Aquatic Ecotones Research Articles

Riverscape Genomics Clarifies Neutral and Adaptive Evolution in an Amazonian Characin Fish (Triportheus albus)

Understanding the role of natural selection in the evolution of wild populations is challenging due to the spatial complexity of natural systems. The richest diversity of freshwater fishes in the world is found in the Amazon Basin, a system where marked hydrochemical differences exist at the interface of major rivers with distinct “water colors” (i.e., black, white, and clear water). We hypothesize that divergent natural selection associated with these “aquatic ecotones” influences population-level adaptive divergence in the non-migratory Amazonian fish fauna. This hypothesis was tested using a landscape genomics framework to compare the relative contribution of environmental and spatial factors to the evolutionary divergence of the Amazonian characin fishTriportheus albus. The framework was based on spatial data,in situhydrochemical measurements, and 15,251 filtered SNPs (single nucleotide polymorphisms) forT. albussampled from three major Amazonian rivers. Gradient Forest, redundancy analysis (RDA) and BayPass analyses were used to test for signals of natural selection, and model-based and model-free approaches were used to evaluate neutral population differentiation. After controlling for a signal of neutral hierarchical structure which was consistent with the expectations for a dendritic system, variation in turbidity and pH were key factors contributing to adaptive divergence. Variation in genes involved in acid-sensitive ion transport pathways and light-sensitive photoreceptor pathways was strongly associated with pH and turbidity variability. This study improves our understanding of how natural selection and neutral evolution impact on the distribution of aquatic biodiversity from the understudied and ecologically complex Amazonia.

Interactions at surface-subterranean ecotones: structure and function of food webs within spring orifices.

Spring orifices are ecotones between surface and subterranean aquatic ecosystems. Invertebrates of different origins (e.g., surface, spring obligate, and subterranean) coexist in these spatially restricted environments, potentially competing for resources. However, processes that allow for population coexistence in these presumably low resource environments are not well understood. We examined invertebrate communities at two spring complexes in Texas, USA and assessed resource use and food web structure at spring orifices using stable isotopes of carbon (δ13C) and nitrogen (δ15N). Using bulk δ13C and δ15N of organisms and potential food sources, we elucidated dietary sources and found that invertebrate communities exhibited resource partitioning and contained two main food chains (periphyton versus terrestrial organic matter [OM]). In both spring complexes, several endemic spring orifice associated and subterranean taxa derived most of their diet from terrestrial OM. Analysis of compound-specific stable isotopes (i.e., δ13C of essential amino acids, EAAs) from two co-occurring elmid species indicated that the endemic spring orifice-associated species (Heterelmis comalensis) derived > 80% of its EAAs from bacteria, whereas the widespread surface species (Microcylloepus pusillus) derived its EAAs from a more equitable mix of bacteria, fungi, and algae. We additionally calculated niche overlap among of several taxonomically related groups (aquatic beetles and amphipods) that co-occur in spring ecotones and posterior probability estimates indicated little to no niche overlap among related species. Results indicate that invertebrates at subterranean-surface aquatic ecotones are partitioning food resources and highlight the importance of connections to riparian zones for persistence of several endemic invertebrates.

Reservoir fish assemblage structure across an aquatic ecotone: Can river‐reservoir interfaces provide conservation and management opportunities?

AbstractRiver‐reservoir interfaces have been described as aquatic ecotones and contain strong environmental gradients of depth, turbidity and trophic resource abundance. These transitional habitats have traditionally been excluded by riverine and reservoir management schemes despite their prevalence in modern riverscapes. By systematically sampling shoreline habitats along a river‐reservoir interface gradient from riverine to lacustrine zones with trammel nets in 2018–2019, strong patterns were identified in total species captured and individuals captured in the San Juan River‐Lake Powell inflow, USA. Changes in assemblage structure were driven mainly by increases in relative abundance of benthic omnivores towards the riverine zone, including imperiled razorback sucker, Xyrauchen texanus (Abbott), but also by increases in predatory species, such as striped bass, Morone saxatilis (Walbaum). Inter‐annual variation in species distributions along the river‐reservoir interface gradient was likely influenced by variation in reservoir water level that differed by nearly 12 m between years. River‐reservoir interfaces provide high‐quality feeding and potentially spawning areas for both benthic omnivores and piscivores, and these areas should be considered in management and conservation efforts for species using these habitats.

Infection at an ecotone: cross-system foraging increases satellite parasites but decreases core parasites in raccoons.

Ecotones can increase free-living species richness, but little is known about how parasites respond to ecotones. Here, we use parasite communities in raccoons (Procyon lotor) to test the hypothesis that parasite communities can be divided into core and satellite species, each with fundamentally different responses to ecotones. We used published parasite surveys to classify parasites as common core or rare satellite species, and then surveyed raccoons in coastal California to examine how proximity to two aquatic ecotones altered parasite communities. Raccoons near ecotones had more satellite and fewer core parasite species. Specifically, the marine ecotone increased parasite diversity by adding satellite species to a persistent core community, whereas the freshwater ecotone shifted the community from core to satellite species without a net change in parasite richness. We hypothesize that increased parasite richness at the marine ecotone resulted from increased diet diversity, but that raccoons were sinks for some parasites. Increased exposure to rare parasites at ecotones has implications for wildlife health and provides insight into observed associations between ecotones and emerging disease.

Shifts in dragonfly community structure across aquatic ecotones

Dragonflies (Odonata: Anisoptera) are often used as indicators of habitat type and quality due to their varied use of aquatic and terrestrial habitats. Species differ in their preferences for lotic...

Limno-ecological characteristics and distribution patterns of spring habitats and invertebrates from the Lowlands to the Alps

Springs are autochthonous aquatic ecotones with complex functional properties and heterogeneous eco-morphological structures. Within a small spatial extent, invertebrates are highly diverse and mainly composed of species adapted to the surface–subterranean water interface, the aquatic–terrestrial interface or to the spring habitat itself. In this publication, a first synopsis of limno-ecological case studies of springs from the Lowlands of Schleswig-Holstein, the low mountain ranges of Hesse and Thuringia, the pre-Alps of the Jura Mountains in Switzerland and the Alps in Germany and Switzerland is presented. The field surveys conducted in the different areas focus on an ecological assessment of spring habitats, distribution patterns of the invertebrate fauna and specific regional characteristics. A regional faunistic differentiation of spring-related invertebrate species is evident. A change in the faunistic composition in general and a loss of crenobionts owing to climatic and land-use changes are expected. In addition, it should be noted that long-term monitoring data required to make reliable statements about future developments in the distribution of spring species and to predict habitat conditions are not available.

The specifics of the terrestrial–aquatic ecotone of the north Dagestan seacoast

Four blocks of terrestrial–aquatic ecotones, namely, aquatic, fluctuation, dynamic, and distant ecotones, have been distinguished and characterized. The blocks are differentiated in space and time and represent a complete formation. This is proved by species saturation at the level of the modern structure and previous area genetic relations.

Aquatic ecotones-new insights from Arctic Canada.

Aquatic ecotones-new insights from Arctic Canada.

Earliest evidence for the use of pottery

Pottery was a hunter-gatherer innovation that first emerged in East Asia between 20,000 and 12,000 calibrated years before present (cal bp), towards the end of the Late Pleistocene epoch, a period of time when humans were adjusting to changing climates and new environments. Ceramic container technologies were one of a range of late glacial adaptations that were pivotal to structuring subsequent cultural trajectories in different regions of the world, but the reasons for their emergence and widespread uptake are poorly understood. The first ceramic containers must have provided prehistoric hunter-gatherers with attractive new strategies for processing and consuming foodstuffs, but virtually nothing is known of how early pots were used. Here we report the chemical analysis of food residues associated with Late Pleistocene pottery, focusing on one of the best-studied prehistoric ceramic sequences in the world, the Japanese Jōmon. We demonstrate that lipids can be recovered reliably from charred surface deposits adhering to pottery dating from about 15,000 to 11,800 cal bp (the Incipient Jōmon period), the oldest pottery so far investigated, and that in most cases these organic compounds are unequivocally derived from processing freshwater and marine organisms. Stable isotope data support the lipid evidence and suggest that most of the 101 charred deposits analysed, from across the major islands of Japan, were derived from high-trophic-level aquatic food. Productive aquatic ecotones were heavily exploited by late glacial foragers, perhaps providing an initial impetus for investment in ceramic container technology, and paving the way for further intensification of pottery use by hunter-gatherers in the early Holocene epoch. Now that we have shown that it is possible to analyse organic residues from some of the world's earliest ceramic vessels, the subsequent development of this critical technology can be clarified through further widespread testing of hunter-gatherer pottery from later periods.

Composition Influences the Pathway but not the Outcome of the Metabolic Response of Bacterioplankton to Resource Shifts

Bacterioplankton community metabolism is central to the functioning of aquatic ecosystems, and strongly reactive to changes in the environment, yet the processes underlying this response remain unclear. Here we explore the role that community composition plays in shaping the bacterial metabolic response to resource gradients that occur along aquatic ecotones in a complex watershed in Québec. Our results show that the response is mediated by complex shifts in community structure, and structural equation analysis confirmed two main pathways, one involving adjustments in the level of activity of existing phylotypes, and the other the replacement of the dominant phylotypes. These contrasting response pathways were not determined by the type or the intensity of the gradients involved, as we had hypothesized, but rather it would appear that some compositional configurations may be intrinsically more plastic than others. Our results suggest that community composition determines this overall level of community plasticity, but that composition itself may be driven by factors independent of the environmental gradients themselves, such that the response of bacterial communities to a given type of gradient may alternate between the adjustment and replacement pathways. We conclude that community composition influences the pathways of response in these bacterial communities, but not the metabolic outcome itself, which is driven by the environment, and which can be attained through multiple alternative configurations.

Aquatic Biota and the Detection of Climate Change: Are there Consistent Aquatic Ecotones?

In this study, we analyse the cumulative rate of compositional change along an altitudinal gradient in the Swiss Alps for three different groups of aquatic organisms – Cladocera, chironomids, and diatoms. In particular, we are interested in the magnitude of unusually large changes in species composition that allows the detection of critical ecotones for each of these three organism groups. The estimated rate-of-change is the distance in ordination space using principal coordinate analysis based on chord distance and chi-square distance. These analyses highlight the cumulative rate-of-change and the cumulative relative rate-of-change, as the chi-square distance is relative to the total species composition. We found that the major changes in taxonomic composition for the three organism groups and therefore also the major ecotones are just below the modern tree-line (1900–2000 m a.s.l.), which may indirectly be an effect of the tree-line. For diatoms and Cladocera (only chi-square distance) there is also an ecotone at 2055 m a.s.l., which may be a direct or indirect response to climate. Further, the ecotone region below the modern tree-line is much wider for chironomids, with an extension downwards due to a shift in relative abundance patterns. For diatoms there is a stronger rate-of-change above 1650 m a.s.l. when chi-square distance is used. Coupled with the even distribution of diatom richness, this suggests that at higher altitudes the change is more strongly associated with a few species becoming dominant compared to lower elevations. Hence, there are considerable differences among the three organism groups, suggesting that different environmental factors may influence the rates of compositional change within and among groups. This supports the general usefulness of multi-proxy studies, namely the study of several independent groups of organisms to reconstruct past environmental conditions but also points to the importance of careful site selection in such studies.

An Assemblage of Salamanders in the Southern Appalachian Mountains: Competitive and Predatory Behavior

Abstract We conducted behavioral experiments to determine how competition and predation may affect an assemblage of salamanders that meet at and cross forest to aquatic ecotones. At Mountain Lake Biological Station, southwestern Virginia, USA, adults of four abundant species interact at the forest to stream ecotone. Plethodon einereus and the larger P. glutinosus inhabit the forest floor up to the edges of streams while Desmognathus fuscus and Eurycea eirrigera forage from the edges of streams onto the forest floor. Our six laboratory experiments yielded predictions as to how these species affect each others' distributions and abundances in the natural habitats. Previous studies showed that adults of P. cine reus are territorial intraspecifically and toward same-size juveniles of P. glutinosus. In our experiment, territorial residents of P. einereus did not act aggressively toward intruding adults of P. glutinosus and the latter species was neither aggressive nor predatory toward P. einereus. The two species were equally benign in a second experiment when the roles of resident and intruder were reversed. Thus, we predict that the adults of these two species do not influence each others' distributions on the forest floor.

Macrophytes, hydrology, and aquatic ecotones: a GIS-supported ecological survey

The detection of macrophyte-dependent ecotones, the characterization of different hydrological regimes and aspects of sports fishing activities were the main objectives studied in a backwater system of the River Danube in Austria. The macrophyte survey, a dynamic hydrological model and a socio-economic study were all part of the Austrian Ecotone Project. Conclusions were drawn from this database by GIS thematic map interpretation and overlay techniques. Significant transitions existed between stretches of macrophyte vegetation as far as species number and plant mass are concerned. These transitions can be attributed as macrophyte-dependent aquatic/aquatic ecotones. Some plant species and the structural diversity of the aquatic vegetation were found to be characteristic for backwater reaches with different hydrological regimes. In contrast to a hypothesis worked out earlier in the ecotone project the GIS overlays revealed spatial coincidence between the centres of sports fishing activities and survey stretches with high densities of macrophyte vegetation.