Characterization of phytoplankton assemblages in a tropical coastal environment using Kohonen self‐organizing map

This study was aimed at understanding the main abiotic environmental factors controlling the distribution patterns of abundance and composition of phytoplankton (size less than 10 μm) assemblages in the coastal waters of south‐eastern Côte d'Ivoire. Data were collected during two cruises, in January (low‐water period) and October (high‐water period) of 2014. A total of 67 species were identified and assigned to Bacillariophyceae (49%), Cyanophyceae (21%), Chlorophyceae (13%), Euglenophyceae (10%), Dinophyceae (4%) and Chrysophyceae (3%). Three biotic zones (I, IIA and IIB) were distinguishable on a Kohonen self‐organizing map after an unsupervised learning process. The diatom genera Eunotia sp., Navicula sp. and Actinoptychus senarius are significantly associated with I, IIA and IIB biotic zones, respectively. A clear seasonal cum salinity trend was apparent in phytoplankton distribution patterns. Turbidity and nitrate levels were the main abiotic factors controlling phytoplankton distribution in I, the upland tidal regions of the lagoon. In regions along the lagoon–sea continuum, phosphate and turbidity exert the most control during the low‐water season (IIA), while total dissolved solids control phytoplankton distribution during the high‐water season (IIB). These are climate‐sensitive parameters whose concentrations depend on prevailing hydroclimatic processes. Therefore, seasonality can have important consequences on phytoplankton community and inadvertently the productivity of these systems.     

Understanding Plant Community Responses to Combinations of Biotic and Abiotic Factors in Different Phases of the Plant Growth Cycle

Understanding plant community responses to combinations of biotic and abiotic factors is critical for predicting ecosystem response to environmental change. However, studies of plant community regulation have seldom considered how responses to such factors vary with the different phases of the plant growth cycle. To address this deficit we studied an aquatic plant community in an ecosystem subject to gradients in mute swan (Cygnus olor) herbivory, riparian shading, water temperature and distance downstream of the river source. We quantified abundance, species richness, evenness, flowering and dominance in relation to biotic and abiotic factors during the growth-, peak-, and recession-phases of the plant growth cycle. We show that the relative importance of biotic and abiotic factors varied between plant community properties and between different phases of the plant growth cycle. Herbivory became more important during the later phases of peak abundance and recession due to an influx of swans from adjacent pasture fields. Shading by riparian vegetation also had a greater depressing effect on biomass in later seasons, probably due to increased leaf abundance reducing light intensity reaching the aquatic plants. The effect of temperature on community diversity varied between upstream and downstream sites by altering the relative competitiveness of species at these sites. These results highlight the importance of seasonal patterns in the regulation of plant community structure and function by multiple factors.     

Factors affecting migration patterns of juvenile river herring in a coastal Massachusetts stream

Juvenile anadromous river herring (alewives, Alosa pseudoharengus, and blueback herring, Alosa aestivalis) spend 3–7 months in freshwater before migrating to the ocean, often exhibiting waves of early and late migrations. Migratory patterns and associated abiotic and biotic factors were examined for both species migrating in 2003 from Herring River in Bourne Massachusetts. Migrating herring were grouped into two temporal periods and separated by species. Relationships between abiotic (water temperature, lunar phase, and precipitation) and biotic (size, age, growth rate, and hatch date) factors and the timing of out-migration (transition to seawater) were examined. Blueback herring migration coincided with a sharp decrease in temperature consistent with the time of year. Peaks in alewive migration may reflect adaptive traits maximizing likelihood of survival through seasonal marginal stream habitats and also avoiding lethal water temperatures in winter. Migrating bluebacks exhibited a single migratory period (late September–October) which occurred between the early and late migratory pulses of the alewives. These patterns may also represent distinct migration strategies between early and late migrating alewives and between the two species of river herring. Early migration may be a mechanism by which factors such as competition and low food availability are mitigated. In contrast, environmental conditions during the post hatching time of late migrators may allow for a size maximizing strategy that promotes migration from the nursery area as late as possible.     

The effect of seasonal variation in abiotic factors on fish community structure in temporary and permanent pools in a tropical wetland

1. Fish community structure depends on biotic interactions and abiotic variables. Abiotic variables appear to gain importance in highly variable freshwater systems, such as tropical wetlands where a marked seasonal hydroperiod (dry and wet seasons) modifies water quality and quantity, differentially affecting fish survival and, consequently, modifying species richness and abundance. 2. We evaluated the relationship between abiotic variables and fish community structure in variable (temporary) and stable (permanent) pools that were interconnected in a tropical wetland with marked annual dry and wet seasons. 3. All fish species were able to occupy any of the studied pools, but our results showed distinctive fish community structures in permanent and temporary pools. Community structure was related to temperature, depth, pH and macrophyte coverage. Total fish abundance in the wetland was negatively related to water depth and positively related to macrophyte coverage. 4. Null models of co‐occurrence indicated a non‐random pattern at the wetland scale and a random pattern within groups of pools with similar characteristics, suggesting that fish communities are structured according to habitat features. We conclude that seasonal abiotic variation and habitat characteristics in this highly variable pristine wetland play major roles in structuring fish communities.     

Zoosporic true fungi and heterotrophic straminipiles assemblages from soil of Brazilian Cerrado areas

The influence of seasonal fluctuations and environmental factors on the occurrence and distribution of zoosporic true fungi and heterotrophic straminipiles in terrestrial ecosystems is poorly understood. This contribution analyses the species composition, frequency, abundance and diversity of zoosporic true fungi and heterotrophic straminipiles assemblages from two areas of Cerrado in the State of São Paulo, Brazil. Samples of soil were collected at four dates during the rainy and dry seasons. Twenty-one abiotic factors were measured. The assemblages showed a high diversity and evenness and were represented by 30 taxa of Chytridiomycota and Oomycota. Some abiotic factors appeared to have influenced the patterns of distribution and occurrence of the taxa in different areas and/or seasons. Even so, the biotic factors (richness, diversity indices and evenness) and the Sorensen index showed high similarity between the assemblages.     

Induction of pathogen resistance in barley by abiotic stress

Enhanced resistance of barley (Hordeum vulgare L. cv. Ingrid) against barley powdery mildew (Blumeria graminis f. sp. hordei race A6) was induced by abiotic stress in a concentration-dependent manner. The papilla-mediated resistance was not only induced by osmotic stress, but also by proton stress. Resistance was directly correlated with increasing concentrations of various salts in the nutrient solution. Resistance induced by proton stress also depended on the stress intensity. Resistance induction occurred even at low stress intensities. Any specific ion toxicity affecting the fungal growth directly, and therefore leading to enhanced pathogen resistance, can be excluded because of the independence of resistance induction of the ion used and of the time course of sodium accumulation in the leaves. BCI-4, a marker for benzo[1,2,3]thiadiazolecarbothioic acid S-methyl ester (BTH)-induced resistance was not induced by these abiotic stresses. However, resistance was induced in the same concentration-dependent manner by the application of the stress hormone ABA to the root medium. During the relief of water stress, resistance did not decrease constantly. On the contrary, after a phase of decreasing resistance for 24 h the pathogen resistance increased again for 48 h before decreasing finally to control levels.     

Role of biotic interactions and physical factors in determining the distribution of marsh species along an estuarine salinity gradient

Understanding the mechanisms that shape plant distribution patterns is a major goal in ecology. We investigated the role of biotic interactions (competition and facilitation) and abiotic factors in creating horizontal plant zonation along salinity gradients in the Elbe estuary. We conducted reciprocal transplant experiments with four dominant species from salt and tidal freshwater marshes at two tidal elevations. Ten individuals of each species were transplanted as sods to the opposing marsh type and within their native marsh (two sites each). Transplants were placed at the centre of 9‐m² plots along a line parallel to the river bank. In order to disentangle abiotic and biotic influences, we set up plots with and without neighbouring vegetation, resulting in five replicates per site. Freshwater species (Bolboschoenus maritimus and Phragmites australis) transplanted to salt marshes performed poorly regardless of whether neighbouring vegetation was present or not, although 50–70% of the transplants did survive. Growth of Phragmites transplants was impaired also by competition in freshwater marshes. Salt marsh species (Spartina anglica and Puccinellia maritima) had extremely low biomass when transplanted to freshwater marshes and 80–100% died in the presence of neighbours. Without neighbours, biomass of salt marsh species in freshwater marshes was similar to or higher than that in salt marshes. Our results indicate that salt marsh species are precluded from freshwater marshes by competition, whereas freshwater species are excluded from salt marshes by physical stress. Thus, our study provides the first experimental evidence from a European estuary for the general theory that species boundaries along environmental gradients are determined by physical factors towards the harsh end and by competitive ability towards the benign end of the gradient. We generally found no significant impact of competition in salt marshes, indicating a shift in the importance of competition along the estuarine gradient.     

Snapshot of micro-animals and associated biotic and abiotic environmental variables on the edge of the south-west Greenland ice sheet

Microinvertebrates play a role as top consumers on glaciers. In this study we tested what kind of cryoconite material the animals inhabit (mud vs granules) on the edge of the Greenland ice sheet (GrIS) in the south-west. We also tested the links between the densities of micro-fauna in cryoconite material and selected biotic (algae, cyanobacteria, bacterial abundances) and abiotic (water depth, pH, ion content, radionuclides) factors. We collected 33 cryoconite samples. Tardigrada and Rotifera were found in 18 and 61% of samples, respectively. Invertebrates in this study were considerably less frequent and less abundant in comparison with High Arctic glaciers. The highest density of tardigrades and rotifers constituted 53 and 118 ind./ml, respectively. Generalized linear models showed no relationship between the densities of fauna and biotic and abiotic factors. The densities of animals were significantly higher in granules than in mud. The difference in the densities of animals between granules and mud reflects a simple mechanistic removal of invertebrates from the sediment during its erosion by flushing which leads to mud formation. These processes may influence a random distribution of micro-fauna without clear ecological interactions with biotic and abiotic variables at the edge of the GrIS.     

哀牢山中山湿性常绿阔叶林土壤呼吸季节和昼夜变化特征及影响因子比较

 由于受到多种生物和非生物因素的影响,土壤呼吸在不同时间尺度上的动态变化可能不一致。对不同时间尺度的土壤呼吸动态变化的研究有助 于深入了解土壤呼吸变化的机理,也有利于精确推算土壤碳的排放。采用红外CO₂分析法测定哀牢山中山湿性常绿阔叶林季节间(2004年4月～ 2005年3月)和昼夜间 (2004年7、9和11月及2005年1、3和5月共6次)的土壤呼吸。哀牢山中山湿性常绿阔叶林中土壤呼吸的季节变化显著,其中 湿季(5～10月)的土壤呼吸高于干季(11月～翌年4月),全年土壤呼吸的平均值为0.442 g CO₂&;#8226;m^－2&;#8226;h^－1。6 次测定的土壤呼吸日变化模式并不 相同,7和9月、翌年1和3月夜间土壤呼吸大于昼间土壤呼吸,11月和翌年5月则相反;5、7和9月昼夜间的土壤呼吸最大值与最小值的差异比11 月、翌年1和3月的测定结果大。季节间土壤呼吸与土壤温度(p=0.000)和土壤含水量(p=0. 007) 均有显著的指数相关,土壤温度可以解释土壤 呼吸变化的56.1％,土壤含水量可以解释土壤呼吸变化的11.1％。不同季节测定的土壤呼吸日变化与土壤温度、气温和土壤含水量则没有显著 的指数相关。由土壤呼吸与土壤温度拟合的指数方程计算Q₁₀值,在温度为 5.9～16.6 ℃内,全年土壤呼吸的Q₁₀值为4.53,在温度为5.9～ 11.0 ℃内,干季土壤呼吸的Q₁₀值为7.17,在温度为10.3～16.6 ℃内,湿季土壤呼吸的Q₁₀值为2.34。在不同时间尺度上,生物和非生物因素 对哀牢山中山湿性常绿阔叶林的土壤呼吸表现出不同的影响。土壤呼吸的季节变化主要受非生物因子温度和水分变化的调控,而土壤呼吸的昼 夜变化则可能主要受植物的生理活动周期性等生物因素的影响。通过温度的指数函数关系,用土壤呼吸的瞬时值来推算土壤呼吸的日通量和年 通量时,需要考虑温度和水分外的其它生物因子的影响。     

Environment and virulence factors of Vibrio cholerae strains isolated in Argentina

AIMS: To determine the presence of Vibrio cholerae in different areas of Argentina in three sample types, to determine the composition of planktonic communities in areas at which this pathogen was detected and to characterize the virulence properties and antimicrobial resistance of the recovered environmental isolates. METHODS AND RESULTS: Water and plankton samples were collected in marine, brackish and freshwater environments. Vibrio cholerae non-O1, non-O139 was isolated in 36.1% of the samples analysed. The micro-organism was detected in freshwater but not in marine or brackish samples. No relationship was found between isolation of V. cholerae and presence of any species of plankton. All the isolates presented very similar virulence profiles by PCR, lacking ctxA and tcpA El Tor and containing hlyA (98.7%), rtxA (99.0%), toxR (98.7%) and stn-sto (1.9%). Resistance to ampicillin was found in both Tucumán (21%) and Buenos Aires isolates (45%). CONCLUSIONS: We identified two geographic areas in Argentina where V. cholerae was present: freshwaters of the rivers from Tucumán and the Río de la Plata. SIGNIFICANCE AND IMPACT OF THE STUDY: The identification of V. cholerae strains in the environment, carrying both virulence factors and resistance to antimicrobial agents, highlight the need for a continuous and active surveillance of this pathogen.     

Phylogenetic distance–decay patterns are not explained by local community assembly processes in freshwater lake microbial communities

While water and sediment microbial communities exhibit pronounced spatio-temporal patterns in freshwater lakes, the underlying drivers are yet poorly understood. Here, we evaluated the importance of spatial and temporal variation in abiotic environmental factors for bacterial and microeukaryotic community assembly and distance–decay relationships in water and sediment niches in Hongze Lake. By sampling across the whole lake during both Autumn and Spring sampling time points, we show that only bacterial sediment communities were governed by deterministic community assembly processes due to abiotic environmental drivers. Nevertheless, consistent distance–decay relationships were found with both bacterial and microeukaryotic communities, which were relatively stable with both sampling time points. Our results suggest that spatio-temporal variation in environmental factors was important in explaining mainly bacterial community assembly in the sediment, possibly due lesser disturbance. However, clear distance–decay patterns emerged also when the community assembly was stochastic. Together, these results suggest that abiotic environmental factors do not clearly drive the spatial structuring of lake microbial communities, highlighting the need to understand the role of other potential drivers, such as spatial heterogeneity and biotic species interactions.     

The importance of biological inertia in plant community resistance to invasion

Abstract. Insights into the ecology of historic invasions by introduced species can be gained by studying long‐term patterns of invasions by native species. In this paper, we review literature in palaeo‐ecology, forest‐stand simulation modelling, and historical studies of plant species invasions to illustrate the relevance of biological inertia in plant communities to invasion ecology. Resistance to invasion occurs in part because of environmental, demographic, and biotic factors influencing the arrival and establishment of invading species. We propose that biological inertia within the resident community is a fourth component of resistance to invasion, because of the lag time inherent in eliminating resident species and perhaps their traces after environmental conditions become suitable for invasion by immigrating species. Whether or not an introduced species invades can be conditioned by the presence of the pre‐existing community (and/or its legacy) in addition to the other biotic and abiotic factors.     

Amphibian species richness across environmental gradients

Large‐scale field patterns are a fundamental source of inferences on processes responsible for variation in species richness among habitats. We examined species richness of larval amphibian communities in 37 ponds over seven years on the Univ. of Michigan's E. S. George Reserve. Ordination of the community incidence matrix indicated a strong major axis of variation in species associations that was correlated with pond hydroperiod, surface area and forest canopy cover. Communities were significantly nested with those species found in ponds with high canopy cover, small area and short hydroperiod being nested subsets of those found in ponds with contrasting characteristics. Presence of fish had strong negative effects on species richness; relaxation of this effect also was apparent when fish were extirpated from ponds by drought. We employed a model selection analysis to identify the most appropriate statistical model for predicting the long‐term average species richness of these ponds from local abiotic and biotic (predator and competitor density) factors. A model including only the abiotic factors was overwhelmingly superior for the anurans; hierarchical partitioning indicated that area and canopy cover alone accounted for over 70% of the independent effects of predictor variables. The global model including both abiotic and biotic factors was the best supported model for the caudates, and correspondingly hierarchical partitioning suggested that area, hydroperiod, invertebrate predators and caudate biomass all accounted for 9–16% of the independent effects. Overall, biotic factors accounted for much less of the variation in species richness than abiotic factors. The patterns in larger, open‐canopy ponds provided little evidence of competitive effects on species richness, though there were patterns consistent with competitive effects in small, closed‐canopy ponds. The unusual temporal and spatial extent of these data enabled us to critically evaluate ideas regarding patterns in larval amphibian communities, and the effects of area, disturbance (hydroperiod) and productivity (canopy cover) on species richness of these communities. These results have important implications to the conservation of amphibian species richness in freshwater wetlands, which are among the most threatened ecosystems worldwide.     

Spatial structure of fish assemblages in a tropical estuarine lagoon: combining multivariate and geostatistical techniques

The spatial structure and seasonal changes of estuarine fish assemblages in the Ciénaga Grande de Santa Marta (CGSM) were analysed based on four seasonal comprehensive surveys conducted in 1993-1994 and 1997. Geostatistical and multivariate techniques were used to: (a) determine seasonal changes in spatial distribution of the species richness, and (b) identify assemblages of estuarine fish and their relation to abiotic factors. Potential biotic interactions affecting the assemblage structure were also explored. A total of 11075 individuals representing 39 species were collected, with Eugerres plumieri, Diapterus rhombeus, Micropogonias furnieri, Mugil incilis, Cathorops spixii, Elops saurus and Anchovia clupeoides as dominant species between seasons. Spatial distribution of fish richness differed between rainy and dry seasons in each year, whereas species mapping showed spatial patchiness in 1993-1994 and gradients during 1997. Strong evidence of species saturation was found in all seasons, suggesting biotic interactions limiting species richness at a threshold density of ca. 50 ind./5000 m². Marine, marine-estuarine and freshwater species were classified in each season according to their capability to cope with salinity fluctuations. Associations defined by functional feeding guilds were also identified. Empirical and statistic evidence showed that fish assemblages differed between seasons within each year, and each assemblage was always dominated by a small number of species, notably E. plumieri in both years 1993-1994 and 1997. Between-season differences in fish assemblage structure in the CGSM seem to be driven by abiotic factors; however, evidence of species saturation could suggest the existence of density-dependent factors operating together.     

Seasonal flow variation allows 'time-sharing' by disparate aquatic insect communities in montane desert streams

1. Flow variation can drive major abiotic changes in stream environments between seasons. Theoretically, disparate biotic communities could be maintained during different seasons at a single site if suitable refuges and colonist sources were available. Using isolated montane desert streams in south‐east Arizona as a model system, we hypothesised that two disparate aquatic insect faunas (montane temperate and neotropical) could be maintained at the same sites through strong seasonal variation in abiotic conditions. 2. We collected aquatic insects representing 59 families from seven streams during high‐flow (March–April) and low‐flow (June) sampling periods across two years. We assessed changes in aquatic insect community and functional feeding group composition by habitat (riffle, pool) and season (high flow, low flow). 3. Within sites, wetted stream area decreased by an average of 97% between high‐flow (predominately riffles) and low‐flow (predominately pools) seasons. Community composition likewise showed strong seasonal patterns; the montane temperate fauna was strongly associated with the high‐flow season while neotropical hemipterans and coleopterans were associated with the low‐flow season. Increased water temperature was significantly associated with this shift from temperate to neotropical assemblages. 4. Functional feeding group composition shifted dramatically by season. The proportion of predators increased from 24.5% (high flow) to 75.2% (low flow) while collector–filterers and shredders declined from 38.4% (high flow) to 1.7% (low flow). 5. We suggest that habitat ‘time‐sharing’ by disparate communities is facilitated via strong seasonal variation in temperature and flow and the presence of high elevation refuges or diapause stages for temperate montane taxa to survive the dry season.     

Molecular epidemiology of penicillin resistantStreptococcus pneumoniae strains in Turkey. A multicenter study

A total of 539 isolates recovered from various clinical sites were collected from 13 hospitals from different regions of Turkey between 1999 and 2002. Susceptibility to penicillin and cefotaxime was determined by the E-test and the remaining antimicrobials were evaluated by disk diffusion tests. Penicillin resistant and intermediate isolates were serotyped and PFGE patterns were analysed. Overall 16 isolates (3%) were resistant to penicillin, and 143 (26.5%) were intermediate. Resistance and intermediate rates were 3.1% and 29.0% respectively in respiratory tract isolates. Multiple resistance (resistance to ≥3 antibiotics) occurred in 81.8% of the penicillin resistant isolates and the most frequent resistance phenotype was penicillin+trimethoprim/sulphamethoxazole (37.7%). Minimum inhibitory concentrations of cefotaxime were lower than 1 mg/ml for all the isolates. The highest rate of resistance was observed for trimethoprim/ sulphamethoxazole (26.6%) followed by doxycycline (12.6%). Resistance to erythromycin was 10.1%, clindamycin 9.9%, chloramphenicol 4.3%, ofloxacin 5.0% and levofloxacin 0.2%. There was no resistance to vancomycin. Resistant isolates belonged to serogroups 9, 23, and 6. The most frequent serogroups among intermediate isolates were 23, 19, 14, 1, 9, and 6. Five distinct PFGE patterns were observed among penicillin resistant isolates. There was no distinct clustering of specific PFGE patterns in the study centres. No correlation between serotypes, resistance and PFGE patterns was found. There seems to be genetic heterogeneity inStreptococccus pneumoniae isolates in Turkey.     

The recovery of crustacean zooplankton from acidification depends on lake type

Acidification has harmed freshwater ecosystems in Northern Europe since the early 1900s. Stricter regulations aimed at decreasing acidic emissions have improved surface-water chemistry since the late 1980s but the recovery of biotic communities has not been consistent. Generally, the recovery of flora and fauna has been documented only for a few lakes or regions and large-scale assessments of long-term dynamics of biotic communities due to improved water quality are still lacking. This study investigates a large biomonitoring dataset of pelagic and littoral crustacean zooplankton (Cladocera and Copepoda) from 142 acid-sensitive lakes in Norway spanning 24 years (1997–2020). The aims were to assess the changes in zooplankton communities through time, compare patterns of changes across lake types (defined based on calcium and humic content), and identify correlations between abiotic and biological variables. Our results indicate chemical and biological recovery after acidification, as shown by a general increase in pH, acid neutralizing capacity, changes in community composition and increases in the total number of species, number of acid-sensitive species and functional richness through time. However, the zooplankton responses differ across lake types. This indicates that the concentration of calcium (or alkalinity) and total organic carbon (or humic substances) are important factors for the recovery. Therefore, assessment methods and management tools should be adapted to the diverse lake types. Long-term monitoring of freshwater ecosystems is needed to fully comprehend the recovery dynamics of biotic communities from acidification.     

Cell death in individual freshwater phytoplankton species: relationships with population dynamics and environmental factors

ABSTRACT

Understanding and predicting changes in phytoplankton populations requires knowledge of losses due not only to sedimentation and grazing, but also to intrinsic processes (here, collectively termed ‘cell death’). Cell death is poorly understood, especially in freshwater phytoplankton, but experiments in culture often suggest involvement of abiotic factors (e.g. temperature, light, nutrients). The occurrence of cell death was examined in a simple, natural environment: a small, well-mixed, temperate, urban pond during a period of phytoplankton growth, from mid-July to mid-November. Abundances of 18 phytoplankton taxa were measured weekly and fluorescence microscopy and staining was used to detect dead cells (using SYTOX which measures loss of membrane integrity) and cells undergoing cell death (using Annexin-V, which measures lipid inversions of membranes, an early signal of cell death). Dead and dying cells occurred in most phytoplankton taxa, but incidence and timing varied considerably, e.g. species like the chlorophyte Ankistrodesmus spiralis showed 20–30% of cells staining with SYTOX and Annexin in late autumn when the population was decreasing, while the dinoflagellate Peridinium sp. showed staining of up to 50% of cells with STYOX throughout the period, and the cyanobacterium Microcystis aeruginosa occasionally showed staining of 100% of cells with SYTOX. Overall, there was some association between cell death staining and growth phase with 10–15% of the total community showing SYTOX and Annexin staining in late autumn, when most populations were declining. Cell death could not be correlated with thresholds or rapid changes in abiotic conditions (e.g. temperature, irradiance) or with indicators of nutrient limitation (e.g. N:P ratios). While abiotic factors have been clearly implicated in cell death within unialgal culture experiments, in natural freshwater ecosystems interactions between biotic factors, such as pathogens or allelopathy, may play greater roles in losses related to cell death and be distinct for different taxa.     

Seasonal strengths of the abiotic and biotic drivers of a zooplankton community

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Water temperature,not fish morph,determines parasite infections of sympatric Icelandic threespine sticklebacks (Gasterosteus aculeatus)

Parasite communities of fishes are known to respond directly to the abiotic environment of the host, for example, to water quality and water temperature. Biotic factors are also important as they affect the exposure profile through heterogeneities in parasite distribution in the environment. Parasites in a particular environment may pose a strong selection on fish. For example, ecological differences in selection by parasites have been hypothesized to facilitate evolutionary differentiation of freshwater fish morphs specializing on different food types. However, as parasites may also respond directly to abiotic environment the parasite risk does not depend only on biotic features of the host environment. It is possible that different morphs experience specific selection gradients by parasites but it is not clear how consistent the selection is when abiotic factors change. We examined parasite pressure in sympatric morphs of threespine stickleback (Gasterosteus aculeatus) across a temperature gradient in two large Icelandic lakes, Myvatn and Thingvallavatn. Habitat‐specific temperature gradients in these lakes are opposite. Myvatn lava rock morph lives in a warm environment, while the mud morph lives in the cold. In Thingvallavatn, the lava rock morph lives in a cold environment and the mud morph in a warm habitat. We found more parasites in fish living in higher temperature in both lakes, independent of the fish morph, and this pattern was similar for the two dominating parasite taxa, trematodes and cestodes. However, at the same time, we also found higher parasite abundance in a third morph living in deep cold–water habitat in Thingvallavatn compared to the cold‐water lava morph, indicating strong effect of habitat‐specific biotic factors. Our results suggest complex interactions between water temperature and biotic factors in determining the parasite community structure, a pattern that may have implications for differentiation of stickleback morphs.