Chemical communication: does odor plume shape matter?

Many insects use chemical information to gather information about their environment. Infochemicals are spread into the environment as the wind disperses the odor molecules from the source. The structure of an odor plume around a food source is complex and time-dependent. At a large scale, it meanders as it moves with the wind. At a smaller scale, patches with odors are interspersed with regions of clean air. In this study, we compare a plume model that takes the features of a real odor plume into account, a so-called filamentous plume model, with a simplified, time-averaged model, which is commonly used in the literature, and we investigate by simulation their effect on a modeled fruit fly population. During foraging Drosophila melanogaster is attracted to food odors and its aggregation pheromone. Ample knowledge on the attraction to these infochemicals in an experimental set-up exist in the literature. The comparison of the plumes in a simulation study clearly showed that the filamentous plume attracted more fruit flies towards the source than the time-averaged plume. We discuss the results in the light of experimental findings

The Effect of Chemical Information on the Spatial Distribution of Fruit Flies: I Model Results

Animal aggregation is a general phenomenon in ecological systems. Aggregations are generally considered as an evolutionary advantageous state in which members derive the benefits of protection and mate choice, balanced by the costs of limiting resources and competition. In insects, chemical information conveyance plays an important role in finding conspecifics and forming aggregations. In this study, we describe a spatio-temporal simulation model designed to explore and quantify the effects of these infochemicals, i.e., food odors and an aggregation pheromone, on the spatial distribution of a fruit fly (Drosophila melanogaster) population, where the lower and upper limit of local population size are controlled by an Allee effect and competition. We found that during the spatial expansion and strong growth of the population, the use of infochemicals had a positive effect on population size. The positive effects of reduced mortality at low population numbers outweighed the negative effects of increased mortality due to competition. At low resource densities, attraction toward infochemicals also had a positive effect on population size during recolonization of an area after a local population crash, by decreasing the mortality due to the Allee effect. However, when the whole area was colonized and the population was large, the negative effects of competition on population size were larger than the positive effects of the reduction in mortality due to the Allee effect. The use of infochemicals thus has mainly positive effects on population size and population persistence when the population is small and during the colonization of an area

The Effect of Chemical Information on the Spatial Distribution of Fruit Flies: II Parameterization, Calibration, and Sensitivity

In a companion paper (Lof et al., in Bull. Math. Biol., 2008), we describe a spatio-temporal model for insect behavior. This model includes chemical information for finding resources and conspecifics. As a model species, we used Drosophila melanogaster, because its behavior is documented comparatively well

Modelling the effects of odours and spying parasitoids on fruit fly population dynamics

The study of the role of chemical information in species interactions has been mostly restricted to studies at the level of individual organisms. The central question in this thesis is how intraspecific chemical information conveyance and exploitation thereof by a natural enemy affects the spatial population dynamics of a species. To answer this question, I developed a spatio-temporal model where both host and parasitoid can respond to infochemicals. Our model system consists of the fruit fly Drosophila melanogaster, and its natural enemy, the larval parasitoid Leptopilina heterotoma. D. melanogaster uses its aggregation pheromone in combination with odours from fermenting fruits to localise suitable resources for reproduction. L. heterotoma uses these same odours to localise its host. For D. melanogaster, aggregation on a resource can be beneficial when a population is small and has to overcome negative effects associated with low population densities. Such negative effects, known as the Allee effect, can for instance be caused by difficulties in resource exploitation or in finding a mate. Aggregation also involves costs. Individuals within an aggregation frequently experience more severe competition for food, space and mates than they would experience when being on their own. Furthermore, I investigated which behavioural decisions enhance the ability to find - and distinguish between – odour sources that differ in their suitability for reproduction. On the individual level, this research showed that, like real fruit flies, the modelled fruit flies need to have a preference for the presence of both aggregation pheromone and food odours, over food odours alone, to be able to distinguish between the two types of odour sources. The results show that this stronger preference does not have to be innate. As long as fruit flies are able to remember and adjust their current preference based on the odour concentrations that they perceive, more fruit flies find the more attractive odour source. On a population level, this thesis shows that the use of chemical information by D. melanogaster affects its population dynamics. In the absence of its natural enemy, and when the Drosphila population is small, the use of food odours and aggregation pheromone has a positive effect on population growth and enhances the fruit fly’s colonization ability. When the population becomes larger, however, the negative effects of larval competition are stronger than the positive effects of reduced mortality due to the Allee effect. The use of chemical information was crucial to colonize an area from the boundaries. A fruit fly population that was unable to use chemical information could not colonize the area and went extinct. When parasitoids can use chemical information, parasitism rates are higher, resulting in a slower population growth of their host. No difference was recorded in fruit fly population size and in larval mortality due to parasitism, when parasitoids exploited the aggregation pheromone of the fruit fly adults as compared with the simulations where the parasitoids could only respond to chemicals emitted by the host habitat. In contrast, the use of chemical information by the host enhanced its population growth and enabled it to survive, even at higher parasitoid densities. This research showed that mortality when the population was small had a greater impact on population size than mortality due to competition or parsitism. Food patches are not always abundant in nature. Thus, the reproductive success of fruit flies is mainly determined by their opportunities of producing clutches (i.e. locating patches) rather than by preventing over-aggregation or parasitism. As a result, the use of chemical information has a net positive effect on fruit fly population dynamics, despite the fact that L. heterotoma is able to exploit it.</p

Ecology of Drosophila aggregation pheromone: a multitrophic approach

Many insect species use an aggregation pheromone to form groups with conspecifics in certain localities of the environment. This type of behaviour has a variety of implications for ecological interactions, both directly through the effect of the pheromone on the behaviour of con- and heterospecifics, and indirectly through the consequential aggregative distributions that may affect species interactions. The evolutionary ecology of the use of aggregation pheromone has received only little attention. Yet, these pheromones may play an intricate role in food web interactions by providing an accompanying information web.The aim of this thesis is to further our understanding on the ecological and evolutionary aspects of the use of aggregation pheromone in insects. By unravelling costs and benefits that arise from the use of aggregation pheromone in our ecological model organism, Drosophila melanogaster , we strive to answer why they use an aggregation pheromone and elucidate the ecological consequences of an aggregation pheromone in a food web context.In laboratory and field studies, we identified behaviours and interactions of the fruit fly D. melanogaster that were affected by its aggregation pheromone. The pheromone affected the distribution of adults, their eggs, competitor species and parasitoids. Moreover, a number of costs and benefits to the use of aggregation pheromone were indicated. In subsequent studies, the major hypotheses on costs and benefits were examined.A major benefit of using aggregation pheromone was shown to be aggregated oviposition. Aggregated oviposition enhanced the quality of the larval resource, as indicated by a higher survival of the larvae and larger size of the emerging flies. This Allee effect was characterised by a positive effect of adult density on larval fitness components, and may have arisen from the interaction between adult flies and micro-organisms (yeasts and fungi). Fungi antagonise yeast and larval development, while adults can inoculate yeast on a substrate and temper fungal growth. Larvae also tempered fungal growth, but an increased larval density did not result in an Allee effect but in competition instead.A major cost of using aggregation pheromone arose from an increased risk of parasitism. The parasitoid Leptopilina heterotoma uses the aggregation pheromone of adult fruit flies to localise the larval hosts, and based on this information this parasitoid can differentiate quantitatively at long range between substrates that differ in profitability. After arrival on a substrate, the pheromones no longer play a role in the host searching behaviour. A behaviour-based model was developed to predict the individual risk of parasitism for hosts in differently sized host aggregations. The functional and numerical responses of the parasitoids were combined with a flexible patch leaving decision rule for the parasitoid, to assess whether aggregation could also comprise a benefit to the hosts in terms of a diluted risk ( sensu Hamilton 1971). The model prediction reads that aggregation is not beneficial in the context of the Drosophila - Leptopilina interaction, and these predictions were supported by field data.In a simple spatio-temporal simulation model, the population dynamics arising from several modes of dispersal, food competition and an Allee effect were explored. The model is a first step towards a more extensive model that incorporates the responses of insects to spatially heterogeneous resources and chemical information (e.g., aggregation pheromone).The main conclusion from this thesis is that the aggregation pheromone of D. melanogaster plays an intricate role within a foodweb context, and that a variety of costs and benefits arise from multitrophic interactions. To understand the dynamic interactions in this and many other ecological systems, it is essential to gain more insight into the effect of aggregation pheromone on the behaviour of individuals.</font

MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications

Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described

Generalized averaged Gaussian quadrature and applications

A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal