Institut für Ökologie, Evolution und Diversität
Species distribution modelling of stream macroinvertebrates under climate change scenarios
- There is increasing evidence that climate change will have a severe impact on species’ distributions by altering the climatic conditions within their present ranges. Especially species inhabiting stream ecosystems are expected to be strongly affected due to warming temperatures and changes in precipitation patterns. The aim of this thesis was to
investigate how distributions of aquatic insects, i.e., benthic stream macroinvertebrates would be impacted by warming climates. The methods comprised of an ensemble forecasting technique based on species distribution models (SDMs) and climate change scenarios of the Intergovernmental Panel on Climate Change of the year 2080. Future model projections were generated for a wide variety of species from a number of taxonomic orders for two spatial scales: a stream network within the lower mountain ranges of Germany, and the entire territory across Europe. In addition, the effect of the modelling technique on habitat suitability projections was investigated by modifying the choice of study area (continuous area vs. stream network) and the choice of predictors (standard vs. corrected set).
Projections of future habitat suitability showed that potential climate-change impacts would be dependent on species’ thermal preferences, and with a similar pattern for both spatial scales. Future habitat suitability was projected to remain for most or all of the modelled species, and species were projected to track their climatically suitable conditions by shifting uphill along the river continuum within the lower mountain ranges, and into a north-easterly direction across Europe. Cold-adapted headwater and high-latitude species were projected to lose suitable habitats, whereas gains would be expected for warm-adapted river and low-latitude species along the river continuum and across Europe, respectively. Additionally, habitat specialist species in terms of endemics of the Iberian Peninsula were identified as potential climate-change losers, highlighting their restricted habitat availability and therefore vulnerability to warming climates.
The main findings of this thesis underline the high susceptibility of stream macroinvertebrates to ongoing climate change, and give insights into patterns of possible consequences due to changes in species’ habitat suitability. Concerning the methodology, a clear recommendation can be given for future modelling approaches of stream macroinvertebrates by building models within a stream network and with a careful choice of environmental predictors, to reduce uncertainties and thus to improve model projections.
The role of food quality for local adaptation in Daphnia
- The impact of different food qualites on the local adaptation was investigated at several organization levels in Daphnia.
The associations of the plant-ant Cladomyrma with plants in Southeast Asia
- In over 100 genera of tropical angiosperms, one or more species possess specialised structures for housing ants. The longevity and intimacy of these associations has often facilitated an increasing specialisation of both the ants and the plants, leading to a number of highly specific and obligate symbioses. Early literature contained only few anecdotal reports of the ant genus Cladomyrma WHEELER inhabiting (unidentified) plants. This work presents the new findings on Cladomyrma and its host plants that accumulated over the last two decades. My studies of Cladomyrma reveal that there is a largely overlooked community of south-east Asian plant-ants and their associated plants. Currently the genus consists of at least 12 species. Cladomyrma has been thought to be restricted to the ever-wet part of the West Malesian floristic region, comprising the Malay Peninsula, Borneo, and Sumatra, but recent collections from Thailand and Vietnam indicate that species of the genus penetrate the seasonal tropical forests of Continental Asia. Cladomyrma inhabits 24 plant species belonging to a surprisingly extensive range of plant taxa: Callerya, Saraca, Spatholobus (Fabaceae), Crypteronia (Crypteroniaceae), Drypetes (Putranjivaceae), Ryparosa (Achariaceae), Strychnos (Loganiaceae), Neonauclea (Rubiaceae), Luvunga (Rutaceae) and Sphenodesme (Verbenaceae). In terms of taxonomic diversity on the genus and family level the range of hosts utilised by Cladomyrma is one of the broadest ever recorded for any live stem-nesting plant-ant lineage worldwide. This work provides a species-level overview of all Cladomyrma host plants known from Borneo, the Malay Peninsula and Sumatra, including descriptions of ant-housing structures (domatia), ant inhabitant identity, onset of colonisation during plant ontogeny, nest structure, occupancy rate, and considerations of results obtained from herbarium specimens. Both the regularity of ant association and the degree of morphological specialisation toward myrmecophytism are assessed. The behavioural traits of Cladomyrma are compatible with traits exhibited by other protective plant-ants. This work demonstrates that all species of Cladomyrma investigated (dianeae, maschwitzi, yongi, petalae) confer antiherbivore protection to young leaves of its host. The ants also attack and repell or kill herbivorous insect larvae encountered on young foliage. Cleaning behaviour appears to be a trait shared by all members of the genus, and the two species tested (maschwitzi, petalae) successfully removed termite eggs experimentally placed onto young leaves. Another trait common to all known species of the genus is that the ants preferentially patrol young shoots and leaves ('neophily'). These behavioural traits of Cladomyrma likely reduce stem damage and pathogenic infection of their host. The ants prune encroaching vegetation (tested in dianeae maschwitzi, petalae, yongi, observed in crypteroniae) and attack paper tape used to mark host plants (observed in andrei, dianeae, hobbyi, nudidorsalis, maschwitzi, yongi, petalae). If these traits combined translate into a better reproductive success of the hosts has yet to be verified. Evidence for lifetime fitness benefits is particularly difficult to quantify for the long-lived woody host plants of Cladomyrma. The predominant food source of Cladomyrma appears to be the honeydew of scale insects (Coccidae and Pseudococcidae) which the ants tend inside their nest cavities. Observations on scale insect acquisition by Cladomyrma foundress queens show that hemipteran trophobionts are not transported by the queens on their nuptial flight but they nevertheless arrive on the host plant independently of the ants. Entry into nest chambers is facilitated by small holes kept open by the foundress queen. Most Cladomyrma species have been recorded from only one or two (three) host plant species (andrei, crypteroniae, hobbyi, maschwitzi, nudidorsalis, scopulosa, yongi), but two species, Cladomyrma petalae and C. dianeae, are more catholic in their host usage; the first being a 'generalist' plant-ant colonising hosts across a broad taxonomic range, the second inhabiting several members of the genus Neonauclea. First results of host-choice experiments with C. petalae are presented and the potential mechanisms promoting host specificity are discussed. My studies of the Cladomyrma/plant associations indicate that codiversification and host shifts or host expansions, rather than cospeciation, shape the pattern of species interactions in this system. Finally, I propose a scenario in which three key traits of Cladomyrma –access to live stems, utilisation of indirect food rewards via trophobionts and 'neophily'– are hypothesised to favour niche differentiation and the acquisition of new hosts over evolutionary time.
Entwicklung einer GIS-gestützten Standardmethode (GisMap) zur Untersuchung der pflanzlichen Artenvielfalt in der Normallandschaft
- In der vorliegenden Arbeit wird ein neu entwickeltes Erfassungsinstrument für die pflanzliche Artenvielfalt in der Normallandschaft vorgestellt, dass den Namen GISMap trägt. Die standardisierte Vorgehensweise und eine große Reproduzierbarkeit des Aufnahmeverfahrens sind wichtige Eigenschaften der Methode. GISMap basiert auf der GIS-gestützten Auswertung der Landschaftsstruktur, die in Form eines digitalen Landschaftsmodells (DLM) zugrunde gelegt wird. Im Zentrum der Methode steht ein im Rahmen der Arbeit entwickelter Algorithmus, der eine zufallsgesteuerte Festlegung von Aufnahmeflächen in der zu untersuchenden Landschaft vornimmt und sich dabei an den Ökotonen orientiert, die sich zwischen zwei benachbarten Landschaftselementen ausbilden. Ökotone sind als Übergangsbiotope häufig sehr reich an Strukturen und können daher eine große Artenvielfalt aufweisen. GIS-Map macht sich diese ökologische Gegebenheit zunutze, um auf möglichst kleinem Raum eine große Artenzahl zu erfassen. Die von GISMap errechneten Aufnahmeflächenkoordinaten wurden mit Hilfe eines GPS-Empfängers im Gelände lokalisiert und einer floristischen Untersuchung unterzogen. Als geeignete Aufnahmeflächengröße erwies sich dabei ein Kreis mit einer Fläche von 700 m². Die Flächen wurden mit Magneten markiert, um sie zur Dauerbeobachtung der Flora nutzen zu können. In dem 33 km² großen Untersuchungsgebiet, das im östlichen Bereich des Taunus liegt, wurden insgesamt 141 Aufnahmeflächen für 16 64tel-MTB-Rasterfelder angelegt. Um den mit der Methode zu erzielenden Erfassungsgrad abschätzen zu können, wurden umfangreiche Vergleichsuntersuchungen durchgeführt, die auch eine Auswertung vorliegender Literaturquellen mit einschlossen. In den 16 untersuchten Rasterfeldern konnten durchschnittlich 73 % der insgesamt vorkommenden Arten mit der Methode erfasst werden. Dazu müssen nur 0,3 % der Fläche tatsächlich einer floristischen Untersuchung unterzogen werden. Alle kartierten Arten erhalten dabei eine punktgenaue Koordinate. Die Methode wurde als Basisinstrument konzipiert und sollte mit bereits vorliegenden Fachdaten kombiniert werden, um die Erfassung der Farn- und Samenpflanzen eines Gebietes zu vervollständigen. Diskutiert wird der Einsatz im Rahmen eines Landschaftsinformationssystems (LIS). Durch eine Ergänzung der mit GISMap erhobenen Daten mit anderen vegetationskundlichen Daten aus dem Untersuchungsgebiet konnte der Erfassungs-grad von 73 % auf 85 % gesteigert werden. Im Rahmen der Arbeit werden zahlreiche Möglichkeiten der technischen Weiterentwicklung dargestellt, die zu einer Optimierung der Methode beitragen können. Ausgehend von den Daten des digitalen Landschaftsmodells wurden zur Beschreibung der landschaftlichen Struktur des Untersuchungsgebietes verschiedene Landschaftsstrukturmaße berechnet, wie sie in der modernen landschaftsökologischen Forschung mittlerweile häufig zum Einsatz kommen. Diese wurden mit den erfassten Sippenzahlen korreliert, um Zusammenhänge zwischen der Landschaftsstruktur und dem auftretenden floristischen Ar-tenreichtum darzustellen. Dabei wurde auch der Fragestellung nachgegangen, ob auf der Basis von Maßzahlen für die Landschaftsstruktur Prognosen über die zu erwartende pflanzli-che Artenvielfalt getroffen werden können. Ein weiterer Aspekt der Untersuchungen bestand in der Nutzung des entstandenen Aufnahmeflächennetzes zur langfristigen Beobachtung von Veränderungen der Vegetation des betrachteten Landschaftsausschnittes. Anhand der Frequenzen in den Aufnahmeflächen kann mit GISMap ein langfristiges Monitoring auf der Ebene einzelner Arten durchgeführt werden. Dies wird u. a. in Hinblick auf die im Untersuchungsgebiet auftretenden Neophyten diskutiert. Als Möglichkeit zum Monitoring der gesamten Vegetation wurde der Ansatz verfolgt, die Verteilung der kartierten Arten auf 24 häufig in der Literatur beschriebene Pflanzenformationen festzustellen. Es wird vorgeschlagen, eine langfristige Beobachtung dieses Verteilungsmusters vorzunehmen, um einen Aufschluss über ökologische Veränderungen der Landschaft anhand der Vegetation zu erhalten. Weitere Auswertungen der gesammelten floristischen Daten beziehen sich auf ihre Eignung zum Monitoring von klimatischen Veränderungen. Die Berechnung mittlerer Temperaturzahlen für 6 Höhenstufen erwies sich dabei als ungeeignet, da ihre Unterschiede zwischen den Höhenstufen nicht statistisch abzusichern waren. Darüber hinaus wurde die Verteilung von Kühlezeigern in dem entstandenen Aufnahmeflächennetz für die verschiedenen Höhenstufen untersucht. Hinweise zu ihrer Eignung als Indikatoren für klimatische Veränderungen werden diskutiert.
Biodegradation and elimination of industrial wastewater in the context of whole effluent assessment
- The focus of this thesis is on the assessment of the degradability of indirectly discharged wastewater in municipal treatment plants and on assessing indirectly discharged effluents by coupling the Zahn-Wellens test with effect-based bioassays. With this approach persistent toxicity of an indirectly discharged effluent can be detected and attributed to the respective emission source. In the first study 8 wastewater samples from different industrial sectors were analysed according to the “Whole-Effluent Assessment“ (WEA) approach developed by OSPAR. In another study this concept has been applied with 20 wastewater samples each from paper manufacturing and metal surface treating industry. In the first study generally low to moderate ecotoxic effects of wastewater samples have been determined. One textile wastewater sample was mutagenic in the Ames test and genotoxic in the umu test. The source of these effects could not be identified. After treatment in the Zahn-Wellens test the mutagenicity in the Ames test was eliminated completely while in the umu test genotoxicity could still be observed. Another wastewater sample from chemical industry was mutagenic in the Ames test. The mutagenicity with this wastewater sample was investigated by additional chemical analysis and backtracking. A nitro-aromatic compound (2-methoxy-4-nitroaniline) used for batchwise azo dye synthesis and its transformation products are the probable cause for the mutagenic effects analysed. Testing the mother liquor from dye production confirmed that this partial wastewater stream was mutagenic in the Ames test. The wasteweater samples from paper manufacturing industry of the second study were not toxic or genotoxic in the acute Daphnia test, fish egg test and umu test. In the luminescent bacteria test, moderate toxicity was observed. Wastewater of four paper mills demonstrated elevated or high algae toxicity, which was in line with the results of the Lemna test, which mostly was less sensitive than the algae test. The colouration of the wastewater samples in the visible band did not correlate with algae toxicity and thus is not considered as its primary origin. The algae toxicity in wastewater of the respective paper factory could also not be explained with the thermomechanically produced groundwood pulp (TMP) partial stream. Presumably other raw materials such as biocides might be the source of algae toxicity. In the algae test, often flat dose–response relationships and growth promotion at higher dilution factors have been observed, indicating that several effects are overlapping. The wastewater samples from the printed circuit board and electroplating industries (all indirectly discharged) were biologically pre-treated for 7 days in the Zahn–Wellens test before ecotoxicity testing. Thus, persistent toxicity could be discriminated from non-persistent toxicity caused, e.g. by ammonium or readily biodegradable compounds. With respect to the metal concentrations, all samples were not heavily polluted. The maximum conductivity of the samples was 43,700 micro S cm -1 and indicates that salts might contribute to the overall toxicity. Half of the wastewater samples proved to be biologically well treatable in the Zahn–Wellens test with COD elimination above 80%, whilst the others were insufficiently biodegraded (COD elimination 28–74%). After the pre-treatment in the Zahn–Wellens test, wastewater samples from four companies were extremely ecotoxic especially to algae. Three wastewater samples were genotoxic in the umu test. Applying the rules for salt correction to the test results following the German Wastewater Ordinance, only a small part of toxicity could be attributed to salts. In one factory, the origin of ecotoxicity has been attributed to the organosulphide dimethyldithiocarbamate (DMDTC) used as a water treatment chemical for metal precipitation. The assumption, based on rough calculation of input of the organosulphide into the wastewater, was confirmed in practice by testing its ecotoxicity at the corresponding dilution ratio after pre-treatment in the Zahn–Wellens test. The results show that bioassays are a suitable tool for assessing the ecotoxicological relevance of these complex organic mixtures. The combination of the Zahn–Wellens test followed by the performance of ecotoxicity tests turned out to be a cost-efficient suitable instrument for the evaluation of indirect dischargers and considers the requirements of the IPPC Directive.
Natural or human mediated - biogeography of widespread Mediterranean invertebrates with poor dispersal capacities
Impact of land-use on savanna vegetation and populations of non-timber forest product-providing tree species in West Africa
- Savannas are the most important timber and non-timber forest products (NTFPs) providing ecosystems in West Africa. They have been shaped by traditional human land-use (i.e. agriculture, grazing, and harvesting) for thousands of years. In the last decades, land-use has drastically changed due to the rapid population growth and the growing production of cash-crop in West Africa and this process is still continuing. The percentage of land intensively used for agriculture has increased, while the length of fallow periods has decreased. Such changes have enormous ecological, economic, and social consequences. In the context of land-use changes, there is an urgent need to better understand and evaluate the impact of land-use on savannas. Such an understanding provides insights on appropriate management activities that ensure the maintenance of savannas and guarantee the availability of savanna products for subsistence and commercial use of rural West African people.
The major objective of the present thesis was to study the impact of land-use on savanna vegetation and diversity as well as on populations of two important NTFP-providing tree species in a semi-arid area in West Africa. The study area was located in the south-eastern part of Burkina Faso and comprised the protected W National Park and its adjacent communal area.
In the first study (chapter 2), I investigated in cooperation with a colleague from Burkina Faso (Blandine Nacoulma) the impact of land-use on the savanna vegetation. We analyzed which environmental factors determine the occurrence of the vegetation types and investigated the effect of land-use on vegetation structure and the occurrence of life forms and highly valued tree species. Furthermore, we tested whether land-use has an impact on plant diversity pattern and if this impact differed between the vegetation types and layers (woody and herb layer). Vegetation relevés were performed and the vegetation and plant diversity of the protected W National Park were compared with those of its surrounding communal area. Our results reveal five vegetation types occurring in both areas. Elevation and physical soil characteristics and thus soil water availability for plants played the most important role for the occurrence of the vegetation types. The influence of land-use on plant diversity differed between the five vegetation types and the two layers. The impact was highest on the vegetation types with the most favorable soil conditions for cultivation and lowest on rocky habitats with poor soils. While the diversity of the woody layer was increased under human land-use, the diversity of the herb layer was diminished. Overall, as land-use effects were not only negative, our findings suggest that land-use does not automatically lead to a loss of plant species and to a degradation of savanna habitats. We conclude that both protected and communal areas are of great importance for the conservation of savanna vegetation and diversity. Our study highlights furthermore the importance of different management strategies for each vegetation type.
In the following two studies (chapter 3 and 4), the impact of land-use - and in particular of harvesting - on populations of Adansonia digitata L., the baobab tree, and Anogeissus leiocarpa (DC.) Guill. & Perr. was examined. These two tree species were chosen as they provide several NTFPs for the local population and as they show different levels of human protection and opposed life histories. Thus, they may react differently to land-use. Stands of the protected W National Park were compared with those of its surrounding communal area (in fallows, croplands, and villages). I applied dendrometric methods to study the population structures and combined it with rates and patterns of NTFP-harvesting (debarking and chopping/pruning). Furthermore, the impact of land-use and harvesting on the fruit production of A. digitata and on the sprouting ability of A. leiocarpa were studied. The inverse J-shaped size class distribution curve indicates that the stands of A. digitata were in a healthy state in the park, while the low number of smaller size classes in fallows, croplands, and villages may give evidence of an ageing population. However, a high number of seedlings were recorded in villages. The stands of A. leiocarpa were also in healthy states in the park and likewise in fallows. In contrast, the absence of saplings gives evidence of a declining population in croplands. Both species were strongly harvested by local people and harvesting was tree size-specific. Pruning in interaction with tree-size had a significant impact on fruit production of A. digitata. While smaller trees were more vulnerable to pruning, bigger trees benefited from slight-pruning. A. leiocarpa had a great ability to respond to chopping by sprouting. The sprouting ability increased even with higher chopping intensity. Results suggest that despite the intense harvesting and the land-use impact, populations of both species are still well preserved. While A. digitata can withstand the harvesting and land-use pressure by its longevity, extremely low adult mortality rates, and particularly due to positive human influences, A. leiocarpa is able to withstand the use pressure by its fast growing, high recruitment, and high sprouting ability. I conclude that a none protected tree species (A. leiocarpa) might not necessarily be at higher risk to the harvesting and land-use impact than a protected tree species (A. digitata) as the adverse impact of harvesting and land-use can be compensated by its specific life history.
Important additional information to such ecological findings can be provided by local people. Learning from traditional knowledge and management systems of local people will help to produce culturally and ecologically reasonable conservation and management strategies. Thus, I investigated local uses and management strategies of A. digitata and A. leiocarpa in the last two studies (chapter 5 and 6). Quantitative ethnobotanical surveys among the Gulimanceba people were conducted in the communal area in order to document uses of the different plant parts, harvesting modes, perceptions about the population status, and conservation status of both species. Hereby, differences in knowledge between gender, generations, and people from different villages were tested. Interviews reveal that both species are harvested for multipurpose and emphasize the high importance of both species for local people. Especially the leaves and fruits of A. digitata add valuable minerals and vitamins to the otherwise micronutrient-“poor” staple crops of the Gulimanceba people. In comparison with other studies in West Africa, it has turned out that people in this area could benefit even more from A. leiocarpa, e.g. for dyeing of clothes, for treatment of malaria and skin problems. Local knowledge did not differ between genders and generations, while it slightly differed between people from different villages. The lack of age differences suggests that the traditional knowledge about these two species is passed on from one generation to another. Differences between people from different villages might be explained by influences from the neighboring countries Niger and Benin. Current local harvesting modes and management strategies of both species resulted in sustainable use. However, ongoing land-use intensifications require adapted harvesting and management techniques to guarantee the persistence of these economically important species. These results provide, in combination with the ecological findings (chapter 3 and 4), appropriate management recommendations for A. digitata and A. leiocarpa that are reliable under currently practiced management strategies.
Assessing the combined effects of xenobiotics, climate change and predators on aquatic organisms in multiple stressor experiments : a case study with pyrimethanil
- The environmental impact of climate change is meanwhile not only discussed in the scientific community but also in the general public. However, little is known about the interaction between climate change and pollutants like pesticides. A combination of multiple stressors (e.g. temperature, pollutants, predators) may lead to severe alterations for organisms such as changes in time of reproduction, reproductive success and growth performance, mortality and geographic distribution. The questions if aquatic organisms tend to react more sensitive towards incidents under climate change conditions remains. Therefore, within the present thesis the aquatic ecotoxicological profile of the fungicide pyrimethanil, as an exemplarily anthropogenic used contaminant, was examined.
A large test battery of ecotoxicological standard tests and supplement bioassays with non-model species was conducted to investigate if species-specific or life stage-specific differences occur or if temperature alteration may change the impact of the fungicide. Two of the most sensitive species (Chironomus riparius and Daphnia magna) were used to investigate the acute and chronic thermal dependence of pyrimethanil effects. The results clearly depict that the ecotoxicity of pyrimethanil at optimal thermal conditions did not depend on the trophic level, but was species-specific. With regard to EC10 values the acute pyrimethanil toxicity on C. riparius increased with higher temperature (6.78 mg L-1 at 14°C and 3.06 mg L-1 at 26°C). The chronic response of D. magna to the NOEC (no observed effect concentration) of the fungicide (0.5 mg L-1) was examined in an experiment which lasted for several generations under three simulated near-natural temperature regimes (‘cold year, today’ (11 to 22.7°C), ‘warm year, today’ (14 to 25.2°C) and ‘warm year, 2080’ (16.5 to 28.1°C)). A pyrimethanil-induced mortality increase was buffered by the strongly related increase of the general reproductive capacity, while population growth was stronger influenced by temperature than by the fungicide. At a further pyrimethanil concentration (LOEC – lowest observed effect concentration: 1 mg L-1), a second generation could not be established by D. magna under all thermal regimes.
Besides daphnids, the midge C. riparius was used for a second multigeneration study. In a bifactorial test design it was tested if climate change conditions alter or affect the impact of a low fungicide concentration on life history and genetic diversity. The NOAEC/2 (half of the no observed adverse effect concentration derived from a standard toxicity test) was used as a low pyrimethanil concentration to which laboratory populations of the midges were chronically exposed under the mentioned temperature scenarios. During the 140-day-multigeneration study, survival, emergence, reproduction, population growth, and genetic diversity of C. riparius were analyzed. The results reveal that high temperatures and pyrimethanil act synergistically on life history parameters of C. riparius. In simulated present-day scenarios, a NOAEC/2 of pyrimethanil provoked only slight to moderate beneficial or adverse effects. In contrast, an exposure to a NOAEC/2 concentration of pyrimethanil at a thermal situation likely for a summer under the future expactations uncovered adverse effects on mortality and population growth rate. In addition, genetic diversity was considerably reduced by pyrimethanil in the ‘warm year, 2080’ scenario, but only slightly under current climatic conditions. The multigeneration studies under near-natural thermal conditions indicate that not only the impact of climate change, but also low concentrations of pesticides may pose a reasonable risk for aquatic invertebrates in the future. This clearly shows that thermal and multigenerational effects should be considered when appraising the ecotoxicity of pesticides and assessing their future risk for the environment.
In addition to temperature further multiple abiotic and biotic stressors alterate pollutant effects. Moreover, to better discriminate and understand the intrinsic and environmental correlates of changing aquatic ecosystems, it was experimentally unraveled how the effects of a low-dose of pyrimethanil on daphnids becomes modified by different temperatures (15°C, 20°C, 25°C) and in the presence/ absence of predator kairomones of Chaoborus flavicans larvae. The usage of a fractional multifactorial test design provided the possibility to investigate the individual growth, reproduction and population growth rate of Daphnia pulex via different exposure routes to the fungicide pyrimethanil at an environmentally relevant concentration (0.05 mg L-1) - either directly (via the water phase), indirectly (via algae food), dually (via water and food) or for multiple generations (fungicide treated source population).
The number of neonates increased with increasing temperatures. At a temperature of 25°C no significant differences between the individual treatment groups were observed although the growth was overall inhibited due to pyrimethanil. Besides, at 15 and 20°C it is obvious that daphnids which were fed with contaminated algae had the lowest reproduction and growth rate. The obtained results clearly demonstrate that multiple stress factors can modify the response of daphnids to pollutants. The exposure routes of the contaminant are of minor importance, while temperature and the presence of a predator are the dominant factors impacting the reproduction of D. pulex. It can be concluded that low concentrations of pyrimethanil may disturb the zooplankton community at suboptimal temperature conditions, but the effects will become masked if chaoborid larvae are present. Therefore it seems necessary to observe prospectively if the combination of several stress factors like pesticide exposure and suboptimal temperature may influence the life history and sensitivity of several aquatic invertebrates differently.
Besides standard test organisms it is inevitable to conduct test with aquatic invertebrate which are not yet considered regularly in ecotoxicological experiments. For example molluscs represent one of the largest phyla of macroinvertebrates with more than 100.000 species, being ecologically and economically important. Therefore, within the present study embryo, juvenile, half- and full-life cycle toxicity tests with the snail Physella acuta were performed to investigate the impact of pollutants on various life stages. Different concentrations of pyrimethanil (0.06-0.5 or 1.0 mg L-1) assessed at three temperatures (15°C, 20°C, 25°C) revealed that pyrimethanil caused concentration-dependent effects independent of temperature. Interestingly, the ecotoxicity of pyrimethanil was higher at lower temperature for the embryo hatching and F1 reproduction, but its ecotoxicity for the growth of juveniles and the F0 reproduction increased with increasing temperature. More specifically, it could have been observed that especially during the reproduction test high mortality rates occurred at the highest concentration of 1 mg L-1 at all temperatures. Due to high mortality rates no snails were available for the F1 at the highest concentrations (0.5 and 1.0 mg L-1). Compared to the F0, overall more egg masses were produced in the F1, being all fertile and no mortality occurred. For the F1-generation the strongest pyrimethanil effects were detected at 15°C. A comparison of effect concentrations between both generations showed that the F1 is more sensitive than the F0.
These results indicate that an exposure over more than one generation may give a better overview of the impact of xenobiotics. With the establishment of an embryo and reproduction test under different temperatures and various concentrations of pyrimethanil with P. acuta we could successfully show that molluscs can respond more sensitive than model organisms and that both, chemical and thermal stressor strongly influence the behaviour of the pulmonates. It can be concluded that the high susceptibility for the fungicide observed in gastropods clearly demonstrates the complexity of pesticide-temperature interactions and the challenge to draw conclusions for the ecotoxicological risk assessment of pesticides under the impact of global climate change.