Antixenosis phloem‐based resistance to aphids: is it the rule?

1. The concept of plant defence syndrome states that plant species growing in similar biotic or abiotic constraints should have convergent defensive traits. This article is a first step to test the prediction of this concept, by conducting experiments on wild Solanum species (or accessions) that originated from the Andes. The nature and the tissue localisation of the resistance of five wild Solanum species known to be resistant against the aphids Myzus persicae and Macrosiphum euphorbiae were determined by olfactometry and electrical penetration graph experiments. 2. Volatile organic compounds may contribute to wild Solanum resistance, depending on Solanum accessions and aphid species. Volatiles of S. bukasovii and S. stoloniferum PI 275248 were not attractive to M. persicae, whereas S. bukasovii was repulsive to M. euphorbiae. In contrast, volatiles of S. stoloniferum PI 275248 were attractive for M. euphorbiae. 3. Some wild Solanum species presented a generalised resistance in all plant tissues, so as for S. bukasovii and S. stoloniferum PI 275248 against M. persicae. However, except for S. bukasovii which was susceptible to M. euphorbiae, all tested Solanum species presented a phloem‐based antixenosis resistance against the two aphid species. 4. A review of articles focused on the nature of resistance of wild Solanum species against aphids corroborated with our results, i.e. a phloem‐based antixenosis resistance against aphids is the rule concerning the system aphids–wild Solanum species.     

Responses of woody vegetation to exclusion of large herbivores in semi‐arid savannas

The Nkuhlu large‐scale long‐term exclusion experiment in Kruger National Park was designed to study the long‐term effects of large herbivores on vegetation. One treatment excludes elephants, another excludes all herbivores larger than hares and another one comprises an open, control area. Vegetation monitoring was implemented in 2002 when a baseline survey was conducted prior to exclusion. Monitoring was repeated 5 years after exclusion. Data from the surveys were analysed to establish how structure and composition of woody vegetation had changed 5 years after herbivore exclusion. The analysis showed that neither plant assemblage nor mean vegetation height had changed significantly since exclusion. However, both species richness and density of woody plants increased 5 years after exclusion of all large herbivores, but not after the exclusion of elephants alone. One already common species, Dichrostachys cinerea, became more common after excluding all large herbivores compared with either no exclusion or elephant exclusion, possibly leading to competitive suppression of other species. Species other than D. cinerea tended to either increase or decrease in density, but the changes were insufficient to induce significant shifts in the overall assemblage of woody plants. The results indicate that after 5 years of exclusion, the combined assemblage of large herbivores, and not elephants alone, could induce changes in species richness and abundances of woody plants, but the effect was so far insufficient to induce measureable shifts in the assemblages of woody plants. It is possible that assemblages will change with time and increasing elephant numbers may amplify future changes.     

Homoplasy and the delineation of holophyletic genera in some insect groups

Abstract. Some groups of insects, such as certain Ichneumonidae and fungus-feeding Phlaeothripidae, appear to have undergone frequent reversal or parallelism (homoplasy) of characters during evolution so that extant species present almost every imaginable permutation and combination of characters. Recognition of holophyletic genera in such groups is difficult. Large monothetically defined genera are often not holophyletic, whilst small genera need to be defined by a large and invariable character-suite. Any classification produced by adopting small genera will not possess one of the valuable attributes of the classical Linnaean system, its predictive ability; a large proportion of new species will require new genera. For groups exhibiting a high degree of homoplasy it is suggested that a polythetic classification be erected. Polythetic genera can be holophyletic groups and are not merely phenetic assemblages. The probability of correctly assigning a species (either a new one or when making an identification) is shown to be higher for a polythetic classification. A simple key device, the polyclave, is given to enable practical separation of two polythetic taxa. It is suggested that homoplasy, and its associated problems in classification, may be associated with a particular type of biology in which population size is not limited by direct competition.     

Characterization of nine microsatellite loci in impala (Aepyceros melampus)

Nine microsatellite loci were isolated from a genomic DNA library created from impala (Aepyceros melampus). Observed and expected levels of heterozygosity were computed utilizing 25 individuals from a population in central Kenya. Tests for Hardy–Weinberg equilibria were conducted and found that three of the nine loci deviated from equilibrium in this population. These markers were developed to analyse the genetic effects of culling and isolation on a game preserve in Kenya.     

Identifying from recent sediment records the effects of nutrients and climate on diatom dynamics in Loch Leven

1. Changes in nutrients and climate have occurred over approximately the same timescales in many European lake catchments. Here, we attempt to interpret the sedimentary diatom record of a large shallow lake, Loch Leven, in relation to these pressures using information gained from analysis of long‐term data sets of water quality, climate and planktonic diatoms. 2. The core data indicate the enrichment of Loch Leven starting in c. 1800–1850, most likely from agricultural practices in the catchment, with a more marked phase since c. 1940–1950 caused by increased phosphorus inputs from sewage treatment works, land drainage and a woollen mill. 3. While the recent diatom plankton remains are dominated by taxa associated with nutrient‐rich conditions, an increase in Aulacoseira subarctica relative to Stephanodiscus taxa since the mid‐1980s suggests that reductions in external catchment sources of nutrients (since 1985) may have resulted in partial recovery. This observation accords well with the long‐term monitoring series of water chemistry and phytoplankton. 4. On a decadal‐centennial scale, the eutrophication signal in the sediment record outweighs any evidence of climate as a control on the diatom community. However, at an inter‐annual scale, while the diatom data exhibit high variability, there are several changes in species composition in the recent fossil record that may be attributed to climatic controls. 5. The study highlights the value of a palaeolimnological approach, particularly when coupled with long‐term data sets, for developing our understanding of environmental change at a range of temporal scales. The diatom record in the sediment can be used effectively to track recovery from eutrophication, but requires greater understanding of contemporary ecology to fully interpret climate impacts. 6. The study illustrates the complexity of ecosystem response to synchronous changes in nutrients and climate, and the difficulty of disentangling the effects of these multiple, interacting pressures.