Evolution of Protein Molecules

ECOLOGY/EVOLUTION: Phenotypic Plasticity

Effects of sediment geochemical properties on heavy metal bioavailability.

Predicting the ecological causes and consequences of global climate change requires a variety of approaches, including the use of experiments, models, and surveys. Among experiments, mesocosms have become increasingly popular because they provide an important bridge between smaller, more tightly controlled, microcosm experiments (which can suffer from limited realism) and the greater biological complexity of natural systems (in which mechanistic relationships often cannot be identified). A new evaluation of the contribution of the mesocosm approach, its potential for future research, as well as its limitations, is timely. As part of this review, we constructed a new database of over 250 post-1990 studies that have explored different components of climate change across a range of organisational levels, scales, and habitats. Issues related to realism, reproducibility and control are assessed in marine, freshwater, and terrestrial systems. Some general patterns emerged, particularly at the ecosystem level, such as consistent and predictable effects on whole-system respiration rates. There are, however, also many seemingly idiosyncratic, contingent responses, especially at the community level, both within and among habitat types. These similarities and differences in both the drivers and responses highlight the need for caution before making generalisations. Finally, we assess future directions and prospects for new methodological advances and the need for greater international coordination and interdisciplinarity.

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Mesocosm Experiments as a Tool for Ecological Climate-Change Research

Nutrient availability, in particular of phosphorus (P), is a key factor for the structure and functioning of shallow lakes, and not least the sediment plays an important role by acting as both a nutrient source and sink. We used 21 years of monthly mass balance and lake water data from six shallow (mean depth = 1.2–2.7 m) and fast flushed (mean hydraulic retention time = 0.6–2.6 months) eutrophic Danish lakes (mean summer P concentrations ranging from 0.09 to 0.61 mg/l) to investigate long-term trends in yearly and seasonal patterns of P retention. To one of the lakes, the external P input was reduced by 70% in the early 1990s, whereas none of the other lakes have experienced major changes in external P loading for more than 20 years. All lakes showed a distinct seasonal pattern with high P concentrations and typically negative P retention during summer (up to −300% of the external loading from May to August). During winter, P retention was overall positive (up to 50% of the external loading from December to April). Internal P loading from the sediment delayed lake recovery by approximately 10 years in the lake with the most recently reduced external loading, but in all the lakes net release of P from the sediment occurred during summer. P release in the six lakes has not abated during the past decade, indicating that the sediment of eutrophic and turbid shallow lakes remains a net source of P during summer. The seasonal variations in P retention became more pronounced with increasing P levels, and retention decreased with increasing temperature, but increased if clear water conditions were established.

Persistent internal phosphorus loading during summer in shallow eutrophic lakes

Animals can be important in nutrient cycling through a variety of direct and indirect pathways. A high biomass of animals often represents a large pool of nutrients, leading some ecologists to argue that animal assemblages can represent nutrient sinks within ecosystems. The role of animals as sources vs. sinks of nutrients has been debated particularly extensively for freshwater fishes. We argue that a large pool size does not equate to a nutrient sink; rather, animals can be nutrient sinks when their biomass increases, when emigration rates are high, and/or when nutrients in animal carcasses are not remineralized. To further explore these ideas, we use a simple model to evaluate the conditions under which fish are phosphorus (P) sources or sinks at the ecosystem (lake) level, and at the habitat level (benthic and water column habitats). Our simulations suggest that, under most conditions, fish are sinks for benthic P but are net P sources to the water column. However, P source and sink strengths depend on fish feeding habits (proportion of P consumed from the benthos and water column), migration patterns, and especially the fate of carcass P. Of particular importance is the rate at which carcasses are mineralized and the relative importance of benthic vs. pelagic primary producers in taking up mineralized P (and excreted P). Higher proportional uptake of P by benthic primary producers increases the likelihood that fish are sinks for water column P. Carcass bones and scales are relatively recalcitrant and can represent a P sink even if fish biomass does not change over time. Thus, there is a need for better documentation of the fraction of carcass P that is remineralized, and the fate of this P, under natural conditions. We urge a more holistic perspective regarding the role of animals in nutrient cycling, with a focus on quantifying the rates at which animals consume, store, release, and transport nutrients under various conditions.

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When are fish sources vs. sinks of nutrients in lake ecosystems

Summary
Morphometric-based condition indices are widely used to assess proximate body composition and, collaterally, feeding and living conditions of fish. However, the exact relationship between condition indices and proximate body composition of fish and its relatedness to life history traits and seasonality has yet to be fully explored. Therefore, the aim of this study was to examine how the Fulton's condition factor (K-factor) is related to the chemical composition (i.e. lipid, protein, water and carbon content, and molar carbon : nitrogen ratio), length and gonadal development of fish, and how these relationships are influenced by gender and seasonality in three freshwater fish species: Amur sleeper (Perccottus glenii), pumpkinseed (Lepomis gibbosus) and rudd (Scardinius erythrophthalmus). It was found that the strength and direction of association between the K-factor and proximate body composition can vary markedly among fish species. The K-factor correlated positively with gonadal development in pumpkinseed and Amur sleeper, while no such relationship existed in rudd. Condition factor can be a reliable measure of lipid content; however, the relationship was stronger in species with higher and more variable lipid contents. Moreover, a striking and consistently negative linkage was found between the K-factor and water content of the fish body, which corresponds to the findings of several other studies. In turn, any relationship between the K-factor and the protein content of fish was not detected. Gender seemed to exert a negligible effect on the relationship between the K-factor and proximate body composition, while seasonal variance was obvious in most relationships.

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Relationship between Fulton’s condition factor and proximate body composition in three freshwater fish species

One of the central questions of ecological stoichiometry theory is to what extent animal species maintain constant elemental composition in their bodies Although several recent studies demonstrate intraspecific variation in animal elemental composition, relatively little is known about ontogenetic changes in vertebrates, especially during early life stages We studied the intraspecific and interspecific ontogenetic variation in the body stoichiometry of two fish species in two different orders; fathead minnow (Pimephales promelas) and sheepshead minnow (Cyprinodon variegatus), reared under controlled laboratory conditions During ontogeny, we measured the chemical composition of fish bodies, including carbon (C), nitrogen (N), phosphorus (P), calcium (Ca), and ribonucleic acid (RNA) contents We found that N and RNA contents were relatively high in early life stages and declined substantially during development In contrast, body C and C:N ratios were relatively low in embryos, post-embryos and larvae, and increased remarkably thereafter Concentrations and ratios of some elements (eg, Ca, P, Ca:P) did not exhibit consistent ontogenetic trends, but fluctuated dynamically between consecutive developmental stages in both species Specific growth rates correlated significantly with RNA contents in both species Analyses of the relative importance of different P pools at each developmental stage revealed that RNA was a considerable P pool in post-embryos, while bone-associated P was the dominant body P pool in later stages Our results suggest that the elemental composition of fish bodies changes considerably during ontogeny Each ontogenetic stage has its own stoichiometric signature, but the timing, magnitude and direction of ontogenetic changes can vary substantially between taxa

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Ontogenetic variation in the body stoichiometry of two fish species

Redox potential is a significant factor in aquatic systems to regulate the availability of nutrients and some metals. To assess the driving variables regulating redox potential, background parameters (dissolved oxygen, pH, temperature, chlorophyll-a, soluble reactive and total phosphorus content of water, coverage and height of submerged macrophytes) and redox potential profiles around the sediment–water interface (SWI) were measured in simulated shallow lake ecosystems. There were two nutrient regimes (enriched and non-enriched) and three temperature scenarios (unheated; +3.5°C; +5°C) installed in the experimental setups, which were constructed to study the effects of global climate change. Temperature did not have any detectable effect on redox potentials, and we presume that nutrient addition had only indirect positive effects through triggering phytoplankton dominance which causes macrophyte absence. When submerged macrophytes were present in high density (80–100% coverage), redox potentials at the SWI varied between 60–215 mV and the mean redox potential was 133 ± 34 mV (mean ± 1 SD). In contrast to this, when phytoplankton dominance was coupled to low macrophyte density (0–20% coverage), the range of redox potentials at the SWI was 160–290 mV and the mean redox potential was 218 ± 34 mV. The results revealed the primary importance of submersed macrophytes; macrophyte coverage determined alone the redox potential of the sediment–water interface by 81%. This study suggests that possible positive effects of macrophytes on redox potential can be suppressed by their negative effects in case of 80–100% coverage and total inhabitation of the water column.

Influence of submerged macrophytes, temperature, and nutrient loading on the development of redox potential around the sediment-water interface in lakes

Gergely Boros

Papers

When are fish sources vs. sinks of nutrients in lake ecosystems

Relationship between Fulton’s condition factor and proximate body composition in three freshwater fish species

Ontogenetic variation in the body stoichiometry of two fish species

Influence of submerged macrophytes, temperature, and nutrient loading on the development of redox potential around the sediment-water interface in lakes

Gut content microbiota of introduced bigheaded carps (Hypophthalmichthys spp.) inhabiting the largest shallow lake in Central Europe.