The influence of a parasitoid's response to temperature on the performance of a tri‐trophic food web

1. Food web interactions are complex and can respond to environmental changes in unpredictable ways that do not necessarily equate to the individual responses of each of the components of the food web. 2. Biomass can be used to evaluate the productivity of the three individual trophic levels, in the form of the Net Generational Productivity (NGP) and the performance of the entire food web with the newly developed tri‐trophic food web performance ratio (?_3t). 3. These parameters were used to evaluate the performance of nine plant‐based tri‐trophic food webs composed of: potato, Solanum tuberosum L. and two cultivars of bell pepper Capsicum annuum L; three biotypes of the aphid Macrosiphum euphorbiae Thomas (Hemiptera: Aphididae) and the parasitoid wasp Aphidius ervi (Haliday) (Hymenoptera: Braconidae). 4. The NGP showed that the thermal window for biomass productivity for each trophic level is different and is reduced by approximately 4 °C with respect to the inferior level. Aphidius ervi had the smallest thermal window for biomass productivity and development. 5. The present results showed that the performance (?_3t) of the tested food webs is influenced in a top‐down fashion, where the intra‐specific variation of the food web, namely the host plant, played a major role in the productivity of each of the subsequent trophic levels. 6. The ?_3t suggested that exposure to high and low temperatures might severely affect the effectiveness of A. ervi as a biocontrol agent of the aphid M. euphorbiae in bell pepper and potato crops.     

Vertical transmission in feather mites: insights into its adaptive value

1. The consequences of symbiont transmission strategies are better understood than their adaptive causes. 2. Feather mites are permanent ectosymbionts of birds assumed to be transmitted mainly vertically from parents to offspring. The transmission of Proctophyllodes doleophyes Gaud (Astigmata, Proctophyllodidae) was studied in two European populations of pied flycatchers, Ficedula hypoleuca Pallas (Passeriformes, Muscicapidae). 3. The vertical transmission of this mite species is demonstrated here with an acaricide experiment. This study also compared (for two distant populations during 4 years) patterns in reductions in mite intensity in adult birds, from egg incubation to chick‐rearing periods, with the predictions of three hypotheses on how host survival prospects and mite intraspecific competition might drive feather mites' transmission strategy. 4. The results are in agreement with previous studies and show that feather mites transmit massively from parents to chicks. 5. The magnitude of the transmission was closer to that predicted by the hypothesis based on intraspecific competition, while a bet‐hedging strategy is also partially supported.     

Use of tree rings to study the effect of climate change on trembling aspen in Québec

In this paper, we present a new approach, based on a mixed model procedure, to quantify the tree‐ring‐based growth‐climate relationship of trembling aspen along a latitudinal gradient from 46 to 54 °N in eastern Canada. This approach allows breaking down the growth response into general intersite and local climatic responses, and analyzing variations of absolute ring width as well as interannual variations in tree growth. The final model also integrates nonclimatic variables such as soil characteristics and the occurrence of insect outbreaks into the growth predictions. Tree level random effects on growth were important as intercepts but were nonsignificant for the climatic variables, indicating that a single climate–growth relationship was justified in our case. The response of tree growth to climate showed, however, a strong dependence on the spatial scale at which the analysis was performed. Intersite variations in tree growth were mostly dependent on variations in the thermal heat sum, a variable that showed low interannual and high intersite variation. When variation for a single site was analyzed, other variables showed up to be important while the heat sum was unimportant. Finally, future growth under six different climate change scenarios was simulated in order to study the potential impact of climate change. Results suggest only moderate growth increases in the northern portion of the gradient and a growth decrease in the southern portion under future climatic conditions.     

Competence of Genetic Transformation correlated with the Occurrence of Fimbriae in Three Bacterial Species

THE involvement of bacterial fimbriae (pili) in some cases of phage infection and in bacterial conjugation has been known or presumed for some years¹. Studies in our laboratories show that fimbriae are also associated with genetic transformation in several bacterial species.     

Efficiency of intermittent exercise on adiposity and fatty liver in rats fed with high-fat diet

Objective: This study aimed to examine and compare the effects of continuous or intermittent exercises on adiposity and fatty liver in rats fed with high‐fat diet. Methods and Procedures: Wistar rats were divided according to diet composition—chow diet (C) or high‐fat diet (H)—and kinds of exercise—sedentary (S), continuous (CE), or intermittent (IE) exercises. The CE group swam 90 min/day, and the IE group swam 3 × 30 min/day (at 4‐h intervals between sessions); both groups exercised 5 days/week during 8 weeks. Body weight and food intake were recorded daily. Lipogenesis rate in vivo was determined by the incorporation of ³H₂O into saponified lipids in retroperitoneal (RET), epididymal (EPI), and visceral (VIS) white adipose tissues, brown adipose tissue (BAT), liver (L), and gastrocnemius muscle (GAST) using the gravimetric method. Total cholesterol, high‐density lipoprotein (HDL)‐cholesterol, and triacylglycerol (TG) were analyzed. Results: The major finding of this study is that IE was more efficient than CE in reducing the adverse effects of high‐fat diet and sedentarism. There was an improvement in the lipid profile and a reduction in food intake, body weight gain, visceral and central adiposity, and fatty liver, contributing to the control of obesity and other comorbidities, including nonalcoholic fat liver diseases. Discussion: Earlier studies have discussed the effects of diet consumption on adiposity and their relation to chronic diseases and obesity. This study discusses the effects of high‐fat diet consumption and the different kinds of exercise on weight gain, adiposity, fatty liver, and lipid profile in rats. The results may depend on the exercise, time of each session, age, gender, and experimental period.     

HOW AND WHEN DO LAMBS RECOGNIZE THE BLEATS OF THEIR MOTHERS?

ABSTRACT

In domestic sheep Ovis aries, the mother and the young display a preferential bond for each other that relies on multimodal inter-individual recognition. Lambs show a preference for their own dam shortly after birth, and this is important for their survival. The role of acoustic cues in this early preference for the mother is not clear. The aim of the present work was to analyze the timing of acoustic recognition of the mother and to identify the physical parameters used in the recognition of maternal bleats by the lamb.

In a first study, we investigated the ability of lambs to discriminate between the bleats of their own mother and an alien equivalent mother in a two-choice test. Both ewes were hidden behind a canvas sheet and lambs were not allowed to approach the dams closer than 1 m, thus preventing visual as well as olfactory perception. Tests were conducted 12 hr, 24 hr or 48 hr after birth (n=19 or 20/group). An indication of vocal discrimination was already present at 24 hr and at 48 hr lambs spent significantly more time near their mother than near the alien dam.

In a second step, we investigated which physical parameters of the bleats were important for recognition. For this, we conducted playback experiments with modified bleats at two weeks postpartum. Ours results show that lambs pay attention to a combination of various time, energy and frequency parameters: timbre (distribution of energy within the spectrum), amplitude and frequency modulations appear to be the most important parameters encoding the individual signature.

We conclude that vocal recognition between the ewe and her lamb plays an important role in the display of preferential mother-young bond from very early on. Our studies also demonstrate that the encoding of the individual signature is not limited to the frequency domain but rather involves a multiparametric encoding process.     

Cell- and region-specific miR30-based gene knock-down with temporal control in the rat brain

Background  

RNA interference (RNAi) emerges as a powerful tool to induce loss-of-function phenotypes. In the context of the brain, gene manipulation is best targeted to specific subsets of cells in order to achieve a physiologically relevant outcome. Polymerase II-based viral expression systems can be used to cell-specifically express constructs incorporating flanking and loop sequences from endogenous microRNA (miRNA), which directs the designed hairpins into the endogenous gene silencing machinery. While many studies have documented non-cell-selective gene knock-down in the brain, it has not been tested whether different cell types or different areas of the central nervous system (CNS) are equally amenable to this approach. We have evaluated this issue using a tetracycline (Tet)-controllable and cell-specific miRNA 30 (miR30)-based short hairpin (shRNA) interference system.