shown to fluctuate in phase with that of MPF along meiotic and mitotic cell cycle (23, 25). Microinjection of α-naphthylphosphate (α-NP), a potent phosphatase inhibitor, increased considerably (from 15 to 546 picomoles/min/mg protein) the activity of this major cycling kinase in homogenates. Although this result supported the view that kinase phosphorylation might induce its own activation, this hypothesis was eliminated because injection of cytoplasm from hormone-stimulated enucleated oocytes, which contained the fully activated kinase but no MPF, failed to trigger kinase activation in recipient oocytes. In contrast, kinase activation was induced in recipient oocytes injected with either cytoplasm taken from nucleated maturing oocytes, which contained high MPF and kinase activities, or cytoplasm taken later from hormone-stimulated and ATP-γ-S-injected oocytes which contained high MPF but low kinase activites. These results indicate that inhibiting dephosphorylation of some regulatory protein activates the M-phase-specific protein kinase. The possibility that the M-phase or maturation-promoting factor (MPF) might be this regulatory protein is discussed.     

Revision of the class Sorberacea (benthic tunicates) with descriptions of seven new species

The benthic deep-sea class Sorberacea (Tunicata) is revised. All known species are redescribed and figured and seven new species are added. Diagnoses of the genera Sorbera, Gasterascidia, Oligotrema and Hexadactylus are given. The new generic name Hexadactylus replaces Hexacrobylm and a tabular key to the 12 species is provided. Hypotheses about the evolutionary processes in the Sorberacea are proposed and a comparison with Ascidiacea is given. The geographical distribution of sorberacean species and biogeographical affinities are discussed. The bathymetric distribution is particularly large since this class is characteristic of deep-sea bottoms.     

Theoretical habitat templets, species traits, and species richness: aquatic macrophytes in the Upper Rhône River and its floodplain

• 1 The objective of this study, which is based on forty-two species of hydrophytes and helophytes, is to investigate: (i) relationships among species traits; (ii) habitat utilization by species; (iii) the relationship between species traits and habitat utilization; (iv) trends in species traits in the framework of spatial–temporal habitat variability, and if trends match predictions from the river habitat templet; and (v) trends in species richness in the framework of spatial–temporal habitat variability, and if trends match predictions of the patch dynamics concept.
• 2 Two data sets were used for this analysis: species traits (mainly reproductive and morphological characteristics) were documented from the literature; and species distribution across eight habitat types was from field surveys conducted in the floodplain of the Upper Rhone River, France. This information was structured by a fuzzy coding technique and analysed by ordination methods.
• 3 Several species traits, which are related to disturbances and reflect resistance (e.g. attachment to soil or substrate) or resilience (e.g. potential for regeneration of an individual), are closely related for aquatic macrophytes.
• 4 Habitat utilization by aquatic macrophytes separates the habitat types along a gradient of connectivity with the main channel, which corresponds to a gradient in flood disturbance frequency and the permanence of the different water-bodies.
• 5 The relationship between species traits and habitat utilization is highly significant, indicating that a particular set of habitat types is used by taxa with a particular set of species trait modalities.
• 6 Observations in one habitat templet (in which scaling of the templet is primarily based on water level fluctuations for the temporal variability axis and on substrate characteristics for the spatial variability axis) generally do not support predictions on trends in species traits but do support predictions on trends in species richness.
• 7 Observations in an alternative habitat templet (in which scaling of the templet is based on frequency of flood scouring for the temporal variability axis and on heterogeneity of the substrate for the spatial variability axis) support theoretical predictions on trends for about half of the species traits for which predictions were available. However, trends in species richness in this alternative habitat templet are only partly in agreement with predictions.

     

High Altitude Adaptation in Mammals

The physiological, morphological, and biochemical characteristicsof several species of mammals resident at high altitude arecompared with those of their sea level counterparts. The differencesnoted in these characteristics are in a direction that facilitatesthe acclimatization of those living at high altitude. The differencesamong species point to the fact that the mechanism of adaptationto altitude (i.e., hypoxia) is still not understood. This reviewemphasizes that the adaptive process is complex and made upof several components, that these components are inter-related,and that neither the physiological nor morphological adaptationscan fully account for the tolerance to hypoxia. Although onlysuperficially studied as yet, the biochemical adaptations appearmost important.