Geographical gradients in the biodiversity of Chinese freshwater molluscs: Implications for conservation

Beetle mania: Understanding pond aquatic beetles diversity patterns through a multiple-facet approach

Ecological studies searching for drivers of biodiversity variation have frequently focused on taxonomic richness. However, more aspects of biodiversity, namely diversity facets can be considered to properly assess biotic-environment relationships. Here, we explore the environmental factors that could control the four biodiversity facets of aquatic Coleoptera from 93 regionally sampled Patagonian ponds. We also explore which are the ponds with high diversity values of all facets to prioritize them with a high conservation value. We fitted generalized additive models (GAM) to test relationships among environment (i.e., local and climatic variables) and aquatic beetles diversity facets (i.e., richness (SD), functional diversity (FD), phylogenetic diversity (PD), and local contribution to local beta diversity (LCBD). Climatic drivers were the most important predictors of beetle diversity facets, which exhibited linear and nonlinear responses. Thus, ponds from warmer Patagonia exhibited the highest values of SD and PD, whereas LCBD also peaked on colder sites suggesting that ponds under extreme temperatures sustain unique beetle assemblages. Moreover, ponds located in areas with higher precipitation variability exhibit the highest values of LCBD (i.e., unique assemblages). This result in addition to arid conditions in Patagonia prevailing since 16 m.y.a made us think that Patagonian beetle pond-dwellers are basally adapted to aridity. We calculated an index that summarizes the four facets patterns, to assign high conservation value to those ponds with higher index values. The relative importance of each facet varies from pond to pond. Hence, this multifaceteded approach not only allows us to identify priority areas for biodiversity conservation but also focuses on the importance of including multiple facets to understand biodiversity spatial patterns.

Biodiversity patterns diverge along geographic temperature gradients

Models applying space-for-time substitution, including those projecting ecological responses to climate change, generally assume an elevational and latitudinal equivalence that is rarely tested. However, a mismatch may lead to different capacities for providing climatic refuge to dispersing species. We compiled community data on zooplankton, ectothermic animals that form the consumer basis of most aquatic food webs, from over 1200 mountain lakes and ponds across western North America to assess biodiversity along geographic temperature gradients spanning nearly 3750 m elevation and 30° latitude. Species richness, phylogenetic relationships, and functional diversity all showed contrasting responses across gradients, with richness metrics plateauing at low elevations but exhibiting intermediate latitudinal maxima. The nonmonotonic/hump-shaped diversity trends with latitude emerged from geographic interactions, including weaker latitudinal relationships at higher elevations (i.e. in alpine lakes) linked to different underlying drivers. Here, divergent patterns of phylogenetic and functional trait dispersion indicate shifting roles of environmental filters and limiting similarity in the assembly of communities with increasing elevation and latitude. We further tested whether gradients showed common responses to warmer temperatures and found that mean annual (but not seasonal) temperatures predicted elevational richness patterns but failed to capture consistent trends with latitude, meaning that predictions of how climate change will influence diversity also differ between gradients. Contrasting responses to elevation- and latitude-driven warming suggest different limits on climatic refugia and likely greater barriers to northward range expansion.

Loss of lateral hydrological connectivity impacts multiple facets of molluscan biodiversity in floodplain lakes

Lateral hydrological connectivity (LHC) is a key process in maintaining aquatic biodiversity in river floodplain ecosystems. However, the effects of LHC loss on aquatic biodiversity are rarely studied. Here, we evaluated, for the first time, the responses of multiple facets (i.e., taxonomic, functional and phylogenetic) of alpha and beta diversity of freshwater molluscs to the LHC loss in 23 floodplain lakes in the Yangtze River Basin in China. Our results showed that taxonomic and functional alpha diversities were all significantly higher in connected lakes (CLs) than in disconnected lakes (DLs), whereas phylogenetic alpha diversity (Δ⁺) was lower in CLs than in DLs. For beta diversity facets, taxonomic (Tβ_sor) and phylogenetic (Pβ_sor) dissimilarities were slightly more contributed by the turnover component or equally contributed by the turnover and nestedness-resultant components both in CLs and DLs. Instead, functional beta diversity (Fβ_sor), generally showing much lower values than Tβ_sor and Pβ_sor, was mainly contributed by the nestedness-resultant component (76.6-84.0%), especially in DLs. We found that only functional dissimilarities were significantly higher in DLs than CLs, indicating a high level of functional diversity loss without replacement of species possessing traits sensitive to hydrological disconnection (i.e., large body size, lamellibranch body form, filter feeding, ovoviviparity and burrowing habits). In general, lake area, hydrological connectivity, aquatic vegetation coverage and nutrient levels (TN and TP) played important roles in structuring variation in molluscan alpha and beta diversities, although the three diversity facets responded to different environmental factors. Our results suggest that loss of connectivity to the mainstem river has negative impacts on molluscan assemblages in floodplain lakes. More importantly, as taxonomic, functional and phylogenetic diversities responded somewhat differently to the loss of hydrological connectivity, all of these biodiversity facets should be better incorporated into aquatic biodiversity assessment and conservation programs in large river floodplains.

Responses of multiple facets of macroinvertebrate alpha diversity to eutrophication in floodplain lakes

The accelerated eutrophication of freshwater lakes has become an environmental problem worldwide. Increasing numbers of studies highlight the need to incorporate functional and phylogenetic information of species into bioassessment programms, but it is still poorly understood how eutrophication affects multiple diversity facets of freshwater communities. Here, we assessed the responses of taxonomic, phylogenetic and functional diversity of benthic macroinvertebrates to water eutrophication in 33 lakes in the Yangtze River floodplain in China. Our results showed that macroinvertebrate assemblage structure was significantly different among four lake groups (river-connected, macrophyte-dominated, macrophyte-algae transition, and algae-dominated). Three taxonomic, two phylogenetic and two functional diversity indices were significantly different among the lake groups. Except for the increasing trend of Lambda⁺, these metrics showed a clear decreasing trend with increasing levels of eutrophication, with highest values detected in river-connected and macrophyte-dominated lakes, followed by macrophyte-algae transition lakes and algal-dominated lakes. Although differing in the number and identity of key environmental and spatial variables among the explanatory models of different diversity indices, environmental factors (eutrophication-related water quality variables) played more important role than spatial factors in structuring all three facets of alpha diversity. The predominant role of environmental filtering can be attributed to the strong eutrophication gradient across the studied lakes. Among the three diversity facets, functional diversity indices performed best in portraying anthropogenic disturbances, with variations in these indices being solely explained by environmental factors. Spatial factors were mostly weak or negligible in accounting for the variation in functional diversity indices, implying that trait-based indices are robust in portraying anthropogenic eutrophication in floodplain lakes. However, variation in some taxonomic and phylogenetic diversity indices were also affected by spatial factors, indicating that conservation practitioners and environmental managers should use these metrics with caution when providing solutions for addressing eutrophication in floodplain lakes.

Distribution and Assemblage Variation of Benthic Macroinvertebrates: A Uniform Elevational Biodiversity Pattern Among Different Groups?

Biodiversity patterns along the elevational gradient of vertebrates have been widely focused on in previous studies, but they are still insufficient on invertebrates in lakes to a wide elevational extent. Based on field samplings and literature, we compared biodiversity patterns among different taxonomic groups of benthic macroinvertebrates in 104 lakes of China and India along an elevational gradient of 2–5,010 m a.s.l. and revealed the key driving factors, and then, we discussed the key mechanisms underlying elevational biodiversity patterns. We found that elevational biodiversity patterns of different taxonomic groups were not uniform, e.g., an exponentially decreasing pattern of Bivalvia, a first horizontal and then decreasing pattern of Gastropoda, and a linear decreasing pattern of Oligochaeta and Insecta. Elevation and elevation-controlled variables (temperature and salinity) were the key driving factors to biodiversity patterns. Their effects were strongest on Bivalvia and less on Gastropoda, whereas they were relatively weak on Oligochaeta and Insecta. Finally, we discussed three important mechanisms that shaped elevational biodiversity patterns and assemblage variations of benthic macroinvertebrates by linking our results with the classic hypotheses about biodiversity patterns, including climate/productivity, environmental heterogeneity, and dispersal/history. These results could improve our understanding of biodiversity patterns and biodiversity conservation.

Effects of dam construction and fish invasion on the species, functional and phylogenetic diversity of fish assemblages in the Yellow River Basin

An understanding of the consequences of human-mediated disturbances from multi-facet diversity (i.e. species, functional and phylogenetic) perspectives is of great significance in biodiversity assessment and conservation planning. Most previous studies have concentrated on anthropogenic effects on species diversity in the Yellow River Basin (YRB) in China, but information on anthropogenic effects on phylogenetic and functional facets is still pending. Here, we identified the temporal changes in species, functional, and phylogenetic alpha diversity of fish assemblages in 18 reaches (i.e. 15 mainstream reaches and 3 tributaries) of the YRB under the background of long-term cascade hydropower construction and widespread introduction of non-native fish species. The results showed that native fishes experienced a sharp decline through time, with an average of 25.6 (extirpation rate 46.7%) native species extirpated per sub-region, and 89 of 182 (48.9%) native species extirpated across the whole basin during the period considered. However, the number of non-native fish species substantially increased, with an average increase of 8.6 species (invasion rate 26.9%) per sub-region. Furthermore, the percentage of non-native species showed a significant unimodal relationship with average altitude, with highest invasion rates (ca. 70%) in upstream reaches. The extirpation rate was negatively related to altitude, increasing from upstream to downstream reaches. Interestingly, the functional diversity indices (FE_ve, FD_iv, FD_is, RaoQ) and phylogenetic diversity indices (Δ⁺ and Λ⁺) of the entire fish fauna significantly increased through time, whereas these indices based on native fish fauna only did not change. Such increases in functional and phylogenetic diversities were mainly triggered by introductions of non-native species, which were functionally distinct and phylogenetically distant from native species, and extirpation of congeneric endemic species. In general, the present study revealed anthropogenic impacts on the multi-faceted diversity of fish assemblages in a large river and highlighted the negative effects of cascaded hydropower developments and non-native fish invasions on native fish. Moreover, evaluating the responses of multi-faceted diversity to anthropogenic disturbances is a suitable means to understand assemblage reorganization and to assess how such impacts lead to the decline of biodiversity. The complementary information derived from using the multi-faceted diversity approach indicate functional and phylogenetic diversity measures could be implemented in biodiversity planning in the sediment-laden and ecologically important Yellow River Basin.

Developing a statistical-weighted index of biotic integrity for large-river ecological evaluations

The efficiency, accuracy and universality of ecological assessment methods comprise an important foundation for comprehensive assessment and restoration of large river ecological health at the watershed scale. New evaluation metrics and methods are urgently needed to be developed to adapt the characteristics of large rivers, including geographical differences in surface runoff, regional ecological complexity, and seasonal changes. In this study, a bacteria-weighted index of biotic integrity was developed to assess the ecological health of large rivers (lrBW-IBI) based on compositional and functional characteristics of sediment bacterial communities from 33 sections of the lower mainstream of Yangtze River. Five key metrics were determined by range, responsiveness, and redundancy tests. Principal component analysis (PCA), entropy method, criteria importance through intercriteria correlation and random forest were applied to calculate weighted coefficients of key metrics. The optimal lrBW-IBI was observed through the sum of PCA weighted-metrics: the relative abundance of Latescibacteria (0.234), Gemmatimonadaceae (0.149), Nitrospira spp. (0.234), Rhizobiales (0.228), and nitrogenase NifH (0.156). According to PCA based lrBW-IBI, 12.12%, 24.24%, 39.39%, and 24.24% of river sections were labeled excellent, good, moderate, and relatively poor, respectively. The ecological status of the lower mainstream of the Yangtze River did not change significantly across seasons but declined gradually from upstream to downstream. This study provides a new assessment tool for the ecological health of large rivers and highlights the importance of microbial ecological index in river ecology.

Multifaceted biodiversity measurements reveal incongruent conservation priorities for rivers in the upper reach and lakes in the middle-lower reach of the largest river-floodplain ecosystem in China

Biological conservation necessitates robust understanding of multifaceted biodiversity from local to regional scales. Mismatches among multifaceted diversity and conservation trade-offs are the most important challenge for conservation planning. The Yangtze River floodplain is among the most speciose whereas threatened and poorly protected ecosystems in China. Here we evaluated multifaceted (taxonomic, phylogenetic, and functional) alpha and beta fish diversity by simultaneously addressing two typical habitats (FRs, floodplain rivers and FLs, floodplain lakes) in this basin, to reliably aid conservation planning across local and regional scales. Our results demonstrated spatially incongruent multifaceted fish diversity between FRs and FLs. Characterizing by flocks of phylogenetic close species, we detected significantly higher species richness while lower phylogenetic and functional alpha diversity in FRs. In contrast, fish assemblages in FLs exhibited significantly higher functional alpha diversity characterized by functional unique species. Consequently, conservation planning should fasten on clusters of phylogenetic close endemic species to sustain high intrinsic species richness in FRs, and sustain high functional diversity as well as protecting fish species with unique functions in FLs. Meanwhile, for all the taxonomic, phylogenetic, and functional facets, our results demonstrated significantly higher turnover components in FRs, and the dominant contribution of the nestedness components to overall beta diversity in FLs. As a result, conservation planning in FLs may just focus on several richest lakes, while multiple spatially disjunct river networks should be protected in FRs. Contradicting the anthropocentric "new conservation", our study advocated protecting intrinsic uniqueness and peculiarity of multifaceted biodiversity as well as the ecological integrity.

Patterns of Mekong Mollusc Biodiversity: Identification of Emerging Threats and Importance to Management and Livelihoods in a Region of Globally Significant Biodiversity and Endemism

The Lower Mekong Basin (LMB) is a key biodiversity hotspot. To facilitate conservation and management, we examine mollusc biodiversity patterns and distribution along LMB’s longitudinal gradients, identify environmental drivers, and discuss the importance of these drivers to management. Cluster analysis, redundancy analysis (RDA), and variation partitioning were conducted using mollusc data collected from 63 sampling sites. Results indicated that species diversity is dominated by gastropods (61%) and bivalves (39%) and feeding trait diversity by scrapers (52%) and filter-collectors (37%). Only 48 species (49%) out of 98 taxa have been assessed by the International Union for Conservation of Nature (IUCN) including a growing number of invasive species. The lack of complete, up-to-date information highlights the need for more research on both native and alien species. Cluster analysis revealed a clear mollusc biodiversity structure along the LMB’s longitudinal segments. Diversity was lowest in upstream tributaries, increased in upstream main channels, and was highest in downstream channels and the Mekong delta, the exception being the observed high gastropod abundance in Chi-Mun river mouth and Luang Prabang areas. The RDA and variation partitioning demonstrated that combined physical–chemical and climatic conditions are the key drivers of biodiversity patterns. Given the potential spread of invasive alien species and increasing anthropogenic impacts, further ecological research, regular monitoring, and adaptive management are needed to sustain mollusc biodiversity and associated ecosystem services, which contribute to food security, nutrition, and livelihoods in the LMB.

Phylogenetic position of Aculamprotula polysticta, comb. res. (Bivalvia : Unionidae) inferred from phylogenetic relationships in Unionida

Accurate phylogenies are important for understanding the evolutionary histories of organisms, their reproductive traits and ecological habits. The freshwater mussel order Unionida is currently thought to include six families. However, assignment of particular species to these families has been unstable, particularly for species that have been described solely on conchological characters. Unio polystictus Heude, 1877 represents such a species. Based on DNA sequence data from five genes (COI, 16S rRNA, 18S rRNA, 28S rRNA and histone H3) and complete mitochondrial genomes, we investigated the phylogenetic position and generic affinities of U. polystictus using various analytical methods. Both the five-gene and mitogenome datasets strongly supported transferring U. polystictus from Margaritiferidae to Unionidae as Aculamprotula polysticta, comb. res. Our results also supported the following intrageneric relationships: (Aculamprotula tortuosa, ((Aculamprotula polysticta, Aculamprotula scripta), (Aculamprotula fibrosa, Aculamprotula tientsinersis))). In addition, by comparing the morphological features of Aculamprotula (Unionidae, Unioninae), Lamprotula (Unionidae, Gonideinae) and Gibbosula (Margaritiferidae, Gibbosulinae) species, potential issues of relying solely on shell morphology for high-level classification of freshwater mussels are highlighted. Confirmation of classification position and genetic relationship for Aculamprotula polysticta will helpful to understand the ecological characteristics, reproductive strategies and host-fish requirements, which can be inferred from closely related taxa.

Spatially Structured Environmental Variation Plays a Prominent Role on the Biodiversity of Freshwater Macrophytes Across China

Different non-mutually exclusive mechanisms interactively shape large-scale diversity patterns. However, our understanding of multi-faceted diversity and their determinants in aquatic ecosystems is far from complete compared to terrestrial ones. Here, we use variation partitioning based on redundancy analysis to analyze the relative contribution of environmental and spatial variables to the patterns of phylogenetic, taxonomic, and functional diversity in macrophyte assemblages across 214 Chinese watersheds. We found extremely high spatial congruence among most aspects of biodiversity, with some important exceptions. We then used variation partitioning to estimate the proportions of variation in macrophyte biodiversity explained by environmental and spatial variables. All diversity facets were optimally explained by spatially structured environmental variables, not the pure environment effect, implying that macrophyte are taxonomically, phylogenetically, and functionally clustered in space, which might be the result of the interaction of environmental and/or evolutionary drives. We demonstrate that macrophytes might face extensive dispersal limitations across watersheds such as topography and habitat fragmentation and availability.

Multiple facets of stream macroinvertebrate alpha diversity are driven by different ecological factors across an extensive altitudinal gradient

Environmental filtering and spatial structuring are important ecological processes for the generation and maintenance of biodiversity. However, the relative importance of these ecological drivers for multiple facets of diversity is still poorly understood in highland streams. Here, we examined the responses of three facets of stream macroinvertebrate alpha diversity to local environmental, landscape-climate and spatial factors in a near-pristine highland riverine ecosystem. Taxonomic (species richness, Shannon diversity, and evenness), functional (functional richness, evenness, divergence, and Rao's Quadratic entropy), and a proxy of phylogenetic alpha diversity (taxonomic distinctness and variation in taxonomic distinctness) were calculated for macroinvertebrate assemblages in 55 stream sites. Then Pearson correlation coefficient was used to explore congruence of indices within and across the three diversity facets. Finally, multiple linear regression models and variation partitioning were employed to identify the relative importance of different ecological drivers of biodiversity. We found most correlations between the diversity indices within the same facet, and between functional richness and species richness were relatively strong. The two phylogenetic diversity indices were quite independent from taxonomic diversity but correlated with functional diversity indices to some extent. Taxonomic and functional diversity were more strongly determined by environmental variables, while phylogenetic diversity was better explained by spatial factors. In terms of environmental variables, habitat-scale variables describing habitat complexity and water physical features played the primary role in determining the diversity patterns of all three facets, whereas landscape factors appeared less influential. Our findings indicated that both environmental and spatial factors are important ecological drivers for biodiversity patterns of macroinvertebrates in Tibetan streams, although their relative importance was contingent on different facets of diversity. Such findings verified the complementary roles of taxonomic, functional and phylogenetic diversity, and highlighted the importance of comprehensively considering multiple ecological drivers for different facets of diversity in biodiversity assessment.

Analysis of mitochondrial genomes resolves the phylogenetic position of Chinese freshwater mussels (Bivalvia, Unionidae)

The Yangtze River basin is one of the most species-rich regions for freshwater mussels on Earth, but is gravely threatened by anthropogenic activities. However, conservation planning and management of mussel species has been hindered by a number of taxonomic uncertainties. In order to clarify the taxonomic status and phylogenetic position of these species, mitochondrial genomes of four species (Acuticostachinensis, Schistodesmuslampreyanus, Cuneopsisheudei and Cuneopsiscapitatus) were generated and analyzed along with data from 43 other mitogenomes. The complete F-type mitogenomes of A.chinensis, S.lampreyanus, C.heudei, and C.capitatus are 15652 bp, 15855 bp, 15892 bp, and 15844 bp, respectively, and all four F-type mitogenomes have the same pattern of gene arrangement. ML and BI trees based on the mitogenome dataset are completely congruent, and indicate that the included Unionidae belong to three subfamilies with high bootstrap and posterior probabilities, i.e., Unioninae (Aculamprotula, Cuneopsis, Nodularia, and Schistodesmus), Anodontinae (Cristaria, Arconaia, Acuticosta, Lanceolaria, Anemina, and Sinoanodonta), and Gonideinae (Ptychorhynchus, Solenaia, Lamprotula, and Sinohyriopsis). Results also indicate that A.chinensis has affinities with Arconaialanceolata and Lanceolariagrayii and is a member of the subfamily Anodontinae.

Changes in multiple facets of macroinvertebrate alpha diversity are linked to afforestation in a subtropical riverine natural reserve

Land use change is one of the major factors impacting freshwater biodiversity. Afforestation could convert new lands from agriculture or urban land uses to reduce erosion and lead to landscape alterations and biodiversity changes. Here, we examined the changes in the three facets of macroinvertebrate alpha diversity (i.e., taxonomic, functional, and phylogenetic diversity) and further explored possible mechanisms driving their variations before (2007) and after (2016) afforestation along the undammed Chishui River, the core of the National Nature Reserve of Rare and Endemic Fishes in the Upper Yangtze River. We found that taxonomic diversity measures (e.g., species richness, Shannon-Wiener index and Simpson index) increased but all measures of functional diversity (e.g., FRic, FEve, FDiv, and RaoQ) and phylogenetic diversity (e.g., indices of taxonomic distinctness) exhibited stability after the afforestation practice. We also found that only significant taxonomic diversity variation was detected and it showed a relationship to alterations of land use rather than local environmental condition changes across the 10-year afforestation practice. Moreover, hydrology and nutrients levels showed changes after afforestation, but these changes had no effect on the biodiversity changes based on multiple linear regression models. In each survey, the three facets of alpha diversity were significantly explained by natural physical factors and showed inconsistent responses to these underlying environmental variables. In addition, the biodiversity-environment relationships remained stable before and after afforestation, indicating that the inherent mechanisms that drive macroinvertebrate community variation have not changed. Our findings highlight that different alpha diversity measures of lotic macroinvertebrates provide different information about biodiversity and respond differently to various environmental variables. Thus, it is necessary to integrate them into one framework when applying routine monitoring, assessment, and conservation procedures based on lotic macroinvertebrates.

Functional and Taxonomic Differentiation of Macrophyte Assemblages Across the Yangtze River Floodplain Under Human Impacts

Human activities and the consequent extirpations of species have been changing the composition of species assemblages worldwide. These anthropogenic impacts alter not only the richness of assemblages but also the biological dissimilarity among them. One of the main gaps in the assessment of biodiversity change in freshwater ecosystems is our limited understanding regarding how taxonomic and functional facets of macrophyte assemblages respond to human impacts on regional scales. Here, we assess the temporal (before 1970s against after 2000s) changes in taxonomic and functional richness and compositional dissimilarities, partitioned into its turnover and nestedness components, of freshwater macrophyte assemblages across the floodplain lakes of the Yangtze River in China. We found that functional and taxonomic assemblage differentiation occurred simultaneously under increasing human impact, concomitant to a general decrease in functional and taxonomic richness. However, this effect weakened when the historical level of taxonomic dissimilarity among assemblages was high. Macrophyte species with large dispersal range and submersed life form were significantly more susceptible to extirpation. The impact of human activities on differentiation was complex but habitat loss and fishery intensity were consistently the main drivers of assemblage change in these lakes, whereas water quality (i.e., light pollution and nutrient enrichment) had weaker effects. Further, macrophyte taxonomic and functional differentiation was mainly driven by the nestedness component of dissimilarity, accounting for changes in assemblage composition related to changes in species richness independent of species replacement. This result, markedly different from previous studies on freshwater fish assemblages conducted in these lakes, represents a novel contribution toward achieving a more holistic understanding of how human impacts contribute to shape community assemblages in natural ecosystems.