One like all? Behavioral response range of native and invasive amphipods to neonicotinoid exposure.

Native and invasive species often occupy similar ecological niches and environments where they face comparable risks from chemical exposure. Sometimes, invasive species are phylogenetically related to native species, e.g. they may come from the same family and have potentially similar sensitivities to environmental stressors due to phylogenetic conservatism and ecological similarity. However, empirical studies that aim to understand the nuanced impacts of chemicals on the full range of closely related species are rare, yet they would help to comprehend patterns of current biodiversity loss and species turnover. Behavioral sublethal endpoints are of increasing ecotoxicological interest. Therefore, we investigated behavioral responses (i.e., change in movement behavior) of the four dominant amphipod species in the Rhine-Main area (central Germany) when exposed to the neonicotinoid thiacloprid. Moreover, beyond species-specific behavioral responses, ecological interactions (e.g. parasitation with Acanthocephala) play a crucial role in shaping behavior, and we have considered these infections in our analysis. Our findings revealed distinct baseline behaviors and species-specific responses to thiacloprid exposure. Notably, Gammarus fossarum exhibited biphasic behavioral changes with hyperactivity at low concentrations that decreased at higher concentrations. Whereas Gammarus pulex, Gammarus roeselii and the invasive species Dikerogammarus villosus, showed no or weaker behavioral responses. This may partly explain why G. fossarum disappears in chemically polluted regions while the other species persist there to a certain degree. But it also shows that potential pre-exposure in the habitat may influence behavioral responses of the other amphipod species, because habituation occurs, and potential hyperactivity would be harmful to individuals in the habitat. The observed responses were further influenced by acanthocephalan parasites, which altered baseline behavior in G. roeselii and enhanced the behavioral response to thiacloprid exposure. Our results underscore the intricate and diverse nature of responses among closely related amphipod species, highlighting their unique vulnerabilities in anthropogenically impacted freshwater ecosystems.

Ecologically and medically important black flies of the genus Simulium: Identification of biogeographical groups according to similar larval niches.

The black fly genus Simulium includes medically and ecologically important species, characterized by a wide variation of ecological niches largely determining their distributional patterns. In a rapidly changing environment, species-specific niche characteristics determine whether a species benefits or not. With aquatic egg, larval and pupal stages followed by a terrestrial adult phase, their spatial arrangements depend upon the interplay of aquatic conditions and climatic-landscape parameters in the terrestrial realm. The aim of this study was to enhance the understanding of the distributional patterns among Simulium species and their ecological drivers. In an ecological niche modelling approach, we focused on 12 common black fly species with different ecological requirements. Our modelling was based on available distribution data along with five stream variables describing the climatic, land-cover, and topographic conditions of river catchments. The modelled freshwater habitat suitability was spatially interpolated to derive an estimate of the adult black flies' probability of occurrence. Based on similarities in the spatial patterns of modelled habitat suitability we were able to identify three biogeographical groups, which allows us to confirm old assessments with current occurrence data: (A) montane species, (B) broad range species and (C) lowland species. The five veterinary and human medical relevant species Simulium equinum, S. erythrocephalum, S. lineatum, S. ornatum and S. reptans are mainly classified in the lowland species group. In the course of climatic changes, it is expected that biocoenosis will slightly shift towards upstream regions, so that the lowland group will presumably emerge as the winner. This is mainly explained by wider ecological niches, including a higher temperature tolerance and tolerance to various pollutants. In conclusion, these findings have significant implications for human and animal health. As exposure to relevant Simulium species increases, it becomes imperative to remain vigilant, particularly in investigating the potential transmission of pathogens.

Rapid development of increased neonicotinoid tolerance in non-target freshwater amphipods.

The comprehensive assessment of the long-term impacts of constant exposure to pollutants on wildlife populations remains a relatively unexplored area of ecological risk assessment. Empirical evidence to suggest that multigenerational exposure affects the susceptibility of organisms is scarce, and the underlying mechanisms in the natural environment have yet to be fully understood. In this study, we first examined the arthropod candidate species, Gammarus roeselii that - unlike closely related species - commonly occurs in many contaminated river systems of Central Europe. This makes it a suitable study organism to investigate the development of tolerances and phenotypic adaptations along pollution gradients. In a 96-h acute toxicity assay with the neonicotinoid thiacloprid, we indeed observed a successive increase in tolerance in populations coming from contaminated regions. This was accompanied by a certain phenotypic change, with increased investment into reproduction. To address the question of whether these changes are plastic or emerged from longer lasting evolutionary processes, we conducted a multigeneration experiment in the second part of our study. Here, we used closely-related Hyalella azteca and pre-exposed them for multiple generations to sublethal concentrations of thiacloprid in a semi-static design (one week renewal of media containing 0.1 or 1.0 µg/L thiacloprid). The pre-exposed individuals were then used in acute toxicity assays to see how quickly such adaptive responses can develop. Over only two generations, the tolerance to the neonicotinoid almost doubled, suggesting developmental plasticity as a plausible mechanism for the rapid adaptive response to strong selection factors such as neonicotinoid insecticides. It remains to be discovered whether the plasticity of rapidly developed tolerance is species-specific and explains why closely related species - which may not have comparable adaptive response capabilities - disappear in polluted habitats. Overall, our findings highlight the neglected role of developmental plasticity during short- and long-term exposure of natural populations to pollution. Moreover, our results show that even pollutant levels seven times lower than concentrations found in the study region have a clear impact on the developmental trajectories of non-target species.

Uncovering the Grinnellian niche space of the cryptic species complex Gammarus roeselii.

Background: The discovery of cryptic species complexes within morphologically established species comes with challenges in the classification and handling of these species. We hardly know to what extent species within a species complex differ ecologically. Such knowledge is essential to assess the vulnerability of individual genetic lineages in the face of global change. The abiotic conditions, i.e., the Grinnellian niche that a genetic lineage colonizes, provides insights into how diverse the ecological requirements of each evolutionary lineage are within a species complex. Material and Methods: We sampled the cryptic species complex of the amphipod Gammarus roeselii from Central Germany to Greece and identified genetic lineages based on cytochrome c oxidase subunit I (COI) barcoding. At the same time, we recorded various abiotic parameters and local pollution parameters using a series of in vitro assays to then characterize the Grinnellian niches of the morphospecies (i.e., Gammarus roeselii sensu lato) as well as each genetic lineage. Local pollution can be a significant factor explaining current and future distributions in times of increasing production and release of chemicals into surface waters. Results: We identified five spatially structured genetic lineages in our dataset that differed to varying degrees in their Grinnellian niche. In some cases, the niches were very similar despite the geographical separation of lineages, supporting the hypothesis of niche conservatism while being allopatrically separated. In other cases, we found a small niche that was clearly different from those of other genetic lineages. Conclusion: The variable niches and overlaps of different dimensions make the G. roeselii species complex a promising model system to further study ecological, phenotypic and functional differentiation within this species complex. In general, our results show that the Grinnellian niches of genetically distinct molecular operational taxonomic units (MOTUs) within a cryptic species complex can differ significantly between each other, calling for closer inspection of cryptic species in a conservational and biodiversity context.

A novel approach for the assessment of invertebrate behavior and its use in behavioral ecotoxicology.

Sublethal effects are becoming more relevant in ecotoxicological test methods due to their higher sensitivity compared to lethal endpoints and their preventive nature. Such a promising sublethal endpoint is the movement behavior of invertebrates which is associated with the direct maintenance of various ecosystem processes, hence being of special interest for ecotoxicology. Disturbed movement behavior is often related to neurotoxicity and can affect drift, mate-finding, predator avoidance, and therefore population dynamics. We show the practical implementation of the ToxmateLab, a new device that allows monitoring the movement behavior of up to 48 organisms simultaneously, for behavioral ecotoxicology. We quantified behavioral reactions of Gammarus pulex (Amphipoda, Crustacea) after exposure to two pesticides (dichlorvos and methiocarb) and two pharmaceuticals (diazepam and ibuprofen) at sublethal, environmentally relevant concentrations. We simulated a short-term pulse contamination event that lasted 90 min. Within this short test period, we successfully identified behavioral patterns that were most pronounced upon exposure to the two pesticides: Methiocarb initially triggered hyperactivity, after which baseline behavior was restored. On the other hand, dichlorvos induced hypoactivity starting at a moderate concentration of 5 µg/L - a pattern we also found at the highest concentration of ibuprofen (10 µg/L). An additional acetylcholine esterase inhibition assay revealed no significant impact of the enzyme activity that would explain the altered movement behavior. This suggests that in environmentally realistic scenarios chemicals can induce stress - apart from mode-of-action - that affects non-target organisms' behavior. Overall, our study proves the practical applicability of empirical behavioral ecotoxicological approaches and thus represents a next step towards routine practical use.

Flushing away the future: The effects of wastewater treatment plants on aquatic invertebrates.

Wastewater treatment plants (WWTP) are essential infrastructure in our developing world. However, with the development and release of novel entities and without modern upgrades, they are ineffective at fully removing micropollutants before treated effluents are released back into aquatic environments. Thus, WWTPs may represent additional point source impacts to freshwater environments, further pressuring aquatic fauna and already vulnerable insect communities. Previous studies - mostly focusing on single WWTPs - have shown general trends of freshwater invertebrate communities becoming dominated by pollution tolerant taxa. To expand on these findings, the current study is the first to comprehensively investigate data on the effects of 170 WWTPs on invertebrate taxonomic composition. We compared data for several diversity and pollution indices, as well as the taxonomic composition both upstream and downstream of the WWTPs (366 sampling sites). In terms of abundance, the three most frequent and negatively impacted orders were the Plecoptera, Trichoptera and Gastropoda, while the Turbellaria, Hirudinea and Crustacea increased in abundance. Although strong changes in community composition were observed between upstream and downstream sites (mean species turnover of 61%), commonly used diversity indices were not sensitive to these changes, highlighting their potential inadequacy in accurately assessing ecological health. Our results indicate that WWTPs change downstream conditions in favour of pollution tolerant taxa to the detriment of sensitive taxa. Order-level taxonomic responses can be informative but should be interpreted with caution, since they can be driven by a few taxa, or opposing responses of species in the same group can result in an overall low order-level response. Upgrading WWTPs via additional treatment steps or merging may be beneficial, provided upstream sections are unimpacted and/or are in a good chemical and structural condition.

Cryptic Species in Ecotoxicology.

The advent of genetic methods has led to the discovery of an increasing number of species that previously could not be distinguished from each other on the basis of morphological characteristics. Even though there has been an exponential growth of publications on cryptic species, such species are rarely considered in ecotoxicology. Thus, the particular question of ecological differentiation and the sensitivity of closely related cryptic species is rarely addressed. Tackling this question, however, is of key importance for evolutionary ecology, conservation biology, and, in particular, regulatory ecotoxicology. At the same time, the use of species with (known or unknown) cryptic diversity might be a reason for the lack of reproducibility of ecotoxicological experiments and implies a false extrapolation of the findings. Our critical review includes a database and literature search through which we investigated how many of the species most frequently used in ecotoxicological assessments show evidence of cryptic diversity. We found a high proportion of reports indicating overlooked species diversity, especially in invertebrates. In terrestrial and aquatic realms, at least 67% and 54% of commonly used species, respectively, were identified as cryptic species complexes. The issue is less prominent in vertebrates, in which we found evidence for cryptic species complexes in 27% of aquatic and 6.7% of terrestrial vertebrates. We further exemplified why different evolutionary histories may significantly determine cryptic species' ecology and sensitivity to pollutants. This in turn may have a major impact on the results of ecotoxicological tests and, consequently, the outcome of environmental risk assessments. Finally, we provide a brief guideline on how to deal practically with cryptic diversity in ecotoxicological studies in general and its implementation in risk assessment procedures in particular. Environ Toxicol Chem 2023;42:1889-1914. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Infection with acanthocephalans increases tolerance of Gammarus roeselii (Crustacea: Amphipoda) to pyrethroid insecticide deltamethrin.

Crustacean amphipods serve as intermediate hosts for parasites and are at the same time sensitive indicators of environmental pollution in aquatic ecosystems. The extent to which interaction with the parasite influences their persistence in polluted ecosystems is poorly understood. Here, we compared infections of Gammarus roeselii with two species of Acanthocephala, Pomphorhynchus laevis, and Polymorphus minutus, along a pollution gradient in the Rhine-Main metropolitan region of Frankfurt am Main, Germany. Prevalence of P. laevis was very low at the unpolluted upstream reaches (P ≤ 3%), while higher prevalence (P ≤ 73%) and intensities of up to 9 individuals were found further downstream-close to an effluent of a large wastewater treatment plant (WWTP). Co-infections of P. minutus and P. laevis occurred in 11 individuals. Highest prevalence of P. minutus was P ≤ 9% and one parasite per amphipod host was the maximum intensity recorded. In order to assess whether the infection affects survival in the polluted habitats, we tested the sensitivity of infected and uninfected amphipods towards the pyrethroide insecticide deltamethrin. We found an infection-dependent difference in sensitivity within the first 72 h, with an effect concentration (24 h EC50) of 49.8 ng/l and 26.6 ng/l for infected and uninfected G. roeselii, respectively. Whereas final host abundance might partially explain the high prevalence of P. laevis in G. roeselii, the results of the acute toxicity test suggest a beneficial effect of acanthocephalan infection for G. roeselii at polluted sites. A strong accumulation of pollutants in the parasite could serve as a sink for pesticide exposure of the host. Due to the lack of a co-evolutionary history between parasite and host and a lack of behavioral manipulation (unlike in co-evolved gammarids), the predation risk by fish remains the same, explaining high local prevalence. Thus, our study exemplifies how organismic interaction can favor the persistence of a species under chemical pollution.

Natural variation in social conditions affects male mate choosiness in the amphipod Gammarus roeselii.

The extent of male mate choosiness is driven by a trade-off between various environmental factors associated with the costs of mate acquisition, quality assessment and opportunity costs. Our knowledge about natural variation in male mate choosiness across different populations of the same species, however, remains limited. In this study, we compared male mate choosiness across 10 natural populations of the freshwater amphipod Gammarus roeselii (Gervais 1835), a species with overall high male mating investments, and evaluated the relative influence of population density and sex ratio (both affecting mate availability) on male mate choosiness. We investigated amplexus establishment after separating mating pairs and presenting focal males with a novel, size-matched female from the same population. Our analysis revealed considerable effects of sex ratio and (to a lesser extent) population density on time until amplexus establishment (choosiness). Male amphipods are able to perceive variable social conditions (e.g., sex ratio) and modify their mating strategy accordingly: We found choosiness to be reduced in increasingly male-biased populations, whereas selectivity increases when sex ratio becomes female biased. With this, our study expands our limited knowledge on natural variations in male mate choosiness and illustrates the importance of sex ratio (i.e., level of competition) for male mating decisions in natural environments. Accounting for variation in sex ratios, therefore, allows envisioning a distinctive variation of choosiness in natural populations and highlights the importance of considering social background information in future behavioral studies.

Invasive fish retain plasticity of naturally selected, but diverge in sexually selected traits.

Invasive alien species (IAS) have become a major threat to ecosystems worldwide. From an evolutionary ecological perspective, they allow teasing apart the relative contributions of plasticity and evolutionary divergence in driving rapid phenotypic diversification. When IAS spread across extensive geographic ranges, climatic variation may represent a source of strong natural selection through overwinter mortality and summer heat stress. This could favour local adaptation, i.e., evolutionary divergence of certain traits. IAS, however, are likely to show plasticity in survival-related traits, and environmental fluctuation in their new distribution range could favour the maintenance of this pre-existing phenotypic plasticity. By contrast, sexually selected traits are more likely to undergo evolutionary divergence when components of sexual selection differ geographically. Here, using data from a common-garden rearing experiment of Western mosquitofish (Gambusia affinis Baird and Girard, 1853) from five populations across the species' invasive range in China, we show that invasive mosquitofish have retained plasticity in key physiological (thermal tolerances), morphological and life-history traits even 100 years after their introduction to China, but exhibit heritable population differences in several sexually selected traits, including the shape of the male copulatory organ. Adaptive plasticity of traits linked to immediate survival in different thermal environments-while likely responsible for the species' extraordinary invasion success-could slow down genetic evolution. Several sexually selected traits could diverge geographically and show rapid evolutionary change, e.g., because climate alters selective landscapes arising from mate competition as an indirect consequence of variation in overwinter mortality.

The Occurrence of Intersex in Different Populations of the Marine Amphipod Echinogammarus marinus in North-West Brittany - A Longterm-Study.

In the past two decades, an increasing body of studies has been published on the intersex phenomenon in separate-sexed crustaceans from marine and freshwater ecosystems. Various causes are being considered that could have an influence on the occurrence of intersex. Besides genetic factors, environmental conditions such as photoperiodicity, temperature, salinity and parasitism, but also environmental pollution with endocrine disrupting chemicals (EDCs) are discussed. As part of a long-term monitoring (2012 - 2020) in north-west Brittany, we recorded the occurrence of intersex in the marine amphipod Echinogammarus marinus. We quantified the intersex incidence at marine and estuarine sites and analyzed the incidence in relation to the endocrine potential of the sediments. Intersex occurred with mean frequencies between 0.87% and 12%. It was striking that the incidence of intersex increased with increasing distance from the sea. Since the highest incidence was observed at the range boundary of this stenohaline species, we assume that intersex is triggered by endocrine potential and increasing stress due to increasing freshwater content - and thus an interplay of different environmental factors.

Off to new shores: Climate niche expansion in invasive mosquitofish (Gambusia spp.).

AIM: Formerly introduced for their presumed value in controlling mosquito-borne diseases, the two mosquitofish Gambusia affinis and G. holbrooki (Poeciliidae) are now among the world's most widespread invasive alien species, negatively impacting aquatic ecosystems around the world. These inconspicuous freshwater fish are, once their presence is noticed, difficult to eradicate. It is, therefore, of utmost importance to assess their geographic potential and to identify their likely ability to persist under novel climatic conditions. LOCATION: Global. METHODS: We build species distribution models using occurrence data from the native and introduced distribution ranges to identify putative niche shifts and further ascertain the areas climatically suitable for the establishment and possible spread of mosquitofish. RESULTS: We found significant niche expansions into climatic regions outside their natural climatic conditions, emphasizing the importance of integrating climatic niches of both native and invasive ranges into projections. In particular, there was a marked shift toward tropical regions in Asia and a clear niche shift of European G. holbrooki. This ecological flexibility partly explains the massive success of the two species, and substantially increases the risk for further range expansion. We also showed that the potential for additional expansion resulting from climate change is enormous-especially in Europe. MAIN CONCLUSIONS: Despite the successful invasion history and ongoing range expansions, many countries still lack proper preventive measures. Thus, we urge policy makers to carefully evaluate the risk both mosquitofish pose to a particular area and to initiate appropriate management strategies.

Global Size Pattern in a Group of Important Ecological Indicators (Diptera, Chironomidae) Is Driven by Latitudinal Temperature Gradients.

Size is one of the most outwardly obvious characteristics of animals, determined by multiple phylogenetic and environmental variables. Numerous hypotheses have been suggested to explain the relationship between the body size of animals and their geographic latitude. Bergmann's Rule, describing a positive relationship between the body size of endothermic animals and their geographic latitude, is especially well known. Whether or not insects exhibit a similar pattern has long been a subject for debate. We hypothesize that latitudinal size gradients are coupled to temperature variation affecting the metabolic rate of these merolimnic insects. We showcase a strong latitudinal size gradient in non-biting midges (Diptera: Chironomidae), based on the examination of 4309 specimens of these midges from around the world. Although phylogenetic position was a key predictor of wing length, we also found that wing length decreases by 32.4 µm per every 1 °C of mean annual temperature increase. This pattern was found across different taxa and could be detected in 20 of 24 genera studied. We discuss the reasons for this pattern origin and its palaeoecological implications.

Recovery from air pollution and subsequent acidification masks the effects of climate change on a freshwater macroinvertebrate community.

Freshwater ecosystems are dynamic, complex systems with a multitude of physical and ecological processes and stressors which drive fluctuations on the community-level. Disentangling the effects of different processes and stressors is challenging due to their interconnected nature. However, as protected areas (i.e. national parks) are less anthropogenically impacted, they are ideal for investigating single stressors. We focus on the Bavarian Forest National Park, a Long-Term Ecological Research (LTER) site in Germany, where the major stressors are climate warming, air pollution (i.e. acidification) and bark beetle infestations. We investigated the effects of these stressors on freshwater macroinvertebrates using comprehensive long-term (1983-2014) datasets comprising high-resolution macroinvertebrate and physico-chemical data from a near-natural stream. Macroinvertebrate communities have undergone substantial changes over the past 32 years, highlighted by increases in overall community abundance (+173%) and richness (+51.6%) as well as taxonomic restructuring driven by a disproportional increase of dipterans. Prior to the year 2000, regression analyses revealed a decline in sulphate deposition and subsequent recovery from historical acidification as potential drivers of the increases in abundance and richness rather than to increases in water temperature (1.5 °C overall increase). Post 2000, however, alterations to nutrient cycling caused by bark beetle infestations coupled with warming temperatures were correlated to taxonomic restructuring and disproportional increases of dipterans at the expense of sensitive taxa such as plecopterans and trichopterans. Our results highlight the challenges when investigating the effects of climate change within a multi-stressor context. Even in conservation areas, recovery from previous disturbance might mask the effects of ongoing disturbances like climate change. Overall, we observed strong community restructuring, demonstrating that stenothermal headwater communities face additional stress due to emerging competition with tolerant taxa. Conservation efforts should consider the temporal variability of communities and their recovery from disturbances to adequately identify species vulnerable to local or widespread extinction.

A century later: Adaptive plasticity and rapid evolution contribute to geographic variation in invasive mosquitofish.

One century after their introduction to Europe, eastern mosquitofish (Gambusia holbrooki) represent a natural experiment to determine the relative contributions of adaptive plasticity and rapid evolutionary change in creating large-scale geographic variation in phenotypes. We evaluated the population-genetic structure and invasion history based on allele length polymorphisms of 15 nuclear microsatellites, which we quantified for N = 660 individuals from 23 populations sampled in 2013 across the invasive range of G. holbrooki in Europe. We analysed body-shape and life-history variation in N = 1331 individuals from 36 populations, sampled in 2013 and 2017, and tested heritability of phenotypic differences in a subset of four populations using a common-garden experiment. The genetic structure of wild-caught individuals suggested a single introduction for all European mosquitofish, which were genetically impoverished compared to their native counterparts. We found some convergent patterns of phenotypic divergence across native and invasive climatic gradients (e.g., increased body size in colder/more northern populations); however, several phenotypic responses were not consistent between sampling years, pointing towards plastic phenotypes. Our analysis of common-garden reared individuals uncovered moderate heritability estimates only for two measures of male body size (intraclass correlation coefficient, ICC = 0.628 and 0.556) and offspring fat content (ICC = 0.734), while suggesting high levels of plasticity in most other phenotypic traits (ICC ≤ 0.407). Our results highlight the importance of phenotypic plasticity in invasive species during range expansions and demonstrate that strong selective pressures-in this case towards increased body size in colder environments-simultaneously promote rapid evolutionary divergence.

Complex and nonlinear climate-driven changes in freshwater insect communities over 42 years.

The ongoing biodiversity crisis becomes evident in the widely observed decline in abundance and diversity of species, profound changes in community structure, and shifts in species' phenology. Insects are among the most affected groups, with documented decreases in abundance up to 76% in the last 25-30 years in some terrestrial ecosystems. Identifying the underlying drivers is a major obstacle as most ecosystems are affected by multiple stressors simultaneously and in situ measurements of environmental variables are often missing. In our study, we investigated a headwater stream belonging to the most common stream type in Germany located in a nature reserve with no major anthropogenic impacts except climate change. We used the most comprehensive quantitative long-term data set on aquatic insects available, which includes weekly measurements of species-level insect abundance, daily water temperature and stream discharge as well as measurements of additional physicochemical variables for a 42-year period (1969-2010). Overall, water temperature increased by 1.88 °C and discharge patterns changed significantly. These changes were accompanied by an 81.6% decline in insect abundance, but an increase in richness (+8.5%), Shannon diversity (+22.7%), evenness (+22.4%), and interannual turnover (+34%). Moreover, the community's trophic structure and phenology changed: the duration of emergence increased by 15.2 days, whereas the peak of emergence moved 13.4 days earlier. Additionally, we observed short-term fluctuations (<5 years) in almost all metrics as well as complex and nonlinear responses of the community toward climate change that would have been missed by simply using snapshot data or shorter time series. Our results indicate that climate change has already altered biotic communities severely even in protected areas, where no other interacting stressors (pollution, habitat fragmentation, etc.) are present. This is a striking example of the scientific value of comprehensive long-term data in capturing the complex responses of communities toward climate change.

Cambios Complejos y No Lineales Causados por el Clima en Comunidades de Insectos de Agua Dulce durante 42 Años Resumen La continua crisis de la biodiversidad se vuelve evidente en la ampliamente documentada declinación en la abundancia y diversidad de especies, cambios profundos en la estructura de las comunidades y modificaciones en la fenología de las especies. Los insectos se encuentran entre los grupos más afectados; se han documentado reducciones en la abundancia de hasta el 76% en los últimos 25-30 años en algunos ecosistemas terrestres. La identificación de los causantes subyacentes es un gran obstáculo porque la mayoría de los ecosistemas están afectados por varios factores estresantes simultáneamente y con frecuencia faltan las medidas in situ de las variables ambientales. Investigamos un flujo naciente perteneciente al tipo de arroyo más común en Alemania ubicado dentro de una reserva natural sin impactos antropogénicos importantes a excepción del cambio climático. Usamos el conjunto más completo disponible de datos cuantitativos de largo plazo para insectos acuáticos que incluye las medidas semanales de abundancia de insectos a nivel especie, las medidas diarias de la temperatura del agua y la descarga del flujo y las medidas de variables físico-químicas adicionales durante 42 años (1969 - 2010). En general, la temperatura del agua incrementó 1.88°C y los patrones de descarga cambiaron significativamente. Estos cambios estuvieron acompañados por una declinación del 81.6% en la abundancia de insectos, pero también de un incremento en la riqueza (+8.5%), la diversidad Shannon (+22.7%), la uniformidad (+22.4%) y la renovación interanual (+34%). Además, la estructura trófica y la fenología de la comunidad cambiaron: la duración del surgimiento incrementó en 15.2 días y el pico del surgimiento ocurrió con 13.4 días de anticipación. Observamos fluctuaciones a corto plazo (<5 años) en casi todas las medidas, así como respuestas complejas y no lineales de la comunidad hacia el cambio climático que podrían haber sido ignoradas si sólo se usaran datos instantáneos o series de tiempo más cortas. Nuestros resultados indican que el cambio climático ya ha alterado seriamente a las comunidades bióticas, incluso en áreas protegidas en las que no están presentes otros factores estresantes en interacción (contaminación, fragmentación del hábitat, etc.). Ésto es un ejemplo notable del valor científico que tienen los datos completos de escalas de tiempo a largo plazo para la captura de las respuestas complejas de las comunidades ante el cambio climático.

Small-scale phenotypic differentiation along complex stream gradients in a non-native amphipod.

BACKGROUND: Selective landscapes in rivers are made up by an array of selective forces that vary from source to downstream regions or between seasons, and local/temporal variation in fitness maxima can result in gradual spatio-temporal variation of phenotypic traits. This study aimed at establishing freshwater amphipods as future model organisms to study adaptive phenotypic diversification (evolutionary divergence and/or adaptive plasticity) along stream gradients. METHODS: We collected Gammarus roeselii from 16 sampling sites in the Rhine catchment during two consecutive seasons (summer and winter). Altogether, we dissected n = 1648 individuals and quantified key parameters related to morphological and life-history diversification, including naturally selected (e.g., gill surface areas) as well as primarily sexually selected traits (e.g., male antennae). Acknowledging the complexity of selective regimes in streams and the interrelated nature of selection factors, we assessed several abiotic (e.g., temperature, flow velocity) and biotic ecological parameters (e.g., conspecific densities, sex ratios) and condensed them into four principal components (PCs). RESULTS: Generalized least squares models revealed pronounced phenotypic differentiation in most of the traits investigated herein, and components of the stream gradient (PCs) explained parts of the observed differences. Depending on the trait under investigation, phenotypic differentiation could be ascribed to variation in abiotic conditions, anthropogenic disturbance (influx of thermally polluted water), or population parameters. For example, female fecundity showed altitudinal variation and decreased with increasing conspecific densities, while sexual dimorphism in the length of male antennae-used for mate finding and assessment-increased with increasing population densities and towards female-biased sex ratios. CONCLUSIONS: We provide a comprehensive protocol for comparative analyses of intraspecific variation in life history traits in amphipods. Whether the observed phenotypic differentiation over small geographical distances reflects evolutionary divergence or plasticity (or both) remains to be investigated in future studies. Independent of the mechanisms involved, variation in several traits is likely to have consequences for ecosystem functions. For example, leaf-shredding in G. roeselii strongly depends on body size, which varied in dependence of several ecological parameters.

Elevated temperatures translate into reduced dispersal abilities in a natural population of an aquatic insect.

Rising global temperatures force many species to shift their distribution ranges. However, whether or not (and how fast) such range shifts occur depends on species' dispersal capacities. In most ecological studies, dispersal-related traits (such as the wing size or wing loading in insects) are treated as fixed, species-specific characteristics, ignoring the important role of phenotypic plasticity during insect development. We tested the hypothesis that dispersal-related traits themselves vary in dependence of ambient environmental conditions (temperature regimes, discharge patterns and biotic interactions during individual development). We collected data over 8 years from a natural population of the crane fly Tipula maxima in central Germany. Using linear mixed-effect models, we analysed how phenotypic traits, phenological characteristics and population densities are affected by environmental conditions during the preceding 3, 6 and 12 months. We found a moderate (5.6%) increase in wing length per 1°C increase in mean annual temperatures during the previous year. At the same time, body weight increased by as much as 17.8% in females and 26.9% in males per 1°C, likely driven by increased habitat productivity, which resulted in a 16.4% (female) and 19.3% (male) increased wing loading. We further found a shorter, more synchronized emergence period (i.e. a narrower time frame for dispersal) with increasing temperatures. Altogether, our results suggest that dispersal abilities of T. maxima were negatively affected by elevated temperatures, and we discuss how similar patterns might affect the persistence of populations of other aquatic insects, especially stenoecious taxa with narrow distribution ranges. Our study calls for integration of information on temperature-induced phenotypic plasticity of dispersal-related traits into models forecasting range shifts in the face of climate change. Furthermore, the patterns reported here are likely to affect metapopulation dynamics of aquatic insects under climate change conditions and may contribute to the ongoing decline of insect biomass and diversity.

Reintroduction of freshwater macroinvertebrates: challenges and opportunities.

Species reintroductions - the translocation of individuals to areas in which a species has been extirpated with the aim of re-establishing a self-sustaining population - have become a widespread practice in conservation biology. Reintroduction projects have tended to focus on terrestrial vertebrates and, to a lesser extent, fishes. Much less effort has been devoted to the reintroduction of invertebrates into restored freshwater habitats. Yet, reintroductions may improve restoration outcomes in regions where impoverished regional species pools limit the self-recolonisation of restored freshwaters. We review the available literature on macroinvertebrate reintroductions, focusing on identifying the intrinsic and extrinsic factors that determine their success or failure. Our study reveals that freshwater macroinvertebrate reintroductions remain rare, are often published in the grey literature and, of the attempts made, approximately one-third fail. We identify life-cycle complexity and remaining stressors as the two factors most likely to affect reintroduction success, illustrating the unique challenges of freshwater macroinvertebrate reintroductions. Consideration of these factors by managers during the planning process and proper documentation - even if a project fails - may increase the likelihood of successful outcomes in future reintroduction attempts of freshwater macroinvertebrates.