Cascading effects of caffeine intake by primary consumers to the upper trophic level

Secondary metabolites are central to understanding the evolution of plant–animal interactions. Direct effects on phytophagous animals are well-known, but how secondary consumers adjust their behavioural and physiological responses to the herbivore's diet remains more scarcely explored for some metabolites. Caffeine is a neuroactive compound that affects both the behaviour and physiology of several animal species, from humans to insects. It is an alkaloid present in nectar, leaves and even sap of numerous species of plants where it plays a role in chemical defences against herbivores and pathogens. Caffeine effects have been overlooked in generalist herbivores that are not specialized in coffee or tea plants. Using a host–parasitoid system, we show that caffeine intake at a relatively low dose affects longevity and fecundity of the primary consumer, but also indirectly of the secondary one, suggesting that this alkaloid and/or its effects can be transmitted through trophic levels and persist in the food chain. Parasitism success was lowered by ≈16% on hosts fed with caffeine, and parasitoids of the next generation that have developed in hosts fed on caffeine showed a reduced longevity, but no differences in mass and size were found. This study helps at better understanding how plant secondary metabolites, such as caffeine involved in plant–animal interactions, could affect primary consumers, could have knock-on effects on upper trophic levels over generations, and could modify interspecific interactions in multitrophic systems.

Abyssal deposit feeders are secondary consumers of detritus and rely on nutrition derived from microbial communities in their guts

Trophic ecology of detrital-based food webs is still poorly understood. Abyssal plains depend entirely on detritus and are among the most understudied ecosystems, with deposit feeders dominating megafaunal communities. We used compound-specific stable isotope ratios of amino acids (CSIA-AA) to estimate the trophic position of three abundant species of deposit feeders collected from the abyssal plain of the Northeast Pacific (Station M; ~ 4000 m depth), and compared it to the trophic position of their gut contents and the surrounding sediments. Our results suggest that detritus forms the base of the food web and gut contents of deposit feeders have a trophic position consistent with primary consumers and are largely composed of a living biomass of heterotrophic prokaryotes. Subsequently, deposit feeders are a trophic level above their gut contents making them secondary consumers of detritus on the abyssal plain. Based on δ13C values of essential amino acids, we found that gut contents of deposit feeders are distinct from the surrounding surface detritus and form a unique food source, which was assimilated by the deposit feeders primarily in periods of low food supply. Overall, our results show that the guts of deposit feeders constitute hotspots of organic matter on the abyssal plain that occupy one trophic level above detritus, increasing the food-chain length in this detritus-based ecosystem.

Selective Fatty Acid Retention and Turnover in the Freshwater Amphipod Pallaseopsis quadrispinosa

Gammarid amphipods are a crucial link connecting primary producers with secondary consumers, but little is known about their nutritional ecology. Here we asked how starvation and subsequent feeding on different nutritional quality algae influences fatty acid retention, compound-specific isotopic carbon fractionation, and biosynthesis of ω-3 and ω-6 polyunsaturated fatty acids (PUFA) in the relict gammarid amphipod Pallaseopsis quadrispinosa. The fatty acid profiles of P. quadrispinosa closely matched with those of the dietary green algae after only seven days of refeeding, whereas fatty acid patterns of P. quadrispinosa were less consistent with those of the diatom diet. This was mainly due to P. quadrispinosa suffering energy limitation in the diatom treatment which initiated the metabolization of 16:1ω7 and partly 18:1ω9 for energy, but retained high levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) similar to those found in wild-caught organisms. Moreover, α-linolenic acid (ALA) from green algae was mainly stored and not allocated to membranes at high levels nor biosynthesized to EPA. The arachidonic acid (ARA) content in membrane was much lower than EPA and P. quadrispinosa was able to biosynthesize long-chain ω-6 PUFA from linoleic acid (LA). Our experiment revealed that diet quality has a great impact on fatty acid biosynthesis, retention and turnover in this consumer.

A Low-Pressure, N2/CO2 Atmosphere Is Suitable for Cyanobacterium-Based Life-Support Systems on Mars

The leading space agencies aim for crewed missions to Mars in the coming decades. Among the associated challenges is the need to provide astronauts with life-support consumables and, for a Mars exploration program to be sustainable, most of those consumables should be generated on site. Research is being done to achieve this using cyanobacteria: fed from Mars's regolith and atmosphere, they would serve as a basis for biological life-support systems that rely on local materials. Efficiency will largely depend on cyanobacteria's behavior under artificial atmospheres: a compromise is needed between conditions that would be desirable from a purely engineering and logistical standpoint (by being close to conditions found on the Martian surface) and conditions that optimize cyanobacterial productivity. To help identify this compromise, we developed a low-pressure photobioreactor, dubbed Atmos, that can provide tightly regulated atmospheric conditions to nine cultivation chambers. We used it to study the effects of a 96% N2, 4% CO2 gas mixture at a total pressure of 100 hPa on Anabaena sp. PCC 7938. We showed that those atmospheric conditions (referred to as MDA-1) can support the vigorous autotrophic, diazotrophic growth of cyanobacteria. We found that MDA-1 did not prevent Anabaena sp. from using an analog of Martian regolith (MGS-1) as a nutrient source. Finally, we demonstrated that cyanobacterial biomass grown under MDA-1 could be used for feeding secondary consumers (here, the heterotrophic bacterium E. coli W). Taken as a whole, our results suggest that a mixture of gases extracted from the Martian atmosphere, brought to approximately one tenth of Earth's pressure at sea level, would be suitable for photobioreactor modules of cyanobacterium-based life-support systems. This finding could greatly enhance the viability of such systems on Mars.

Rainfall as a trigger of ecological cascade effects in an Australian groundwater ecosystem

Groundwaters host vital resources playing a key role in the near future. Subterranean fauna and microbes are crucial in regulating organic cycles in environments characterized by low energy and scarce carbon availability. However, our knowledge about the functioning of groundwater ecosystems is limited, despite being increasingly exposed to anthropic impacts and climate change-related processes. In this work we apply novel biochemical and genetic techniques to investigate the ecological dynamics of an Australian calcrete under two contrasting rainfall periods (LR—low rainfall and HR—high rainfall). Our results indicate that the microbial gut community of copepods and amphipods experienced a shift in taxonomic diversity and predicted organic functional metabolic pathways during HR. The HR regime triggered a cascade effect driven by microbes (OM processors) and exploited by copepods and amphipods (primary and secondary consumers), which was finally transferred to the aquatic beetles (top predators). Our findings highlight that rainfall triggers ecological shifts towards more deterministic dynamics, revealing a complex web of interactions in seemingly simple environmental settings. Here we show how a combined isotopic-molecular approach can untangle the mechanisms shaping a calcrete community. This design will help manage and preserve one of the most vital but underrated ecosystems worldwide.

Effects of a diatom ecosystem engineer (Didymosphenia geminata) on stream food webs: implications for native fishes

Stream habitat changes affecting primary consumers often indirectly impact secondary consumers such as fishes. Blooms of the benthic algae Didymosphenia geminata (Didymo) are known to affect stream macroinvertebrates, but the potential indirect trophic impacts on fish consumers are poorly understood. In streams of the Kootenai River basin, we quantified the diet, condition, and growth rate of species of trout, char, and sculpin. In 2018, macroinvertebrate taxa composition was different between a stream with Didymo and a stream without, but trout diets, energy demand, and growth rates were similar. Trout abundance was higher in the stream with Didymo, but the amount of drifting invertebrates was higher in the stream without. In 2019, we surveyed 28 streams with a gradient of coverage. Didymo abundance was correlated only with the percentage of aquatic invertebrates in trout diets and was not related to diets of char or sculpin or condition of any species. Thus, we found no evidence for a trophic link between Didymo blooms and the condition or growth of trout, char, or sculpin in mountainous headwater streams.

Phenological Response in the Trophic Levels to Climate Change in Korea

The response of the phenological events of individual species to climate change is not isolated, but is connected through interaction with other species at the same or adjacent trophic level. Using long-term phenological data observed since 1976 in Korea, whose temperature has risen more steeply than the average global temperature, this study conducted phenological analysis (differ-ences in the phenology of groups, differences in phenological shifts due to climate change, differ-ences in phenological sensitivity to climate by groups, and the change of phenological day differ-ences among interacting groups). The phenological shift of the producer group (plants) was found to be negative in all researched species, which means that it blooms quickly over the years. The regression slope of consumers (primary consumers and secondary consumers) was generally posi-tive which means that the phenological events of these species tended to be later during the study period. The inter-regional deviation of phenological events was not large for any plant except for plum tree and Black locust. In addition, regional variations in high trophic levels of secondary consumers tended to be greater than that of producers and primary consumers. Among the studied species, plum was the most sensitive to temperature, and when the temperature rose by 1 °C, the flowering time of plum decreased by 7.20 days. As a result of checking the day differences in the phenological events of the interacting species, the phenological events of species were reversed, and butterflies have appeared earlier than plum, Korean forsythia, and Korean rosebay since 1990. Using long-term data from Korea, this study investigated differences in phenological reactions among trophic groups. There is a possibility of a phenological mismatch between trophic groups in the future if global warming continues due to differences in sensitivity to climate and phenological shifts between trophic levels.

Extreme Levels of Ocean Acidification Restructure the Plankton Community and Biogeochemistry of a Temperate Coastal Ecosystem: A Mesocosm Study

The oceans’ uptake of anthropogenic carbon dioxide (CO2) decreases seawater pH and alters the inorganic carbon speciation – summarized in the term ocean acidification (OA). Already today, coastal regions experience episodic pH events during which surface layer pH drops below values projected for the surface ocean at the end of the century. Future OA is expected to further enhance the intensity of these coastal extreme pH events. To evaluate the influence of such episodic OA events in coastal regions, we deployed eight pelagic mesocosms for 53 days in Raunefjord, Norway, and enclosed 56–61 m3 of local seawater containing a natural plankton community under nutrient limited post-bloom conditions. Four mesocosms were enriched with CO2 to simulate extreme pCO2 levels of 1978 – 2069 μatm while the other four served as untreated controls. Here, we present results from multivariate analyses on OA-induced changes in the phyto-, micro-, and mesozooplankton community structure. Pronounced differences in the plankton community emerged early in the experiment, and were amplified by enhanced top-down control throughout the study period. The plankton groups responding most profoundly to high CO2 conditions were cyanobacteria (negative), chlorophyceae (negative), auto- and heterotrophic microzooplankton (negative), and a variety of mesozooplanktonic taxa, including copepoda (mixed), appendicularia (positive), hydrozoa (positive), fish larvae (positive), and gastropoda (negative). The restructuring of the community coincided with significant changes in the concentration and elemental stoichiometry of particulate organic matter. Results imply that extreme CO2 events can lead to a substantial reorganization of the planktonic food web, affecting multiple trophic levels from phytoplankton to primary and secondary consumers.

Feeding Ecology of Sicydium bustamantei (Greeff 1884, Gobiidae) Post-Larvae: The “Little Fish” of São Tomé Island

The rivers of São Tomé Island are colonized by Sicydium bustamantei (Greeff 1882), an amphidromous fish that spawns in those areas. After hatching, larvae drift to the ocean with the river flow. In the marine realm, the planktonic larvae develop and migrate to freshwater as post-larvae. The migrations of post-larvae support important local fisheries at the mouth of rivers in tropical volcanic islands. Amphidromous post-larvae rely on plankton as their main source of organic matter. However, the biology and ecology of S. bustamantei in the West African islands are understudied, despite its importance for local fisheries. Thus, this study aimed to start bridging this gap by studying its feeding ecology. Our objectives were to identify the main prey of S. bustamantei post-larvae, combining gut content with stable isotope analyses. The gut contents included zooplankton (Chaetognatha, Ostracoda, and unidentified crustaceans), debris from plant and/or macroalgae-derived material, and microplastics (including microfibers). The stable isotopes analysis indicated that zooplankton and macroalgae detritus were the main sources of organic matter assimilated by this species. We also demonstrated that S. bustamantei post-larvae are omnivorous and secondary consumers. These data provide pioneering information that can be used in management plans that still need to be developed.