Response properties of the prothoracic AN2 auditory interneurone to model calling songs in the cricket Gryllus bimaculatus

Sound processing properties for calling song (CS) models, as described for the prothoracic L3 auditory neurone in Acheta domesticus, are investigated for the homologous auditory neurone 2 (AN2) in female Gryllus bimaculatus De Geer. AN2 of G. bimaculatus responds selectively to the syllable period (SP) of models of a male CS. The selectiveness of this response parallels the selectivity of phonotaxis females perform in response to the same SPs. Both, the responses of AN2 and female behaviour show clear interindividual variability. The SP‐selective responses of AN2 result from an SP‐dependent reduction in the spiking to subsequent syllables of the model CSs, measured as the percentage decrement. This SP‐dependent response does not primarily result from inbuilt properties of the AN2 membrane. Rather, it is dependent on inhibitory input to the AN2. However, clear inhibitory postsynaptic potentials in dendritic recordings of the AN2 are not encountered. This immediate response of AN2 to CSs is followed by an increased rate of tonic firing between stimulus CSs, which is termed the prolonged response, and is dependent on the carrier frequencies that make up the male CSs. With stimulation on the contralateral side of the soma of AN2s, more than 50% of AN2s exhibit a prolonged response. However, with stimulation from the ipsilateral side of the soma, most AN2s exhibit a prolonged response. The prolonged response of AN2 at 5 kHz may be even more sensitive than the immediate response. Thus, the AN2 neurone could provide a basis for phonotaxis that is selective for both the SPs and the carrier frequencies of potentially attractive calling songs.     

西方蜜蜂幼虫发育温度对成体翅膀形态的影响

为探讨不同恒定温度条件对培育蜜蜂蛹翅膀形态特征的影响,作者将进入蛹期的西方蜜蜂(Apismellifera)放入人工气候箱里,分别在32、35和36℃的恒定温度条件培育,直到蜜蜂蛹羽化出房为止。测量了蜜蜂翅膀的标准形态特征,包括翅的大小、肘脉长和11个翅肘脉角,所得到的数据进行多变量比较分析、相关性分析、主成分分析和区别分析。研究结果表明,不同温度条件对蜜蜂翅膀形态特征有明显的影响     

Processing of model calling songs by the prothoracic AN2 neurone and phonotaxis are significantly correlated in individual female Gryllus bimaculatus

Syllable period (SP) selective calling song processing has been demonstrated for the prothoracic, AN2 auditory neurone that correlates very well with SP‐selective phonotaxis by female cricket Gryllus bimaculatus De Geer. Both SP‐selective processing by the AN2 and the phonotactic behaviour of the female exhibit substantial plasticity. Thus, the question remains as to whether the selective responses of the AN2 neurone and the selective behaviour of the female match in an individual female. The present study is designed to answer that question. The SP‐selective phonotactic behaviour of individual females is evaluated, followed immediately by measuring the SP‐selective responses of the same female's AN2 neurone. Very significant correlations are found between the selective responses of the AN2 neurone and the same female's selective behaviour. In 208 possible comparisons (26 females, eight behavioural and neuronal tests each), 186 resulted in matches between behaviour and neuronal processing. Dividing the SP‐selective females into two groups (one group that responded phonotactically to the shortest SP tested and a second group that did not respond to this SP) resulted in significantly more selective responses to this shortest SP by the AN2 neurone in the females that responded phonotactically to the SP than for the females who did not respond to the shortest SP. The behavioural responses by these two groups to the other SPs tested are shown to be essentially identical.     

Regulation of nitrous oxide emission associated with benthic invertebrates

1. A number of freshwater invertebrate species emit N₂O, a greenhouse gas that is produced in their gut by denitrifying bacteria (direct N₂O emission). Additionally, benthic invertebrate species may contribute to N₂O emission from sediments by stimulating denitrification because of their bioirrigation behaviour (indirect N₂O emission). 2. Two benthic invertebrate species were studied to determine (i) the dependence of direct N₂O emission on the preferred diet of the animals, (ii) the regulation of direct N₂O emission by seasonally changing factors, such as body size, temperature and availability and (iii) the quantitative relationship between direct and indirect N₂O emission. 3. Larvae of the mayfly Ephemera danica, which prefer a bacteria‐rich detritus diet, emitted N₂O at rates of up to 90 pmol Ind.^?1 h^?1 under in situ conditions and 550 pmol Ind.^?1 h^?1 under laboratory conditions. In contrast, larvae of the alderfly Sialis lutaria, which prefer a bacteria‐poor carnivorous diet, emitted N₂O at invariably low rates of 0–20 pmol Ind.^?1 h^?1. The N₂O emission rate of E. danica larvae was positively correlated with seasonally changing factors (body size, temperature and availability). Direct N₂O emission by E. danica larvae was limited by low temperature in winter, larval development in spring and low availability in summer. 4. Both E. danica and the non‐emitting S. lutaria increased the total N₂O and N₂ emission from sediment in a density‐dependent manner. While N₂O directly emitted by benthic invertebrates can be partially consumed in the sediment (E. danica), non‐emitting species can still indirectly contribute to total N₂O emission from sediment (S. lutaria).     

Over‐expression of bacterial γ‐glutamylcysteine synthetase (GSH1) in plastids affects photosynthesis,growth and sulphur metabolism in poplar (Populus tremula × Populus alba) dependent on the resulting γ‐glutamylcysteine and glutathione levels

We compared three transgenic poplar lines over‐expressing the bacterial γ‐glutamylcysteine synthetase (GSH1) targeted to plastids. Lines Lggs6 and Lggs12 have two copies, while line Lggs20 has three copies of the transgene. The three lines differ in their expression levels of the transgene and in the accumulation of γ‐glutamylcysteine (γ‐EC) and glutathione (GSH) in leaves, roots and phloem exudates. The lowest transgene expression level was observed in line Lggs6 which showed an increased growth, an enhanced rate of photosynthesis and a decreased excitation pressure (1‐qP). The latter typically represents a lower reduction state of the plastoquinone pool, and thereby facilitates electron flow along the electron transport chain. Line Lggs12 showed the highest transgene expression level, highest γ‐EC accumulation in leaves and highest GSH enrichment in phloem exudates and roots. This line also exhibited a reduced growth, and after a prolonged growth of 4.5 months, symptoms of leaf injury. Decreased maximum quantum yield (F_v/F_m) indicated down‐regulation of photosystem II reaction centre (PSII RC), which correlates with decreased PSII RC protein D1 (PsbA) and diminished light‐harvesting complex (Lhcb1). Potential effects of changes in chloroplastic and cytosolic GSH contents on photosynthesis, growth and the whole‐plant sulphur nutrition are discussed for each line.     

Patterns and gradients of diversity in South Patagonian ombrotrophic peat bogs

Many north‐hemispherical mires seemingly untouched by drainage and cultivation are influenced by a diffuse sum of man‐made environmental changes, such as atmospherical nitrogen deposition that mask general patterns in species richness and functional group responses along resource gradients. To obtain insights into natural diversity‐environment relationships, we studied the vegetation and the peat chemistry of pristine bog ecosystems in southern Patagonia along a west–east transect across the Andes. The studied bog ecosystems covered a floristic gradient from hyperoceanic blanket bogs dominated by cushion building vascular plants via a transitional mixed type to Sphagnum‐dominated raised bogs east of the mountain range. To test the influence of resource availability on diversity patterns, species richness and functional groups were related to environmental variables by calculating general regression models and generalized additive models. Species richness showed strong linear correlations to peat chemical features and the general regression model resulted in three major environmental variables (water level, total nitrogen, NH₄Cl soluble calcium), altogether explaining 76% of variance. Functional group response illustrated a clear separation along environmental gradients. Mosses dominated at the low end of a nitrogen gradient, whereas cushion plants had their optimum at intermediate levels, and graminoids dominated at high nitrogen contents. Further shifts were related to NH₄Cl soluble calcium and water level. The models documented partly non‐linear relationships between functional group response and trophical peat properties. Within the three bog types, the calculated models differed remarkably illustrating the scale‐dependency of the explanatory factors. Our findings confirmed several general patterns of species richness and functional shifts along resource gradients in a surprisingly clear way and underpin the significance of undisturbed peatlands as reference systems for testing of ecological theory and for conservation and ecological restoration in landscapes with strong human impact.     

Meristem temperature substantially deviates from air temperature even in moderate environments: is the magnitude of this deviation species‐specific?

Meristem temperature (T_meristem) drives plant development but is hardly ever quantified. Instead, air temperature (T_air) is usually used as its approximation. Meristems are enclosed within apical buds. Bud structure and function may differ across species. Therefore, T_meristem may deviate from T_air in a species‐specific way. Environmental variables (air temperature, vapour pressure deficit, radiation, and wind speed) were systematically varied to quantify the response of T_meristem. This response was related to observations of bud structure and transpiration. Tomato and cucumber plants were used as model plants as they are morphologically distinct and usually growing in similar environments. T_meristem substantially deviated from T_air in a species‐specific manner under moderate environments. This deviation ranged between ?2.6 and 3.8 °C in tomato and between ?4.1 and 3.0 °C in cucumber. The lower T_meristem observed in cucumber was linked with the higher transpiration of the bud foliage sheltering the meristem when compared with tomato plants. We here indicate that for properly linking growth and development of plants to temperature in future applications, for instance in climate change scenarios studies, T_meristem should be used instead of T_air, as a species‐specific trait highly reliant on various environmental factors.     

Sixteen years of winter stress: an assessment of cold hardiness,growth performance and survival of hybrid poplar clones at a boreal planting site

In recent years, thousands of hectares of hybrid poplar plantations have been established in Canada for the purpose of carbon sequestration and wood production. However, boreal planting environments pose special challenges that may compromise the long‐term survival and productivity of such plantations. In this study, we evaluated the effect of winter stress, that is, frequent freeze‐thaw and extreme cold events, on growth and survival of 47 hybrid poplar clones in a long‐term field experiment. We further assessed physiological and structural traits that are potentially important for cold tolerance for a selected set of seven clones. We found that trees with narrow xylem vessels showed reduced freezing‐induced embolism and showed superior productivity after 16 growing seasons. With respect to cold hardiness of living tissues, we only observed small differences among clones in early autumn, which were nonetheless significantly correlated to growth. Maximum winter cold hardiness and the timing of leaf senescence and budbreak were not related to growth or survival. In conclusion, our data suggest that reduction of freezing‐induced embolism due to small vessel diameters is an essential adaptive trait to ensure long‐term productivity of hybrid poplar plantations in boreal planting environments.     

Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus)

A hybrid zone along an environmental gradient should contain a clinal pattern of genetic and phenotypic variation. This occurs because divergent selection in the two parental habitats is typically strong enough to overcome the homogenizing effects of gene flow across the environmental transition. We studied hybridization between two parapatric tree squirrels (Tamiasciurus spp.) across a forest gradient over which the two species vary in coloration, cranial morphology and body size. We sampled 397 individuals at 29 locations across a 600‐km transect to seek genetic evidence for hybridization; upon confirming hybridization, we examined levels of genetic admixture in relation to maintenance of phenotypic divergence despite potentially homogenizing gene flow. Applying population assignment analyses to microsatellite data, we found that Tamiasciurus douglasii and T. hudsonicus form two distinct genetic clusters but also hybridize, mostly within transitional forest habitat. Overall, based on this nuclear analysis, 48% of the specimens were characterized as T. douglasii, 9% as hybrids and 43% as T. hudsonicus. Hybrids appeared to be reproductively viable, as evidenced by the presence of later‐generation hybrid genotypes. Observed clines in ecologically important phenotypic traits—fur coloration and cranial morphology—were sharper than the cline of putatively neutral mtDNA, which suggests that divergent selection may maintain phenotypic distinctiveness. The relatively recent divergence of these two species (probably late Pleistocene), apparent lack of prezygotic isolating mechanisms and geographic coincidence of cline centres for both genetic and phenotypic variation suggest that environmental factors play a large role in maintaining the distinctiveness of these two species across the hybrid zone.