Evaluating the performance of benthic multi-metric indices across broad-scale environmental gradients

The usefulness of benthic multi-metric indices when assessing seafloor integrity across broad environmental gradients should be deliberated, as their lack of transparency might hide important sources of variation and fail to identify environmental change. This study compares the performance of two multi-metric indices; the Benthic Quality Index (BQI) and the Brackish water Benthic Index (BBI) between three sub-basins in the Baltic Sea. Both indices reflect the salinity-driven gradient in macroinvertebrate diversity and composition as well as changes in bottom water oxygen concentrations. The relative contribution of predictor variables for explaining index variation does, however, differ between sub-basins, resulting in the indices representing different aspects of the benthic community along the environmental gradient. This context-dependency is caused by inherent differences in benthic community characteristics between the sub-basins of the Baltic Sea, and how the communities are portrayed by the indices. An increased transparency of the importance of the different predictors for directing index values is needed for coherent classifications over broad environmental gradients, such as those occurring in large estuarine water bodies. Use of a weight of evidence table to combine multiple indicators would preserve transparency and be more likely to provide a robust assessment method that would detect seafloor degradation at an early stage.     

Comparison of the temporal properties of medium latency responses induced by cortical and peripheral stimulation

Sudden foot dorsiflexion lengthens soleus muscle and activates stretch-based spinal reflexes. Dorsiflexion can be triggered by activating tibialis anterior (TA) muscle through peroneal nerve stimulation or transcranial magnetic stimulation (TMS) which evokes a response in the soleus muscle referred to as Medium Latency Reflex (MLR) or motor-evoked potential-80 (Soleus MEP80), respectively. This study aimed to examine the relationship between these responses in humans. Therefore, latency characteristics and correlation of responses between soleus MEP80 and MLR were investigated. We have also calculated the latencies from the onset of tibialis activity, i.e., subtracting of TA-MEP from MEP80 and TA direct motor response from MLR. We referred to these calculations as Stretch Loop Latency Central (SLLc) for MEP80 and Stretch Loop Latency Peripheral (SLLp) for MLR. The latency of SLLc was found to be 61.4 ± 5.6 ms which was significantly shorter (P = 0.0259) than SLLp (64.0 ± 4.2 ms) and these latencies were correlated (P = 0.0045, r = 0.689). The latency of both responses was also found to be inversely related to the response amplitude (P = 0.0121, r = 0.451) probably due to the activation of large motor units. When amplitude differences were corrected, i.e. investigating the responses with similar amplitudes, SLLp, and SLLc latencies found to be similar (P = 0.1317). Due to the identical features of the soleus MEP80 and MLR, we propose that they may both have spinal origins.     

Why did heterospory evolve?

The primitive land plant life cycle featured the production of spores of unimodal size, a condition called homospory. The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. The importance of desiccation‐resistant spores for colonization of the land is well known, but the adaptive value of heterospory has never been well established. It was an addition to a sexual life cycle that already involved male and female gametes. Its role as a precursor to the evolution of seeds has received much attention, but this is an evolutionary consequence of heterospory that cannot explain the transition from homospory to heterospory (and the lack of evolutionary reversal from heterospory to homospory). Enforced outcrossing of gametophytes has often been mentioned in connection to heterospory, but we review the shortcomings of this argument as an explanation of the selective advantage of heterospory. Few alternative arguments concerning the selective forces favouring heterospory have been proposed, a paucity of attention that is surprising given the importance of this innovation in land plant evolution. In this review we highlight two ideas that may lead us to a better understanding of why heterospory evolved. First, models of optimal resource allocation – an approach that has been used for decades in evolutionary ecology to help understand parental investment and other life‐history patterns – suggest that an evolutionary increase in spore size could reach a threshold at which small spores yielding small, sperm‐producing gametophytes would return greater fitness per unit of resource investment than would large spores and bisexual gametophytes. With the advent of such microspores, megaspores would evolve under frequency‐dependent selection. This argument can account for the appearance of heterospory in the Devonian, when increasingly tall and complex vegetative communities presented competitive conditions that made large spore size advantageous. Second, heterospory is analogous in many ways to anisogamy. Indeed, heterospory is a kind of re‐invention of anisogamy within the context of a sporophyte‐dominant land plant life cycle. The evolution of anisogamy has been the subject of important theoretical and empirical investigation. Recent work in this area suggests that mate‐encounter dynamics set up selective forces that can drive the evolution of anisogamy. We suggest that similar dispersal and mating dynamics could have underlain spore size differentiation. The two approaches offer predictions that are consistent with currently available data but could be tested far more thoroughly. We hope to re‐establish attention on this neglected aspect of plant evolutionary biology and suggest some paths for empirical investigation.     

Rare species habitat suitability assessment and reliability evaluation of an expert-based model: A case study of the insectivorous plant Pinguicula crystallina Sibth. et Smith subsp. hirtiflora (Ten.) Strid (Lentibulariaceae)

The development of habitat suitability models requires a large amount of data which are rarely available. In this case, researchers need to get information on the ecological features of the studied species, based on the opinion of experts or on the literature, to construct a qualitative model. However, such models cannot be rigorously evaluated, as in most cases absence points are not available. In this paper, we assess the habitat suitability for a vulnerable insectivorous plant, Pinguicula crystallina Sibth. et Smith subsp. hirtiflora (Ten.) Strid (Lentibulariaceae) in the Campania region. Our aim was to develop an expert-based, presence-only model in support of possible conservation actions. Topographic and geological features of this species suggested by the literature were used in our model. Both the Boyce index and field surveys were chosen to evaluate the model's reliability. During field surveys, 31 absence sites and 1 new presence site were identified, and differences between sites with regard to water chemistry and quality were investigated, water being an element in the species habitat. Factors that affect reliability of the model, such as the lack of a large amount of information on the species and the limited spatial resolution of geographical information system data, are discussed.     

Recommended gas transport properties of argon at low density using ab initio potential

The most important transport properties of argon have been calculated using classical kinetic theory expressions in conjunction with high-quality ab initio potential energy values computed by Patkowski and Szalewicz. Dilute gas transport properties have been calculated for the viscosity, thermal conductivity, self-diffusion coefficient and thermal diffusion factor from 83 to 10,000 K. Comparisons between experimental transport property data and values presently calculated indicate that the present theoretical predictions may be employed as recommended values for this set of transport properties over a wide temperature range.     

Influence of light on plant allelochemicals: A synergistic defense in higher plants

Plant phototoxins are broad-spectrum biocides which adversely affect an array of potential plant enemies, including among others disease-causing pathogens, nematodes, insect herbivores, and competing plant species. Thus far, plants which contain these broad-spectrum allelochemicals have been found to occur in open habitats (i.e., in full sunlight) where a defensive mechanism mediated by light would seem to operate most effectively. The levels of available light in shaded environments, although considerably lower than full sun (1–10% of full sun), are equivalent to the intensities of light used to kill phototoxin-treated insects in laboratory studies. This suggests that phototoxic reactions might mediate important organismal interactions in shaded environments as well. In this study, more than 230 Costa Rican rainforest plants were bioassayed for phototoxic metabolites in an effort to ascertain their prevalence among plants growing in moderate to extreme shade. Microbial bioassays, employing Bacillus cereus (a gram positive bacterium), Escherichia coli (a gram negative bacterium), and Saccharomyces cerevisiae (a yeast) were used to rapidly and sensitively indicate phototoxic action and potential for insecticidal action. Tissue extracts from 12 plant families tested positive for phototoxins. This is the first report of phototoxins occurring in eight of those families (Acanthaceae, Campanulaceae, Gesnariaceae, Loganiaceae, Malpigaceae, Phytolaccaceae, Piperaceae, and Sapotaceae). The presence of phototoxins in rainforest plants suggests that phototoxic plant allelochemicals may function as important defenses in low-light, as well as high-light, environments.     

Gas exchange and resource-use patterns along a Mediterranean successional gradient

Abstract. Gas exchange, leaf-nitrogen concentration and water potential were measured in early and late spring in early successional herbaceous plants occurring after cutting and after fire, and in mature woody species from the Mediterranean climax community Quercetum ilicis in central Italy. Net photosynthesis peaked in early spring in all species studied when values for temperature and light were lower but leaf-nitrogen content was higher as compared to late spring, suggesting that nitrogen more than energy input controlled photosynt-hetic rates. Herbaceous pioneer species occurring after cutting showed higher field photo synthetic capacity than evergreen climax trees and shrubs. By contrast, net photosynthesis of herbaceous species occurring in a persistent stage after fire, was in the same range as that of climax trees. This evidence suggests that carbon-gaining appears to be partly related to the dynamic stage of succession and not solely to the growth form.     

The effect of water stress on the vacuole-extravacuole compartmentation of proline in potato cell suspension cultures

Solute compartmentation in cells is an important component of metabolic regulation. There is only little information on how stress treatment of cells effects this component. Therefore, the effect of water stress [10% (w/v) PEG 6000] on the vacuolar-extravacuolar proline compartmentation was studied in a cell suspension culture of Svlanum tuberosum L, cv, HH258, In non-stressed cells 34% of the total cellular proline was located in the vacuole. After 20 h of water stress the proline pool of the cells was increased 4-6 fold and only t6% of it was found in the vacuole. A negative correlation between the total cellular proline content and its percentage in the vacuole was observed, irrespective of the culture method (stress or non-stress culture). The stress-induced changes in proline compartmentation are discussed.     

Coping with drought: diapause plasticity in katydid eggs at high,mid-, and low elevations

1. Semi-arid rangeland productivity is limited by precipitation, and yet droughts are projected to increase in frequency and duration with unknown impacts on insect populations. As some katydids prolong diapause and remain in an egg bank as a blastoderm for multiple growing seasons, is it possible that drought could prolong diapause and promote outbreaks by synchronising embryonic development and hatching of Mormon crickets, Anabrus simplex, after moisture is restored? 2. In this study, a high-elevation Wyoming population (WY) was compared with a mid-elevation Idaho (ID) and a low-elevation Oregon population (OR). It was predicted that eggs from the drier ID and OR habitats would be more tolerant of desiccation. Developmental state and water loss of eggs were measured after drought treatments, and when moisture was restored. 3. The two drier treatments had significantly more WY eggs prolonging diapause until after drought ended compared with the two wetter treatments. Whether WY eggs developed in the second or subsequent warm periods was independent of drought treatments. Significantly fewer OR embryos developed in the driest treatment compared with the others, whereas almost all ID eggs developed irrespective of the drought treatment. 4. In conclusion, Mormon crickets can delay embryonic development to improve drought tolerance. Although drought did not synchronise development and hatching, diapause plasticity allowed insects to cope and await more favourable conditions. 5. Unexpectedly, eggs from WY (the highest, wettest site) were more tolerant, because postponing development resulted in less water loss than in developed embryos. OR egg loss was also reduced by prolonging diapause, relative to ID, which developed in even the driest conditions.