Spatial patterns in the distribution of European springtails (Hexapoda: Collembola)

Using a large database on the spatial distribution of European springtails (Collembola) we investigated how range sizes and range distribution across European countries and major islands vary. Irrespective of ecological guild, islands tended to contain more endemic species than mainland countries. Nestedness and species co‐occurrence analysis based on country species lists revealed latitudinal and longitudinal gradients of species occurrences across Europe. Species range sizes were much more coherent and had fewer isolated occurrences than expected from a null model based on random colonization. We did not detect clear postglacial colonization trajectories that shaped the faunal composition across Europe. Our results are consistent with a multiregional postglacial colonization. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 498–506.     

Effect of host diet and adult parasitoid diet on egg load dynamics and egg size of braconid parasitoids attacking Anastrepha ludens

The quantity and quality of host nutrients can affect fitness‐related traits in hymenopteran parasitoids, including oogenesis. The present study tested the prediction that a high host quality will influence oogenesis‐related traits positively in synovigenic parasitoids, and that a high‐quality adult parasitoid diet can positively affect the same parameters, potentially compensating for development on low‐quality hosts. Four braconid parasitoid species with contrasting life histories are reared on a low‐quality diet [Anastrepha ludens Loew (Diptera: Tephritidae) larvae reared on mango] or a high‐quality (artificial) diet. Adult parasitoids are provided with a high‐quality (honey ad libitum), moderate‐quality (honey every other day) or low‐quality (guava pulp) diet. Generalist species that encounter high variation in host quality naturally are predicted to be more flexible in dealing with nutrient shortfalls than specialist species. By contrast to the predictions, low‐quality hosts yield parasitoids with higher egg loads in two species: Opius hirtus Fisher and Diachasmimorpha longicaudata Ashmead. However, as predicted, a high‐quality adult diet exerts a positive effect on egg load (Utetes anastrephae Viereck), egg size (Doryctobracon crawfordi Viereck) and egg maturation rate (D. longicaudata, O. hirtus and U. anastrephae). The generalist D. longicaudata varies in egg load and maturation rate depending on host quality and adult diet, respectively. Evidence of the combined effect of both factors on parasitoid fertility is presented for the specialist O. hirtus. The theoretical and practical implications of these findings are discussed.     

Changes of Genotype,Sensitivity and Aggressiveness in Phytophthora infestans Isolates Collected in European Countries in 1997, 2006 and 2007

A total of 241 isolates of Phytophthora infestans were collected in 1997, 2006 and 2007 in eight European countries and characterized with molecular markers (simple sequence repeats, SSR genotypes) and phenotypic traits such as sensitivity to fungicides, mating type and aggressiveness. The mating type distribution changed from mainly A1 in 1997 to a majority of A2 in 2007. No resistant isolates were detected for fluazinam and mandipropamid, whereas the proportion of isolates resistant to mefenoxam (MFX) was high and increased over the years. There was no genetic link between mating type and MFX resistance. Aggressiveness (product between lesion expansion and sporulation capacity) was slightly higher for MFX‐resistant compared to sensitive isolates and for isolates collected later compared to earlier in the same season. It was about equally high for A1 and A2 types, and for French isolates in 1997 and British isolates in 2007, but lower for French isolates in 2007. Six different SSR genotype families were distinguished. In 1997, populations were dominated by genotype families I and III/IV, which significantly declined in 2007 being largely displaced by genotype families II (‘blue 13’ type) and V, which are by coincidence mainly A2 MFX resistant and A1 MFX sensitive, respectively. However, mating type and MFX resistance were genetically not linked to SSR genotypes.     

Land-use intensification systematically alters the size structure of aquatic communities in the Neotropics

Land-use and land-cover transitions can affect biodiversity and ecosystem functioning in a myriad of ways, including how energy is transferred within food-webs. Size spectra (i.e. relationships between body size and biomass or abundance) provide a means to assess how food-webs respond to environmental stressors by depicting how energy is transferred from small to larger organisms. Here, we investigated changes in the size spectrum of aquatic macroinvertebrates along a broad land-use intensification gradient (from Atlantic Forest to mechanized agriculture) in 30 Brazilian streams. We expected to find a steeper size spectrum slope and lower total biomass in more disturbed streams due to higher energetic expenditure in physiologically stressful conditions, which has a disproportionate impact on large individuals. As expected, we found that more disturbed streams had fewer small organisms than pristine forest streams, but, surprisingly, they had shallower size spectrum slopes, which indicates that energy might be transferred more efficiently in disturbed streams. Disturbed streams were also less taxonomically diverse, suggesting that the potentially higher energy transfer in these webs might be channelled via a few efficient trophic links. However, because total biomass was higher in pristine streams, these sites still supported a greater number of larger organisms and longer food chains (i.e. larger size range). Our results indicate that land-use intensification decreases ecosystem stability and enhances vulnerability to population extinctions by reducing the possible energetic pathways while enhancing efficiency between the remaining food-web linkages. Our study represents a step forward in understanding how land-use intensification affects trophic interactions and ecosystem functioning in aquatic systems.     

Effects of adults body size and larvae diet on the fecundity and percent fertility of eggs laid by Xylotrechus arvicola (Coleoptera: Cerambycidae) females,insect pest in Spanish vineyards

Xylotrechus arvicola is a pest of grape in some vine‐producing regions of the Iberian Peninsula. Biological parameters and relationships (fecundity and percent fertility of eggs in relationship to body size) of females obtained in the laboratory and captured in vineyards were studied. In laboratory conditions, the mean developmental time of larvae ranged from 384 to 392 days and pupal stage varied between 12 to 14 days. Body size (BS) of X. arvicola females was significantly bigger than males. Fecundity was greater in the laboratory (147 eggs) than in the field (50 eggs) females, but the percent fertility of the laboratory eggs was lower (16 eggs). Laboratory females showed a bigger relationship between the production of eggs and BS than females captured in vineyards. Wild females (PDO Ribera del Duero and Tierra de León) had a positive relationship between the percent fertility of eggs and the BS. No correlation between the percent fertility of eggs and the BS was displayed by females captured in PDO Toro, but these females had a higher percent fertility (53 eggs) than the others PDO's. These biological parameters and relationships studied suggest that the artificial diet may lack certain essential nutrients that vine varieties can provide that favor the fertility of eggs. This explains why wild females have the potential to become a problem pest in the Tempranillo grape variety, with bilateral cordon and bush vines training systems that have the highest incidence of this cerambycid.     

Mineral nutrient supply, cell wall adjustment and the control of leaf growth

The possibility that changes in the plasticity of expanding cell walls are involved in regulating early leaf growth responses to nutrient deficiencies in monocot plants was investigated. Intact maize seedlings (Zea mays L.) which were hydroponically grown with their roots in low-nutrient solution (1 mol m^?3 CaCl₂) showed early inhibition of first-leaf growth, as compared with seedlings on complete nutrient solution. This early inhibition of leaf growth was not associated with reduced cell production. However, segmental elongation along the cell expansion zone at the base of the leaf and the lengths of mature epidermal cells were reduced by the low-nutrient treatment. Solute (osmotic) potentials in the expanding leaf tissues were unchanged. In contrast, low-nutrient treatments significantly altered leaf plasticity, i.e. the irreversible extension caused by applying a small force in the direction of leaf growth. For example, in vivo plasticity decreased, along with leaf growth, after transfer of seedlings from complete nutrient solution to low-nutrient solution for 15 h. Conversely, in vivo plasticity increased, along with leaf growth, after transfer of plants previously grown on low-nutrient solution to complete nutrient solution for 15 h. The nutrient treatments also induced similar changes in the in vitro plasticity of the expanding leaf cell walls. There were no consistent changes in elasticity. Thus, reductions in the plasticity of expanding leaf cell walls appear to be involved in controlling the early inhibition of maize leaf growth by root imposition of nutrient stress.     

A Study on Size Hierachies of Individuals OF Elymus nutans Population under Different Densities

The size hierachies of a perennial grass population, Elymus nutans, which distributes throghout the subalpine meadow has been studied. A two-year experiment was designed to include seven treatments of different densities and measurements of inequality and distributions of individual mass of the population at different harvest time from 1987 to 1989. Individual mass under each of the seven treatments did not reveal a normal or lognormal distribution. No skewness values smaller than 0.5 occurred in our 48 sets of data, which implied that the distribution of the indiciduals of E. nutans population at any density skewed to small individuals. This result emphasized an evidence that there were differences between perennial grasses and annual grasses in responding to intraspecies competition. Size inequality did not increase with increasing population densities. This however, was not in concert with the results of experiments from others. Size inequality, on the other hand, was wore prominent in the period of vegetative growth than in the period of maturity.