In situ interactions between the effects of season,current velocity and pollution on a river biofilm

1. The development of periphytic algae and bacteria is controlled by a combination of interacting biotic processes and abiotic factors. Distinguishing between the selection pressure resulting from pollution and that of natural environmental factors is therefore one of the most critical aspects of assessing the impact of pollutants on the diversity and function of benthic microbial communities in natural ecosystems. 2. We studied how current velocity and season affect the ability of river biofilms to cope with complex chemical pollution. We compared the diversity, structure and production of periphytic algae and bacteria from four sampling zones with differing chemical water quality levels and different flow velocities over the course of two seasons (summer and winter). 3. The three factors tested all influenced biofilm development, but this depended on the biological variable being measured. Bacterial and algal densities were highly dependent on season and chemical water quality. Algal density was lower in summer than in winter, but bacterial density and production increased from upstream (reference) to downstream (polluted), and this increase was more marked in winter. The impact of chemical water quality was also dependent on the season. 4. An interaction between current velocity and pollution was also detected. During the summer, there was no difference in bacterial density or production between the upstream and downstream segments in the fast current zones, whereas both variables were higher downstream in the slow current zones. Such interactions between environmental factors and the impact of water quality on biofilms must be taken into account in assessments of the effects of chemicals on biofilm community structure and functioning in rivers.     

Genome scan in the mosquito Aedes rusticus: population structure and detection of positive selection after insecticide treatment

Identification of genes involved in local adaptation is particularly challenging for species functioning as a network of interconnected populations undergoing frequent extinctions–recolonizations, because populations are submitted to contrasted evolutionary pressures. Using amplified fragment length polymorphism markers, population genetic structure of the mosquito Aedes rusticus was analysed in five geographical areas of the French Rhône‐Alpes region. We included a number of sites that were treated with the bio‐insecticide Bacillus thuringiensis israelensis (Bti) for more than 15 years. Analysis of molecular variance revealed that most of the genetic variability was found within populations (96%), with no significant variation among geographical areas, although variation among populations within areas (4%) was significant. The global genetic differentiation index F_ST was low (0.0366 ± 0.167). However, pairwise F_ST values were significant and no isolation‐by‐distance at the regional level was observed, suggesting a metapopulation structure in this species. Bti‐treatment had no effect on genetic structure and on within‐population genetic diversity. Potential signatures of positive selection associated with Bti‐treatment were detected for five loci, even though toxicological bioassays performed on field‐collected larvae showed no significant difference in mortality between Bti‐treated and nontreated sites. The difficulty of detecting moderate resistance in field‐collected larvae together with possible differential persistence of toxins in the environment may explain our inability to detect a toxicological response to Bti in treated sites. The evidence for positive selection occurring at several genomic regions suggests a first step towards Bti resistance in natural mosquito populations treated with this bio‐insecticide. Furthermore, this signal was detectable using genomic tools before any toxicological evidence for resistance could be identified.     

Phylogenetic and phenotypic originality and abundance in a cerrado plant community

The originality of a species is how much that species contributes to the rarity of traits in a community. Here we tested the relation between abundance and both phylogenetic and phenotypic originality. We measured nine traits associated with defence against herbivory, as well as phylogenetic information and abundance for woody plant species in a woodland cerrado in southeastern Brazil. About 90% of the species accounted for about 50% of the phylogenetic and phenotypic originality: most woody species had low originality. Abundance was related to tougher leaves, lower specific leaf area and lower originality based on nutritional quality. Our results suggest that herbivory may reduce the abundance of species with low resistance to herbivory and with different nutritional quality. Nevertheless, abundance was not related to either phylogenetic or phenotypic originality, so extinction of rare species may not endanger overall community function as long as more abundant species are retained. We argue that this is a consequence of the low complementarity of a large number of woody species.     

Effects of fertilisation on amino acid mobilisation by a plant‐manipulating insect

1. Phytophagous insects frequently manipulate their host‐plant to improve their immediate environment. This generally implies substantial modifications of host metabolism, and sometimes an alteration of nitrogen allocation within the host‐plant. However, the outcome of plant manipulation on amino acid or protein content can be modulated by environmental factors and host‐plant traits. 2. It was investigated whether the pseudogall induced by the aphid Phloeomyzus passerinii (Signoret) (Aphididae: Phloeomyzinae) in the bark of its host‐plant affects the amino acid content in bark tissues, and whether the strength of the modification is modulated by the fertilisation regime and/or the resistance level of the host‐plant. The development of aphid colonies on a resistant and a susceptible poplar genotype, under three fertilisation regimes, was studied. After the development of colonies, the free and protein‐bound amino acid content of the infested bark were quantified. 3. Fertilisation enhanced poplar growth and increased the free amino acid content of bark tissues. Infestation also triggered accumulations of both free and protein‐bound amino acids in the feeding sites, but in the susceptible genotype only. The increase in amino acid content was more pronounced when fertilisation was low, and fertilisation did not enhance aphid development. 4. In conclusion, infestation by P. passerinii triggers an accumulation of amino acids, but the effect is influenced by both the fertilisation regime and the resistance level of the host‐plant. This suggests that P. passerinii could affect the allocation of nutrients within trees during outbreaks.     

Identity and combinations of arbuscular mycorrhizal fungal isolates influence plant resistance and insect preference

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DNA‐based discrimination between the sibling species Aphis gossypii Glover and Aphis frangulae Kaltenbach

Abstract Morphologically similar species occur in various groups of insects, including aphid pests. In Europe, Aphis frangulae Kaltenbach and Aphis gossypii Glover (sometimes considered as subspecies) are differentiated usually on the basis of life cycle and host plant. We used a sexual population of A. frangulae collected on the primary host and samples of A. gossypii collected on cucurbits or cotton for the development of molecular markers. DNA sequence data for the gene encoding cytochrome b and for the barcode region of cytochrome oxidase I, as well as a length polymorphism for an intron in the sodium channel para‐type gene discriminated unambiguously between the two taxa. These markers were also used as identification keys for aphids collected on crops belonging to the Solanaceae. The cytochrome b marker differentiates host‐related Aphis gossypii haplotypes, and the para‐type gene intron might be suitable for the resolution of taxonomic problems in other aphid species complexes.     

Testing Global Positioning System Performance for Wildlife Monitoring Using Mobile Collars and Known Reference Points

Abstract: To determine the spatial resolution of Global Positioning System (GPS) receiver data, rigorous testing is essential. We tested performance of the Lotek 3300 GPS collar for medium-sized mammals (Lotek Engineering, Inc., Newmarket, ON, Canada). To mimic real wildlife monitoring situations, we performed both static (stationary receiver) and mobile tests, placing the receiver collar on a dog. We compared fix locations of the mobile receiver with the actual trajectory described by a portable Trimble high-precision GPS. We determined performance in relation to habitat type and leaf cover. Location error was habitat-dependent, with the best results in open habitat and much poorer ones in forest, particularly coniferous-dominated forest. For both static and mobile tests, location accuracy was higher when the number of satellites contacted was high and when the residual positional dilution of precision (PDOP) value was low. However, location error was highly variable, even for a given PDOP value and a given number of satellites contacted. Finally, mobile collars performed less well than their static counterparts, presumably because of frequent changes of GPS position and orientation.     

Reproductive dynamics of three amphibian species in Mediterranean wetlands: the role of local precipitation and hydrological regimes

1. Although the influence of water availability and precipitation regimes on amphibians has been studied at large scales, whether and how interannual rainfall and hydrological variations affect amphibians dynamics at a local scale have rarely been addressed. In this respect, accounting for variations in species detectability in space and time has also been overlooked. 2. We assessed the effects of rainfall and hydrological variations on the breeding dynamics of three amphibian taxa: Pelodytes punctatus, Hyla meridionalis and Pelophylax spp. in 20 ponds of the Camargue region (southern France) over a 7‐year study period. 3. We used multiple season occupancy models to test the effect of winter–spring rainfall and interannual variations in hydroperiod, mean water depth and drought events on tadpole presence in spring (March–June), a proxy for breeding dynamics. 4. We used an independent survey with spatial replicates (dipnet sweeps) to disentangle the relative contributions of phenology and detectability to the absence of records in a given month. For the three taxa considered, the probability of missing a species when that species was actually present in a pond was most often negligible. Hence, we could consider that multiseason models properly tracked changes in species phenology. 5. Pelodytes punctatus was first detected in March, while the two other taxa appeared later in April. Hyla meridionalis appeared as a mid‐season species with much more synchronous pond occupancy than Pelodytes punctatus. The detection peak of Pelophylax spp. was short and unexpectedly early for this taxon. 6. Seasonal winter–spring rainfall was associated with a decrease in extinction rates and even more strongly with an increase in colonisation rates at individual ponds. 7. Colonisation rate increased following an annual drought and was best modelled as a negative quadratic effect of the variance of pond hydroperiod. Extinction probability was best modelled by a negative quadratic effect of mean water level. Hence, breeding was more stochastic (i) in unpredictable and shallow ponds because of yearly drying up and (ii) in highly predictable and deep ponds, possibly due to the presence of predators such as fish and crayfish. 8. Overall, we show that ponds with intermediate rather than extreme variations in environmental conditions currently correspond to optimal breeding sites. Our study demonstrates that amphibian monitoring coupled with fine‐scale analysis of environmental conditions is necessary to understand species dynamics in the long run and to inform conservation efforts for these species.     

Statistical methods in spatial genetics

The joint analysis of spatial and genetic data is rapidly becoming the norm in population genetics. More and more studies explicitly describe and quantify the spatial organization of genetic variation and try to relate it to underlying ecological processes. As it has become increasingly difficult to keep abreast with the latest methodological developments, we review the statistical toolbox available to analyse population genetic data in a spatially explicit framework. We mostly focus on statistical concepts but also discuss practical aspects of the analytical methods, highlighting not only the potential of various approaches but also methodological pitfalls.