Three fishes in one: cryptic species in an Amazonian floodplain forest specialist

Accurately describing biodiversity in tropical regions such as Amazonia is difficult because of insufficient morphological inventories and the lack of studies on the distribution of genetic diversity. Aquatic organisms from Amazonian flooded forests are generally expected to move laterally along the forests during the annual inundation cycle, a behaviour that should promote admixture of populations and reduce within‐drainage speciation. We used an unprecedented fine‐scale sampling effort and multiple DNA markers to quantify region‐wide population differentiation in an Amazonian floodplain forest specialist, the black‐wing hatchet fish Carnegiella marthae ( Myers, 1927 ). Our study revealed three previously unsuspected and ancient cryptic species of black‐wing hatchet fish in the Rio Negro floodplain (RNF), in central Amazonia. Two species produce occasional first‐generation hybrids. The third and rarer species, although found in extreme sympatry with another species, appears to be reproductively isolated, and also differs in external morphology and dentition. Our findings have important implications for guiding conservation management because C. marthae is harvested commercially in the RNF ornamental fishery. They also suggest that the diversity of Amazonian ichthyofauna is vastly underestimated, including that found in landscapes lacking contemporary barriers to account for population divergence and speciation. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 391–403.     

Spatial and host related genomic variation in partially sympatric cactophagous moth species

Surveys of patterns of genetic variation in natural sympatric and allopatric populations of recently diverged species are necessary to understand the processes driving intra- and interspecific diversification. The South American moths Cactoblastis cactorum, Cactoblastis doddi and Cactoblastis bucyrus are specialized in the use of cacti as host plants. These species have partially different geographic ranges and differ in patterns of host plant use. However, there are areas that overlap, particularly, in northwestern Argentina, where they are sympatric. Using a combination of genome-wide SNPs and mitochondrial data we assessed intra and interspecific genetic variation and investigated the relative roles of geography and host plants on genetic divergence. We also searched for genetic footprints of hybridization between species. We identified three well delimited species and detected signs of hybridization in the area of sympatry. Our results supported a hypothetical scenario of allopatric speciation in the generalist C. cactorum and genetic interchange during secondary geographic contact with the pair of specialists C. bucyrus and C. doddi that probably speciated sympatrically. In both cases, adaptation to new host plants probably played an important role in speciation. The results also suggested the interplay of geography and host plant use as drivers of divergence and limiting gene flow at intra and interspecific levels.     

The roles of host evolutionary relationships (genus: Nasonia) and development in structuring microbial communities

The comparative structure of bacterial communities among closely related host species remains relatively unexplored. For instance, as speciation events progress from incipient to complete stages, does divergence in the composition of the species’ microbial communities parallel the divergence of host nuclear genes? To address this question, we used the recently diverged species of the parasitoid wasp genus Nasonia to test whether the evolutionary relationships of their bacterial microbiotas recapitulate the Nasonia phylogenetic history. We also assessed microbial diversity in Nasonia at different stages of development to determine the role that host age plays in microbiota structure. The results indicate that all three species of Nasonia share simple larval microbiotas dominated by the γ‐proteobacteria class; however, bacterial species diversity increases as Nasonia develop into pupae and adults. Finally, under identical environmental conditions, the relationships of the microbial communities reflect the phylogeny of the Nasonia host species at multiple developmental stages, which suggests that the structure of an animal's microbial community is closely allied with divergence of host genes. These findings highlight the importance of host evolutionary relationships on microbiota composition and have broad implications for future studies of microbial symbiosis and animal speciation.     

Patterns of speciation are similar across mountainous and lowland regions for a Neotropical plant radiation (Costaceae: Costus)

High species richness and endemism in tropical mountains are recognized as major contributors to the latitudinal diversity gradient. The processes underlying mountain speciation, however, are largely untested. The prevalence of steep ecogeographic gradients and the geographic isolation of populations by topographic features are predicted to promote speciation in mountains. We evaluate these processes in a species-rich Neotropical genus of understory herbs that range from the lowlands to montane forests and have higher species richness in topographically complex regions. We ask whether climatic niche divergence, geographic isolation, and pollination shifts differ between mountain-influenced and lowland Amazonian sister pairs inferred from a 756-gene phylogeny. Neotropical Costus ancestors diverged in Central America during a period of mountain formation in the last 3 million years with later colonization of Amazonia. Although climatic divergence, geographic isolation, and pollination shifts are prevalent in general, these factors do not differ between mountain-influenced and Amazonian sister pairs. Despite higher climatic niche and species diversity in the mountains, speciation modes in Costus appear similar across regions. Thus, greater species richness in tropical mountains may reflect differences in colonization history, diversification rates, or the prevalence of rapidly evolving plant life forms, rather than differences in speciation mode.     

Microsatellite markers for the cardinal tetra Paracheirodon axelrodi,a commercially important fish from central Amazonia

The cardinal tetra Paracheirodon axelrodi is a very popular aquarium fish and the most important ornamental fishery resource for riverine communities inhabiting the Rio Negro floodplain in central Amazonia. Here we describe the isolation and characterization of 14 microsatellite DNA loci for cardinal tetras. Number of alleles and heterozygosity per locus in a sample of 30 fish ranged from 2 to 22 and from 0.49 to 0.92, respectively. These markers provide powerful tools for studies on conservation and management of cardinal tetra resources and for investigating evolutionary processes underlying population diversification in Amazonian flooded forest fishes.     

Parasite species coexistence and limiting similarity: a multiscale look at phylogenetic,functional and reproductive distances

The factors that control biodiversity have been the focus of numerous recent investigations; these include species interactions, speciation, environmental gradients and heterogeneity, all of these operating differently at each observation scale. We used a null model to examine the influence of two forces shaping the community structure of Dactylogyrus species parasitic on roach (Rutilus rutilus) gills: interspecific competition that might prevent the coexistence of the most similar species and environmental filters that might result in the most similar species coexisting together. The study was carried out on two sets of fish from two different localities in the Morava river basin (Czech Republic) to evaluate the consistency of the results across host populations, and at three different scales of observation to test for the scale dependence of assembly rules. In decreasing order, from largest to smallest, the three spatial scales investigated were: the individual fish, the individual gill arch and individual sections of each gill arch. The similarity between pairs of parasite species was measured using three different criteria: (1) phylogeny, (2) quantitative functional traits consisting of parasite size and morphometric measurements of the attachment organ’s sclerotized parts and (3) qualitative attributes of reproductive organs. First, our study reveals a strong conservatism of ecological characters for the nine Dactylogyrus parasite species, in particular regarding the attributes of their copulatory organs. Second, our study did not find any limitation of similarity among coexisting Dactylogyrus species due to interspecific competition, irrespective of the scale and the similarity measures considered. Conversely, our results support the niche filtering hypothesis, preventing the co-occurrence of species too dissimilar from one another. This process is particularly apparent at the scale of the individual fish and for functional traits associated with the hard parts of the parasites’ attachment organs. In both localities, the Dactylogyrus species that occur on the same fish individuals tend to have similar values for the haptor dimensions. Our study supports previous studies on monogenean parasite communities indicating a weak influence of competition as a structuring force, but it goes a step further by identifying environmental filtering as a key process shaping these communities.     

Co‐evolutionary patterns in congeneric monogeneans: a review of Dactylogyrus species and their cyprinid hosts

Patterns associated with the evolution of parasite diversity, speciation and diversification were analysed using Dactylogyrus species (gill monogeneans) and their cyprinid hosts as a model. The aim of this study was to use this highly specific host–parasite systems to review: (1) the diversity and distribution of Dactylogyrus species, (2) the patterns of organization and structure of Dactylogyrus communities, (3) the evolution and determinants of host specificity and (4) the mode of Dactylogyrus speciation and co‐evolutionary patterns in this Dactylogyrus–cyprinid systems. Dactylogyrus are a highly diverse group of parasites, with their biogeography and distribution clearly linked to the evolutionary history of their cyprinid hosts. The coexistence of several Dactylogyrus species on one host is facilitated by increasing niche distances and the differing morphology of their reproductive organs. The positive interspecific and intraspecific interactions seem to be the most important factors determining the structure of Dactylogyrus communities. Host specificity is partially constrained by parasite phylogeny. Being a strict specialist is an ancestral character for Dactylogyrus, being the intermediate specialists or generalists are the derived characters. The evolution of attachment organ morphology is associated with both parasite phylogeny and host specificity. Considering larger and long‐lived hosts or hosts with several ecological characters as the measures of resource predictability, specialists with larger anchors occurred on larger or longer‐living fish species. Intra‐host speciation, a mode of speciation not often recorded in parasites, was observed in Dactylogyrus infecting sympatric cyprinids. Sister parasite species coexisting on the same host occupied niches that differed in at least one niche variable. Intra‐host speciation, however, was not observed in Dactylogyrus species of congeneric hosts from geographically isolated areas, which suggested association by descent and host‐switching events.     

The ecology of the phyllosphere: geographic and phylogenetic variability in the distribution of bacteria on tree leaves

Large populations of bacteria live on leaf surfaces and these phyllosphere bacteria can have important effects on plant health. However, we currently have a limited understanding of bacterial diversity on tree leaves and the inter‐ and intra‐specific variability in phyllosphere community structure. We used a barcoded pyrosequencing technique to characterize the bacterial communities from leaves of 56 tree species in Boulder, Colorado, USA, quantifying the intra‐ and inter‐individual variability in the bacterial communities from 10 of these species. We also examined the geographic variability in phyllosphere communities on Pinus ponderosa from several locations across the globe. Individual tree species harboured high levels of bacterial diversity and there was considerable variability in community composition between trees. The bacterial communities were organized in patterns predictable from the relatedness of the trees as there was significant correspondence between tree phylogeny and bacterial community phylogeny. Inter‐specific variability in bacterial community composition exceeded intra‐specific variability, a pattern that held even across continents where we observed minimal geographic differentiation in the bacterial communities on P. ponderosa needles.     

Broad Scale Distribution of Ferns and Lycophytes along Environmental Gradients in Central and Northern Amazonia,Brazil

Establishing which factors determine species distributions is of major relevance for practical applications such as conservation planning. The Amazonian lowlands exhibit considerable internal heterogeneity that is not apparent in existing vegetation maps. We used ferns as a model group to study patterns in plant species distributions and community composition at regional and landscape scales. Fern species composition and environmental data were collected in 109 plots of 250 × 2 m distributed among four sites in Brazilian Amazonia. Interplot distances varied from 1 to ca 670 km. When floristically heterogeneous datasets were analyzed, the use of an extended Sørensen dissimilarity index rather than the traditional Sørensen index improved model fit and made interpretation of the results easier. Major factors associated with species composition varied among sites, difference in cation concentration was a strong predictor of floristic dissimilarity in those sites with pronounced heterogeneity in cation concentration. Difference in clay content was the most relevant variable in sites with uniform cation concentrations. In every case, environmental differences were invariably better than geographic distances in predicting species compositional differences. Our results are consistent with the ideas that: (1) the relative predictive capacity of the explanatory variables depend on the relative lengths of the observed gradients; and (2) environmental gradients can be hierarchically structured such that gradients occur inside gradients. Therefore, site‐specific relationships among variables can mask the bigger picture and make it more difficult to unravel the factors structuring plant communities in Amazonia.     

Host community similarity and geography shape the diversity and distribution of haemosporidian parasites in Amazonian birds

Identifying the mechanisms driving the distribution and diversity of parasitic organisms and characterizing the structure of parasite assemblages are critical to understanding host–parasite evolution, community dynamics, and disease transmission risk. Haemosporidian parasites of the genera Plasmodium and Haemoproteus are a diverse and cosmopolitan group of bird pathogens. Despite their global distribution, the ecological and historical factors shaping the diversity and distribution of these protozoan parasites across avian communities and geographic regions remain unclear. Here we used a region of the mitochondrial cytochrome b gene to characterize the diversity, biogeographical patterns, and phylogenetic relationships of Plasmodium and Haemoproteus infecting Amazonian birds. Specifically, we asked whether, and how, host community similarity and geography (latitude and area of endemism) structure parasite assemblages across 15 avian communities in the Amazon Basin. We identified 265 lineages of haemosporidians recovered from 2661 sampled birds from 330 species. Infection prevalence varied widely among host species, avian communities, areas of endemism, and latitude. Composition analysis demonstrated that both malarial parasites and host communities differed across areas of endemism and as a function of latitude. Thus, areas with similar avian community composition were similar in their parasite communities. Our analyses, within a regional biogeographic context, imply that host switching is the main event promoting diversification in malarial parasites. Although dispersal of haemosporidian parasites was constrained across six areas of endemism, these pathogens are not dispersal‐limited among communities within the same area of endemism. Our findings indicate that the distribution of malarial parasites in Amazonian birds is largely dependent on local ecological conditions and host evolutionary relationships.     

RIVERSCAPE GENETICS IDENTIFIES REPLICATED ECOLOGICAL DIVERGENCE ACROSS AN AMAZONIAN ECOTONE

Ecological speciation involves the evolution of reproductive isolation and niche divergence in the absence of a physical barrier to gene flow. The process is one of the most controversial topics of the speciation debate, particularly in tropical regions. Here, we investigate ecologically based divergence across an Amazonian ecotone in the electric fish, Steatogenys elegans. We combine phylogenetics, genome scans, and population genetics with a recently developed individual‐based evolutionary landscape genetics approach that incorporates selection. This framework is used to assess the relative contributions of geography and divergent natural selection between environments as biodiversity drivers. We report on two closely related and sympatric lineages that exemplify how divergent selection across a major Amazonian aquatic ecotone (i.e., between rivers with markedly different hydrochemical properties) may result in replicated ecologically mediated speciation. The results link selection across an ecological gradient with reproductive isolation and we propose that assortative mating based on water color may be driving the divergence. Divergence resulting from ecologically driven selection highlights the importance of considering environmental heterogeneity in studies of speciation in tropical regions. Furthermore, we show that framing ecological speciation in a spatially explicit evolutionary landscape genetics framework provides an important first step in exploring a wide range of the potential effects of spatial dependence in natural selection.     

Disentangling the assembly mechanisms of ant cuticular bacterial communities of two Amazonian ant species sharing a common arboreal nest

Bacteria living on the cuticle of ants are generally studied for their protective role against pathogens, especially in the clade of fungus‐growing ants. However, little is known regarding the diversity of cuticular bacteria in other ant host species, as well as the mechanisms leading to the composition of these communities. Here, we used 16S rRNA gene amplicon sequencing to study the influence of host species, species interactions and the pool of bacteria from the environment on the assembly of cuticular bacterial communities on two phylogenetically distant Amazonian ant species that frequently nest together inside the roots system of epiphytic plants, Camponotus femoratus and Crematogaster levior. Our results show that (a) the vast majority of the bacterial community on the cuticle is shared with the nest, suggesting that most bacteria on the cuticle are acquired through environmental acquisition, (b) 5.2% and 2.0% of operational taxonomic units (OTUs) are respectively specific to Ca. femoratus and Cr. levior, probably representing their respective core cuticular bacterial community, and (c) 3.6% of OTUs are shared between the two ant species. Additionally, mass spectrometry metabolomics analysis of metabolites on the cuticle of ants, which excludes the detection of cuticular hydrocarbons produced by the host, were conducted to evaluate correlations among bacterial OTUs and m/z ion mass. Although some positive and negative correlations are found, the cuticular chemical composition was weakly species‐specific, suggesting that cuticular bacterial communities are prominently environmentally acquired. Overall, our results suggest the environment is the dominant source of bacteria found on the cuticle of ants.     

Temporally consistent species differences in parasite infection but no evidence for rapid parasite‐mediated speciation in Lake Victoria cichlid fish

Parasites may have strong eco‐evolutionary interactions with their hosts. Consequently, they may contribute to host diversification. The radiation of cichlid fish in Lake Victoria provides a good model to study the role of parasites in the early stages of speciation. We investigated patterns of macroparasite infection in a community of 17 sympatric cichlids from a recent radiation and 2 older species from 2 nonradiating lineages, to explore the opportunity for parasite‐mediated speciation. Host species had different parasite infection profiles, which were only partially explained by ecological factors (diet, water depth). This may indicate that differences in infection are not simply the result of differences in exposure, but that hosts evolved species‐specific resistance, consistent with parasite‐mediated divergent selection. Infection was similar between sampling years, indicating that the direction of parasite‐mediated selection is stable through time. We morphologically identified 6 Cichlidogyrus species, a gill parasite that is considered a good candidate for driving parasite‐mediated speciation, because it is host species‐specific and has radiated elsewhere in Africa. Species composition of Cichlidogyrus infection was similar among the most closely related host species (members of the Lake Victoria radiation), but two more distantly related species (belonging to nonradiating sister lineages) showed distinct infection profiles. This is inconsistent with a role for Cichlidogyrus in the early stages of divergence. To conclude, we find significant interspecific variation in parasite infection profiles, which is temporally consistent. We found no evidence that Cichlidogyrus‐mediated selection contributes to the early stages of speciation. Instead, our findings indicate that species differences in infection accumulate after speciation.     

Diversity and biogeography of vascular epiphytes in Western Amazonia, Yasuní, Ecuador

Aim Although vascular epiphytes are important components of species richness and complexity of Neotropical forests, vascular epiphytes are under‐represented in large scale biogeographical analyses. We studied the diversity, biogeography and floristic relationships of the epiphytic flora of the Yasuní region (Western Amazonia) in a Neotropical context, with special emphasis on the influence of the Andean flora on floristic composition and diversity of surrounding lowland forests. Location Western Amazonian lowland rainforest, Tiputini Biodiversity Station (0°38′ S 76°09′ W, 230 m a.s.l., 650 ha), Yasuní National Park, Ecuador. Methods We compared the vascular epiphyte flora of Yasuní with 16 published Neotropical epiphyte inventories. Secondly, based on a floristic database with records of more than 70,000 specimens of vascular epiphytes from the Neotropics the elevational composition of eight selected inventories was analysed in detail. Results The vascular epiphyte flora of Yasuní is characterized by a very high species richness (313 spp.). A moderate portion of species is endemic to the Upper Napo region (c. 10%). However, this figure is much higher than previous analyses primarily based on woody species suggested. Geographical ranges of these species match with a proposed Pleistocene forest refuge. Compared with Northern and Central Amazonian sites, Western Amazonian epiphyte communities are characterized by a higher portion of montane and submontane species. Species richness of vascular epiphytes at the sites was correlated with the amount of rainfall, which is negatively correlated with the number of dry months. Main conclusion Recent and historic patterns of rainfall are the driving forces behind diversity and floristic composition of vascular epiphytes in Western Amazonia: high annual rainfall in combination with low seasonality provides suitable conditions to harbour high species richness. The proximity to the Andes, the most important centre of speciation for most Neotropical epiphytic taxa, in combination with the climatic setting has allowed a continuous supply of species richness to the region. At least for epiphytes, the borderline between the Andean and Amazonian flora is much hazier than previously thought. Moreover, the comparatively moist climate in Western Amazonia during the Pleistocene has probably led to fewer extinctions and/or more speciation than in more affected surrounding lowlands.     

Community assembly of a euryhaline fish microbiome during salinity acclimation

Microbiomes play a critical role in promoting a range of host functions. Microbiome function, in turn, is dependent on its community composition. Yet, how microbiome taxa are assembled from their regional species pool remains unclear. Many possible drivers have been hypothesized, including deterministic processes of competition, stochastic processes of colonization and migration, and physiological ‘host‐effect’ habitat filters. The contribution of each to assembly in nascent or perturbed microbiomes is important for understanding host–microbe interactions and host health. In this study, we characterized the bacterial communities in a euryhaline fish and the surrounding tank water during salinity acclimation. To assess the relative influence of stochastic versus deterministic processes in fish microbiome assembly, we manipulated the bacterial species pool around each fish by changing the salinity of aquarium water. Our results show a complete and repeatable turnover of dominant bacterial taxa in the microbiomes from individuals of the same species after acclimation to the same salinity. We show that changes in fish microbiomes are not correlated with corresponding changes to abundant taxa in tank water communities and that the dominant taxa in fish microbiomes are rare in the aquatic surroundings, and vice versa. Our results suggest that bacterial taxa best able to compete within the unique host environment at a given salinity appropriate the most niche space, independent of their relative abundance in tank water communities. In this experiment, deterministic processes appear to drive fish microbiome assembly, with little evidence for stochastic colonization.     

Competition from sea to mountain: Interactions and aggregation in low‐diversity monogenean and endohelminth communities in twospot livebearer Pseudoxiphophorus bimaculatus (Teleostei: Poeciliidae) populations in a neotropical river

1. The role of interspecific interactions in structuring low‐diversity helminth communities is a controversial topic in parasite ecology research. Most parasitic communities of fish are species‐poor; thus, interspecific interactions are believed to be unimportant in structuring these communities.
2. We explored the factors that might contribute to the richness and coexistence of helminth parasites of a poeciliid fish in a neotropical river.
3. Repeatability of community structure was examined in parasitic communities among 11 populations of twospot livebearer Pseudoxiphophorus bimaculatus in the La Antigua River basin, Veracruz, Mexico. We examined the species saturation of parasitic communities and explored the patterns of species co‐occurrence. We also quantified the associations between parasitic species pairs and analyzed the correlations between helminth species abundance to look for repeated patterns among the study populations.
4. Our results suggest that interspecific competition could occur in species‐poor communities, aggregation plays a role in determining local richness, and intraspecific aggregation allows the coexistence of species by reducing the overall intensity of interspecific competition.

     

Diversification by host switching and dispersal shaped the diversity and distribution of avian malaria parasites in Amazonia

Understanding how pathogens and parasites diversify through time and space is fundamental to predicting emerging infectious diseases. Here, we use biogeographic, coevolutionary and phylogenetic analyses to describe the origin, diversity, and distribution of avian malaria parasites in the most diverse avifauna on Earth. We first performed phylogenetic analyses using the mitochondrial cytochrome b (cyt b) gene to determine relationships among parasite lineages. Then, we estimated divergence times and reconstructed ancestral areas to uncover how landscape evolution has shaped the diversification of Parahaemoproteus and Plasmodium in Amazonia. Finally, we assessed the coevolutionary patterns of diversification in this host–parasite system to determine how coevolution may have influenced the contemporary diversity of avian malaria parasites and their distribution among Amazonian birds. Biogeographic analysis of 324 haemosporidian parasite lineages recovered from 4178 individual birds provided strong evidence that these parasites readily disperse across major Amazonian rivers and this has occurred with increasing frequency over the last five million years. We also recovered many duplication events within areas of endemism in Amazonia. Cophylogenetic analyses of these blood parasites and their avian hosts support a diversification history dominated by host switching. The ability of avian malaria parasites to disperse geographically and shift among avian hosts has played a major role in their radiation and has shaped the current distribution and diversity of these parasites across Amazonia.     

Patterns of environmental variability influence coral‐associated bacterial and algal communities on the Mesoamerican Barrier Reef

A coral's capacity to alter its microbial symbionts may enhance its fitness in the face of climate change. Recent work predicts exposure to high environmental variability may increase coral resilience and adaptability to future climate conditions. However, how this heightened environmental variability impacts coral‐associated microbial communities remains largely unexplored. Here, we examined the bacterial and algal symbionts associated with two coral species of the genus Siderastrea with distinct life history strategies from three reef sites on the Belize Mesoamerican Barrier Reef System with low or high environmental variability. Our results reveal bacterial community structure, as well as alpha‐ and beta‐diversity patterns, vary by host species. Differences in bacterial communities between host species were partially explained by high abundance of Deltaproteobacteria and Rhodospirillales and high bacterial diversity in Siderastrea radians. Our findings also suggest Siderastrea spp. have dynamic core bacterial communities that likely drive differences observed in the entire bacterial community, which may play a critical role in rapid acclimatization to environmental change. Unlike the bacterial community, Symbiodiniaceae composition was only distinct between host species at high thermal variability sites, suggesting that different factors shape bacterial versus algal communities within the coral holobiont. Our findings shed light on how domain‐specific shifts in dynamic microbiomes may allow for unique methods of enhanced host fitness.     

Embryonic development characteristics and host mussel utilization of flat bitterling <Emphasis Type="Italic">Acheilognathus rhombeus</Emphasis> (Cyprinidae) during winter in Korea

This study aimed to investigate the embryonic development characteristics and host mussel utilization of Acheilognathus rhombeus to determine its adaptations or host utilization for improving survival during winter in the wild; the study was conducted from August 2014 to May 2015. Spawning of A. rhombeus occurred between mid-September and early November, peaking between late September and early October of 2014 when the water temperature was 19–21°C. The embryos of A. rhombeus were first found in early October of 2014 and remained inside the host mussel for 7 months. Development retardation and diapause in embryonic stages (stages C and D) occurred before eye pigmentation and continued until late March of 2015. Subsequently, the embryos resumed development (stage E) when the water temperature increased to about 10 °C. The positions during the development of A. rhombeus embryos in the mussels were mainly present in the farthest suprabranchial cavity and not in the water tube. The embryos were frequently found in the two inner demibranches of the four gills of the mussels regardless of their sex. We assume that embryonic diapause and use of suprabranchial cavity and inner demibranches of the gills of the mussels by A. rhombeus might be the optimal adaptation to maintain high embryonic survival in low water temperature during winter and to avoid interspecific competition.     

The legacy of human use in Amazonian palm communities along environmental and accessibility gradients

Aim

Palms are iconic and dominant elements of neotropical forests. In the Amazon region, palms have been used and managed by humans for food, material, medicine and other purposes for millennia. It is, however, debated to what extent the structure of modern palm communities reflects long-term human modification. Here, we investigate the complex interplay of ecological and societal factors that influence the distributions of both human-used and non-used palms in western Amazonia.

Location

Amazonia.

Time period

Present.

Major taxa studied

Palms (Arecaceae).

Methods

We used Bayesian hierarchical joint species distribution models to predict the distributions and environmental niche dimensions of 78 western Amazonian species, and to explore their relationships with their diversity of human uses and with specific uses (food, construction and medicine). The models were parameterized with a comprehensive set of field- and satellite-derived environmental predictors.

Results

Our results suggest that a combination of ecological and anthropogenic factors drive the present-day distributions of Amazonian palms. The modelled ecological niches of the species revealed use-related species-sorting along soil, climatic, accessibility and drainage gradients. We found peaks in the proportions of useful palms and their diversity of uses in fertile soils, close to rivers, and on floodplains. These are habitats favourable for human settlement, although they harbour naturally restricted palm species pools. We also found a negative correlation between predicted palm species richness and number of human uses across western Amazonia.

Main conclusions

Soil characteristics, accessibility, and species pool size all contribute to defining palm–human relationships. At the basin scale, the signature of human use on palm communities was predicted to be stronger in the species-poor south-west than in central-western Amazonia. Overall, we conclude that environmental conditions have influenced modern Amazonian palm distributions both directly and indirectly, by regulating human settlement patterns and natural resource use over extended time periods.