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Manipulation of host phenotypes by parasites is hypothesized to be an adaptive strategy enhancing parasite transmission across hosts and generations. Characterizing the molecular mechanisms of manipulation is important to advance our understanding of host–parasite coevolution. The trematode (Levinseniella byrdi) is known to alter the colour and behaviour of its amphipod host (Orchestia grillus) presumably increasing predation of amphipods which enhances trematode transmission through its life cycle. We sampled 24 infected and 24 uninfected amphipods from a salt marsh in Massachusetts to perform differential gene expression analysis. In addition, we constructed novel genomic tools forO. grillusincluding a de novo genome and transcriptome. We discovered that trematode infection results in upregulation of amphipod transcripts associated with pigmentation and detection of external stimuli, and downregulation of multiple amphipod transcripts implicated in invertebrate immune responses, such as vacuolar ATPase genes. We hypothesize that suppression of immune genes and the altered expression of genes associated with coloration and behaviour may allow the trematode to persist in the amphipod and engage in further biochemical manipulation that promotes transmission. The genomic tools and transcriptomic analyses reported provide new opportunities to discover how parasites alter diverse pathways underlying host phenotypic changes in natural populations.

 

Nutrient enrichment impacts ecosystems globally. Population history, especially past resource environments, of numerically dominant plant species may affect their responses to subsequent changes in nutrient availability. Eutrophication can also alter plant–microbe interactions via direct effects on associated microbial communities or indirect effects on dominant species’ biomass production/allocation as a result of modified plant–soil interactions.

We combined a greenhouse common garden and a field reciprocal transplant of a salt marsh foundation species (Spartina alterniflora) within a long‐term, whole‐ecosystem, nutrient‐enrichment study to determine whether enrichment affects plant production and microbial community structure differently depending on plant population history. For the greenhouse portion, we collected 20S. alternifloragenotypes—10 from an enriched creek that had received elevated nutrient inputs for 10 years and 10 from an unenriched reference creek—and reared them in a common garden for 1 year. For the field portion, we conducted a 2‐year, fully crossed reciprocal transplant experiment with two gardens each at the enriched and unenriched sites; we examined the effects of source site (i.e. population history), garden site and plant genotype.

After 2 years, plants in enriched gardens had higher above‐ground biomass and altered below‐ground allocation compared to plants in unenriched gardens. However, performance also depended on plant population history: plants from the enriched site had decreased above‐ground and rhizome production compared to plants from the unenriched site, most notably in unenriched gardens. In addition, almost all above‐ and below‐ground traits varied depending on plant genotypic identity.

Effects of nutrient enrichment on the associated microbial community were also pronounced. Following 1 year in common garden, microbial community structure varied by plant population history andS. alternifloragenotypic identity. However, at the end of the reciprocal transplant, microbial communities differed primarily between enriched and unenriched gardens.

Synthesis. Nutrient enrichment can impact plant foundation species and associated soil microbes in the short term. Most importantly, nutrient enrichment can also have long‐lasting effects on plant populations and associated microbial communities that potentially compromise their ability to respond to changing resource conditions in the future.

 

Global change is impacting plant community composition, but the mechanisms underlying these changes are unclear. Using a dataset of 58 global change experiments, we tested the five fundamental mechanisms of community change: changes in evenness and richness, reordering, species gains and losses. We found 71% of communities were impacted by global change treatments, and 88% of communities that were exposed to two or more global change drivers were impacted. Further, all mechanisms of change were equally likely to be affected by global change treatments—species losses and changes in richness were just as common as species gains and reordering. We also found no evidence of a progression of community changes, for example, reordering and changes in evenness did not precede species gains and losses. We demonstrate that all processes underlying plant community composition changes are equally affected by treatments and often occur simultaneously, necessitating a wholistic approach to quantifying community changes.

 

Salt marshes sequester carbon at rates more than an order of magnitude greater than their terrestrial counterparts, helping to mitigate climate change. As nitrogen loading to coastal waters continues, primarily in the form of nitrate, it is unclear what effect it will have on carbon storage capacity of these highly productive systems. This uncertainty is largely driven by the dual role nitrate can play in biological processes, where it can serve as a nutrient‐stimulating primary production or a thermodynamically favorable electron acceptor fueling heterotrophic metabolism. Here, we used a controlled flow‐through reactor experiment to test the role of nitrate as an electron acceptor, and its effect on organic matter decomposition and the associated microbial community in salt marsh sediments. Organic matter decomposition significantly increased in response to nitrate, even at sediment depths typically considered resistant to decomposition. The use of isotope tracers suggests that this pattern was largely driven by stimulated denitrification. Nitrate addition also significantly altered the microbial community and decreased alpha diversity, selecting for taxa belonging to groups known to reduce nitrate and oxidize more complex forms of organic matter. Fourier Transform‐Infrared Spectroscopy further supported these results, suggesting that nitrate facilitated decomposition of complex organic matter compounds into more bioavailable forms. Taken together, these results suggest the existence of organic matter pools that only become accessible with nitrate and would otherwise remain stabilized in the sediment. The existence of such pools could have important implications for carbon storage, since greater decomposition rates as N loading increases may result in less overall burial of organic‐rich sediment. Given the extent of nitrogen loading along our coastlines, it is imperative that we better understand the resilience of salt marsh systems to nutrient enrichment, especially if we hope to rely on salt marshes, and other blue carbon systems, for long‐term carbon storage.

 

Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation‐funded Long‐Term Ecological Research (LTER) network addressing the core research area of “populations and communities.” The objective of this effort was to show the importance of long‐term data collection and experiments for addressing the hardest questions in scientific ecology that have significant implications for environmental policy and management. Each LTER site developed at least one compelling case study about what their site could look like in 50–100 yr as human and environmental drivers influencing specific ecosystems change. As the case studies were prepared, five themes emerged, and the studies were grouped into papers in this LTER Futures Special Feature addressing state change, connectivity, resilience, time lags, and cascading effects. This paper addresses the “connectivity” theme and has examples from the Phoenix (urban), Niwot Ridge (alpine tundra), McMurdo Dry Valleys (polar desert), Plum Island (coastal), Santa Barbara Coastal (coastal), and Jornada (arid grassland and shrubland) sites. Connectivity has multiple dimensions, ranging from multi‐scalar interactions in space to complex interactions over time that govern the transport of materials and the distribution and movement of organisms. The case studies presented here range widely, showing how land‐use legacies interact with climate to alter the structure and function of arid ecosystems and flows of resources and organisms in Antarctic polar desert, alpine, urban, and coastal marine ecosystems. Long‐term ecological research demonstrates that connectivity can, in some circumstances, sustain valuable ecosystem functions, such as the persistence of foundation species and their associated biodiversity or, it can be an agent of state change, as when it increases wind and water erosion. Increased connectivity due to warming can also lead to species range expansions or contractions and the introduction of undesirable species. Continued long‐term studies are essential for addressing the complexities of connectivity. The diversity of ecosystems within the LTER network is a strong platform for these studies.

 

Abstract A parasite can change its host’s behavior in spectacular ways. When the saltmarsh amphipod Orchestia grillus (Bosc, 1802) is infected with the trematode Levinseniella byrdi (Heard, 1968) it is bright orange and is found in the open unlike uninfected individuals. I tested the hypothesis that infected amphipods are found in the open because L. byrdi reverses their innate photophobia. During daytime treatments and when placed in a dark chamber, 0% of the uninfected and 20% of the infected amphipods, on average, moved to the light chamber after 30 minutes. When placed in a light chamber, 91% of the uninfected and 53% of the infected amphipods, on average, went to the dark side after 30 minutes. These results clearly indicate that O. grillus is normally photophobic, but not drawn to light when infected with L. byrdi. Instead, L. byrdi appears to neutralize the amphipod’s photophobia. Uninfected O. grillus are typically found under vegetation. I hypothesize that O. grillus with L. byrdi infections wander into open, unvegetated habitats randomly. In addition, 94% of infected amphipods could be touched by a finger in the field suggesting they can be easily caught by predators. Levinseniella byrdi infects at least three other amphipod hosts, Chelorchestia forceps (Smith & Heard, 2001), Uhlorchestia spartinophila (Bousfield & Heard, 1986), and U. uhleri (Shoemaker, 1930). The parasite-manipulation hypothesis suggests that the parasite-induced changes (conspicuous body color and neutralized light response) are adaptive for L. byrdi to make amphipod hosts more susceptible to bird predators, the definitive hosts. This hypothesis remains to be tested. 

The use of nutrients by diverse phytoplankton communities in estuarine systems, and their response to changes in physical and biogeochemical processes in these natural systems, is a significant ongoing area of research. We used a whole ecosystem 15NO3− tracer experiment to determine the uptake of different nitrogen (N) forms in phytoplankton functional groups over a mid- to neap tidal cycle in a salt marsh creek in Plum Island Estuary, Massachusetts, USA. We quantified the biomass and δ15N for three groups corresponding to micro- (20–200 μm; microP), nano- (3–20 μm; nanoP), and picophytoplankton (< 3 μm; picoP). All three size classes showed distinct use of recycled N sources throughout the 11-day sampling period and minimal direct assimilation of the 15NO3− tracer. MicroP consistently used high amounts of creek-derived 15NH4+, even with a shift at neap tide from diatom- to dinoflagellate-dominated communities (including members of the harmful genus Alexandrium). NanoP use of recycled 15NH4+ increased over the mid-neap tidal cycle, while picoP use decreased. Both biomass and NH4+ use (as highest δ15N values) of all size groups were maximized during neap tide. This study demonstrates partitioning of recycled N use among size-based phytoplankton groups in the estuary, with distinct effects of tidal cycle on the nutrient uptake of each group, and with important implications for the roles of diverse phytoplankton communities in estuarine nutrient cycling.