Parasitismus und ‘Endokrine Disruption’ in Fischen

Background

Since the 1960s the scientific community has become increasingly aware of the need for integrative and holistic approaches to solve environmental issues. It has not only been recognized that changing environmental conditions can alter toxicological properties of pollutants but also that susceptibility of organisms to man-made chemicals strongly depends on environmental factors. This is especially true with respect to the endocrine control of reproductive processes in many aquatic species including fish, which are mainly influenced by changes in the surrounding environment such as day length, temperature, water flow, etc. Thus, it is astounding that the use of integrative approaches to address the question of the ecotoxicological relevance of the disruption of endocrine and related reproductive functions is rate. As a consequence of this shortcoming, there is increasing demand both among scientists and politicians regarding more holistic approaches in the endocrine disruptor research.

Aim

This contribution aims to critically discuss current strategies and approaches as well as to identify alternative strategies in context with the environmental risk assessment of endocrine disruptors. This will be exemplified using an ecotoxicological study with bream (Abramis brama) that was conducted along a major European river, the Elbe.

Results and Discussion

Local bream (Abramis brama) populations collected along the river Elbe were characterized by different magnitudes and/or types of endocrine alterations. Although there is a relatively extensive data set available regarding its contamination with wide range of chemicals in the Elbe, it has not been possible to conclusively relate the observed endocrine effects to the exposure to individual compounds or mixtures of chemicals. However, during the gross morphological evaluations of the fish it was observed that at some locations a great number of the individuals caught were parasitized with the tapeworm Ligula intestinalis. Furthermore, statistical analysis revealed that a relatively great percentage of the variation of the biological endpoints observed both among individuals and sampling sites could be explained by the occurrence of this parasite. Overall, the findings of these studies indicate that there is a complex interaction not only among the exposure to chemicals and parasitism but also of both of these aspects with the occurrence of biological effects in fish.

Conclusions

The gaps in our current knowledge as well as the findings from the few studies available indicate, the there is a need to revise our current approaches to characterize and evaluate exposure scenarios regarding their potential to cause endocrine disruption in wild organisms. Given the complexity of most environmental exposure scenarios, involving multiple factors including anthropogenic and natural influences and their interactions, I therefore see the urgent need to initiate a discussion on more integrative approaches in this field in favor of true ‘ecotoxicological studies’ that integrate both ecology and toxicology.     

Predators choosing between patches with standing crop: the influence of switching rules and input types

Where prey arriving in a patch are not consumed immediately, they will accumulate. Predators are then presented with a prey density or standing crop that increases through further input, and decreases through the consumption by predators. Firstly, I show that the switching rule of predators has a significant influence on the expected predator equilibrium distribution in such a dynamic system. Three rules are compared; for all rules, analytical solutions are calculated (where possible). To test their plausibility for natural situations, predator distributions are simulated given the assumption that each predator obtains individual patch profitability estimates by using a common learning rule. As long as prey arrive in the patches in constant numbers per time unit, the first rule leads to input matching because predators stop switching when consumption in the two patches is equal. The other two rules, where predators continue to sample both patches even in the equilibrium state, lead to predator distributions where the more profitable patch is underused. The final equilibrium depends on the exact assumptions of the switching rule; however, it is independent of interference. But if the input delivered into a patch is a function of the current prey standing crop (for example in a reproducing prey population), predator and prey distributions will not reach an equilibrium in most cases: either standing crops increase indefinitely, or they approach zero, with all predators concentrating on the better patch. Only a small number of parameter sets show intermediate crops that are reasonably stable. With this input type, only up to 54% of the simulations reach the expected distribution. In a system with competition for dynamic standing crop, it is therefore essential to know the type of input and the switching-rule used by predators to be able to predict equilibrium predator distributions. Received: 17 March 1995/Accepted after revision: 5 November 1995     

Storage and metabolism of radioactively labeled pyrrolizidine alkaloids by butterflies and larvae of Mechanitis polymnia (Lepidoptera: Nymphalidae,Ithomiinae)

Summary. Tracer feeding studies with radioactively labeled pyrrolizidine alkaloids (PAs) were performed to attain experimental information about the specificity and mechanisms of uptake, metabolism and storage of PAs in the alkaloid sequestering ithomiine butterfly Mechanitis polymnia. Adult butterflies easily ingest the tracers offered dissolved in a saturated sugar solution. Feeding of [¹⁴C]rinderine (free base) confirmed that M. polymnia is well adapted to sequester and maintain PAs of the lycopsamine type. Approximately 80% of the ingested radioactivity can be recovered in methanol extracts of the butterflies over a period of at least 6 hours. Labeled rinderine is efficiently N-oxidized and transformed into a metabolite of still unknown structure. These two metabolites are formed in almost equal amounts and account for more than 90% of total radioactivity. After four hours the toxic free base is only detectable in traces. Radioactively labeled senecioylretronecine (free base), a PA that often accompanies PAs of the lycopsamine type in plants, is metabolized in a different manner. The toxic free base disappeared as fast as the tertiary rinderine, but the final products which accumulated in a stable ratio after 12 hours were mainly two polar metabolites of unknown structure; senecioylretronecine N-oxide accounts for less than 10% of total PAs. Labeled senecionine a macrocyclic PA, which never has been found in wild caught M. polymnia is only slowly N-oxidized. In females ca 50% of the ingested senecionine is still present as free base after 24 hours, whereas under the same conditions in males this percentage is only ca 20%. This difference in N-oxidation was the only significant sex-specific difference observed in various experiments. Larvae of M. polymnia which feed on Solanum tabacifolium, a plant that does not contain PAs, are able to sequester and partly N-oxidize labeled senecioylretronecine and senecionine. However, the storage is not very efficient; with the two tracers less than 5% of radioactivity remained in the bodies after 24 hours. Received 19 October 1999; accepted 24 November 1999     

The Baltic haline conveyor belt or the overturning circulation and mixing in the Baltic

A study of the water-mass circulation of the Baltic has been undertaken by making use of a three dimensional Baltic Sea model simulation. The saline water from the North Atlantic is traced through the Danish Sounds into the Baltic where it upwells and mixes with the fresh water inflow from the rivers forming a Baltic haline conveyor belt. The mixing of the saline water from the Great Belt and Oresund with the fresh water is investigated making use of overturning stream functions and Lagrangian trajectories. The overturning stream function was calculated as a function of four different vertical coordinates (depth, salinity, temperature and density) in order to understand the path of the water and where it upwells and mixes. Evidence of a fictive depth overturning cell similar to the Deacon Cell in the Southern Ocean was found in the Baltic proper corresponding to the gyre circulation around Gotland, which vanishes when the overturning stream function is projected on density layers. A Lagrangian trajectory study was performed to obtain a better view of the circulation and mixing of the saline and fresh waters. The residence time of the water masses in the Baltic is calculated to be 26-29 years and the Lagrangian dispersion reaches basin saturation after 5 years.     

Prediction of lichen diversity in an UNESCO biosphere reserve – correlation of high resolution remote sensing data with field samples

The present study focuses on developing models to predict lichen species richness in a UNESCO Biosphere Reserve of the Swiss Pre-Alps following a gradient of land-use intensity combining remote sensing data and regression models. The predictive power of the models and the obtained r ranging from 0.5 for lichens on soil to 0.8 for lichens on trees can be regarded as satisfactory to good, respectively. The study revealed that a combination of airborne and spaceborne remote sensing data produced a variety of ecological meaningful variables.     

Nutrients on Asphalt Parking Surfaces in an Urban Environment

Amounts of readily soluble nutrients on asphalt parking lot surfaceswere measured at four locations in metropolitan Phoenix, Arizona, U.S.A. Using a rainfall simulator, short intense rainfall events were generated to simulate `first flush' runoff. Samples were collected from 0.3 m² sections of asphalt at 8 to 10 sites on each of four parkinglots, during the pre-monsoon season in June-July 1998 and analyzed for dissolved NO₃ ^--N, NH₄ ⁺-N, soluble reactive phosphate (SRP), and dissolved organic carbon (DOC). Runoff concentrations varied considerably for NO₃ ^--N and NH₄ ⁺-N (between 0.1 and 115.8 mg L^-1) and DOC (26.1 to 295.7 mg L^-1), but less so for SRP (0.1 to 1.0 mg L^-1), representing average surface loadings of 191.3, 532.2, and 1.8 mg m^-2 respectively. Compared with similar data collected from undeveloped desert soil surfaces outside the city, loadings of NO₃ ^--N and NH₄ ⁺-N on asphalt surfaces were greater by factors of 91 and 13, respectively. In contrast, SRP loads showed little difference between asphalt and desert surfaces. Nutrient fluxes in runoff from a storm that occurred shortly after the experiments were used to estimate input-output budgets for 3 of the lots under study. Measured outputs of DOC and SRP were similar to those predicted using rainfall and experimentally determined surface loadings, but for NH₄ ⁺-N and particularly for NO₃ ^--N, estimated rainfall inputs and surface runoff were significantly higher than exports in runoff. This suggests that parking lots may be important sites for nutrient accumulation and temporary storage in arid urban catchments.     

波罗的海高盐传送带,或波罗的海中的翻转环流及咸、淡水的混合

我们使用三维波罗的海模型模拟的做法进行了一项波罗的海水团环流的研究.来自北大西洋的咸水经丹麦海峡流入波罗的海,在波罗的海上涌并与从各河流流入的淡水混合形成"波罗的海高盐传送带".我们利用翻转流量函数和拉格朗日轨迹线对来自大贝尔特和厄勒海峡的成水与淡水的混合情况进行了调查.该翻转流量函数被作为一种具有4个不同垂直坐标(深度、盐度、温度和密度)的函数进行计算,以便了解水的路径以及它在什么地方上涌并混合.在波罗的海本体内发现了与南大洋中的迪肯环流(Deacon Cell)类似的虚拟深度翻转环流的存在,它与哥特兰岛附近的旋转环流相符,当翻转流量函数投射在密度层上时,这一虚拟深度翻转环流就消失了.我们已经开展了一项拉格朗日轨迹线研究,以便更好地认识该环流以及咸水与淡水的混合情况.对这些水团在波罗的海中的停留时间的计算结果为26～29年,而拉格朗日扩散在5年后达到海盆饱和.