Niche Differences Research Articles

Biotic Deterioration and Homogenization: Why It Matters

AbstractGlobally, locally, and regionally, there are different patterns of biotic diversity and community composition reflecting past evolutionary history shaped by differences in niches, productivity, climate, and other ambient factors, as well as migration barriers. Historically, humans have impacted and eroded these biotic patterns, notably by the impact of agriculture in a wide sense, but to an increasing extent also by logging, overharvesting, spreading of species, urbanization, and climate change. Besides causing (in most cases) a declining diversity, it also implies a biotic homogenization where ecosystem communities become spatially more similar, often by replacement of locally adopted specialist species with more widespread generalist species. Besides discussing these drivers of biotic degradation and homogenization, I also discuss why and how it matters both from a biocentric and anthropocentric point of view, how biotic and cultural homogenization are integrated via agricultural impacts, loss of habitats that also are home to indigenous people as well as by travel, trade, and consumption. In fact, the global cultural homogenization towards western consumerism is the overarching cause of biotic homogenization, biodiversity loss as well as climate change. Finally, solutions are discussed. There are local and regional means to counteract biotic losses and homogenization by retaining and restoring landscape elements, yet globally these trends can only be countered through systemic societal changes.

New Insights into Fish Diversity in the Yellow and Bohai Seas Based on Environmental DNA Technology

Marine biodiversity is increasingly threatened by overfishing and marine pollution. A comprehensive understanding of the biodiversity in the Yellow and Bohai Seas is essential for resource conservation. This study conducted a large-scale survey of fishery resources in the Yellow and Bohai Seas to investigate fish community structure and diversity using eDNA technology. The results showed that 57 and 65 fish species were recorded in spring and summer, respectively, with 46 species identified in both seasons. A total of nine dominant species were identified in spring, mainly belonging to Perciformes, while seven dominant species were identified in summer, primarily from Clupeiformes. In different regions, no significant differences in fish α diversity were observed between spring and summer. However, significant seasonal differences were found in both α and β diversity. At the spatial level, fish species in the Yellow and Bohai Seas occupied similar ecological niches. However, at the temporal level, there are certain differences in the ecological niches of fish communities between seasons. Phylogenetic diversity showed no significant differences at the spatial scale, yet notable seasonal variations were observed at the temporal scale, with spring (661.46) significantly exceeding summer (540.30). The Mantel test indicated that nitrate and salinity were key environmental factors influencing α diversity. RDA analysis revealed that the dominant species in spring were mainly influenced by chlorophyll-a and water temperature, while those in summer were mainly affected by water depth, nitrite, water temperature, and salinity.

The distribution of beneficial mutational effects between two sister yeast species poorly explains natural outcomes of vineyard adaptation.

Domesticated strains of Saccharomyces cerevisiae have adapted to resist copper and sulfite, two chemical stressors commonly used in winemaking. S. paradoxus has not adapted to these chemicals despite being consistently present in sympatry with S. cerevisiae in vineyards. This contrast could be driven by a number of factors including niche differences or differential access to resistance mutations between species. In this study, we used a comparative mutagenesis approach to test whether S. paradoxus is mutationally constrained with respect to acquiring greater copper and sulfite resistance. For both species, we assayed the rate, effect size, and pleiotropic costs of resistance mutations and sequenced a subset of 150 mutants. We found that the distributions of mutational effects displayed by the two species were similar and poorly explained the natural pattern. We also found that chromosome VIII aneuploidy and loss of function mutations in PMA1 confer copper resistance in both species, whereas loss of function mutations in REG1 were only a viable route to copper resistance in S. cerevisiae. We also observed a de novo duplication of the CUP1 gene in S. paradoxus but not in S. cerevisiae. For sulfite, loss of function mutations in RTS1 and KSP1 confer resistance in both species, but mutations in RTS1 have larger effects in S. paradoxus. Our results show that even when available mutations are largely similar, species can differ in the adaptive paths available to them. They also demonstrate that assays of the distribution of mutational effects may lack predictive insight concerning adaptive outcomes.

Gradient of acid mine drainage regulates microbial community assembly and the diversity of species associated with native plants

Acid mine drainage (AMD) is considered as one of the most important global environmental challenges. Therefore, understanding the impact of AMD on the diversity of microbial communities associated with native plants is important for phytoremediation. In this study, the community assembly and microbial diversity associated with native plants growing along an AMD impact gradient was investigated using metabarcoding and high throughput iChip technique. The study revealed that across both domains of bacteria and fungi, richness and species diversity decreased according to AMD impact. Bacterial species diversity was more stratified according to the pH gradient than fungi, and the AMD impact on the plant-associated microbial diversity decreased towards the plant roots. The microbial community composition of the undisturbed site was significantly different from the AMD impacted sites, and the communities in the AMD impacted sites were further stratified according to the degree of impact. The overall microbial diversity was mediated by the AMD impact, niche differences and plant species differences. Dispersal limitation was the most important community assembly process in the undisturbed site, while the homogenous selection of Burkholderia, Actinospica, Puia and Bradyrhizobium increased along the AMD impact gradient. Differential abundance analysis further revealed that Umbelopsis, Burkholderia and Sphingomonas were among the biomarkers of the AMD impacted sites. Several strains of some of these responsive genera were subsequently isolated using the iChip. Overall, this study presents novel insight into the ecology of plant-associated microbial communities that are relevant for environmental monitoring and for enhancing the revegetation of AMD impacted sites.

Water and nitrogen coupling regulates the present and future restoration trends under Spartina alterniflora invasion in a coastal salt marsh

Global change can easily cause the wetland ecosystem structure and function to be damaged by alien species. Former studies on Spartina alterniflora invasion only focused on the effect of aboveground communities, ignoring the potential regeneration of soil seed banks. Therefore, the study aimed to find the key resources that limit the S. alterniflora invasion and the regulation mechanism for S. alterniflora regeneration. Through investigating the S. alterniflora communities with different invasion stages, we studied the structure and composition of the aboveground communities and the soil seed banks, in response to the soil properties and water and nitrogen addition. The dominant competitive advantage of S. alterniflora was mainly affected by the aboveground biomass, which was regulated by soil NH4+-N and moisture content. Although the richness was same in the soil seed banks under the S. alterniflora communities with different coverage, S. alterniflora seeds maintained its specific competitive dominance. The niche breadth of S. alterniflora and the niche overlap between S. alterniflora and Tripolium pannonicum was the highest under low aboveground coverage. The soil seed bank germination experiments showed that the S. alterniflora density decreased when the soil nitrogen concentration exceeded 1 g/kg, while the density of native species E. crusgalli and T. pannonicum decreased when the water depth above the soil surface exceeded 2 cm. The successful naturalization of S. alterniflora invasion regulated by nitrogen-water coupling is a bet-hedging of the niche and fitness differences between invasive and native species in the coastal salt marsh of eastern China.

Deterministic responses of biodiversity to climate change through exotic species invasions.

Biodiversity is increasingly threatened by local extinction under global climate change. This may reflect direct effects of climate on poorly adapted native species or increased impacts of exotic species in these conditions, but their relative importance is poorly understood. By examining global occurrence records of 142 plant species found in the Yangtze River Valley, we found that the climatic niches of exotic species differed from those of natives, mainly reflecting exotics being most common in warmer, drier and more isothermal climates in their native ranges. These differences in climatic niches, especially temperature, predicted invasion intensity in 459 plots along a 1,800-km transect in the Yangtze River Valley. On the basis of this strong match between model predictions and field survey results, we predict that invasions will probably be more intense in future climatic conditions, especially from warming at the coldest sites. The direct negative effect of warming on native diversity was larger than the indirect effects mediated through increased invasions. However, moderate invasion increased communities' overall species diversity. More broadly, our study highlights the role of exotic species in the ecological response of regional biodiversity to global climate change.

Same but Different: Intersexual and Age‐Related Habitat Use of the Threatened West African Trionyx triunguis Clade—A Four‐Country Comparative Study

ABSTRACTBiological communities are structured by a variety of biotic and abiotic relationships, whose understanding forms the basis for effective conservation. Among the myriad factors influencing community dynamics, resource partitioning stands out, potentially enriching ecosystem complexity but also carrying risks for conservation if disregarded. In this study, we investigated intersexual and ontogenetic niche differences among populations of the West African softshell turtle Trionyx triunguis in Liberia, Cote d'Ivoire, Ghana and Nigeria. We observed that these distinct populations exhibited similar habitat preferences, favouring large rivers with abundant riverbank and aquatic vegetation, and muddy substrates. Disparities in habitat preferences were evident among populations and across various life stages, indicating the adaptability of the species. We found that the species was active throughout the year, but most of our sightings and captures occurred during the wet season. In light of the species' vulnerability to overhunting, our research findings provide important data on the ecology of this species that can assist in its effective conservation across all life stages.

Soil mycobiome dissimilarity, independent of fungal guild, is associated with increased probability of plant coexistence

Abstract Major theories regarding microbe‐mediated plant community dynamics assume that plant species cultivate distinct microbial communities. However, few studies empirically assess the role of species‐associated microbial community dissimilarity in plant competitive dynamics. In this study, we paired a competition experiment between eight annual forbs with characterisation of species‐associated fungal communities to assess whether mycobiome dissimilarity is associated with pairwise competitive dynamics. Using a quantitative approach informed by modern coexistence theory, we found that fungal dissimilarity was correlated with both increased stabilising niche differences and fitness inequalities. Additionally, we found that the probability of coexistence increased with mycobiome dissimilarity. When subsetting the community into different fungal functional groups (pathotrophs, saprotrophs, symbiotrophs), overall relationships between dissimilarity and competitive dynamics were independent of these functional groups. Synthesis. These results suggest that fungal community divergence may play an important role in mediating plant competitive dynamics. Although fungal community dissimilarity is associated with both niche and fitness differences, complex biotic and/or abiotic interactions below‐ground may result in an observed correlation between fungal community dissimilarity and plant coexistence. Ultimately, this study suggests a novel approach to better understanding how microbiome dissimilarity may impact host community dynamics.

Germination phenology alters species coexistence outcomes

Abstract Species‐specific phenological responses to changing climate are reshuffling the timing of species interactions, however we do not fully understand the consequences of these changes for species' population dynamics and community composition. In this study, we experimentally manipulated the timing of germination for five annual plant species from southern California and used pairwise competition experiments and coexistence theory to quantify how phenological shifts may impact species interactions and coexistence. We found that phenological shifts may help promote coexistence when they confer an advantage for competitively inferior species, but in other cases promote dominance by competitively superior species. Earlier germination generally increased species' performance relative to competitors, but the relative changes in intra‐and inter‐specific interactions caused more complex effects on niche and fitness differences. Phenological differences tended to reduce stabilising niche differences for many species pairs and reduced overall coexistence probabilities. Synthesis. While phenological differences among species have typically been considered a form of niche partitioning, it seems increasingly likely that phenological offsets could destabilise species coexistence. The net effects of changing phenology on species coexistence will depend on the complex combinations of effects on intra‐ and inter‐specific interactions, which remain challenging to predict.

Competitive exclusion drives termite community assembly process on islands

ContextAbiotic filtering, including environmental and dispersal filtering, is frequently observed resulting in reduced diversity and more similar species assemblages following habitat fragmentation. Nonetheless, the significance of competitive exclusion is often underestimated.ObjectivesWe investigated the dominant assembly process among termite communities on land-bridge islands, focusing on species known for their high territoriality. We hypothesized that competitively superior species tend to dominate more favorable habitats, such as larger and less isolated islands. Consequently, we anticipated lower diversity and greater similarity in species assemblages than would be expected.MethodsTermite communities were surveyed using standardized transects on 24 islands. We quantified the standardized effects of island area and isolation on taxonomic, phylogenetic and functional diversity by comparing observed patterns with randomly generated communities (i.e., stochastic process). A phylogenetic generalized linear mixed model (PGLMM) was conducted to examine species-specific responses to environmental factors and competition intensity (i.e., heterospecific abundance).ResultsWe found that taxonomic, phylogenetic and functional diversity were lower than expected on larger and less isolated islands, suggesting that competitive exclusion was the dominant mechanism shaping termite communities in TIL. PGLMM showed that two fungus-growing species with larger body sizes increased with competition intensity, while other species exhibited negative responses. Notably, the abundance of fungus-growing species showed sharper increase with island area and decrease with isolation compared to other feeding groups. These findings demonstrate that competitively superior species prefer high-quality habitats and are more sensitive to habitat fragmentation.ConclusionsOur study highlights the significance of competitive exclusion in shaping termite communities and emphasizes the need to consider both competitive and niche difference among species or functional groups when predict changes in community structure and biodiversity loss resulting from habitat fragmentation.

Contrasting demographic history and mutational load in three threatened whitebark pines (Pinus subsect. Gerardianae): implications for conservation.

Demographic history and mutational load are of paramount importance for the adaptation of the endangered species. However, the effects of population evolutionary history and genetic load on the adaptive potential in endangered conifers remain unclear. Here, using population transcriptome sequencing, whole chloroplast genomes and mitochondrial DNA markers, combined with niche analysis, we determined the demographic history and mutational load for three threatened whitebark pines having different endangered statuses, Pinus bungeana, P. gerardiana and P. squamata. Demographic inference indicated that severe bottlenecks occurred in all three pines at different times, coinciding with periods of major climate and geological changes; in contrast, while P. bungeana experienced a recent population expansion, P. gerardiana and P. squamata maintained small population sizes after bottlenecking. Abundant homozygous-derived variants accumulated in the three pines, particularly in P. squamata, while the species with most heterozygous variants was P. gerardiana. Abundant moderately and few highly deleterious variants accumulated in the pine species that have experienced the most severe demographic bottlenecks (P. gerardiana and P. squamata), most likely because of purging effects. Finally, niche modeling showed that the distribution of P. bungeana might experience a significant expansion in the future, and the species' identified genetic clusters are also supported by differences in the ecological niche. The integration of genomic, demographic and niche data has allowed us to prove that the three threatened pines have contrasting patterns of demographic history and mutational load, which may have important implications in their adaptive potential and thus are also key for informing conservation planning.

Plasticity and overlap of trophic niches in tropical breeding Laridae

Trophic ecology of seabirds in tropical regions remains poorly understood despite the large number of multispecies breeding colonies supported by these ecosystems. Here, we used the isotopic niche (δ15N and δ13C) of 5 Laridae species at 2 breeding areas in Cuba to analyze the plasticity and interspecific overlap of trophic niche determined from chick down and feather samples. The down samples reflected the female trophic regime before laying, while the feather samples incorporated the trophic regime of the chicks provided by the parents during rearing. Two main species groups were identified by their isotopic niche characteristics: species with small and quite stable isotopic niches (trophic specialists) and species with large and highly variable isotopic niches (trophic generalists). Laughing gull Leucophaeus atricilla, royal tern Thalasseus maximus, and sandwich tern T. sandvicensis were the generalists and showed significant isotopic niche differences between breeding areas and phases. Bridled tern Onychoprion anaethetus and roseate tern Sterna dougallii were trophic specialists, but only the former exhibited significant variations in isotopic niche breadth between breeding phases. Overall, trophic (inferred from isotopic) niche overlap was relatively low, suggesting that these tropical seabirds reduce competition through niche partitioning. We concluded that trophic niche plasticity and segregation appear to constitute an important adaptive strategy to ensure the breeding success of sympatrically breeding Laridae in north-central Cuba.

Comparisons of isotopic niche between females and male alternative reproductive tactics of Chinook salmon (Oncorhynchus tshawytscha) from Lake Ontario

Chinook salmon (Oncorhynchus tshawytscha) have complex life histories with two distinct male alternative reproductive tactics (ARTs). The larger and older “hooknose” males battle for position to spawn with nesting females whereas the precociously maturing “jack” males use a sneaking tactic to gain access to females. Although dietary niche is known to differ between ARTs of other fish taxa, no research to date has examined these differences in a salmonid. Here, we used δ15N and δ13C stable isotope analyses to compare the dietary niches of female, hooknose male, and jack male Chinook salmon sampled from a Lake Ontario tributary. We found that all three life histories shared similar δ15N values, whereas jack males had greater δ13C values compared to hooknose males, with females having intermediate values. Jack males also had notably little overlap in their isotopic niche space with hooknose males and females, indicating that jack males occupy a distinct isotopic niche in Lake Ontario. We discuss habitat partitioning and differences in dietary niche as explanatory factors. Altogether, these data unveil novel distinctions in isotopic niche within the complex life history strategies of Chinook salmon in Lake Ontario that can inform management decisions and provide avenues for future research.

Niche breadth and divergence in sympatric cryptic coral species (Pocillopora spp.) across habitats within reefs and among algal symbionts.

While the presence of morphologically cryptic species is increasingly recognized, we still lack a useful understanding of what causes and maintains co-occurring cryptic species and its consequences for the ecology, evolution, and conservation of communities. We sampled 724 Pocillopora corals from five habitat zones (the fringing reef, back reef, and fore reef at 5, 10, and 20 m) at four sites around the island of Moorea, French Polynesia. Using validated genetic markers, we identified six sympatric species of Pocillopora, most of which cannot be reliably identified based on morphology: P. meandrina (42.9%), P. tuahiniensis (25.1%), P. verrucosa (12.2%), P. acuta (10.4%), P. grandis (7.73%), and P. cf. effusa (2.76%). For 423 colonies (58% of the genetically identified hosts), we also used psbA ncr or ITS2 markers to identify symbiont species (Symbiodiniaceae). The relative abundance of Pocillopora species differed across habitats within the reef. Sister taxa P. verrucosa and P. tuahiniensis had similar niche breadths and hosted the same specialist symbiont species (mostly Cladocopium pacificum) but the former was more common in the back reef and the latter more common deeper on the fore reef. In contrast, sister taxa P. meandrina and P. grandis had the highest niche breadths and overlaps and tended to host the same specialist symbiont species (mostly C. latusorum). Pocillopora acuta had the narrowest niche breadth and hosted the generalist, and more thermally tolerant, Durusdinium gynnii. Overall, there was a positive correlation between reef habitat niche breadth and symbiont niche breadth-Pocillopora species with a broader habitat niche also had a broader symbiont niche. Our results show how fine-scale variation within reefs plays an important role in the generation and coexistence of cryptic species. The results also have important implications for how niche differences affect community resilience, and for the success of coral restoration practices, in ways not previously appreciated.

Variation in Isotopic Trophic Niche of Sablefish (Anoplopoma fimbria) and Shortraker Rockfish (Sebastes borealis) in the Northeast Pacific

Sablefish (Anoplopoma fimbria, Anoplopomatidae) and shortraker rockfish (Sebastes borealis, Sebastidae), co-occur in deepwater marine habitats in the northeast Pacific. Both species are economically valuable, but their ecologies are not well known. We used stable isotope analysis of carbon and nitrogen to explore isotopic niches of A. fimbria and S. borealis in two distinct locations—a deep strait in the inside passage area and an open coastal area of the continental shelf, both in southeast Alaska, USA. Anoplopoma fimbria and S. borealis exhibited similar positions of isotopic niches based on nitrogen and carbon isotopic ratios, suggesting potential interspecific competition, especially in the inside location. In addition, S. borealis had a smaller niche breadth compared to A. fimbria in the coastal location. Both species had enriched nitrogen and carbon isotopic ratios in the inside location compared to the coastal location. Differences in isotopic niches between these two locations suggest the possibility of location-specific variation in isotopic niches of these two species of widespread, abundant deepwater fishes.

Different species or altitudinal morphotypes? Testing the taxonomic value of Dianthus brachycalyx (Caryophyllaceae)

AbstractDefining species boundaries within plant groups distributed along wide elevational and geographic gradients may lead to unstable taxonomic delimitations using morphological data only. Within the taxonomically challenging genus Dianthus, through an integrative approach we tested the taxonomic value of D. brachycalyx, a putative species endemic to mountain peaks of the central‐southern Apennines, with respect to the widespread central‐Mediterranean D. virgineus. We measured 30 morphological characters in 452 individuals from 25 populations and obtained 3202 single nucleotide polymorphisms using ddRAD‐seq techniques in 394 individuals from 36 populations. For climatic niche comparison, we built a dataset of 348 occurrence points. By comparing morphometric, genetic, and climatic niche data, we showed that D. brachycalyx cannot be considered a distinct species. Morphometric separation between the two species is detectable, but high‐elevation populations of D. virgineus are similar to D. brachycalyx. Genetic analyses revealed that the genetic structure of populations of D. brachycalyx and D. virgineus is mainly shaped by isolation‐by‐distance, irrespective of their taxonomic attribution. The climatic niches of the two species are overlapping, and the niche differences are just due to different availability of climatic conditions in their ranges. Accordingly, multiple lines of evidence do not support a separation of D. brachycalyx from D. virgineus, and the former should be considered a heterotypic synonym of the latter.

Root foraging strategies and niche segregation of three mediterranean shrub species

Shrubs are usually adapted to stressful environments in which soil resources are limited, and thus, roots are fundamental for their biological success. However, root measures are challenging to collect, especially in field conditions and at the individual level. For this study, we collected data on the three‐dimensional distribution of fine root biomass of twenty‐three individuals belonging to three shrub species in a mediterranean shrubland in central Spain: gum rockrose Cistus ladanifer, rosemary Salvia rosmarinus, and hairy‐fruited broom Cytisus striatus. Our goal was to determine the soil‐foraging strategies adopted by the plants. We hypothesized that plants would show stabilizing niche differences explaining the high plant biodiversity characteristic of mediterranean shrublands and that they would follow the game theory model's prediction of exploitative segregation of roots behaving territorially but also over‐proliferating roots close to their stem and engaging in a root tragedy of the commons. We found that two‐thirds to three‐fourths of the biomass was belowground, and the system's productivity was roughly 500–600 g C m−2 year−1. Only rosemary plants competed with neighbors following the exploitative segregation predictions. Broom plants had the shallowest and most widespread root systems but significantly reduced their root range toward competing neighbors. Gum rockrose presented deep, narrow root systems avoiding extensive overlap with neighbors but did not appear to respond to competitive pressure levels. Shrubs appeared to stratify their roots at different soil depths, supporting the niche segregation hypothesis.

Ecological niche modeling of the Leopardus tigrinus complex sheds light on its elusive evolutionary history

Abstract The evolutionary history and taxonomy of the Leopardus tigrinus species complex have been studied based on several approaches, mostly employing genetic and morphological data, leading to distinct classification schemes. We approached this problem from an ecological perspective, with 2 main goals: (i) to evaluate ecological niche differences among regional L. tigrinus populations to determine the extent of ecological divergence among them; and (ii) to identify environmental barriers to historical dispersal that could have driven differentiation among the proposed groups. We modeled the ecological niche of all taxonomic/geographic groups proposed so far to comprise the L. tigrinus complex using the Maximum Entropy algorithm, and evaluated geographic and ecological niche differences among them. Furthermore, we investigated possible environmental barriers to historical dispersal that could have driven differentiation among regional groups. We evaluated 4 hypothetical barriers across 3 time periods to assess their potential historical effect. We found high ecological divergence between northeastern tigrina populations and the northern Andean and Central American tigrinas. Other groups within the L. tigrinus complex are less divergent. In addition, the Guiana Shield tigrina, where the type locality of the species is located, seems to be ecologically similar to populations from northeastern Brazil while also showing some overlap with Andean populations. The Panama center, the Llanos of Colombia and Venezuela, and the Amazon region were identified as historical barriers for tigrina dispersal across all time periods. The inferred historical barriers and ecological divergence observed in this study contribute to the inference of evolutionary differentiation among geographic groups comprising the L. tigrinus complex, revealing areas of consistently low habitat suitability that have likely contributed to divergence among regional populations.

Genomic data provides insights into the evolutionary history and adaptive differentiation of two tetraploid strawberries.

Over the decades, evolutionists and ecologists have shown intense interest in the role of polyploidization in plant evolution. Without clear knowledge of the diploid ancestor(s) of polyploids, we would not be able to answer fundamental ecological questions such as the evolution of niche differences between them or its underlying genetic basis. Here, we explored the evolutionary history of two Fragaria tetraploids, Fragaria corymbosa and Fragaria moupinensis. We de novo assembled five genomes including these two tetraploids and three diploid relatives. Based on multiple lines of evidence, we found no evidence of subgenomes in either of the two tetraploids, suggesting autopolyploid origins. We determined that Fragaria chinensis was the diploid ancestor of F. corymbosa while either an extinct species affinitive to F. chinensis or an unsampled population of F. chinensis could be the progenitor of F. moupinensis. Meanwhile, we found introgression signals between F. chinensis and Fragaria pentaphylla, leading to the genomic similarity between these two diploids. Compared to F. chinensis, gene families related to high ultraviolet (UV)-B and DNA repair were expanded, while those that responded towards abiotic and biotic stresses (such as salt stress, wounding, and various pathogens) were contracted in both tetraploids. Furthermore, the two tetraploids tended to down-regulate defense response genes but up-regulate UV-B response, DNA repairing, and cell division gene expression compared to F. chinensis. These findings may reflect adaptions toward high-altitude habitats. In summary, our work provides insights into the genome evolution of wild Fragaria tetraploids and opens up an avenue for future works to answer deeper evolutionary and ecological questions regarding the strawberry genus.

Mercury concentrations and differences in isotopic niches of fish from upstream and downstream of an Amazon reservoir dam.

Reservoir construction promotes many environmental impacts, including the enhancement of mercury concentrations in fish. The processes that can influence mercury concentrations in fish in Amazonian reservoirs are still little explored in depth, especially when we consider the possible particularities of the ecosystems in question. This study aims to investigate how mercury concentrations in fish could be influenced by the Tucuruí dam, considering possible changes in their feeding and trophic position according to the dam position (up or downstream). Fish were sampled upstream and downstream of the Tucuruí reservoir, and total mercury (THg) and stable isotopes of carbon and nitrogen (δ15N and δ13C) were measured in muscles. We observed three different Hg bioaccumulation patterns influenced by the dam. These differences occurred due to species trophic niche changes corroborated by the isotope analysis. Higher THg concentrations downstream compared to those upstream ones were only observed for Geophagus proximus. On the contrary, Plagioscion squamosissimus, from downstream, presented lower concentrations than upstream ones. The isotopic niche of these two species presented different changes according to the sampled site. THg biomagnification was higher upstream compared to downstream, considering that the regression slope was approximately two times higher upstream versus downstream. THg concentrations in fish were explained by the differences in their feeding habits according to their location in relation to the dam. The difference in THg biomagnification was able to reflect differences in structure of the food web chain in ecosystems under the dam's influence.