Salt-Stimulated Bicarbonate-Dependent Photosynthesis in the Marine Angiosperm Zostera muelleri

Millhouse, J. and Strother, S. 1986. Salt-stimulated bicarbonate-dependentphotosynthesis in the marine angiosperm Zostera muelleri.—J.exp. Bot. 37: 965–976. Photosynthetic oxygen evolution in the seagrass Zostera muelleriIrmisch ex Aschers. was inhibited in iso-osmotic sucrose. Theapparent affinity of the leaves for CO₂ in seawater increasesfrom pH 8?2 to 8?9 indicating that as well as CO₂ may act as a substrate for photosynthesis. Theaffinity for CO₂ was lower in iso-osmotic sucrose and was notaffected by pH. Under these conditions was not a substrate for photosynthesis. The differencebetween the photosynthetic rate in seawater and iso-osmoticsucrose at the same concentration of CO₂ was used to estimate assimilation. The Briggs-Maskell equation, which allows for an unstirred layer around the tissuewas more appropriate than the Michaelis-Menten theory for calculatingthe apparent affinity of the leaf slices for CO₂. The apparentK_m CO₂ was calculated as 116 mmol m^–3 at pH 8?2 by Michaelis-Mentenkinetics but only 8?10 mmol m^–3 by the Briggs-Maskellequation. The stimulation by various ions in Seawater of use was investigated. The cations,in decreasing order of effectiveness were Ca²⁺, Mg²⁺, K⁺ andNa⁺ Anions were ineffective. No single cation at its concentrationin seawater was capable of supporting use at the rate observed in seawater. Acetazolamide,an inhibitor of carbonic anhydrase, inhibited the use of for photosynthesis but had littleeffect on CO₂ photosynthesis. Thus, carbonic anhydrase activityis required for -dependent photosynthesis. Key words: Zostera muelleri, photosynthesis, salinity     

Impact of non‐pathogenic bacteria on insect disease resistance: importance of ecological context

1. The aerial surface of plants is a habitat for large and diverse microbial communities; termed the phyllosphere. These microbes are unavoidably consumed by herbivores, and while the entomopathogens are well studied, the impact of non‐pathogenic bacteria on herbivore life history is less clear. 2. Previous work has suggested that consumption of non‐entomopathogenic bacteria induces a costly immune response that might decrease the risk of infection. However, we hypothesised that insect herbivores should be selective in how they respond to commonly encountered non‐pathogenic bacteria on their host plants to avoid unnecessary and costly immune responses. 3. An ecologically realistic scenario was used in which we fed cabbage looper, Trichoplusia ni Hübner, larvae on cabbage or cucumber leaves treated with the common non‐entomopathogenic phyllosphere bacteria, Pseudomonas fluorescens and P. syringae. Their constitutive immunity and resistance to a pathogenic bacterium (Bacillus thuringiensis; Bt) and a baculovirus (T. ni single nucleopolyhedrovirus) were then examined. 4. While feeding on bacteria‐treated leaves reduced the growth rate and condition of T. ni, there was no effect on immunity (haemolymph antibacterial and phenoloxidase activities and haemocyte numbers). Phyllosphere bacteria weakly affected the resistance of T. ni to Bt but the direction of this effect was concentration dependent; resistance to the virus was unaffected. Host plant had an impact, with cucumber‐fed larvae being more susceptible to Bt. 5. The lack of evidence for a costly immune response to non‐entomopathogenic bacteria suggests that T. ni are probably adapted to consuming common phyllosphere bacteria, and highlights the importance of the evolutionary history of participants in multi‐trophic interactions.     

locuseater and shadowboxer: programs to optimize experimental design and multiplexing strategies for genetic mark–recapture

Genetic mark–recapture requires efficient methods of uniquely identifying individuals. ‘Shadows’ (individuals with the same genotype at the selected loci) become more likely with increasing sample size, and bias harvest rate estimates. Finding loci is costly, but better loci reduce analysis costs and improve power. Optimal microsatellite panels minimize shadows, but panel design is a complex optimization process. locuseater and shadowboxer permit power and cost analysis of this process and automate some aspects, by simulating the entire experiment from panel design to harvest rate estimation.     

Rapid climate change-related growth decline at the southern range edge of Fagus sylvatica

Studies on Fagus sylvatica show that growth in populations toward the southern limit of this species' distribution is limited strongly by drought. Warming temperatures in the Mediterranean region are expected to exacerbate drought where they are not accompanied by increases in precipitation. We studied levels of annual growth in mature F. sylvatica trees over the last half‐century in the Montseny Mountains in Catalonia (northeast Spain). Our results show significantly lower growth of mature trees at the lower limit of this species' distribution when compared with trees at higher altitudes. Growth at the lower Fagus limit is characterized by a rapid recent decline starting in approximately 1975. By 2003, growth of mature trees had fallen by 49% when compared with predecline levels. This is not an age‐related phenomenon, nor is it seen in comparable populations at higher altitudes. Analysis of climate‐growth relationships suggests that the observed decline in growth is a result of warming temperatures and that, as precipitation in the region has not increased, precipitation is now insufficient to ameliorate the negative effects of increased temperatures on tree growth. As the climate‐response of the studied forest is comparable with that of F. sylvatica forests in other southern European regions, it is possible that this growth decline is a more widespread phenomenon. Warming temperatures may lead to a rapid decline in the growth of range‐edge populations and a consequent retreat of the species distribution in southern Europe. Assessment of long‐term growth trends across the southern range edge of F. sylvatica therefore merits further attention.     

Species richness estimates of Blattodea s.s. (Insecta: Dictyoptera) from northern Guyana vary depending upon methods of species delimitation

Cockroaches (Order: Blattodea) comprise a taxon that, although very abundant in tropical forests, remains largely unstudied. Making sense of the diversity of species is a challenging task hindered by the large numbers of species and the abundance of cryptic or polymorphic forms. Here, we estimated species richness of cockroaches (s.s.) from northern Guyana while applying a method to deal with these confounding factors. We utilized two interpretations of abundance data, the first using only morphological information, and the second using both morphological and genetic barcode information. The two methods of species delimitation greatly influenced the resulting estimates of species richness. When incorporating genetic barcodes, our total species richness estimate decreased by 26%. Our results emphasize the importance of using independent datasets to delimit species boundaries and expert identification of specimens when possible.     

What evidence exists for alternative ecological regimes in salinising wetlands?

1. Land clearing in Australia's southwest has led to widespread salinisation of aquatic ecosystems. Four different ecological regimes (clear, submerged macrophyte‐dominated; clear, benthic microbial community‐dominated; turbid, phytoplankton‐dominated; and turbid, sediment‐dominated) have previously been identified in the salinising wetlands of this region. 2. Monitoring data from seven saline wetlands over an 18‐month period were used to evaluate whether a continuum, simple threshold or alternative regimes conceptual model (sensu Hydrobiologia, 200/201, 1990, 367; Hydrobiologia, 200/201, 1990, 475) most appropriately represented transitions between these ecological regimes. We also aimed to identify whether factors other than salinity played a major role in defining ecological regimes or causing shifts between them. 3. Ordination of biological variables revealed a separation of benthic microbial community‐dominated from submerged macrophyte‐dominated sites and times. The mean salinities of these two groups were very similar, suggesting that a salinity threshold was not responsible for benthic microbial versus macrophyte dominance. No other environmental variable was found to have a strong, direct influence on the groupings. 4. The dynamics of regime change in saline wetlands appear not to be driven by any single variable, but by the combined effects of salinity and water regime on species life histories and competitive abilities. Macrophytes were powerful competitors, able to germinate and establish under a range of salinities, turbidities and water depths, and were favoured by seasonal drying. 5. Data from the seven wetlands indicated that the continuum, simple threshold and alternative regimes conceptual models did not appropriately represent transitions between ecological regimes in seasonally drying wetlands. Macrophyte and benthic microbial regimes occurred at overlapping salinity levels, excluding both the continuum and threshold models, and the regular occurrence of drying appeared to preclude the alternative regimes model. Drying prevented the development of strong positive feedback mechanisms, which might otherwise have maintained the benthic microbial community‐dominated regime. We hypothesise that an alternative regimes model might still be valid for salinising ecosystems holding permanent water.