Peak Abundance Research Articles

In Situ Combustion Characteristics of Heavy Oil in the Liaohe Oilfield at Different Temperatures

This study conducted in situ combustion oxidation experiments on crude oil from Block D within the Liaohe Oilfield, utilizing a kettle furnace low-pressure oxidation reaction method at various temperatures. The molecular composition of oxidation products was analyzed using gas chromatography–mass spectrometry (GC–MS) and high-resolution mass spectrometry. The results reveal that the molecular composition of the products remains relatively stable up to 300 °C, exhibiting a slight increase in C13-C30 alkanes. The ratio of the peak area for C21 to bisnorhopane is 0.082. From 300 °C to 450 °C, compounds with long alkyl chains gradually undergo thermal cracking, resulting in a significant increase in the production of alkanes within the C10–C30 range. The concentration of saturated hydrocarbons produced through thermal cracking reaches its maximum at a temperature of 400 °C. The most abundant peak of n-alkane is observed at C21, with a quantified ratio of peak area for C21 to bisnorhopane at 6.5, indicating a two-order magnitude increase compared to crude oil. From 500 °C to 600 °C, compounds undergo more profound thermal cracking and condensation processes. The predominant hydrocarbons consist of aromatic molecules containing two to six rings substituted with short side chains. The double bond equivalent (DBE) values of carbazoles and carboxylic acids are determined as 30 and 25, respectively. At 600 °C, the peak area ratio of naphthalene to biodecane is 300, indicating a remarkable increase of five orders of magnitude compared to the crude oil. The present study elucidates the correlation between the characteristics of combustion components in crude oil and the corresponding combustion temperature. Primary cracking reactions within crude oil are promoted effectively when keeping the combustion zone at 350 °C and 450 °C. This process significantly reduces the viscosity of heavy oil and enhances its fluidity.

Seasonal dynamics and habitat preferences of juvenile fish assemblages in the Wanquan Estuary, South China: Implications for conservation and management

Tropical estuaries encompass diverse habitats, which are crucial for supporting juvenile fish by providing nurseries, refuges, and migration routes. In the present study, we investigated the seasonal and spatial dynamics of juvenile fish assemblages in the Wanquan Estuary, Hainan Island, China, examining variations during the wet and dry seasons across four types of habitats. Our research aimed to test the hypotheses: (1) the wet season supports a greater abundance and species richness of juvenile fish compared to the dry season, and (2) juvenile fish showed varying habitat preferences across seasons. We recorded a total of 3617 individuals belonging to 33 families, 50 genera, and 78 taxa. Our findings revealed significant seasonal fluctuations in the assemblage structure, with peak abundance during the wet season in August, primarily consisting of diadromous species. A notable shift towards marine species was observed in March. Spatially, juvenile fish exhibited significant habitat preferences, with a strong preference for sand substrates for most species. Contrary to common expectations, mangrove fringe habitats were not identified as the primary nursery grounds for juvenile fish. Instead, our study highlights the importance of habitat diversity and connectivity in enhancing nursery functions. Water temperature and salinity were the key drivers influencing the seasonal and temporal patterns of juvenile fish assemblages in the Wanquan River estuary The pronounced temporal dynamics of these assemblages, driven by seasonal environmental alterations affecting water variations and habitat connectivity, were more significant than spatial differences. The findings emphasize the need for focused connectivity of various habitats to support the conservation of diverse fish communities in tropical estuarine ecosystems.

ECOLOGICAL AND FAUNAL REVIEW RHOPALOCERA IN THE TERRITORY OF THE SOUTH-EASTERN PART OF THE CRIMEA

The research results provided original data on the Rhopalocera species composition, ecological and biological features, and Rhopalocera population structure, of the south-eastern part of the peninsula, which live in some open biocenoses. The role of Rhopalocera representatives in the ecosystem is twofold: representatives of the family act as pests at some stages of development, and as beneficial pollinators of flowering plants at others, which affects the development of the ecosystem as a whole. In the studied territory of the southeastern part of Crimea, 36 species of Lepidoptera were found. The studied fauna of Rhopalocera included 5 species listed in the Red Data Book of Ukraine. One species of the family Lycaenidae is listed in the Red Data Butterflies Book of Europe. Of the studied inpatients the most densely inhabited biotopes a juniper grove, meadows, and a steppe area turned out to be. By the number of species, the largest trophic group among the detected ones was the group of oligophagous. Four phenological groups were distinguished: spring-early summer, summer, late summer, and polyvoltine, of which the richest is the polyvoltine group. The peak of diversity and abundance of species occurred in the middle summer period when almost 90% of Rhopalocera species of the studied area were found.

Pervasive accumulations of chert in the Equatorial Pacific during the early Eocene climatic optimum

Biosiliceous cherts hosting the transformation of biogenic silica to paracrystalline opal-CT, deposited in the low-latitude realms of Jurassic to Neogene, were recently interpreted as developing during episodes of elevated primary productivity along upwelling areas in equatorial and sub-equatorial paleo-latitudes. Geographically widespread distribution of chert and other rock types of biosiliceous origin, including porcellanite and siliceous claystones throughout the Eocene however indicates these diagenetic deposits are not in any case the dependable markers of latitude-driven upwelling regimes. This study aims to explore the dominance of early Eocene chert occurrences in the Equatorial Pacific (EP) sediments, and their contribution to the Cenozoic global climate change. Our new assessment of the age-abundance dispersal of EP Cenozoic chert sections accommodated by Deep Sea Drilling Project (DSDP)- and Ocean Drilling Program (ODP)-cored deposits realized that the cherts transformed from deposited opal-A sediments most commonly in the early Eocene, with a peak in abundance at ∼50 Ma. This age interval of significant chert occurrences coincided with the period of seawater-temperature maxima of the early Eocene climatic optimum (EECO), during which the world ocean was supposedly marked by highly reduced upwelling intensity and siliceous bioproduction. The spatio-temporal distribution model of the EP Cenozoic cherts with the peak occurrences during the EECO presented in this study bears close similarities to the global distribution patterns of chert during the Cenozoic, which strongly correspond to a global paleoclimatic driver rather than upwelling regimes. Following our survey, cherts occurred less frequently in the post-early Eocene, which is characterized by cooling bottom waters and amplified upwelling and bioproductivity. This model suggests the paleo-seawater rich in dissolved silicon (DSi) would have been imperative for peak incidences of early Eocene chert production, despite extreme surface warmth and greenhouse conditions of the EECO, making DSi available to opal-secreting phytoplankton via deep-water ventilation. These imply that the paleo-climate was more impactful to diagenetic chert production than latitudinally mediated ocean upwelling. The chert distribution events during the early Eocene reduced siliceous bioproductivity appear to have been insufficient to compensate for the significant silica input to the basin mainly from climate-controlled continental weathering. The DSi uptake by precipitation of authigenic clays which accompanies opal-A diagenesis in many depositional systems has been operative, with higher rates in carbonate- than clay-dominated sediments, so as to sustain balance between DSi released to the ocean from terrestrial sources and the silica expelled in sediments during the EECO weakened upwelling.

Effects of the Three Gorges Dam on the mandarin fish larvae (Siniperca chuatsi) in the middle reach of the Yangtze River: Spatial gradients in abundance, feeding, growth, and survival

AbstractLarge dams significantly impact river ecosystems by disrupting connectivity, altering physicochemical variables, and modifying flow regimes. These modifications influence the spatial and temporal dynamics of biological processes and species distributions. While much research has focused on potamodromous species, there remains a gap in understanding the recovery gradients of resident species in dam‐altered rivers. This study examines the responses of larvae of a resident species, the mandarin fish (Siniperca chuatsi), to environmental alterations caused by the Three Gorges Dam (TGD) in the middle reach of the Yangtze River. We hypothesized that larval abundance, feeding, growth, and survival would exhibit longitudinal recovery gradients, improving with the increased distance from the TGD. Our results confirm this hypothesis, showing that larvae further from the TGD exhibited higher abundance, increased feeding intensity, enhanced growth rates, improved survival rate, and earlier peak abundance and hatching dates. Key environmental factors, including water temperature and discharge, increased downstream, while transparency decreased. Major tributary inputs significantly contributed to these recovery gradients. The observed longitudinal gradients in larval attributes mirrored environmental changes, underscoring the TGD impact on population recruitment. These results highlight the broader implications of dam‐induced changes on resident species recruitment, potentially affecting entire fish communities. Our study contributes to understanding the distinct spatial patterns of population trends, providing valuable insights for designing more effective conservation and management practices for resident freshwater fishes in large regulated rivers.

Fauna and abundance of ixodids (Parasitiformes, Ixodidae) on Askold island (Primorsky krai): uniqueness, infection with pathogens

Collecting of hard ticks by a flag from vegetation in Askold Island (Primorsky Territory) in May 17, 2023 has revealed the following 3 species: Haemaphysalis longicornis Neumann, 1901 (809 specimens), Haemaphysalis japonica douglasi Nuttall et Warburton, 1915 (223), Ixodes persulcatus Schulze, 1930 (4). A total of 1036 tick specimens were collected. The territory of the western part of the island was surveyed: a broad-leaved maple forest (925 ticks were collected) and a large-grass meadow (111). Identification of tick species was carried out according to morphological characters. The hard tick fauna of Askold Island is characterized by: 1) the dominance of H. longicornis, which is absent on neighboring islands; 2) a high proportion of nymphs in May among representatives of the genus Haemaphysalis (H. longicornis 96.0%, H. japonica 25.1%), the peak abundance of which is common in July–August; 3) a high abundance of ticks (more than 90.0 individuals per flag-hour; 4) absence of males in H. longicornis (32 females were collected). PCR did not detect infection of 160 nymphs (pools of 20 individuals) H. longicornis with markers of nucleic acids of tick-borne encephalitis virus, borrelia, anaplasma, ehrlichia and West Nile fever. However, since representatives of the genus Haemaphysalis are known as carriers of many other pathogens, the high abundance of hard ticks and the incompleteness of data on their infection rate do not allow us to classify the territory of Askold Island as an epidemiologically low-risk territory.

Dissolved oxygen affinities of hundreds of benthic foraminiferal species

Over the past decades, fossil assemblages of benthic foraminifera have been used to reconstruct the variability of oxygen-depleted areas, including oxygen minimum zones. These areas currently represent almost a tenth of the global oceans' surface area, and further expansion is expected due to global warming; with major impacts on marine ecosystems, biodiversity, and fisheries. To predict their future evolution, accurate estimates and quantification of past oceanic oxygenation are needed, and thus consistent calibration of the O2 estimation transfer functions is required.Here, we combine the BENFEP database that compiles all the benthic foraminiferal census data published for the East Pacific Ocean, with dissolved oxygen data interpolated from the WOA18 and GLODAPV2.2022 databases, to describe the oxygen affinities of the 1526 benthic foraminiferal taxa from the BENFEP database among 1691 samples. The affinities of the most common 202 species of the database are detailed here. For each of these taxa, the range of oxygen concentration, average O2 value where the species is usually found, and O2 value associated with its peak in relative abundance are listed and used to assign each taxon to the oxygen categories anoxic, dysoxic, suboxic, low oxic, and high oxic.Finally, using the relative abundance of each of these five oxygen assemblages and their associated taxa, transfer function indices of dissolved oxygen estimation were refined. The new BFAex extends the range of applicability of the formerly published BFA index, here updated using all the available samples BFAup and extended from 0.04 to 2.58 mL L−1 to 0.02–6.62 mL L−1.

Pollen metabarcoding reveals the origin and multigenerational migratory pathway of an intercontinental-scale butterfly outbreak

Migratory insects may move in large numbers, even surpassing migratory vertebrates in biomass. Long-distance migratory insects complete annual cycles through multiple generations, with each generation's reproductive success linked to the resources available at different breeding grounds. Climatic anomalies in these grounds are presumed to trigger rapid population outbreaks. Here, we infer the origin and track the multigenerational path of a remarkable outbreak of painted lady (Vanessa cardui) butterflies that took place at an intercontinental scale in Europe, the Middle East, and Africa from March 2019 to November 2019. Using metabarcoding, we identified pollen transported by 264 butterflies captured in 10 countries over 7months and modeled the distribution of the 398 plants detected. The analysis showed that swarms collected in Eastern Europe in early spring originated in Arabia and the Middle East, coinciding with a positive anomaly in vegetation growth in the region from November 2018 to April 2019. From there, the swarms advanced to Northern Europe during late spring, followed by an early reversal toward southwestern Europe in summer. The pollen-based evidence matched spatiotemporal abundance peaks revealed by citizen science, which also suggested an echo effect of the outbreak in West Africa during September-November. Our results show that population outbreaks in a part of species' migratory ranges may disseminate demographic effects across multiple generations in a wide geographic area. This study represents an unprecedented effort to track a continuous multigenerational insect migration on an intercontinental scale.

Limnological Characteristics, Phytoplankton Assemblage and Environmental Assessment of Hadejia River, North-Western Nigeria: A Comprehensive Survey

Study’s Excerpt/Novelty This study is the first of its kind that offers a comprehensive analysis of phytoplankton dynamics in the Hadejia River, highlighting significant spatial and temporal variations in relation to key limnological variables. It uniquely identifies the influence of environmental factors on specific phytoplankton species and provides baseline data for future ecological monitoring. The research showcases the impact of anthropogenic activities on water quality, particularly at Station B, contributing critical insights into the river's ecological health and informing conservation strategies. Full Abstract This study assesses variations in phytoplankton abundance, composition, and distribution in the Hadejia River in relation to key limnological characteristics across both spatial and temporal dimensions. Over six months in 2018, water samples were collected from the river and analyzed for environmental variables alongside the quantification and identification of phytoplankton using standard protocols. pH and temperature measurements were conducted in situ. Results indicated significant variations (P < 0.05) in pH, temperature, turbidity, nitrate, and phosphate levels across different months, although no significant differences were observed between sampling stations. The highest nitrate value (5.41 mg/L) and phosphate levels (6.55 mg/L) were recorded in August at Station B (STB). 693 Phytoplankton individuals from five divisions were identified, with peak abundance, composition, and distribution observed during the dry season. Key species such as Selenastrum bibraianum, Tetraedron regulare, Tabellaria flocculosa, Gomphosphaeria lacustris, Microcystis aeruginosa, Rhabdoderma lineare and Tabellaria fenestrate were consistently present throughout the study period. Shannon_H diversity index values for Cyanophyta, Pyrrophyta, and Euglenophyta ranged between 1.34-2.02, while Bacillariophyta and Cyanophyta exhibited reduced diversity (1-1.32) and species richness (0.55-0.68) at STB. Canonical correspondence analysis revealed that the selected environmental variables strongly influenced phytoplankton abundance and diversity, with the exception noted for Microcystis aeruginosa, Gomphosphaeria lacustris, Rhabdoderma lineare, and Chlamydomonas ehrenbergii. These results suggest deterioration in water quality, particularly at STB, possibly due to anthropogenic activities. Furthermore, this study provides valuable baseline data for future research endeavors aimed at monitoring and managing the ecological health of River Hadejia

Long-Term Trends in Mosquito Vector Populations and Their Impact on Yellow Fever Outbreaks in Atlantic Forest Fragments of Rio De Janeiro, Brazil (2016-2021).

Among all living beings, mosquitoes account for the highest number of human fatalities. Our study aimed to determine mosquito egg abundance fluctuation from 2015 to 2020, in order to observe which years had the highest mosquito vector densities and whether they coincided with yellow fever virus outbreaks in both human and nonhuman primates. The study area included Atlantic Forest fragments in the state of Rio de Janeiro. Studies from the Diptera Laboratory at FIOCRUZ were selected and compared along a timeline period of the field collections. The highest peak in egg abundance from the analyzed studies was observed from 2016 to 2017 and from 2015 to 2016. The lowest egg abundance was during the collection periods from 2018 to 2019 and 2019 to 2020. The species with the highest abundance throughout all the periods of the studies analyzed was Haemagogus leucocelaenus, representing 87% of all epidemiological species identified. The species with the lowest abundance was Hg. Janthinomys, representing only 1%. Monitoring the population of mosquitoes is imperative for disease surveillance, as the rise in specimens of various vector species directly impacts the occurrence of yellow fever cases in both nonhuman primates and human populations.

Temporal and Spatial Dynamics of Vibrio harveyi: An Environmental Parameter Correlation Investigation in a 4-Metre-Deep Dicentrarchus labrax Aquaculture Tank.

Nowadays, European seabass (Dicentrarchus labrax) aquaculture is undergoing a significant expansion. Nevertheless, the aquaculture industry is plagued by vibriosis. The spatial and temporal dynamics of Vibrio harveyi were studied on a European seabass farm in northern France during seven months of 2022. Concrete specimens were suspended and water was pumped from different depths (0.3 m, 2.15 m and 4 m deep), providing insights into the biofilm and planktonic V. harveyi dynamics. The abundances of V. harveyi, in the biofilm and free-living forms, were positively correlated. The water parameters revealed seasonal fluctuations in temperature, pH, and salinity, with no significant differences observed across the water column. Quantification of V. harveyi revealed no significant differences between depths, but seasonality, with peak abundances observed in August, correlated with temperature increases. Principal component analysis identified temperature as a primary driver, but also additional parameters, such as salinity and pH. Vibriosis occurred during the sampling period, providing valuable insights into the conditions before, during, and after the outbreaks. This study underscores the importance of understanding V. harveyi behaviour in aquaculture, particularly in the context of global warming, for effective disease management and sustainable practices.

Circadian control of tumor immunosuppression affects efficacy of immune checkpoint blockade.

The circadian clock is a critical regulator of immunity, and this circadian control of immune modulation has an essential function in host defense and tumor immunosurveillance. Here we use a single-cell RNA sequencing approach and a genetic model of colorectal cancer to identify clock-dependent changes to the immune landscape that control the abundance of immunosuppressive cells and consequent suppression of cytotoxic CD8+ T cells. Of these immunosuppressive cell types, PD-L1-expressing myeloid-derived suppressor cells (MDSCs) peak in abundance in a rhythmic manner. Disruption of the epithelial cell clock regulates the secretion of cytokines that promote heightened inflammation, recruitment of neutrophils and the subsequent development of MDSCs. We also show that time-of-day anti-PD-L1 delivery is most effective when synchronized with the abundance of immunosuppressive MDSCs. Collectively, these data indicate that circadian gating of tumor immunosuppression informs the timing and efficacy of immune checkpoint inhibitors.

Energetic particle precipitation influences global secondary ozone distribution

The secondary ozone layer is a global peak in ozone abundance in the upper mesosphere-lower thermosphere (UMLT) around 90-95 km. The effect of energetic particle precipitation (EPP) from geomagnetic processes on this UMLT ozone remains largely unexplored. In this research we investigated how the secondary ozone responds to EPP using satellite observations. In addition, the residual Mean Meridional Circulation (MMC) derived from model simulations and the atomic oxygen [O], atomic hydrogen [H], temperature measurements from satellite observations were used to characterise the residual circulation changes during EPP events. We report regions of secondary ozone enhancement or deficit across low, mid and high latitudes as a result of global circulation and transport changes induced by EPP. The results are supported by a sensitivity test using an empirical model.

Long-term climate and hydrologic regimes shape stream invertebrate community responses to a hurricane disturbance.

Disturbances can produce a spectrum of short- and long-term ecological consequences that depend on complex interactions of the characteristics of the event, antecedent environmental conditions, and the intrinsic properties of resistance and resilience of the affected biological system. We used Hurricane Harvey's impact on coastal rivers of Texas to examine the roles of storm-related changes in hydrology and long-term precipitation regime on the response of stream invertebrate communities to hurricane disturbance. We detected declines in richness, diversity and total abundance following the storm, but responses were strongly tied to direct and indirect effects of long-term aridity and short-term changes in stream hydrology. The amount of rainfall a site received drove both flood duration and flood magnitude across sites, but lower annual rainfall amounts (i.e. aridity) increased flood magnitude and decreased flood duration. Across all sites, flood duration was positively related to the time it took for invertebrate communities to return to a long-term baseline and flood magnitude drove larger invertebrate community responses (i.e. changes in diversity and total abundance). However, invertebrate response per unit flood magnitude was lower in sub-humid sites, potentially because of differences in refuge availability or ecological-evolutionary interactions. Interestingly, sub-humid streams had temporary large peaks in invertebrate total abundance and diversity following recovery period that may be indicative of the larger organic matter pulses expected in these systems because of their comparatively well-developed riparian vegetation. Our findings show that hydrology and long-term precipitation regime predictably affected invertebrate community responses and, thus, our work underscores the important influence of local climate to ecosystem sensitivity to disturbances.

Ontogenetic diet shifts and temporal separations in gonad development of two icefish species in Hongze Lake, China

Abstract Resource partitioning through temporal, spatial and/or trophic dimensions is suggested as a mechanism for long‐term coexistence among sympatric species. However, how the combined effects of the different dimensions contribute to the partitioning during the ontogenetic process is unclear. We sampled two sympatric icefish species [Protosalanx hyalocranius (Abbott, 1901) and Neosalanx taihuensis (Chen, 1956)] monthly from July 2015 to June 2016 in Hongze Lake, China. We evaluated the hypothesis that combined effects of separation in gonad development dynamics and ontogenetic diet shifts facilitate resource partitioning in temporal and trophic dimensions during the entire life cycle process of the two icefish species. Increased gonadosomatic index (GSI) of female P. hyalocranius occurred during October 2015 to January 2016, and that of female N. taihuensis occurred during January to March 2016. Thus, energy and nutrition investments in gonad development separated seasonally between the two species. Consequently, temporal separations in gonad development between P. hyalocranius (GSI peaked in January) and N. taihuensis (GSI peaked in March) indicated potential segregations in spawning time and consequent larval abundance peaks, suggesting reduced overlap of prey consumption during the early life stages. The dominant diet of P. hyalocranius shifted from cladocerans to copepods, and then shrimp, and finally to fish during its ontogeny, whereas the dominant diet of N. taihuensis changed gradually from cladocerans to copepods during its ontogeny. The diet overlap in cladocerans during May was high between the two species. Our findings support the hypothesis of an associative strategy, combining temporal (separations in gonad development and subsequently spawning time) and trophic (ontogenetic diet shifts) dimensions, for the resource partitioning between P. hyalocranius and N. taihuensis, which may be an important mechanism for long‐term coexistence among sympatric short‐lived fishes.

A First Look at the Relationship Between Large Herbivore-Induced Landscape Modifications and Ixodes ricinus Tick Abundance in Rewilding Sites.

Background: While the influence of landscape and microclimatic conditions on tick populations is well-documented, there remains a gap in more specific data regarding their relationship to rewilding efforts with large herbivore activity. Objective: This pilot study, spanning from 2019 to 2021, explores the effects of naturalistic grazing by large semi-wild ungulates on tick abundance in the Milovice Reserve, Czechia. Methods: Tick collection was observed using flagging techniques at two distinct sites of rewilding area: one grazed, actively utilized by animals involved in the rewilding project, and one ungrazed, left fallow in neighboring areas utilized only by wild animals. Transects, each measuring 150 m in length and 5 m in width (750 m2), were established at these two sampling locations from March to September between 2019 and 2021. To minimize potential bias resulting from tick movement, a 300 m buffer zone separated the two sites. Data analysis employed a generalized estimating equations (GEE) model with negative binomial regression. The study assessed potential variations in tick abundance between selected transects, considering factors such as plant cover seasonality, temperature, and humidity. Results: During the collection periods, we gathered 586 live ticks, with 20% found in grazed areas and 80% in ungrazed areas. Notably, tick abundance was significantly higher in ungrazed areas. Peaks in tick abundance occurred in both grazed and ungrazed areas during spring, particularly in April. However, tick numbers declined more rapidly in grazed areas. Microclimatic variables like temperature and humidity did not significantly impact tick abundance compared to landscape management and seasonal factors. Conclusion: Rewilding efforts, particularly natural grazing by large ungulates, influence tick abundance and distribution. This study provides empirical data on tick ecology in rewilded areas, highlighting the importance of landscape management and environmental factors in tick management and conservation. Trophic rewilding plays a crucial role in shaping ecosystems and tick population dynamics in transformed landscapes.

Strong habitat and seasonal phenology effects on the evolution of self-compatibility, clonality and pollinator shifts in Lachenalia (Asparagaceae: Scilloideae).

Plants employ a diversity of reproductive safeguarding strategies to circumvent the challenge of pollen limitation. Focusing on southern African Lachenalia (Asparagaceae: Scilloideae), we test the hypothesis that the evolution of reproductive safeguarding traits (self-compatibility, autonomous selfing, bird pollination and clonal propagation) is favoured in species occupying conditions of low insect abundance imposed by critically infertile fynbos heathland vegetation and by flowering outside the austral spring insect abundance peak. We trace the evolution of these traits and selective regimes on a dated, multi-locus phylogeny of Lachenalia and assess their evolutionary associations using ordinary and phylogenetic regression. Ancestral state reconstructions identify an association with non-fynbos vegetation and spring flowering as ancestral in Lachenalia, the transition to fynbos vegetation and non-spring flowering taking place multiple times. They also show that self-compatibility, autofertility, bird pollination and production of multiple clonal offsets have evolved repeatedly. Regression models suggest that bird pollination and self-compatibility are selected for in fynbos and in non-spring flowering lineages, with autofertility being positively associated with non-spring flowering. These patterns support the interpretation of these traits as reproductive safeguarding adaptations under reduced insect pollinator abundance. We find no evidence to support the interpretation of clonal propagation as a reproductive safeguarding strategy.

Growth and mortality rates of picophytoplankton in the Baltic Sea Proper

Picophytoplankton (<2 µm diameter), a diverse group of picocyanobacteria and photosynthetic picoeukaryotes, are significant contributors to primary production. Predatory mortality controls picophytoplankton biomass and thereby energy transfer in the marine food web. The 2 major pathways of picophytoplankton mortality are grazing and viral lysis. Grazing passes carbon directly to higher trophic levels, while lysis products are passed into the viral loop. Picophytoplankton are abundant in the Baltic Sea but little is known about their predatory mortality. Using a modification of the dilution approach, we calculated growth and mortality rates of picophytoplankton and studied the effect of predation on community structure during late August and September. The experiments were conducted coinciding with the peak in picophytoplankton abundance (∼105 cells ml-1) at the Linnaeus Microbial Observatory in the Baltic Sea Proper. The results showed that grazing is an important controller of picocyanobacteria and photosynthetic picoeukaryote populations, while no significant viral lysis effect was detected. Grazing on picocyanobacteria was proportional to growth rates, while grazing on photosynthetic picoeukaryotes exceeded growth. Selective grazing of phylogenetically distinct picocyanobacterial clades had a significant effect on community structure, suggesting that grazing has an impact on the seasonal dynamics of co-occurring clades. Picocyanobacteria had a higher carbon transfer contribution to higher trophic levels than photosynthetic picoeukaryotes at the time of the experiments. The study shows that picophytoplankton are important contributors to carbon cycling in the Baltic Sea microbial food web and should be considered for future ecological models.

Diverging phenology of American lobster (Homarus americanus) larvae and their zooplankton prey in a warming ocean

Abstract We build on previous research describing correlative links between changes in the abundance of the copepod Calanus finmarchicus, a foundational zooplankton species of the pelagic food web, and diminishing recruitment of young-of-year American lobster (Homarus americanus) to benthic nurseries in the Gulf of Maine. Using parallel 31-year time series of lobster larvae and zooplankton collected on the New Hampshire coast between 1988 and 2018, we investigated how changes in phenology of stage I larval lobster and their putative copepod prey, C. finmarchicus, affect their temporal overlap and potential to interact during the larval season. We found that over the time series both the lobster egg hatch and first appearance of larvae began earlier in the season, a trend significantly correlated with ocean warming. The last appearance of larvae in late summer has been delayed, however, thereby extending the larval season. Even with the longer larval lobster season, the C. finmarchicus season has increasingly been ending before the peak abundance of stage I lobster larvae. The net effect is a widening mismatch in phenology of the two species, an outcome consistent with the hypothesis that changes in abundance and phenology of C. finmarchicus have contributed to recent declines in lobster recruitment.

Transcriptomic insights into the dominance of two phototrophs throughout the water column of a tropical hypersaline-alkaline crater lake (Dziani Dzaha, Mayotte).

Saline-alkaline lakes often shelter high biomasses despite challenging conditions, owing to the occurrence of highly adapted phototrophs. Dziani Dzaha (Mayotte) is one such lake characterized by the stable co-dominance of the cyanobacterium Limnospira platensis and the picoeukaryote Picocystis salinarum throughout its water column. Despite light penetrating only into the uppermost meter, the prevailing co-dominance of these species persists even in light- and oxygen-deprived zones. Here, a depth profile of phototrophs metatranscriptomes, annotated using genomic data from isolated strains, is employed to identify expression patterns of genes related to carbon processing pathways including photosynthesis, transporters and fermentation. The findings indicate a prominence of gene expression associated with photosynthesis, with a peak of expression around 1 m below the surface, although the light intensity is very low and only red and dark red wavelengths can reach it, given the very high turbidity linked to the high biomass of L. platensis. Experiments on strains confirmed that both species do grow under these wavelengths, at rates comparable to those obtained under white light. A decrease in the expression of photosynthesis-related genes was observed in L. platensis with increasing depth, whereas P. salinarum maintained a very high pool of psbA transcripts down to the deepest point as a possible adaptation against photodamage, in the absence and/or very low levels of expression of genes involved in protection. In the aphotic/anoxic zone, expression of genes involved in fermentation pathways suggests active metabolism of reserve or available dissolved carbon compounds. Overall, L. platensis seems to be adapted to the uppermost water layer, where it is probably maintained thanks to gas vesicles, as evidenced by high expression of the gvpA gene. In contrast, P. salinarum occurs at similar densities throughout the water column, with a peak in abundance and gene expression levels which suggests a better adaptation to lower light intensities. These slight differences may contribute to limited inter-specific competition, favoring stable co-dominance of these two phototrophs.