Density-dependent dispersal complicates spatial synchrony in tri-trophic food chains

Spatial synchrony can increase extinction risk and undermines metapopulation persistence. Both dispersal and biotic interactions can strongly affect spatial synchrony. Here, we explore the spatial synchrony of a tri-trophic food chain in two patches connected by density-dependent dispersal, namely the strategies of prey evasion (PE) and predator pursuit (PP). The dynamics of the food chain are depicted by both the Hastings–Powell model and the chemostat model, with synchrony measured by the Pearson correlation coefficient. We use the density-independent dispersal in the system as a baseline for comparison. Results show that the density-independent dispersal of a species in the system can promote its dynamic synchrony. Dispersal of intermediate species in the tri-trophic food chain is the strongest synchronizer. In contrast, the density-dependent PP and PE of intermediate species can desynchronize the system. Highly synchronized dynamics emerged when the basal species has a strong PE strategy or when the top species has a moderate PP strategy. Our results reveal the complex relationship between density-dependent dispersal and spatial synchrony in tri-trophic systems.     

蝇蛹俑小蜂对寄主及果实的趋性反应

【背景】蝇蛹俑小蜂是实蝇类害虫蛹期重要的寄生蜂之一。有关植物果实和寄主挥发物在蝇蛹俑小蜂寻找寄主过程中的作用尚不明确。【方法】采用"Y"型嗅觉仪测试了寄主和果实(健康果实和虫害诱导果实)对蝇蛹俑小蜂的引诱作用。【结果】虫伤1 d的番石榴和杨桃果实对蝇蛹佣小蜂雌蜂具有显著的引诱作用;寄主蛹——3日龄橘小实蝇蛹和4日龄瓜实蝇蛹对蝇蛹俑小蜂雌蜂也具有显著的引诱作用。蝇蛹俑小蜂雌蜂对雄蜂有显著的吸引作用。橘小实蝇性诱剂甲基丁香酚对蝇蛹俑小蜂的搜索行为则无显著影响。【结论与意义】寄主蛹和幼虫危害1 d的果实能释放对蝇蛹俑小蜂有引诱作用的物质,这可为利用蝇蛹俑小蜂防治实蝇类害虫提供基础信息。     

Biological control through provision of additional food to predators: a theoretical study

In this paper we analyze a variation of a standard predator-prey model with type II functional response which represents predator-prey dynamics in the presence of some additional food to the predator. The aim is to study the consequences of providing additional food on the system dynamics. We conclude that handling times for the available foods play a key role in determining the eventual state of the ecosystem. It is interesting to observe that by varying the quality and quantity of additional food we can not only control and limit the prey, but also limit and eradicate the predators. In the context of biological pest control, the results caution the manager on the choice of quality and quantity of the additional food used for this purpose. An arbitrary choice may have opposite effects leading to increase in pest concentration and eradication of the predator. This study offers insight into the possible management strategies that involve manipulation of quality and supply level of additional food to predators, for the benefit of biological control. The theoretical conclusions agree with results of some practical biological control experiments.     

The rules of engagement: how to defend against combinations of predators

Studies of inducible defenses have traditionally examined prey responses to one predator at a time. However, prey in nature encounter combinations of predators that should force them to produce phenotypic compromises. We examined how snails (Helisoma trivolvis) alter their phenotype in the presence of three different predator species that were presented alone and in pairwise combinations. When snails were exposed to each predator alone, they formed predator-specific defenses that reflected the differences in each predator’s foraging mode. When snails were exposed to pairwise combinations of predators, their phenotype was dependent on their ability to detect each predator, the risk posed by each predator, and the effectiveness of a given defense against each predator. Consequently, responses to combined predators were typically biased towards one of the predators in the pair. This suggests that prey facing combined predators do not form simple intermediate defenses and, as a result, may experience enhanced mortality risk when they encounter natural predator regimes.     

Degradation of 2,5-dimethylpyrazine by <Emphasis Type="Italic">Rhodococcus erythropolis</Emphasis> strain DP-45 isolated from a waste gas treatment plant of a fishmeal processing company

A bacterium, strain DP-45, capable of degrading 2,5-dimethylpyrazine (2,5-DMP) was isolated and identified as Rhodococcus erythropolis. The strain also grew on many other pyrazines found in the waste gases of food industries, like 2,3-dimethylpyrazine (2,3-DMP), 2,6-dimethylpyrazine (2,6-DMP), 2-ethyl-5(6)-dimethylpyrazine (EMP), 2-ethylpyrazine (EP), 2-methylpyrazine (MP), and 2,3,5-trimethylpyrazine (TMP). The strain utilized 2,5-DMP as sole source of carbon and nitrogen and grew optimally at 25°C with a doubling time of 7.6 h. The degradation of 2,5-DMP was accompanied by the growth of the strain and by the accumulation of a first intermediate, identified as 2-hydroxy-3,6-dimethylpyrazine (HDMP). The disappearance of HDMP was accompanied by the release of ammonium into the medium. No other metabolite was detected. The degradation of 2,5-DMP and HDMP by strain DP-45 required molecular oxygen. The expression of the first enzyme in the pathway was induced by 2,5-DMP and HDMP whereas the second enzyme was constitutively expressed. The activity of the first enzyme was inhibited by diphenyliodonium (DPI), a flavoprotein inhibitor, methimazole, a competitive inhibitor of flavin-containing monooxygenases, and by cytochrome P450 inhibitors, 1-aminobenzotriazole (ABT) and phenylhydrazine (PHZ). The activity of the second enzyme was inhibited by DPI, ABT, and PHZ. Sodium tungstate, a specific antagonist of molybdate, had no influence on growth and consumption of 2,5-DMP by strain DP-45. These results led us to propose that a flavin-dependent monooxygenase or a cytochrome P450-dependent monooxygenase rather than a molybdenum hydroxylase catalyzed the initial hydroxylation step and that a cytochrome P450 enzyme is responsible for the transformation of HDMP in the second step.     

Measures of human olfactory perception during pregnancy

Although considerable anecdotal evidence suggests that pregnancy affects olfactory sensitivity, scientific evidence is limited and inconclusive. Whereas hedonic ratings are affected by pregnancy, odor identification is not. The aim of the current study was to examine odor perception in women across pregnancy and in the postpartum period. One hundred nonsmoking women who were pregnant, postpartum, or had never been pregnant were tested on the University of Pennsylvania Smell Identification Test (UPSIT). Intensity ratings and scratch patterns were collected as potential indicators of sensitivity, and participants rated the odors' pleasantness. Participants also rated their own sense of smell. Mean UPSIT scores did not differ significantly across groups indicating no difference in odor identification. Trends in planned comparisons suggested that in the first trimester, odors were rated as more intense and less pleasant. In the first trimester, women scratched the odor strips significantly fewer times. Consistent with previous reports, 90% of pregnant women reported that specific odors smelled less pleasant and 60% reported that some odors smelled more pleasant. Although nearly two-thirds of pregnant women rated their olfactory sensitivity to be enhanced during pregnancy and overall pregnant women's self-rated olfactory sensitivity was higher than controls', self-ratings were not correlated with UPSIT scores nor odor intensity ratings. These results suggest that these and previous findings may reflect the fact that the effect of pregnancy on olfaction is small and inconsistent.     

A quantitative structure activity analysis on the relative sensitivity of the olfactory and the nasal trigeminal chemosensory systems

We have applied a quantitative structure-activity relationship (QSAR) approach to analyze the chemical parameters that determine the relative sensitivity of olfaction and nasal chemesthesis to a common set of volatile organic compounds (VOCs). We used previously reported data on odor detection thresholds (ODTs) and nasal pungency thresholds (NPTs) from 64 VOCs belonging to 7 chemical series (acetate esters, carboxylic acids, alcohols, aliphatic aldehydes, alkylbenzenes, ketones, and terpenes). The analysis tested whether NPTs could be used to separate out "selective" chemosensory effects (i.e., those resting on the transfer of VOCs from the gas phase to the receptor phase) from "specific" chemosensory effects in ODTs. Previous work showed that selective effects overwhelmingly dominate chemesthetic potency whereas both selective and specific effects control olfactory potency. We conclude that it is indeed possible to use NPTs to separate out selective from specific effects in ODTs. Among the series studied, aldehydes and acids, except for formic acid, show clear specific effects in their olfactory potency. Furthermore, for VOCs whose odor potency rests mainly on selective effects, we have developed a QSAR equation that can predict their ODTs based on their NPTs.     

Dose-dependent nonassociative olfactory learning in a fly

Olfactory sensory stimulation induces a fast-phase arrest response (FPA-R) of the blowfly heart activity that has been described as a sensitive tool for testing insect reactivity to odor perception. We analyzed FPA-R occurrence to repeated olfactory stimulation with low and high 1-hexanol concentrations that are behaviorally attractant and repellent, respectively, in the blowfly. FPA-R occurrence diminished and ceased with repeated presentations of low and medium odor concentrations, according to dynamics inversely related to odor doses. On the other hand, repeated stimulation with higher odor concentrations induced persistent FPA-Rs. Sensory input amplitude to repeated presentations of singly tested odor concentrations did not change throughout stimulation sessions. A spontaneous restoration of FPA-R to olfactory stimulation was recorded 30 min after cessation of FPA-R to a previous olfactory stimulation session. However, a prompt restoration of FPA-R to olfactory stimulation after cessation of FPA-R was obtained following mechano-taste stimulation of labellar sensilla. Our findings show that the FPA-R habituates to olfactory sensory stimulation with low and medium odor concentrations according to dynamics inversely related to odor intensities. On the other hand, the FPA-R does not habituate to higher odor concentrations. Therefore, flies learn to disregard nonaversive odor information, but they cannot ignore iterative detection of a repellent volatile.     

Positive implicit attitudes toward odor words

Associations between certain odors and for instance health effects may lead to positive or negative attitudes toward these odors. However, in experiments we conducted using the Implicit Association Test (IAT), we encountered attitudes even to odor "words." The IAT is based on the principle that reaction times measuring the association between words from a target dimension (in this case, odor vs. a neutral reference category) and an attribute dimension (i.e., positive or negative words) reflect the attitude to the target, where attitude-congruent associations between target and attribute are reflected by shorter reaction times. In a first experiment, we found distinctly positive attitudes to the concept odor in a student sample, which was replicated in a second experiment. In the main experiment, subjects in the aromatherapy group, who prefer using scented consumer products for relaxation purposes, showed a significantly more positive attitude toward odor words in the IAT than a control group, who did not have such a preference. The fact that results from the implicit test were not always associated with explicitly stated attitudes toward the odor words attests to the fact that the IAT measures the attitude of interest in a different way. As such, the IAT has added value in circumstances where explicit tests can be biased.     

Olfactory performance of rats after selective deafferentation of the olfactory bulb by 3-methyl indole

Rats trained to detect propyl acetate and valeric acid and to discriminate between propyl acetate and amyl acetate and between valeric acid and butyric acid were injected with a low dose of 3-methyl indole, a treatment that produces well-defined and selective deafferentation of the olfactory bulbs. Treatment completely deafferented most but not all bulbar loci for aliphatic acids and at least disrupted those for propyl and amyl acetate. In posttreatment tests, experimental rats performed somewhat but not significantly more poorly than controls and about as well on the acid detection and discrimination tasks as on the corresponding acetate tests.