The measurement of stream metabolism (gross primary production and respiration) has become more feasible with the availability of more reliable dissolved oxygen (DO) probes. Such metabolic measurements offer important opportunities in fundamental and applied research, especially in relating stream metabolic responses to human and other pressures. The accurate determination of the reaeration coefficient is one challenge for making reliable ecological inferences from DO measurements made over many diel periods (i.e., months or years). We outline three methods for calculating atmospheric reaeration but concentrate on the use of statistical estimation to simultaneously estimate reaeration and metabolic rates using Bayesian model fitting. While there are existing programs (ModelMaker and Bayesian Metabolic Model [BaMM]), these are either slow or unable to be used easily for fitting multiple days of metabolic data (one to many months). Our implementation, BAyesian Single-station Estimation (BASE), uses freely available software (R and OpenBUGS), includes a batch mode that can fit data for many days, and provides visual and statistical measures of "goodness-of-fit." We compare the results of the BASE, ModelMaker, and BaMM programs.Measures of stream metabolism as rates of aquatic primary production and ecosystem-wide respiration are integrative indicators of aquatic ecosystem condition (Mulholland et al. 2005). Primary production and ecosystem respiration rates are governed by the complex interactions of hydrology, riparian and in-stream vegetation, geomorphology, climate, chemistry and biology of the stream environment, and the condition of the catchment that the stream drains (Mulholland et al. 2001;Grace and Imberger 2006;Young et al. 2008).A major goal of stream metabolism measurements is to use metabolic values to infer the condition of the ecosystem, or to evaluate the response of metabolism to potential pressures, usually of human origins, operating at multiple spatial and temporal scales (Bunn et al. 1999;Fellows et al. 2006). Disentangling the effects of these pressures from other factors affecting metabolic behavior, especially the effect of cloud cover on rates of primary production, is often problematic when analyses rely on profiles from only a few days.Longer-term data collection has become more common (e.g., Roberts and Mulholland 2007) and, when coupled with more reliable measurement of concentrations of dissolved oxygen (DO), offers the prospect of using stream metabolism to investigate differences among systems and evaluation of long-term (e.g., multiyear) trends . The availability of nonconsumptive, fluorescence-based probes for measuring (DO) over the past decade has much enhanced the applicability and convenience of the open-water method because these new generation DO probes have little signal drift, which was a problem for earlier probes (Almeida et al. 2014). Odum (1956) proposed the method for determining stream metabolism in lotic systems by monitoring the temporal change in DO concent...
The brown marmorated stink bug, Halyomorpha halys (Stål) (Hemiptera: Pentatomidae), is native to northeast Asia. It was accidentally introduced to Europe and North America, where it has become a key pest, feeding on many important crops. Previous eco-climatic niche modelling indicates that H. halys could expand its distribution vastly, and numerous border interceptions of this pest in many countries, including Australia and New Zealand, indicate that it would be prudent to prepare for its eventual arrival. Similar niche modelling was used to assess the potential distribution of Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae), the key parasitoid of H. halys in China. Trissolcus mitsukurii (Ashmead) is one of the main parasitoids of H. halys in Japan. It is known to have existed in Australia since the early 20th century and was also specifically introduced to Australia in the 1960s, and it has now also invaded Italy. We used CLIMEX to model the climatic niche of T. mitsukurii to estimate its global potential distribution. We found that T. mitsukurii should be able to significantly expand its range globally, and that there is a significant degree of overlap in the projected ranges of T. mitsukurii, T. japonicus and H. halys. From a biological control perspective, this implies that the two Trissolcus species may be able to help mitigate the potential impacts of H. halys.
Clonality is a common characteristic of successful invasive species, but general principles underpinning the success of clonal invaders are not established. A number of mechanisms could contribute to invasion success including clones with broad tolerances and preferences, specialist clones and adaptation in situ. The majority of studies to date have been of plants and some invertebrate parthenogens, particularly aphids, and have not necessarily caught invasion at very early stages. Here we describe the early stages of an invasion by a Northern Hemisphere Hymenopteran model in three different land masses in the Southern Hemisphere. Nematus oligospilus Förster (Hymenoptera: Tenthredinidae), a sawfly feeding on willows (Salix spp.), was recently introduced to the Southern Hemisphere where it has become invasive and is strictly parthenogenetic. In this study, the number of N. oligospilus clones, their distribution in the landscape and on different willow hosts in South Africa, New Zealand and Australia were assessed using 25 microsatellite markers. Evidence is presented for the presence of two very common and widespread multilocus genotypes (MLGs) or ‘superclones’ dominating in the three countries. Rarer MLGs were closely related to the most widespread superclone; it is plausible that all N. oligospilus individuals were derived from a single clone. A few initial introductions to Australia and New Zealand seemed to have occurred. Our results point towards a separate introduction in Western Australia, potentially from South Africa. Rarer clones that were dominant locally putatively arose in situ, and might be locally favoured, or simply have not yet had time to spread. Data presented represent rare baseline data early in the invasion process for insights into the mechanisms that underlie the success of a global invader, and develop Nematus oligospilus as a valuable model to understand invasion genetics of clonal pests.
Invasive organisms can have major impacts on the environment. Some invasive organisms are parthenogenetic in their invasive range and, therefore, exist as a number of asexual lineages (=clones). Determining the reproductive mode of invasive species has important implications for understanding the evolutionary genetics of such species, more especially, for management-relevant traits. The willow sawfly Nematus oligospilus Förster (Hymenoptera: Tenthredinidae) has been introduced unintentionally into several countries in the Southern Hemisphere where it has subsequently become invasive. To assess the population expansion, reproductive mode and host-plant relationships of this insect, microsatellite markers were developed and applied to natural populations sampled from the native and expanded range, along with sequencing of the cytochrome-oxidase I mitochondrial DNA (mtDNA) region. Other tenthredinids across a spectrum of taxonomic similarity to N. oligospilus and having a range of life strategies were also tested. Strict parthenogenesis was apparent within invasive N. oligospilus populations throughout the Southern Hemisphere, which comprised only a small number of genotypes. Sequences of mtDNA were identical for all individuals tested in the invasive range. The microsatellite markers were used successfully in several sawfly species, especially Nematus spp. and other genera of the Nematini tribe, with the degree of success inversely related to genetic divergence as estimated from COI sequences. The confirmation of parthenogenetic reproduction in N. oligospilus and the fact that it has a very limited pool of genotypes have important implications for understanding and managing this species and its biology, including in terms of phenotypic diversity, host relationships, implications for spread and future adaptive change. It would appear to be an excellent model study system for understanding evolution of invasive parthenogens that diverge without sexual reproduction and genetic recombination.
1. Ecological interactions between parasitoids and their hosts are extremely strong as parasitoid offspring rely entirely on an individual host to complete development. The ability of a parasitoid to use a host is influenced directly by the degree to which the parasitoid can overcome host defences and grow within the host. 2. Hymenopteran parasitoids have evolved different host‐specific strategies to defeat the host immune system, such as the use of venom, endosymbiont virus, or mimicking the host tissue. Dipteran parasitoids from the Tachinidae family do not use these subterfuges and rely mainly on avoiding the host immune system by hiding in specific tissues. 3. Little is known of the effect of this strategy on the host immune system, the absorption of nutrients by the parasitoid larvae, or the implications for parasitoid host range. 4. In this study, the impact of a polyphagous tachinid parasitoid Compsilura concinnata Meigen on a pest lepidopteran Trichoplusia ni Hübner are assessed. Phenoloxidase levels and haemolymph proteins were measured in parasitised T. ni as a function of host immune response. 5. Haemolymph phenoloxidase in the host did not vary with parasitisation but was triggered when a piece of monofilament was implanted in the haemocoel. Haemolymph proteins were depleted in heavily parasitised T. ni. 6. These results indicate that C. concinnata has a strategy that avoids the host immune system, and accesses the necessary nutrients for larval growth. This strategy could explain the success of this tachinid and its wide host range.
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