Ecological differentiation between the Sardinian endemic Maniola nurag and the pan-European M. jurtina

Recently refined evolutionary theories have highlighted that ecological interactions and environmental gradients can play a major role in speciation. This paper reports on a 3‐year field study, in which the ecology of two congeneric butterfly species was used to explore and compare the environmental factors determining their spatial distribution. These data are discussed in the context of possible speciation scenarios between the Sardinian populations of Maniola nurag and M. jurtina. M. nurag is endemic to the island of Sardinia, while M. jurtina is widespread over Europe. In Sardinia, the two species are locally sympatric. Mark–release–recapture experiments were combined with measures of environmental variables in 15 1‐ha plots, established in areas of potential habitat for the butterflies. Constrained linear models were parameterized from mark–recapture data to estimate both individual (survival and capture probabilities) and population (population size and recruitment) parameters. The two species had similar demography, movement patterns, life history, and behaviour. Population sizes developed in a parabolic fashion from beginning to end of the flight season. Differences included local population size, adult phenology, and habitat requirements. Long‐distance movements larger than 1.5 km were observed, suggesting a substantial amount of gene‐flow between populations of the endemic as well as the widespread species. Multivariate analyses revealed four main environmental gradients responsible for the abundance of the butterflies in an area. Both species responded similarly to environmental variables. However, each species’s abundance was correlated with a different environmental gradient determined by vegetation cover and structure. When sympatric, the two species responded to subtle differences in microhabitat structure. This might originally have induced their divergence. This study is an example of how empirical field data on population dynamics, dispersal, and habitat characteristics of two sympatric congeners can further our understanding of how species differentiate despite existing gene‐flow. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89 , 561–574.     

Alterations in light-induced stomatal opening in a starch-deficient mutant of Arabidopsis thaliana L. deficient in chloroplast phosphoglucomutase activity

Stomatal responses to light of Arabidopsis thaliana wild-type plants and mutant plants deficient in starch (phosphoglucomutase deficient) were compared in gas exchange experiments. Stomatal density, size and ultrastructure were identical for the two phenotypes, but no starch was observed in guard cells of the mutant plants whatever the time of day. The overall extent of changes in stomatal conductance during 14 h light–10 h dark cycles was similar for the two phenotypes. However, the slow endogenous stomatal opening occurring in darkness in the wild type was not observed in the mutant plants. Stomata in the mutant plants responded much more slowly to blue light (70 μmol m^?2 s^?1) though the response to red light (250 μmol m^?2 s^?1) was similar to that of wild-type plants. In paradermal sections, stomatal responses to red light (300 μmol m^?2 s^?1) were weak for wild-type plants as well as for mutant plants. Stomatal opening was greater under low blue light (75 μmol m^?2 s^?1) than under red light for the two genotypes. However, in mutant plants, a high chloride concentration (50 mol m^?3) was necessary to achieve the same stomatal aperture as observed for the wild-type plants. These results suggest that starch metabolism, via the synthesis of a counter-ion to potassium (probably malate), is required for full stomatal response to blue light but is not involved in the stomatal response to red light.     

Protein haploinsufficiency drivers identify MYBPC3 variants that cause hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease. Variants in MYBPC3, the gene encoding cardiac myosin-binding protein C (cMyBP-C), are the leading cause of HCM. However, the pathogenicity status of hundreds of MYBPC3 variants found in patients remains unknown, as a consequence of our incomplete understanding of the pathomechanisms triggered by HCM-causing variants. Here, we examined 44 nontruncating MYBPC3 variants that we classified as HCM-linked or nonpathogenic according to cosegregation and population genetics criteria. We found that around half of the HCM-linked variants showed alterations in RNA splicing or protein stability, both of which can lead to cMyBP-C haploinsufficiency. These protein haploinsufficiency drivers associated with HCM pathogenicity with 100% and 94% specificity, respectively. Furthermore, we uncovered that 11% of nontruncating MYBPC3 variants currently classified as of uncertain significance in ClinVar induced one of these molecular phenotypes. Our strategy, which can be applied to other conditions induced by protein loss of function, supports the idea that cMyBP-C haploinsufficiency is a fundamental pathomechanism in HCM.     

SO2-dependent cation competition and compartmentalization in Norway spruce needles

Ion contents in needles from Norway spruce trees [Picea abies (L.) Karst.] growing in Würzburg and in the SO₂-polluted Erzgebirge mountains were analysed to quantify cations which accumulate together with sulphate. In Würzburg there was a positive correlation of potassium (0.680 ± 0.300 Eq Eq^?1 SO₄^?2), magnesium (0.415 ± 0.111 Eq Eq^?1 SO₄^?2) and zinc (0.059 ± 0.006 Eq Eq^?1 SO₄^2?). In the Erzgebirge, potassium was also the stoichiometrically most important cation (0–887 ± 0–180 Eq K⁺ Eq^?1 SO₄^2?). All other correlations examined were weak or statistically non-significant. At both sites the calcium content of spruce needles did not depend on the sulphate content. The lack of a role for Ca²⁺ in neutralizing sulphate is a consequence of the presence of free oxalic acid in needles. Soluble oxalic acid precipitates Ca²⁺, which thereby becomes unavailable as a counterion for SO₄^2?. The activity coefficients of Ca²⁺ and oxalate^2?, and the solubility product of Ca-oxalate, were determined from in vivo data. It is concluded that the chronic accumulation of atmospheric sulphate in spruce needle vacuoles depletes available potassium and thereby strongly interferes with spruce growth and canopy turnover. This leads to impaired spruce vitality, even at sites where acute SO₂ disease symptoms are absent.     

ODOR PERCEPTION OVER LIQUID EMULSIONS CONTAINING SINGLE AROMA COMPOUNDS: EFFECTS OF AROMA CONCENTRATION AND OIL VOLUME FRACTION

This study aimed to check the hypothesis that aroma concentration in the aqueous phase of an oil-in-water emulsion controlled the odor intensity of single aroma compounds. A set of flavored oil-in-water emulsions, prepared according to a 2² experimental design (aroma concentration, oil volume fraction) with two central points, was assessed for odor intensity by a 24-member panel during four sessions. In each session, three of the four-studied aroma molecules (benzaldehyde, ethyl butyrate, linalool and acetophenone) were investigated. Whatever the aroma, the experimental data showed that the oil volume fraction of the emulsion (from 0.12 to 0.48) did not influence the odor intensity. For each emulsion composition, aroma concentrations at equilibrium in both phases were calculated using the oil-water partition coefficient of the compound. Odor intensities, estimated from aroma concentration in the aqueous phase using previously reported modeling of odor intensity above water solutions, were then compared to experimental data. It is confirmed that the perceived odor intensity is governed by the aroma concentration in the aqueous phase at the time of the trial and not by the averaged apparent concentration in the emulsion.     

Elevated CO2 enhances stomatal responses to osmotic stress and abscisic acid in Arabidopsis thaliana

A , carbon assimilation rate
ABA, abscisic acid
Ci , intercellular space CO₂ concentration
g , leaf conductance
WUE, water use efficiency

Carbon dioxide and abscisic acid (ABA) are two major signals triggering stomatal closure. Their putative interaction in stomatal regulation was investigated in well-watered air-grown or double CO₂-grown Arabidopsis thaliana plants, using gas exchange and epidermal strip experiments. With plants grown in normal air, a doubling of the CO₂ concentration resulted in a rapid and transient drop in leaf conductance followed by recovery to the pre-treatment level after about two photoperiods. Despite the fact that plants placed in air or in double CO₂ for 2 d exhibited similar levels of leaf conductance, their stomatal responses to an osmotic stress (0·16–0·24 MPa) were different. The decrease in leaf conductance in response to the osmotic stress was strongly enhanced at elevated CO₂. Similarly, the drop in leaf conductance triggered by 1 μ M ABA applied at the root level was stronger at double CO₂. Identical experiments were performed with plants fully grown at double CO₂. Levels of leaf conductance and carbon assimilation rate measured at double CO₂ were similar for air-grown and elevated CO₂-grown plants. An enhanced response to ABA was still observed at high CO₂ in pre-conditioned plants. It is concluded that: (i) in the absence of stress, elevated CO₂ slightly affects leaf conductance in A. thaliana ; (ii) there is a strong interaction in stomatal responses to CO₂ and ABA which is not modified by growth at elevated CO₂.     

Hydrogen peroxide contributes to motor dysfunction in ulcerative colitis

Ulcerative colitis (UC) affects colonic motor function, but the mechanism responsible for this motor dysfunction is not well understood. We have shown that neurokinin A (NKA) may be an endogenous neurotransmitter mediating contraction of human sigmoid colonic circular muscle (HSCCM). To elucidate factors responsible for UC motor dysfunction, we examined the role of hydrogen peroxide (H(2)O(2)) in the decrease of NKA-induced response of HSCCM. As previously demonstrated, NKA-induced contraction or Ca(2+) increase of normal muscle cells is mediated by release of Ca(2+) from intracellular stores, because it was not affected by incubation in Ca(2+)-free medium (CFM) containing 200 microM BAPTA. In UC, however, CFM reduced both cell contraction and NKA-induced Ca(2+) increase, suggesting reduced Ca(2+) release from intracellular stores. In normal Ca(2+) medium, NKA and KCl caused normal Ca(2+) signal in UC cells but reduced cell shortening. The decreased Ca(2+) signal and contraction in response to NKA or thapsigargin were partly recovered in the presence of H(2)O(2) scavenger catalase, suggesting involvement of H(2)O(2) in UC-induced dysmotility. H(2)O(2) levels were higher in UC than in normal HSCCM, and enzymatically isolated UC muscle cells contained much higher levels of H(2)O(2) than normal cells, which were significantly reduced by catalase. H(2)O(2) treatment of normal cells in CFM reproduced the reduction of NKA-induced Ca(2+) release observed in UC cells. In addition, H(2)O(2) caused a measurable, direct release of Ca(2+) from intracellular stores. We conclude that H(2)O(2) may contribute to reduction of NKA-induced Ca(2+) release from intracellular Ca(2+) stores in UC and contribute to the observed colonic motor dysfunction.     

Role of caveolae in the pathogenesis of cholesterol-induced gallbladder muscle hypomotility

Muscle cells from human gallbladders (GB) with cholesterol stones (ChS) exhibit a defective contraction, excess cholesterol (Ch) in the plasma membrane, and lower binding of CCK-1 receptors. These abnormalities improved after muscle cells were incubated with Ch-free liposomes that remove the excess Ch from the plasma membrane. The present studies were designed to investigate the role of caveolin-3 proteins (Cav-3) in the pathogenesis of these abnormalities. Muscle cells from GB with ChS exhibit higher Ch levels in the plasma membrane that were mostly localized in caveolae and associated with parallel increases in the expression of Cav-3 in the caveolae compared with that in GB with pigment stones (PS). The overall number of CCK-1 receptors in the plasma membrane was not different between muscle cells from GB with ChS and PS, but they were increased in the caveolae in muscle cells from GB with ChS. Treatment of muscle cells from GB with ChS with a Galpha(i3) protein fragment increased the total binding of CCK-1 receptors (from 8.3 to 11.2%) and muscle contraction induced by CCK-8 (from 11.2 to 17.3% shortening). However, Galpha(q/11) protein fragment had no such effect. Moreover, neither fragment had any effect on muscle cells from GB with PS. We conclude that the defective contraction of muscle cells with excessive Ch levels in the plasma membrane is due to an increased expression of Cav-3 that results in the sequestration of CCK-1 receptors in the caveolae, probably by inhibiting the functions of Galpha(i3) proteins.