United in adversity: Aridity and cold influence aggregation behaviour in a social lizard,Egernia stokesii

Sociality has evolved independently many times in a diverse array of animal taxa. While sociality in some invertebrates, birds and mammals is relatively well understood, complex social behaviour in Squamate reptiles is a comparatively recent discovery. The extent to which social behaviour is phylogenetically constrained, or free to respond to environmental conditions is a key question in understanding sociality. We sampled 74 aggregations involving 137 individuals of a social lizard (Egernia stokesii) from 13 sites across a 96 250 km² area showing a wide range of environmental conditions. Over all locations, 70% of the lizards were found in aggregations, supporting the previous suggestion that aggregation in this species is phylogenetically constrained. However, the size of aggregations was negatively related to spatial variation in aridity and daily variation in maximum temperature, suggesting that social behaviour also varied in response to harsh environmental conditions. Lizards aggregated more in arid areas and on cold days. Our results show that it is overly simplistic to regard social behaviour in E. stokesii as either phylogenetically constrained or environmentally determined. A more nuanced appreciation of the extent to which social behaviour is free to vary in response to environmental conditions improves our understanding of social behaviour in Squamate reptiles.     

Volatiles released from foliar extract of host plant enhance landing rates of gravid Polygonia c‐album females,but do not stimulate oviposition

The role of olfactory cues for host search is much less investigated in day‐active butterflies than in their relatives, the nocturnal moths. The goal of this study was to investigate whether host‐plant volatiles from foliar extracts of hop, Humulus lupulus L. (Cannabaceae), evoke electroantennographic (EAG) responses, increase landing rates, and stimulate egg‐laying behavior of gravid Polygonia c‐album L. (Lepidoptera: Nymphalidae) females. Eighty‐nine volatile compounds were detected in a non‐concentrated methanol extract of hop by gas chromatography–mass spectrometry, 11 of which elicited an EAG response. Concentration of the crude extract significantly reduced landing rates on artificial leaves treated with the sample due to loss of volatile compounds, but after landing the oviposition response of gravid females was not affected. A mixture of eight commercially available EAG‐active volatiles increased the landing rate of gravid females to their source but did not act as oviposition stimulants. Dividing the volatile compounds into two groups – consisting of (1) hexanal, (E)‐2‐hexenal, octanal, nonanal, and decanal, and (2) sulcatone, humulene, and benzyl alcohol – obliterated effectiveness, revealing synergism between compounds. Although volatiles did not stimulate oviposition, they significantly contributed to the distribution of eggs by increasing the landing rates on treated artificial leaves.     

Competition and facilitation between Australian and Spanish legumes in seven Australian soils

This paper evaluates the relative performance and competitive ability of seven legumes from the Iberian Peninsula, Spain (one already invasive in Australia), grown singly or pairwise with seven legumes from south‐western Australia in their own soils. Indices of growth used were root, shoot and total mass and shoot dimensions. Water content, xylem water potential during drying and nodule production were also measured. The index of competition used was the intensity of competition coefficient (ICC), which is suitable for additive designs. The Australian species usually grew larger than the Spanish species, in their presence or absence, although the results were sensitive to the index of growth or resource capture used. The Australian legumes usually possessed greater total water content than the co‐occurring Spanish legumes. At least five Australian species were less reduced or not affected at all by inter‐regional competition compared with growth in isolation. Two Australian legumes performed relatively poorly in the presence of at least four Spanish legumes. The ICC identified many instances of growth promotion (facilitation) of the Australian species, which we attribute to extra nitrogen obtained through enhanced nodulation of both cohabiting species. Five of the seven Spanish species were outcompeted by the Australian species, whereas the growth of two was sometimes facilitated. Although the Spanish legumes had greater competitive ability in the more fertile Australian soils, they remained competitively inferior to the Australian legumes in their first season of growth and none is likely to displace the native legumes at this stage of growth. Longer‐term field studies are needed to fully evaluate the potential invasiveness of perennial legumes.     

The response of an Eastern Amazonian rain forest to drought stress: results and modelling analyses from a throughfall exclusion experiment

Warmer and drier climates over Eastern Amazonia have been predicted as a component of climate change during the next 50–100 years. It remains unclear what effect such changes will have on forest–atmosphere exchange of carbon dioxide (CO₂) and water, but the cumulative effect is anticipated to produce climatic feedback at both regional and global scales. To allow more detailed study of forest responses to soil drying, a simulated soil drought or 'throughfall exclusion' (TFE) experiment was established at a rain forest site in Eastern Amazonia, Brazil, for which time-series sap flow and soil moisture data were obtained. The experiment excluded 50% of the throughfall from the soil. Sap flow data from the forest plot experiencing normal rainfall showed no limitation of transpiration throughout the two monitored dry seasons. Conversely, data from the TFE showed large dry season declines in transpiration, with tree water use restricted to 20% of that in the control plot at the peak of both dry seasons. The results were examined to evaluate the paradigm that the restriction on transpiration in the dry season was caused by limitation of soil-to-root water transport, driven by low soil water potential and high soil-to-root hydraulic resistance. This paradigm, embedded in the soil–plant–atmosphere (SPA) model and driven using on-site measurements, provided a good explanation ( R ² > 0.69) of the magnitude and timing of changes in sap flow and soil moisture. This model-data correspondence represents a substantial improvement compared with other ecosystem models of drought stress tested in Amazonia. Inclusion of deeper rooting should lead to lower sensitivity to drought than the majority of existing models. Modelled annual GPP declined by 13–14% in response to the treatment, compared with estimated declines in transpiration of 30–40%.     

Variable effects of arbuscular mycorrhizal fungal inoculation on physiological and molecular measures of root and stomatal conductance of diverse Medicago truncatula accessions

Association with arbuscular mycorrhizal fungi (AMF) can impact on plant water relations; mycorrhizal plants can exhibit increased stomatal conductance (g_s) and root hydraulic conductance (normalized to root dry weight, L_o), and altered expression of aquaporins (AQP). Many factors regulate such responses; however, plant intraspecific diversity effects have yet to be explored. Twenty geographically diverse accessions of Medicago truncatula were inoculated with the AMF Funneliformis mosseae or mock‐inoculated, and grown under well‐watered conditions. Biomass, g_s, shoot nutrient concentrations and mycorrhizal colonization were measured in all accessions, and L_o and gene expression in five accessions. The diverse accessions varied in physiology and gene expression; some accessions were also larger or had higher g_s when colonized by F. mosseae. In the five accessions, L_o was higher in two accessions when colonized by AMF and also maintained within a much smaller range than the mock‐inoculated plants. Expression of MtPIP1 correlated with both g_s and L_o, and when plants were more than 3% colonized, mycorrhizal colonization correlated with L_o. Accession and AMF treatments had profound effects on M. truncatula, including several measures of plant water relations. Correlations between response variables, especially between molecular and physiological variables, across genotypes, highlight the findings of this study.     

Water stress tolerance of shrubs in Mediterranean-type climate regions: Convergence of fynbos and succulent karoo communities with California shrub communities

Mediterranean-type climate regions are highly biodiverse and predicted to be particularly sensitive to climate change. Shrubs of the mediterranean-type climate region of South Africa are highly threatened, and their response to water stress has been comparatively little studied. Resistance to water stress induced xylem cavitation (P(50)) and xylem specific hydraulic conductivity (K(s)) were measured in 15 shrub species from fynbos and succulent karoo communities of South Africa. Species displayed a fivefold variation in cavitation resistance (P(50) of -1.9 to -10.3 MPa) with succulent karoo species displaying greater interspecific variability in P(50) than fynbos species. Principal components analysis (including P(50), minimum seasonal water potential, K(s), and xylem density) showed the response to water stress in fynbos species to be similar to chaparral species from the mediterranean-type climate region of California. The data suggest convergence of community and species-specific water stress "strategies" between these mediterranean-type climate regions with respect to their xylem traits. On the basis of the current study and reported plant death and dieback in these regions, woody species within the fynbos may be more susceptible to climate warming and drying than those within the succulent karoo that appear to be utilizing more diverse xylem strategies in response to water stress.     

Current-voltage relations of the basolateral membrane in tight amphibian epithelia: Use of nystatin to depolarize the apical membrane

Summary Exposure of the mucosal side of toad(Bufo bufo) urinary bladder and frog(Rana ridibunda) skin to the polyene ionophore nystatin, resulted in stable preparations in which the apical resistance was negligible compared to the basolateral resistance. The preparations support passive K currents in both directions and an amiloride-insensitive Na current in the apicalserosal direction which is blocked by ouabain. The nystatintreated toad bladder was used to study the electrical properties of the basolateral membrane by means of current-voltage curves recorded transepithelially. The K current showed strong rectification at cellular potentials negative with respect to the interstitial space. The ouabain-sensitive current increased with membrane voltage at negative voltages but saturated above+20 mV.     

The role of the National Trust in the conservation of British butterflies

The National Trust is of paramount importance in the conservation of butterflies in the UK on account of the scale of its land holding and its ability to manage habitats beneficially. Fifty two of the fifty four species currently regarded as resident in Britain occur on Trust land. The Trust has major responsibilities for the conservation of all bar one of the British rarities, and is of special significance in the conservation of the high brown fritillary and heath fritillary, two protected species. The Trust owns some 35 areas (many of which are large) of national importance for butterflies, plus much other property where the butterfly fauna is of regional importance. The Trust is implementing many dynamic projects aimed at conserving rare species, maintains a butterfly site data base and is developing a butterfly population monitoring programme. It is well placed to address the key issue of butterfly conservation on a metapopulation scale. To do this, it must work in partnership with other conservation organizations.     

Water relations, drought and vesicular-arbuscular mycorrhizal symbiosis

Vesicular-arbuscular mycorrhizal fungi can affect the water balance of both amply watered and droughted host plants. This review summarizes these effects and possible causal mechanisms. Also discussed are host drought resistance and the influence of soil drying on the fungi. Accepted: 30 December 2000     

Gas exchange and water balance of a mistletoe species and its mangrove hosts

Summary The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through the dry and wet season. In addition, carbon isotope ratios of leaf tissue were measured to further evaluate water use efficiency. Under similar light and humidity conditions, mistletoes had higher transpiration rates, lower leaf water potentials, and lower water use efficiencies than their hosts. Potassium content was much higher in mistletoes than in host leaves, but mineral nutrient content in the xylem sap of mistletoes was relatively low. The resistance of the liquid pathway from the soil to the leaf surface of mistletoes was larger than the total liquid flow resistance of host plants. Differences in the daily cycles of osmotic potential of the xylem sap also indicate the existence of a high resistance pathway along the vascular connection between the parasite pathway along the vascular connection between the parasite and its host. P. maritima mistletoes adjust to the different physiological characteristics of the host species which it parasitizes, thus ensuring an adequate water and carbon balance.