Do feather-degrading bacteria affect sexually selected plumage color?

Models of parasite-mediated sexual selection propose that males with more elaborate sexual traits will have fewer parasites. These models have generally been tested using metazoan or protozoan parasites of the blood, gut, or integument. Fewer studies have examined sexual ornaments in relation to bacterial infections. While most surface bacteria are harmless or beneficial, feather-degrading bacteria may have detrimental effects. In this study, we examined the relationships between overall bacterial load, feather-degrading bacterial load, and sexually selected carotenoid-based plumage color in a wild population of house finches (Carpodacus mexicanus). We found that males with the redder plumage preferred by females had similar overall bacterial loads, but lower feather-degrading bacterial loads, than males with less red plumage. These data suggest that plumage color can signal abundance of feather-degrading bacteria to potential mates. It remains unclear whether feather-degrading bacteria directly or indirectly affect plumage color, but the observed correlations suggest that feather-degrading bacteria may play some role in sexual selection.     

From individuals to ecosystem function: toward an integration of evolutionary and ecosystem ecology

An important goal in ecology is developing general theory on how the species composition of ecosystems is related to ecosystem properties and functions. Progress on this front is limited partly because of the need to identify mechanisms controlling functions that are common to a wide range of ecosystem types. We propose that one general mechanism, rooted in the evolutionary ecology of all species, is adaptive foraging behavior in response to predation risk. To support our claim, we present two kinds of empirical evidence from plant-based and detritus-based food chains of terrestrial and aquatic ecosystems. The first kind comes from experiments that explicitly trace how adaptive foraging influences ecosystem properties and functions. The second kind comes from a synthesis of studies that individually examine complementary components of particular ecosystems that together provide an integrated perspective on the link between adaptive foraging and ecosystem function. We show that the indirect effects of predators on plant diversity, plant productivity, nutrient cycling, trophic transfer efficiencies, and energy flux caused by consumer foraging shifts in response to risk are qualitatively different from effects caused by reductions in prey density due to direct predation. We argue that a perspective of ecosystem function that considers effects of consumer behavior in response to predation risk will broaden our capacity to explain the range of outcomes and contingencies in trophic control of ecosystems. This perspective also provides an operational way to integrate evolutionary and ecosystem ecology, which is an important challenge in ecology.     

Geographic variation in a predator-induced defense and its genetic basis

Predator-induced morphological defenses are a well-known form of phenotypic plasticity, but we continue to have a limited understanding of geographic variation in these responses and its genetic basis. Here we examine genetic variation and geographic differentiation in the inducible defenses of tadpoles (Rana pirica) in response to predatory salamander larvae (Hynobius retardatus). To do so, we crossed male and female frogs from a "mainland" Japanese island having predaceous salamanders and a more isolated island not having predaceous salamanders and raised resulting offspring in the presence and absence of H. retardatus. Mainland tadpoles exhibited a higher capacity to express the inducible morphology (a more bulgy body) than those from the predator-free island, and expression of the bulgy morph in mainland-island hybrids produced phenotypes that were intermediate to those produced by pure crosses. In addition, parental sex had no effect on expression of the bulgy morph. Our results support the hypothesis that geographic variation in inducible defenses is linked to the additive effects of autosomal alleles that are shaped by differences in historical exposure to the inducing predator.     

Tissue-specific incorporation and genotoxicity of different forms of tritium in the marine mussel, Mytilus edulis

Marine mussels (Mytilus edulis) were exposed to seawater spiked with tritiated water (HTO) at a dose rate of 122 and 79 μGy h⁻¹ for 7 and 14 days, respectively, and tritiated glycine (T-Gly) at a dose rate of 4.9 μGy h⁻¹ over 7 days. This was followed by depuration in clean seawater for 21 days. Tissues (foot, gills, digestive gland, mantle, adductor muscle and byssus) and DNA extracts from tissues were analysed for their tritium activity concentrations. All tissues demonstrated bio-accumulation of tritium from HTO and T-Gly. Tritium from T-Gly showed increased incorporation into DNA compared to HTO. About 90% of the initial activity from HTO was depurated within one day, whereas T-Gly was depurated relatively slowly, indicating that tritium may be bound with different affinities in tissues. Both forms of tritium caused a significant induction of micronuclei in the haemocytes of mussels. Our findings identify significant differential impacts on Mytilus edulis of the two chemical forms of tritium and emphasise the need for a separate classification and control of releases of tritiated compounds, to adequately protect the marine ecosystem.     

Status of feral oilseed rape in Europe: its minor role as a GM impurity and its potential as a reservoir of transgene persistence

Purpose  

Feral oilseed rape has become widespread in Europe on waysides and waste ground. Its potential as a source of GM impurity in oilseed rape harvests is quantified, for the first time, by a consistent analysis applied over a wide range of study areas in Europe.     

Cumulative impact of GM herbicide-tolerant cropping on arable plants assessed through species-based and functional taxonomies

Background, aim and scope

In a gradualist approach to the introduction of crop biotechnology, the findings of experimentation at one scale are used to predict the outcome of moving to a higher scale of deployment. Movement through scales had occurred for certain genetically modified herbicide-tolerant (GMHT) crops in the UK as far as large-scale field trials. However, the land area occupied by these trials was still <1% of the area occupied by the respective non-GM crops. Some means is needed to predict the direction and size of the effect of increasing the area of GMHT cropping on ecological variables such as the diversity among species and trophic interactions. Species-accumulation curves are examined here as a method of indicating regional-scale impacts on botanical diversity from multiple field experiments.

Materials and methods

Data were used from experiments on the effect of (GMHT) crops and non-GM, or conventional, comparators in fields sown with four crop types (beet, maize, spring and winter oilseed rape) at a total of 250 sites in the UK between 2000 and 2003. Indices of biodiversity were measured in a split-field design comparing GMHT with the farmers’ usual weed management. In the original analyses based on the means at site level, effects were detected on the mass of weeds in the three spring crops and the proportion of broadleaf and grass weeds in winter oilseed rape, but not on indices of plant species diversity. To explore the links between site means and total taxa, accumulation curves were constructed based on the number of plant species (a pool of around 250 species in total) and the number of plant functional types (24), inferred from the general life-history characteristics of a species.

Results

Species accumulation differed between GMHT and conventional treatments in direction and size, depending on the type of crop and its conventional management. Differences were mostly in the asymptote of the curve, indicative of the maximum number of species found in a treatment, rather than the steepness of the curve. In winter oilseed rape, 8% more species were accumulated in the GMHT treatment, mainly as a result of the encouragement of grass species by the herbicide when applied in the autumn. (Overall, GMHT winter oilseed rape had strong negative effects on both the food web and the potential weed burden by increasing the biomass of grasses and decreasing that of broadleaf weeds.) In maize, 33% more species—a substantial increase—were accumulated in the GMHT than in the conventional, consistent with the latter’s highly suppressive weed management using triazine herbicides. In the spring oilseed rape and beet, fewer species (around 10%) were accumulated in the GMHT than the conventional. The GMHT treatments did not remove or add any functional (life history) types, however. Differences in species accumulation between treatments appeared to be caused by loss or gain of rarer species. The generality of this effect was confirmed by simulations of species accumulation in which the species complement at each of 50 sites was drawn from a regional pool and subjected to reducing treatment at each site. Shifts in the species-accumulation parameters, comparable to those measured, occurred only when a treatment removed the rarer species at each site.

Discussion

Species accumulation provided a set of simple curve-parameters that captured the net result of numerous local effects of treatments on plant species and, in some instances, the balance between grass and broadleaf types. The direction of effect was not the same in the four crops and depended on the severity of the conventional treatment and on complex interactions between season, herbicide and crop. The accumulation curves gave an indication of potential positive or negative consequences for regional species pools of replacing a conventional practice with GMHT weed management. In this and related studies, a range of indicators, through which diversity was assessed by both species and functional type, and at both site and regional scales, gave more insight into effects of GMHT treatment than provided by any one indicator.

Conclusions

Species accumulation was shown to discriminate at the regional scale between agronomic treatments that had little effect on species number at the field scale. While a comprehensive assessment of GM cropping needs to include an examination of regional effects, as here, the costs of doing this in all instances would be prohibitive. Simulations of diversity-reducing treatments could provide a theoretical framework for predicting the likely regional effects from in-field plant dynamics.

Recommendations and perspectives

Accumulation curves potentially offer a means of linking within-site effects to regional impacts on biodiversity resulting from any change in agricultural practice. To guide empirical measurement, there is a scope to apply a methodology such as individual-based modelling at the field scale to explore the links between agronomic treatments and the relative abundance of plant types. The framework needs to be validated in practice, using species-based and functional taxonomies, the latter defined by measured rather than inferred traits.     

Modelling livelihoods and household resilience to droughts using Bayesian networks

Over the last four decades, the Indian government has been investing heavily in watershed development (WSD) programmes that are intended to improve the livelihoods of rural agrarian communities and maintain or improve natural resource condition. Given the massive investment in WSD in India, and the recent shift from micro-scale programmes (<500 ha) to meso-scale (~5000 ha) clusters, robust methodological frameworks are needed to measure and analyse impacts of interventions across landscapes as well as between and within communities. In this paper, the sustainable livelihoods framework is implemented using Bayesian networks (BNs) to develop models of drought resilience and household livelihoods. Analysis of the natural capital component model provides little evidence that watershed development has influenced household resilience to drought and indicators of natural capital, beyond an increased area of irrigation due to greater access to groundwater. BNs have proved a valuable tool for implementing the sustainable livelihoods framework in a retrospective evaluation of implemented WSD programmes. Many of the challenges of evaluating watershed interventions using BNs are the same as for other analytical approaches. These are reliance on retrospective studies, identification and measurement of relevant indicators and isolating intervention impacts from contemporaneous events. The establishment of core biophysical and socio-economic indicators measured through longitudinal household surveys and monitoring programmes will be critical to the success of BNs as an evaluation tool for meso-scale WSD.