Ecology of body size in Drosophila buzzatii: untangling the effects of temperature and nutrition

Abstract.

• 1 A method of separating the effects of two important determinants of body size in natural populations, temperature of larval development and level of larval nutrition, by making measurements of thorax length and wing length of adult flies is investigated.
• 2 I show that at any given time variation in body size of Drosophila buzzatii from two sites in eastern Australia is determined primarily by variation in the quality of nutrition available to larvae.
• 3 Throughout the year adult flies are consistently at least 25% smaller in volume than predicted for optimal nutrition at their predicted temperature of larval development.
• 4 Nutritional stress is therefore a year-round problem for these flies.
• 5 Measurements of adult flies emerging from individual breeding substrates (rotting cactus cladodes) show that there is substantial variation among these substrates in the nutrition available to larvae.
• 6 This method will allow study of spatial and temporal variation in the temperature of larval substrates and in the nutritional resources available to flies in natural populations.

     

Evidence for the mechanisms of zinc uptake by rice using isotope fractionation

In an earlier study, we found that rice (Oryza sativa) grown in nutrient solution well‐supplied with Zn preferentially took up light ⁶⁴Zn over ⁶⁶Zn, probably as a result of kinetic fractionation in membrane transport processes. Here, we measure isotope fractionation by rice in a submerged Zn‐deficient soil with and without Zn fertilizer. We grew the same genotype as in the nutrient solution study plus low‐Zn tolerant and intolerant lines from a recombinant inbred population. In contrast to the nutrient solution, in soil with Zn fertilizer we found little or heavy isotopic enrichment in the plants relative to plant‐available Zn in the soil, and in soil without Zn fertilizer we found consistently heavy enrichment, particularly in the low‐Zn tolerant line. These observations are only explicable by complexation of Zn by a complexing agent released from the roots and uptake of the complexed Zn by specific root transporters. We show with a mathematical model that, for realistic rates of secretion of the phytosiderophore deoxymugineic acid (DMA) by rice, and realistic parameters for the Zn‐solubilizing effect of DMA in soil, solubilization and uptake by this mechanism is necessary and sufficient to account for the measured Zn uptake and the differences between genotypes.     

The ecology and status of Thymelicus acteon (Lepidoptera: Hesperiidae) in Britain

ABSTRACT.

• 1 A survey was made of the local butterfly, the Lulworth Skipper (Thymelicus acteon Rott.) in Britain. Adult numbers were estimated on most sites and the habitat was analysed. Changes in numbers were also recorded in five populations over 6 years, and some aspects of behaviour were studied.
• 2 T.acteon forms closed populations. It was found in great abundance throughout its historical range, and appears both to have increased in numbers and to have spread locally. It has not extended its range.
• 3 The wrong larval foodplant is quoted by some modern textbooks. T.acteon requires mature Brachypodium pinnatum Beauv. plants for breeding. Within its range, the butterfly was almost ubiquitous in areas with tall Brachypodium.
• 4 The present abundance and probable increase of T.acteon is attributed to the spread of B.pinnaturn in unimproved calcareous grassland. This has occurred through a decline in grazing, both by domestic stock and, since myxomatosis, by rabbits.

     

Molecular ecology of some Cecidophyopsis mites (Acari: Eriophyidae) on Ribes species and evidence for their natural cross colonisation of blackcurrant (R. nigrum)

Ribosomal DNA from Cecidophyopsis mites from different Ribes species was amplified using the polymerase chain reaction and the products digested using restriction enzymes. After separating the DNA fragments on gels, it was possible to identify specimens of mites obtained from field samples by comparing the profiles of their DNA banding patterns with those of known Cecidophyopsis species. Using this analysis, a non-gall forming mite found infesting blackcurrant buds in New Zealand was identified as the gooseberry mite (C. grossulariae). On wild red currant (Ribes spicatum) from Finland showing two sizes of galled buds, the red currant gall mite (C. selachodon) was identified in the larger galls located at the tips of branches and a distinct mite in the smaller galls located on the lower parts of the branches. A mite with a DNA banding profile indistinguishable from this latter mite from R. spicatum was also identified in galled buds of blackcurrant genotypes growing in Finland, including those containing the blackcurrant gall mite (C. n'ftw)-resistance genes P or Ce. The DNA banding profile of this mite resembled most closely that of C. ribis , but was distinct from it. The occurrence of C. grossulariae and this distinct Cecidophyopsis mite on blackcurrant has implications for the genetic control of Cecidophyopsis mites and possibly for the spread of the reversion disease agent in this crop.     

Indirect Effects of a Keystone Herbivore Elevate Local Animal Diversity

Abstract: We quantified indirect effects of white-tailed deer (Odocoileus virginianus) on ground-dwelling herpetofauna and invertebrates in Cuyahoga Valley National Park, Ohio, USA. We placed cover boards at 12 sites, each consisting of a 10 × 10-m fenced (exclosure) plot and an unfenced (control) plot. Periodically, during May-December 2004 and May-September 2005, we counted salamanders, snakes, and a variety of invertebrate taxa. Salamander, snake, and gastropod abundance as well as invertebrate richness (no. of species or higher level taxa) were higher in control than exclosure plots. Our findings suggest that management actions taken to regulate deer densities could have the unintended effect of reducing local animal diversity.     

Larvae of lycaenid butterflies that parasitize ant colonies provide exceptions to normal insect growth rules

Fourth instar larvae of Maculinea species of lycaenid butterfly live as social parasites inside Myrmica ant nests. They show highly unusual growth patterns, with small but regular growth in early phytophagous instars, followed by >10 times the growth predicted by extrapolating the early growth rate (following Dyar's rule) during the final carnivorous instar. This produces striking allometry between head and body size in full-grown larvae (ratios of 4–5% compared with 8–10%). Larvae of the Myrmica ant hosts have a similar growth. Data for c. 150 other lycaenid species showed that species with similar life-histories exhibit the same unusual growth pattern (Phengaris spp., Lepidochrysops spp., Niphanda fused); all others have regular growth throughout their larval life, including the carnivorous species that are parasitic on ants from the first instar. It is suggested that Maculinea-type growth pattern has arisen convergently in at least three unrelated lineages of lycaenids. Selection pressures might include the need for reduced early growth to produce late instars that are small enough to be integrated as brood mimics into ant social systems, combined with the need to achieve at least the same adult size as the ancestral species. Trophic pressures that operate on both sedentary ant and butterfly larvae, which must survive long periods of starvation and grow rapidly when food is abundant, may also be involved.     

Studies on rose mosaic disease in field-grown roses produced in the United Kingdom

Arabis mosaic virus (AMV) and prunus necrotic ringspot virus (PNRSV), separately or together, caused in field-grown roses the range of symptoms recognised as rose mosaic disease. PNRSV infection alone generally induced chlorotic line patterns, ring-spots or mottles in the leaves at some time during the growing season; AMV plus PNRSV normally caused chlorotic vein-banding. However, during prolonged periods of high temperatures (c. 21 °C or more) vein banding occurred in some roses infected only with PNRSV. Isolates of PNRSV from rose had particles which were similar in shape, protein mol. wt, density and sedimentation coefficients to previously described isolates of PNRSV from cherry, plum and rose; all were cherry serotypes. In graft-inoculated roses, apple serotypes of PNRSV induced stunting and chlorosis, puckering and distortion of leaves, which closely resembled symptoms associated with rose mosaic in the USA and chlorotic mottle rose mosaic in New Zealand. To avoid possible confusion in using the name rose mosaic it is suggested that the virus(es) present in roses should be named.     

Overwintering of Microcystis in Lake Mendota

SUMMARY. Microcystis , an important bloom-forming blue-green alga in Lake Mendota, Wisconsin, was found to accumulate at the lake bottom and overwinter there. Microcystis collected from winter sediments were photosynthetically active, showing temperature and light optima similar to summer and autumn populations. Sediments incubated under in situ conditions in the laboratory maintained photosynthetic activity for at least four months. Such a maintenance ability may be part of an overall strategy by Microcystis populations to ensure a suitable inoculum for the following growth season.     

Pedogenesis, permafrost, and soil moisture as controlling factors for soil nitrogen and carbon contents across the Tibetan Plateau

We investigated the main parameters [e.g. mean annual air temperature , mean annual soil temperature, mean annual precipitation, soil moisture (SM), soil chemistry, and physics] influencing soil organic carbon (C_org), soil total nitrogen (N_t) as well as plant available nitrogen (N_min) at 47 sites along a 1200 km transect across the high‐altitude and low‐latitude permafrost region of the central‐eastern Tibetan Plateau. This large‐scale survey allows testing the hypothesis that beside commonly used ecological variables, diversity of pedogenesis is another major component for assessing carbon (C) and nitrogen (N) cycling. The aim of the presented research was to evaluate consequences of permafrost degradation for C and N stocks and hence nutrient supply for plants, as the transect covers all types of permafrost including heavily degraded areas and regions without permafrost. Our results show that SM is the dominant parameter explaining 64% of C_org and 60% of N variation. The extent of the effect of SM is determined by permafrost, current aeolian sedimentation occurring mostly on degraded sites, and pedogenesis. Thus, the explanatory power for C and N concentrations is significantly improved by adding CaCO₃ content (P=0.012 for C_org; P=0.006 for N_t) and soil texture (P=0.077 for C_org; P=0.015 for N_t) to the model. For soil temperature, no correlations were detected indicating that in high‐altitude grassland ecosystems influenced by permafrost, SM overrides soil temperature as the main driving parameter at landscape scale. It was concluded from the current study that degradation of permafrost and corresponding changes in soil hydrology combined with a shift from mature stages of pedogenesis to initial stages, have severe impact on soil C and plant available N. This may alter biodiversity patterns as well as the development and functioning of the ecosystems on the Tibetan Plateau.