Mating in the afternoon: Time-saving in courtship and remating by females of a polyandrous butterfly Pieris napi L.

Summary Among butterflies where females are polygamous, interactions with males after the first mating entail time costs associated with both courtship and mating. In the green-veined white butterfly, Pieris napi, spermatophore counts on wild-caught females revealed that the average number of matings that females had performed increased gradually from 1.1 during the first week of the flight period to 2.4 during the 4th and final week. By dissecting pairs found in copula in the field, we found that female rematings occurred solely in the afternoon, whereas virgin females mated most frequently earlier in the day. We suggest that non-virgin females minimize the time cost of rematings by allocating them to an hour when the egglaying frequency has decreased to a low level. Virgin females were very attractive to males, judging by their courtship persistence (several minutes), but when mated, females became so unattractive that courting males left them within a few seconds. However, females' attractiveness increased again with time elapsed since the last mating. These observations support the idea that females emit repellent pheromones after mating, which may be male derived. Since newly mated females were not harassed by males or hindered in their egglaying activities, it is conceivable that the time cost of remating may be outweighed by the benefit of the regained ability to curtail male courtship. This advantage to newly remated females may in itself be an explanation for polyandry in P. napi and is alternative or complementary to the idea that females that remate receive a material benefit that can be used to increase their realized fecundity.     

Anwendung des Röntgenbildverstärkers für Feinstrukturuntersuchungen

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Quantitative determination of volatile organic compounds in indoor dust using gas chromatography-UV spectrometry

A novel technique, gas chromatography-UV spectrometry (GC-UV), was used to quantify volatile organic compounds (VOCs) in settled dust from 389 residences in Sweden. The dust samples were thermally desorbed in an inert atmosphere and evaporated compounds were concentrated by solid phase micro extraction and separated by capillary GC. Eluting compounds were then detected, identified, and quantified using a diode array UV spectrophotometer. Altogether, 28 compounds were quantified in each sample; 24 of these were found in more than 50% of the samples. The compounds found in highest concentrations were saturated aldehydes (C5-C10), furfuryl alcohol, 2,6-di-tert-butyl-4-methylphenol (BHT), 2-furaldehyde, and benzaldehyde. Alkenals were also found, notably 2-butenal (crotonaldehyde), 2-methyl-propenal (methacrolein), hexenal, heptenal, octenal, and nonenal. The concentrations of each of the 28 compounds ranged between two to three orders of magnitude, or even more. These results demonstrate the presence of a number of VOCs in indoor dust, and provide, for the first time, a quantitative determination of these compounds in a larger number of dust samples from residents. The findings also illustrate the potential use of GC-UV for analysing volatile compounds in indoor dust, some of which are potential irritants (to the skin, eyes or respiratory system) if present at higher concentrations. The potential use of GC-UV for improving survey and control of the human exposure to particle-bound irritants and other chemicals is inferred.     

An algebraic/graphical tool to compare ecosystems with respect to their pollution V: cluster analysis and Hasse diagrams

In case of large data matrices comparative evaluations of objects/regions with the technique of Hasse diagrams may be troublesome due to a messy system of lines in the graphical representation. Here fuzzy clustering leads to useful simplifications because regions with slightly different pollution pattern are grouped together. However, fuzzy clustering implies to introduce a threshold value for the membership of an object to a cluster and to select the best number of clusters. Therefore many arbitrarities evolve. Within the systematic study presented here we found that some objects are very stable against variations of the threshold value and the number of cluster whereas other objects behaves different. According to their behaviour we investigated a classification of the objects. Formal Concept Analysis shows that in some cases specific pollution pattern imply the membership to one of these classes. For example objects which are characterized by high Pb-, Zn-concentration and moderate S-concentration imply a high stability against variants of the clustering process. Further implications are described in the paper.