Freshwater Biology

Both genetic and phenotypic intraspecific diversity play a crucial role in the ecological and evolutionary dynamics of organisms. Several studies have compared phenotypic divergence (Pst) and differentiation of neutral loci (Fst) to infer the relative roles of genetic drift and natural selection in population differentiation (Pst - Fst comparison). For the first time, we assessed and compared the genetic variation and differentiation at the leaf trait level in two key macrophytes, Phragmites australis and Nuphar lutea. To this aim, we quantified and described the genetic structure and phenotypic diversity of both species in five lake systems in north-central Italy. We then investigated the relative roles of genetic drift and natural selection on leaf trait differentiation (Pst - Fst), assuming that Fst reflects divergence caused only by genetic drift while Pst also incorporates the effects of selective dynamics on the phenotype. In terms of genetic structure, the results for P. australis were in line with those observed for other Italian and European conspecific populations. Conversely, N. lutea showed a more complex genetic structure than expected at the site level, likely due to the combined effect of genetic isolation and its mixed mating system. Both species exhibited high variability in leaf functional traits within and among sites, highlighting a high degree of phenotypic plasticity. Pst - Fst comparisons showed a general tendency towards directional selection in P. australis and a more complex pattern in N. lutea. Indeed, the drivers of phenotypic differentiation in N. lutea showed a variable mix of stabilizing and directional selection or neutral divergence at most sites. The prevalence of vegetative over generative reproduction leads P. australis populations to be dominated by a few clones that are well adapted to local conditions, including phenotypes that respond plastically to the environment. In contrast, in N. lutea the interaction of a mixed mating system and geographical isolation among distant sites tends to reduce the effect of outbreeding depression and provides the genetic basis for adaptive capacity. The first joint analysis of the genetic structure of these two key macrophytes allowed a better understanding of the relative roles of genetic drift and natural selection in the diversification of phenotypic traits within habitats dominated by P. australis and N. lutea.

O_LIEnvironmental conditions bottlenecking species population demographics are less known in cold regions with harsh winters despite of global concerns of declining freshwater mussels (Unionidae). Few studies examined both cold and summer environments in attempts to promote habitat conservation of Unionidae species. C_LIO_LIWe identified the taxonomically confused Unionidae species using phylogenetic analysis with mtDNA (COI region) and tested the hypothesis that winter mortality is the main cause of contrasting population demographics and structures in floodplain lakes in northern Japan. Demographic surveys were conducted in two lakes, which contrasted in recruitment rates, over one year including 4-month ice-covered periods C_LIO_LIAlthough previous studies have identified freshwater mussels as introduced Anemina arcaeformis (Heude 1877) based on morphology, this study confirmed the focal species as potentially native Buldowskia iwakawai (Suzuki, 1939). High winter mortality (30-40%) of adult mussels was found, although the mortality did not significantly differ between the populations with contrasting recruitment. C_LIO_LISurprisingly, the annual mortality was much lower in juveniles (10%) than in gravid and nongravid adult individuals (40-75%). The main inter-population difference was attributed to the higher summer mortality of gravid females, but not juveniles and non-gravid individuals, in the population with low recruitment. C_LIO_LIThese results collectively suggest that summer hypoxia combined with physiological stresses on females in winter is a likely population growth-limiting mechanism. To prevent a chain of adult abundance decreases in winter and high mortality of gravid mussels and newly born juveniles in summer, improvements in summer habitat conditions are necessary, while winter conditions need to be considered simultaneously. Increases in water circulation rates and alleviations of hypoxic conditions is an option for short-term habitat improvement approach. The current study sheds light on the winter-mediated mortality of freshwater mussels in shallow eutrophic floodplain lakes and contributes to improved management strategies for degraded floodplain waterbodies. C_LI

Lake metabolism is often quantified using continuous measures of dissolved oxygen (O2), where a 1: -1 stoichiometry with carbon dioxide (CO2) is assumed because of their roles in photosynthesis and respiration, respectively. However, many other physical, chemical, and biological processes decouple dissolved O2 and CO2 concentrations in lakes. Tracking departures from 1:-1 stoichiometry may provide insights into larger scale ecosystem functioning, particularly during fall when temperatures change and destratification occurs. Using continuous measures of both dissolved O2 and CO2 in a small temperate headwater lake, we looked at the interannual gas departure signals during fall over seven years. The beginning of fall, defined here as the start of leaf colour change, differed among years but coincided well with the onset of lake destratification and a shift in surface gas concentrations. Fall surface CO2 accumulation rates varied considerably, whereas O2 depletion rates were rather similar among years. Departure signals were broadly related to interannual differences in climate: more CO2 accumulated in the surface during the hottest-wettest fall compared to the coldest-driest one (0.81 and 0.37 {micro}mol L-1 d-1, respectively), presumably from more catchment than hypolimnetic inputs. Lower CO2 accumulation occurred during years with prolonged hypolimnetic hypoxia potentially through enhanced CO2 consumption by methanogenesis. Other internal biological phenomena influenced fall departure signals, including a large metalimnetic oxygen peak, and higher fall surface primary production. We suggest gas departures during fall provide an integrative metabolic fingerprint for temperate stratified lakes, as well as insights into winter-priming conditions. HighlightsO_LIAnnual fall surface water CO2 accumulation rates vary more than O2 depletion rates. C_LIO_LIExternal fall inputs and internal processes influence gas departures differently. C_LIO_LIFall gas departures may act as an integrative metabolic signal in temperate lakes. C_LI

Freshwater salinization poses global challenges for aquatic organisms, impacting their physiology and ecology. However, current salinization research predominantly focuses on mortality endpoints in limited model species, overlooking the sublethal effects on a broader spectrum of organisms and the exploration of adaptive mechanisms and pathways under natural field conditions. To address these gaps, we conducted high-throughput sequencing transcriptomic analysis on the gill tissue of the euryhaline fish Gasterosteus aculeatus, investigating its molecular response to salinity stress in the highly urbanized river Boye, Germany. We found that even sublethal concentrations of chloride led to the activation of the energetically costly osmoregulatory system in G. aculeatus, evidenced by the differential expression of genes related to osmoregulation. Our enrichment analysis revealed differentially expressed genes (DEGs) related to transmembrane transport and regulation of transport and other osmoregulation pathways, which aligns with the crucial role of these pathways in maintaining biological homeostasis. Notably, we identified candidate genes involved in increased osmoregulatory activity under salinity stress, including those responsible for moving ions across membranes: ion channels, ion pumps, and ion transporters. Particularly, genes from the solute carrier family SLC, aquaporin AQP1, chloride channel CLC7, ATP-binding cassette transporter ABCE1, and ATPases member ATAD2 exhibited prominent differential expression. These findings provide insights into the molecular mechanisms underlying the adaptive response of euryhaline fish to salinity stress and have implications for their conservation and management in the face of freshwater salinization.

Quagga mussels (Dreissena rostriformis bugensis) are among the most impactful invaders in freshwaters of the Northern Hemisphere. As filter-feeders, they can reduce harmful algal blooms (HABs), but their effects are expected to be dependent on cyanobacteria species and water temperature. However, conclusive studies on these traits and their combination are lacking. Here, we combined laboratory experiments with an analysis of long-term data from a temperate shallow lake 10 years before and after quagga mussel invasion, respectively. We tested the hypotheses that quagga mussel filtration rates in the laboratory would 1) vary among common cyanobacteria species and 2) decrease above a critical temperature. Regarding the field data, we expected that 3) quagga mussels can reduce the summer biovolume of palatable cyanobacteria, but that 4) this effect disappears above a critical temperature. Our results support all four hypotheses. In laboratory experiments, Dolichospermum flos-aquae was classified as palatable to quagga mussels, while Aphanizomenon flos-aquae, Anabaenopsis elenkinii and Microcystis aeruginosa were less-palatable cyanobacteria. Filtration rates decreased above 28.9{degrees}C (CI: 27.6-30.2{degrees}C) with mussels dying at 32{degrees}C. Our long-term lake data show that cyanobacteria biovolumes were lower after quagga mussel invasion, but only below 27.7{degrees}C (CI: 26.9-28.4{degrees}C), confirming a critical thermal window for quagga mussel filtration. Global warming will therefore facilitate HABs by increasing the growth rates of cyanobacteria and reducing the filtration rates of quagga mussels above critical summer water temperatures, which are increasingly being reached in invaded lakes. This critical thermal window must be considered when making HAB predictions. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=93 SRC="FIGDIR/small/707163v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@175851eorg.highwire.dtl.DTLVardef@76a481org.highwire.dtl.DTLVardef@12a3965org.highwire.dtl.DTLVardef@11e3e7d_HPS_FORMAT_FIGEXP M_FIG C_FIG

Trophic cascades, or indirect effects of predators on non-adjacent lower trophic levels, have become paradigmatic in ecology, though they are thought to be stronger in aquatic ecosystems. Most research on freshwater trophic cascades focused on temperate lakes, where fish are present and where Daphnia tend to dominate the zooplankton community. These studies identified that Daphnia often play a key role in facilitating trophic cascades by linking fish to algae with strong food web interactions. However, Daphnia are rare or absent in most tropical and subtropical lowland freshwaters, and fish are absent from small and temporary water bodies, where invertebrates fill the role of top predator. While invertebrate predators are ubiquitous in freshwater systems, most have received little attention in food web research. Therefore, we aimed to test whether trophic cascades are possible in small warmwater ponds where small invertebrates are the top predators and Daphnia are absent. We collected naturally occurring plankton communities from small fishless water bodies in central Texas and propagated them in replicate pond mesocosms. We removed zooplankton from some mesocosms, left the plankton community intact in others, and added one of two densities of the predaceous insect Neoplea striola to others. Following an incubation period we then compared biomasses of plankton groups to assess food web effects between the trophic levels including whether Neoplea caused a trophic cascade by reducing zooplankton. The zooplankton community became dominated by copepods which prefer large phytoplankton and exhibit a fast escape response. Perhaps due to these qualities of the copepods and perhaps due to slow consumption rates by Neoplea on key grazers, no evidence for food web effects were found other than somewhat weak evidence for zooplankton reducing large phytoplankton. More research is needed to understand the behavior and ecology of Neoplea, but trophic cascades may generally be weak or absent in fishless low-latitude lowland water bodies where Daphnia are rare.

Evolution of morphological traits is hypothesized to act on an extended time scale, yet studies have suggested that these changes are possible within a few generations. Trophic polymorphism enabled through niche adaptations and ecological opportunity is one phenomenon that facilitate occurrence of rapid adaptive variation, common in many northern freshwater fish species. One such species is Arctic charr, which is known for its extensive variation in morphology and the occurrence of morphs. However, the speed at which such morphological variation arises is poorly studied despite the importance for understanding the onset of evolution. The aim of this study was to elucidate this process in a gradient of eight lakes that was stocked with Arctic charr in the period from 1910 to 1917 from Lake Tinnsjoen, Norway. We used morphological measurements to test for differences in traits between populations and Haldane and Darwins evolutionary rates to estimate divergence rates in traits. We also tested for correlation between putative genetic and morphological divergence. In addition, we contrasted the morphological divergence with that expected under neutral genetic expectations, using 12 microsatellite markers, to analyze whether and which morphological differences that is following early genetic divergence. A significant genetic differentiation was found between the source population and five of the translocated populations with corresponding differences in morphological traits for four of the populations. Population genetic structuring indicated six different genetic clusters. The translocated populations also exhibited trait divergence estimated with both Haldane and Darwins rates. Differences in morphological traits showed a significant correlation with genetic divergence, and the morphological differences were most likely affected by differences in lake parameters such as maximum depth, lake size and fish community. We conclude that intraspecific morphological and genetic divergence can form on short evolutionary time scales with important implications for conservation and management practices.

Top predators responses to environmental conditions shape food web architecture and influence ecosystem structure and stability. Yet the impacts of fundamental properties like ecosystem size and morphometry on top predators behaviour are poorly understood. We examined how lake morphometry impacts the behaviour (inferred by depth use) of three key fish top predators--the cold-adapted lake trout, the cool-adapted walleye, and the warm-adapted smallmouth bass-- which can each strongly impact local food web structure. We used catch-per-unit-effort data from nearly 500 boreal lakes of Ontario, Canada to evaluate the role of thermal preference in dictating mean depth of capture and biomass index in response to lake morphometry. We found evidence that thermal preferences influence how species depth use and biomass changed with lake size, proportion of littoral area, and maximum lake depth, although we found no relationship with lake shape. However, found no strong evidence that lake morphology influences these species biomasses, despite theory that predicts such a relationship. Our results suggest that some aspects of lake morphometry can alter habitat accessibility and productivity in ways that influence the behaviour and biomass of these top predator species depending on their thermal preferences. Our results have implications for how lake food webs expand and contract with lake morphometry and other key abiotic factors. We argue that several key abiotic factors likely drive top predator depth use in ways that may shape local food web structure and play an important role in determining the ultimate fate of ecosystems with environmental change.

Fishless lakes, critical drivers of biodiversity across freshwater landscapes, are becoming increasingly rare due to fish introductions. Although the impacts of fish introduction are well understood in high-elevation fishless lakes, their effects on fishless kettle lakes remain poorly understood. Many kettle lakes are disconnected from the surface water network and are therefore fishless. In this study, we examined how amphibian and zooplankton communities differ between fishless and fish-bearing kettle lakes by comparing 36 lakes in Quebec, Canada. Some kettle lakes are hydrologically connected to surrounding aquatic ecosystems, allowing natural colonization by fish. We therefore also evaluated how amphibian and zooplankton communities differ between connected and disconnected kettle lakes. Fish presence was associated with differences at each stage of the amphibian life cycle. Reproductive calls of adult amphibians were detected regardless of fish presence, indicating that reproduction occurred in all lake types. However, the presence of fish was associated with fewer amphibian egg masses and lower larval abundance, and the absence of salamanders at the larval stage. Small-bodied zooplankton were more abundant in fish-bearing lakes, while overall species richness was lower. In particular, Chaoborus americanus, a large top-predatory zooplankton species, was found exclusively in fishless lakes. In contrast to fish presence, hydrological connectivity had no significant effect on most communities, except for adult American toads, adult wood frogs, and mink frogs larvae, which responded positively to the interaction between fish presence and connectivity. Based on our results, we recommend avoiding fish stocking of kettle lakes to preserve essential reproductive habitats for amphibians, maintain refuges for sensitive zooplankton species, and safeguard the spatial heterogeneity that underpins landscape-scale biodiversity.

Lakes experience a wide range of variation in resource availability; variation of essential resources such as light and nutrients can cause changes in algae community structure. Changes in light color and nutrient availability could lead to shifts in algal community diversity and composition, including shifting communities to be dominated by cyanobacteria. Due to eutrophication and brownification, lakes are experiencing increases in nutrient concentrations and shifts from blue towards red in the color of light available to algae for photosynthesis. We investigated whether differences in light color and nutrients affect algal community composition and diversity, and whether differences in light color alter the impact that nutrient levels have on algal communities. We used experimental microcosms with a fully factorial experimental design, crossing four light colors with two nutrient levels. We assessed community composition by enumerating algal taxa via light microscopy. We found that light color and the interaction between light color and nutrient availability led to large differences in community diversity, with blue light leading to the greatest diversity and broad light the lowest. Light color, nutrients, and the interaction between the two were all significant drivers of differences in community composition. Overall, we found that light color and nutrient availability interact to affect algal community diversity, composition, and cyanobacteria density. Consequences of light color are infrequently studied in aquatic ecology, but our results show that light color may need to be considered more broadly. Furthermore, our results suggest that concurrent eutrophication and brownification may yield environmental conditions favorable to cyanobacteria, including taxa that can form harmful algal blooms.

Trait-mediated indirect interactions have been intensively studied to understand ecological dynamics in biological communities. Yet, little is known about the relative importance of trait-mediated indirect effects of environmental stressors on population dynamics. How does an environmental stressor indirectly affect the population dynamics of a focal species by altering the traits of interacting species and the strength of interspecific interactions? Here, we quantified the direct and trait-mediated indirect effects of an environmental stressor by combining rotifer-alga experiments and Bayesian parameter estimation of a dynamic model. These days, human activities salinize freshwater lakes globally, thereby increasing the death rates and decreasing birth rates of plankton species. Salinity stress is also known to induce cell clumping in certain phytoplankton species. As larger clumps work as a defense trait against gape-limited predation by zooplankton, the salinity stress can affect zooplankton not only directly but also indirectly through phytoplankton trait changes. We first show that a green alga, Chlamydomonas sphaeroides, formed larger clumps than the two model species of green algae (Chlamydomonas reinhardtii and Chlorella vulgaris) under a moderate salinity stress (0.06M NaCl). Then, by tracking the clump size distributions of Chlamydomonas sphaeroides, we confirmed that small clumps are more vulnerable to predation by rotifers, Brachionus calyciflorus, as previous studies demonstrated. Finally, we co-cultured the green algae and rotifers for a week with and without salinity stress and fitted the Lotka-Volterra predator-prey model. We first estimated how salinity stress increased the rotifer mortality rate using Chlorella vulgaris, which seldom showed clump formation. Then, by using Chlamydomonas sphaeroides, we estimated how salinity stress increased the mortality rate and decreased the attack rate due to clump formation. We found that salinity stress increased the rotifer mortality rate by more than seventeen-fold, and decreased the attack rate on Chlamydomonas sphaeroides to approximately half of that without salinity stress. These results indicate that salinity stress can weaken the predator-prey interaction, and thus salinization can harm freshwater zooplankton species through increasing the mortality rates and decreasing the attack rates. This will be an important step for a quantitative understanding of how environmental stressors can affect community dynamics via trait modifications.

AimA detailed, comparative DNA-barcoding and morphospecies based overview of the vertical and horizontal distribution of Lake Ohrid endemic Gammarus species-flock. Re-evaluation of the origin of the species-flock dating, identification of events that putatively influenced diversification patterns in the species-flock. LocationLake Ohrid: a deep and ancient lake of tectonic origin, biosphere reserve, UNESCO World Heritage Site, located on the Macedonia/Albania border. TaxonGammarus species-flock (Amphipoda, Crustacea) MethodsExtensive sampling and DNA barcoding of 600 individuals were carried out. DNA sequences were analysed using species delimitation methods, haplotype network reconstructions, Bayesian molecular dating and demographic analysis. The COI-based delimitation results were validated with nuclear 28S RNA data. ResultsThe species flock distribution has weak horizontal but clear vertical structure. The diversity across bathymetric gradients correlates with temperature and salinity; and the highest diversity with sublittoral and springs of lakes shore. Two new MOTUs representing putatively new species are revealed and supported also by the nuclear marker. The time of flock radiation overlaps with the time of lake formation. The COI gene shows signs of positive selection and an acceleration in substitution rate. The demographic changes of the flock happened during the last ky. Main conclusionsDistribution of the Gammarus species-flock is vertically structured, reflecting habitat zonation. Parapatric speciation as one of the mechanisms in flocks diversification is suggested. Detection of new MOTU suggests that the flocks diversity is still not fully revealed. Nevertheless, failure to recover three other MOTUs suggests the loss of gammarid diversity in the lake. This represents,together with the current threats to the lake ecosystem (i.e. climate changes, development of tourism), a clear call for conservation efforts. The speciation events and demographic changes within the flock relate presumably to glacial and postglacial water level changes and to colonisation of new depth ranges and the associated springs.

The study explores the individual size distribution (ISD) pattern in ecological communities, characterized by a negative correlation between individual body size and abundance (N [~] M{lambda}). The parameter {lambda} denotes the rate of decline in relative abundance from small to large individuals. Despite known influences of temperature and resource availability on body size, their effects on {lambda} remain diverse. Leveraging data from 2.4 million individual body sizes in continental freshwater streams, the research the hypothesis that {lambda} varies as a function of temperature and resource supply. Surprisingly, despite varied environmental conditions and complete species turnover, minimal variation in {lambda} (mean = -1.2, sd = 0.04) was observed, with no discernible impact from temperature or resource supply. The unexpected {lambda} value of -1.2 suggests a higher-than-expected relative abundance of large individuals, challenging assumptions of metabolic scaling at 0.75 and implying large subsidy inputs to large predators. Simulation and mesocosm experiments support a metabolic scaling coefficient of [~]0.4 for freshwater macroinvertebrates. The findings underscore remarkable consistency of individual size distributions in freshwater streams, likely driven by shallow metabolic scaling and large subsidies to large consumers.

Climate warming impacts ecosystems through multiple interacting pathways, including via direct thermal responses of individual taxa and the combined responses of closely interacting species. In this study we examined how warming and infection by an oomycete parasite affect the dominant zooplankter of Russias Lake Baikal, the endemic cold-adapted stenotherm Epischura baikalensis (Copepoda). We used a combination of laboratory experiments, long-term monitoring data and population modeling. Experiments showed large thermal mismatch between host and parasite, with strong negative effects of warm temperatures on E. baikalensis survival and reproduction and a negative synergistic effect of Saprolegnia infection. However, Saprolegnia infection had an unexpected positive effect on E. baikalensis reproductive output, which may be consistent with fecundity compensation by infected females. Long-term monitoring data showed that Saprolegnia infections were most common during the warmest periods of the year and that infected individuals tended to accumulate in deep water. Population models, parameterized with experimental and literature data, correctly predicted the timing of Saprolegnia epizootics, but overestimated the negative effect of warming on E.baikalensis populations. Models suggest that diel vertical migration may allow E. baikalensis to escape the negative effects of increasing temperatures and parasitism and enable E. baikalensis to persist as Lake Baikal warms. Our results contribute to understanding of how multiple interacting stressors affect warming pelagic ecosystems of cold lakes and oceans and show that the population-level consequences of thermal mismatch between hosts and parasites can vary seasonally, interannual and spatially.

Interannual fluctuations in the abundance of young-of-the-year (YOY) European perch (Perca fluviatilis) were studied in two large French peri-alpine lakes. Using a 12-year dataset of late-summer hydroacoustic surveys, we quantified YOY perch densities and explored their relationship with environmental drivers through Generalized Additive Models (GAMs). Our analysis revealed a strong link between surface temperature during the embryonic phase and YOY recruitment success. Embryonic thermal conditions alone explained 44 to 88% of the variability in YOY density across lakes, confirming temperature as a key predictor of perch recruitment. In contrast, trophic factors and adult stock showed no consistent trends. These findings validate in natura the central role of spring thermal regimes in shaping recruitment and provide a framework to better understand recruitment variability under ongoing climate change.

O_LIPredators are frequently observed to cause evolutionary responses in prey phenotypes, which may, in turn, translate into evolutionary shifts in prey population dynamics. Although a link between predation and population growth has been demonstrated in experimental evolution studies, insights from natural populations are lacking. C_LIO_LIHere we tested for evolutionary changes in the population dynamics of the herbivorous water flea Daphnia pulicaria in response to the invasion of the predatory spiny water flea (Bythotrephes longimanus) in the Great Lakes region, USA. Using a resurrection ecological approach and a 3-month population growth experiment (in the absence of predation) we compared population dynamics in daphnia from pre- and post-invasion time periods. C_LIO_LIPost-invasion daphnia were able to maintain an overall higher population abundance throughout the growth experiment, both in terms of the number of individuals (28% higher) and total population biomass (33% higher). Estimation of population dynamics parameters from a theta-logistic model suggested that this was achieved through an increase in intrinsic population growth rate as well as increased carrying capacity. C_LIO_LIThe observed difference in intrinsic rate of increase could not be predicted based on previous measurements of life-history traits in these clones. This indicates that care should be taken when extrapolating from a few life history traits measured in isolated individuals under controlled conditions to population dynamics. C_LIO_LIWhereas previous experimental evolution studies of predator-prey interactions have demonstrated that genotypes that have evolved under predation have inferior population growth when the predator is absent, this was not the case for the Daphnia. We suggest that complexities in ecological interactions of natural ecosystems, such as the potential for spatial and temporal avoidance of predation, makes it challenging to provide general predictions about evolutionary responses in population dynamics to predators. C_LI

The Laurentian Great Lakes (LGL) formed following the retreat of the Wisconsin glaciation 15-9 ka and provided a vast volume of freshwater habitat for coregonines, which included a diverse endemic complex of ciscoes. However, anthropogenic impacts in the 19th and 20th centuries resulted in declines and losses of ciscoes, leaving only Lake Superior with a relatively intact complex that still dominates its prey fish community. In the 1920s, W. Koelz described six putative cisco species from Lake Superior: Coregonus artedi, C. hoyi, C. kiyi, C. zenithicus, C. reighardi, and C. nigripinnis. Of these, artedi, hoyi and kiyi remain extant and abundant in Lake Superior, zenithicus is considered extirpated throughout the LGL except in Lake Superior, and reighardi and nigripinnis are considered extinct and had been synonymized as zenithicus in Lake Superior. Using an integration of morphological and genetic approaches, we present results reaffirming the presence of artedi, hoyi, and kiyi, and new evidence for the presence of reighardi, a species thought to be extinct. Our analysis did not elucidate the presence of zenithicus and nigripinnis, leaving their status unresolved. The principal morphological characters that discriminate artedi, hoyi, kiyi, and reighardi are related to habitat and trophic (ecological) specialization and foster niche segregation: eye size, gill raker length, and gill raker spacing, the same as those that foster niche segregation in subarctic European whitefishes. The discovery of reighardi is expected to stimulate new interest in the development of conservation and restoration plans for rare and imperiled cisco species in the LGL and other freshwater lakes throughout the Northern Hemisphere, and our integrated morphological and genetic approach can benefit these efforts by providing insights for the evolution, diversity, and ecology of ciscoes.

Dissolved organic carbon (DOC) concentrations in many freshwater ecosystems of the northern hemisphere have increased in recent decades due to additional terrestrial inputs. This phenomenon, known as brownification, can strongly alter the physical, chemical, and biological traits of aquatic ecosystems. Extreme rainfall can also cause sudden brownification, known as blackwater events in rivers, while longer term effects on lakes are unknown. Here, we investigated the resilience of a small, temperate, shallow lake to a strong natural flooding-induced brownification event in 2011-2012. From initial DOC and total phosphorus (TP) concentrations of ~12 and 0.04 mg L-1, respectively, the lake rapidly reached peak DOC and TP concentrations of 60 and 0.35 mg L-1, respectively. By the following year, water levels had returned close to initial values, yet two additional years of monitoring (until summer 2015) and a more recent sample in spring 2019 showed that the lake did not fully return to its pre-brownification state. Instead, DOC and TP concentrations plateaued at concentrations respectively 1.5-fold and twofold greater than pre-brownification values within less than two years and remained at these concentrations in spring 2019. During this initial recovery period the lake exhibited a decline of phytoplankton and a partial recovery of summer periphyton biomass and production, albeit a full return to pre-brownification values was not recorded in either case. DOC and TP concentrations were positively correlated to phytoplankton biomass and negatively to periphyton. As increases in phytoplankton production outpaced decreasing periphyton production, the net result of this brownification event has been an increase in whole-lake areal summertime primary production. This incomplete resilience to a flooding-induced brownification event implies consequences for several ecological and biogeochemical functions of shallow lakes that warrant further investigation and might contribute to the gradual increase of freshwater DOC concentrations in the northern hemisphere.

AbstractThe Metabolic Theory of Ecology (MET) and the Ecological Stoichiometry Theory (EST) are central and complementary in the consumer-driven recycling conceptual basis. The comprehension of physiological processes of organisms at different levels of organizations is essential to explore and predict nutrient recycling behavior in different scenarios, and to design integrated productive systems that efficiently use the nutrient inputs through an adjusted mass balance. We fed with fish-feed three species of decapods from different families and with aquacultural potential to explore the animal-mediated nutrient dynamic and its applicability in productive systems. We tested whether physiological (body mass, body elemental content), ecological (diet), taxonomic and experimental (time of incubation) variables predicts N and P excretion rates and ratios across and within taxa. We also analysed body mass and body elemental content independently as predictors of N and P excretion of decapods across, among and within taxa. Finally, we verified if body content scales allometrically across and within taxa and if differed among taxa. Body mass and taxonomic identity predicted nutrient excretion rates both across and within taxa. When physiological variables were analysed independently, body size best predicted nutrient mineralization in both scales of analyses. Regarding body elemental content, only body P content scaled negatively with body mass across taxa. Results showed higher N-requirements and lower C:N of prawns than anomurans and crabs. The role of crustaceans as nutrient recyclers depends mainly on the species and body mass, and should be considered to select complementary species that efficiently use feed resources. Prawns need more protein in their feed and might be integrated with fish of higher N-requirements, while crabs and anomurans, with fish of lower N-requirements. Our study contributed to the background of MTE and EST through empirical data obtained from decapods and provided useful information to achieve more efficient aquaculture integration systems.

Unionoid freshwater mussels (Bivalvia: Unionidae) are free-living apart from a brief, obligately parasitic, larval stage that infects fish hosts and gravid female mussels have evolved a spectrum of strategies to infect fish hosts with their larvae. In many North American species, this involves displaying a mantle lure: a pigmented fleshy extension that acts as an aggressive mimic of a host fish prey, thereby eliciting a feeding response that results in host infection. The mantle lure of Lampsilis fasciola is of particular interest because it is apparently polymorphic, with two distinct primary lure phenotypes. One, described as "darter-like", has "eyespots", a mottled body coloration, prominent marginal extensions, and a distinct "tail". The other, described as "worm-like", lacks those features and has an orange and black coloration. We investigated this phenomenon to 1) confirm that it is a true polymorphism; 2) investigate its ecological persistence; 3) identify the range of putative model species targeted by this mimicry system within a river drainage; 4) determine whether the mantle lure polymorphism includes a behavioral component. Detection of within-brood lure variation and within-population phylogenomic (ddRAD-seq) analyses of individuals bearing different lures confirmed that this phenomenon is a true polymorphism. It appears stable over ecological timeframes: the ratio of the two lure phenotypes in a River Raisin (MI) population in 2017 was consistent with that of museum samples collected at the same site 6 decades earlier. Within the River Raisin, four main "darter-like" lure motifs visually approximated four co-occurring darter species (Etheostoma blennioides, E. exile, E. microperca, and Percina maculata) and the "worm-like" lure resembled a widespread common leech, Macrobdella decora. Darters and leeches are typical prey of Micropterus dolomieui (smallmouth bass), the primary fish host of L. fasciola. In situ field recordings were made of the L. fasciola "darter" and "leech" lure display behaviors, in addition to the non-polymorphic lure display of co-occurring L. cardium. Despite having putative models in distinct phyla, both L. fasciola lure morphs have similar display behaviors that differ significantly from that of sympatric L. cardium individuals. We conclude that the L. fasciola mantle lure polymorphism does not include a behavioral component. Discovery of discrete within-brood inheritance of the lure polymorphism implies potential control by a single genetic locus and identifies L. fasciola as a promising study system to identify regulatory genes controlling a key adaptive trait of freshwater mussels.