Stomatal Opening in Light of Different Wavelengths: Effects of Blue Light Independent of Carbon Dioxide Concentration

Stomatal opening in Xanthium pennsylvanicum was found to besignificantly greater in blue light than in red. Experimentsin which leaves were placed in a closed system and allowed toestablish their own steady-state carbon dioxide concentrationshowed that when the CO₂ concentration was about the same asthat in red, opening was much greater in blue light. Blue lightof low intensity could cause as great an opening as red of higherintensity, even though the CO₂ concentration was much higherin blue. Stomatal opening in light is considered as involvingat least two reactions: (1) a response to the removal of CO₂by photosynthesis; (2) a response to blue light not dependenton the removal of CO₂. Blue light became increasingly effective, relative to red, asthe length of night was increased over the range 2 to 14 hours.This might, in part, explain previously observed effects ofnight length on rate of opening in light. The initial very rapid phase of closure in darkness appearedto be independent of CO₂ accumulation, for it was not preventedby flushing the intercellular spaces with air free of CO₂. Itis suggested that closure in darkness, like opening in light,should be considered as involving components both dependentupon, and independent of, CO₂ concentration.     

RAPID ALDOSTERONE-INDUCED CELL VOLUME INCREASE OF ENDOTHELIAL CELLS MEASURED BY THE ATOMIC FORCE MICROSCOPE

Atomic force microscopy (AFM) is a useful technique for imaging the surface of living cells in three dimensions. The authors applied AFM to obtain morphological information of individual cultured endothelial cells of bovine aorta under stationary and strain conditions and to simultaneously measure changes in cell volume in response to aldosterone. This mineralocorticoid hormone is known to have acute, non-genomic effects on intracellular pH, intracellular electrolytes and inositol-1,4,5-triphosphate production. In this study whether endothelial cells under tension change their volume in response to aldosterone was tested. Such changes were already shown in human leukocytes measured by Coulter counter. In contrast to leukocytes that are more or less spherical and live in suspension, endothelial cells exhibit a complex morphology and adhere to a substrate. Thus, measurements of discrete cell volume changes in endothelial cells under physiological condition is only feasible with more sophisticated techniques. By using AFM we could precisely measure the absolute cell volume of individual living endothelial cells. Before the addition of aldosterone the cell volume of mechanically stressed endothelial cells mimicking arterial blood pressure was 1827±172fl. Cell volume was found to increase by 28% 5min after hormone exposure. Twenty-five minutes later cell volume was back to normal despite the continuous presence of aldosterone in the medium. Amiloride, a blocker of the plasma membrane Na⁺/H⁺exchanger prevented the initial aldosterone-induced volume increase. Taken together, AFM disclosed a transient swelling of endothelial cells induced by the activation of an aldosterone sensitive plasma membrane Na⁺/H⁺exchanger.     

Population genomics of the inbred Scandinavian wolf

The Scandinavian wolf population represents one of the genetically most well-characterized examples of a severely bottlenecked natural population (with only two founders), and of how the addition of new genetic material (one immigrant) can at least temporarily provide a 'genetic rescue'. However, inbreeding depression has been observed in this population and in the absence of additional immigrants, its long-term viability is questioned. To study the effects of inbreeding and selection on genomic diversity, we performed a genomic scan with approximately 250 microsatellite markers distributed across all autosomes and the X chromosome. We found linkage disequilibrium (LD) that extended up to distances of 50 Mb, exceeding that of most outbreeding species studied thus far. LD was particularly pronounced on the X chromosome. Overall levels of observed genomic heterozygosity did not deviate significantly from simulations based on known population history, giving no support for a general selection for heterozygotes. However, we found evidence supporting balancing selection at a number of loci and also evidence suggesting directional selection at other loci. For markers on chromosome 23, the signal of selection was particularly strong, indicating that purifying selection against deleterious alleles may have occurred even in this very small population. These data suggest that population genomics allows the exploration of the effects of neutral and non-neutral evolution on a finer scale than what has previously been possible.     

Enigmatic tubes associated with microbial crusts from the Late Jurassic of the Northern Calcareous Alps (Austria): a mutualistic sponge–epibiont consortium?

Irregular tube-shaped microfossils incertae sedis are a typical constituent of Late Jurassic shallow-water reefal carbonates of the Northern Calcareous Alps of Austria and are described in open nomenclature. The enigmatic, polymorphous spar-filled tubes with neither observable external nor internal skeletal elements occur either free within peloidal sediments or mostly fixed to skeletal substrates embedded in microbial crusts including the genera Labes Eliášová, Crescentiella Senowbari-Daryan et al . or Isnella Senowbari-Daryan. The tubes are varied in shape and closely resemble different taxa of sponges. As the microbial crusts preferentially occur associated with these tubiform microfossils, this association is suggested to be non-parasitic and mutualistic. Without the surrounding crusts, the existence of these animals would have been masked or perhaps even totally lost in the fossil record expressing the importance of these findings as a characteristic element in the inventory of Late Jurassic reefal biocoenoses.     

Climatic characteristics of heat waves and their simulation in plant experiments

Extreme events such as heat waves are emerging as a key facet of climate change, but to date, experiments on the impacts on plants are scarce. Experimental simulation of heat waves requires knowledge of regional heat wave characteristics, as plant responses depend heavily on meteorological conditions. We analysed nine Western European meteorological datasets, and found that heat waves occurring during the growing season in this region encompass more sunshine (+ 69%), lower precipitation (?78%) and a larger vapour pressure deficit (VPD) (+ 111%) compared with normal conditions. Possible consequences for plant responses are discussed, with emphasis on the likely seasonal variation of heat wave impacts. We explain why infrared heating (which typically increases VPD) is an appropriate technique for heat wave simulation. Finally, we advocate experiments to take into account the smaller nighttime compared with daytime temperature increases observed during heat waves, and the precipitation deficits before and during heat waves.     

Moderating mycorrhizas: arbuscular mycorrhizas modify rhizosphere chemistry and maintain plant phosphorus status within narrow boundaries

Pastures often experience a pulse of phosphorus (P) when fertilized. We examined the role of arbuscular mycorrhizal fungi (AMF) in the uptake of P from a pulse. Five legumes (Kennedia prostrata, Cullen australasicum, Bituminaria bituminosa, Medicago sativa and Trifolium subterraneum) were grown in a moderate P, sterilized field soil, either with (+AMF) or without (?AMF) addition of unsterilized field soil. After 9–10 weeks, half the pots received 15 mg P kg^?1 of soil. One week later, we measured: shoot and root dry weights; percentage of root length colonized by AMF; plant P, nitrogen and manganese (Mn) concentrations; and rhizosphere carboxylates, pH and plant‐available P. The P pulse raised root P concentration by a similar amount in uncolonized and colonized plants, but shoot P concentration increased by 143% in uncolonized plants and 53% in colonized plants. Inoculation with AMF decreased the amount of rhizosphere carboxylates by 52%, raised rhizosphere pH by ～0.2–0.7 pH units and lowered shoot Mn concentration by 38%. We conclude that AMF are not simply a means for plants to enhance P uptake when P is limiting, but also act to maintain shoot P within narrow boundaries and can affect nutrient uptake through their influence on rhizosphere chemistry.     

Molecular phylogeny of telenomine egg parasitoids (Hymenoptera: Platygastridae s.l.: Telenominae): evolution of host shifts and implications for classification

Parasitoid wasps of the subfamily Telenominae (Hymenoptera: Platygastroidea, Platygastridae) develop as immatures within the eggs of other insects (Lepidoptera, Hemiptera, Diptera and Neuroptera). Rearing records indicate that individual species are restricted to attack hosts within only one of these four main groups. We conducted a phylogenetic analysis of the group using sequence data from multiple genes (18S, 28S, COI, EF‐1α) to assess the pattern of shifts among host groups and to test the monophyly of and relationships among genera and species‐groups. Telenominae sensu Masner—that is, including only the nominate tribe Telenomini—is not monophyletic. Representatives of the Psix group of genera (Psix Kozlov & Lê and Paratelenomus Dodd) form a monophyletic group that is sister to Gryon Haliday (Scelioninae: Gryonini) and are excluded from the subfamily. The remaining telenomines are monophyletic. The genus Phanuromyia Dodd and the crassiclava group of Telenomus Haliday, both recorded as parasitoids of planthopper eggs (Hemiptera: Auchenorrhyncha, Fulgoroidea), form a monophyletic group that is sister to all other telenomines exclusive of the Psix group. Twenty‐nine species of the crassiclava and aradi groups of Telenomus are transferred to Phanuromyia as new combinations. Basal elements of the remaining species are all in groups reared from the eggs of true bugs (Heteroptera), primarily the stink bugs (Pentatomoidea) and seed bugs (Lygaeoidea). A shift to parasitism of lepidopteran eggs evolved within a single clade, occurring either one or two times. From this clade a small group of species, the Telenomus tabanivorus group, subsequently shifted to parasitism of egg masses of true flies (Tabanidae and Stratiomyiidae). Aholcus Kieffer and Platytelenomus Dodd both belong to the clade of lepidopteran parasitoids and are considered as junior synonyms of Telenomus (new synonymy for Aholcus). The monophyletic status of the two core genera, Telenomus and Trissolcus could not be resolved using these data. The phylogenetic pattern of host shifts suggests comparisons among taxa that may be fruitful in elucidating mechanisms by which parasitoids locate their hosts, the proximate factors that determine the host range, and the changes in these factors that influence host changes.     

Does bill size polymorphism affect courtship song characteristics in the African finch Pyrenestes ostrinus?

Vocal characteristics of bill morphs of the African finch Pyrenestes ostrinus were investigated to see whether there were differences between the morphs that could potentially lead to assortative mating. Morphological differences between bill morphs are of a scale that could change resonance characteristics, with as a physical consequence, a change in acoustic characteristics. Song and variation in acoustic characteristics are very likely to be an important factor in mate choice. We analysed recordings of large and small-billed birds, and measured 11 acoustic characteristics focusing on frequency use and possibly correlated temporal features. In addition, we investigated in more detail the energy distribution within the frequency limits. We found no differences between bill morphs in acoustic characteristics of courtship song. Our findings contrast with other empirical studies which show an impact of the suprasyringeal vocal tract on song output. One possible explanation could be that the morphological changes affect resonance characteristics in multiple ways which do not operate in concert. Beside proximate aspects, we discuss the role of song and the bill polymorphism in the context of sympatric speciation.