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摘要: Freshwater brown algae have been acknowledged as the least diverse of all groups of freshwater algae. Morphological and molecular investigation were conducted on a freshwater brown alga collected in this study. Morphological characterization and phylogenetic tree based on the rbcL gene confirmed its attribution to Heribaudiella fluviatilis. The complete organelle genomes of H. fluviatilis were determined and assembled from highthroughput sequencing. A circular tetrad structure of 128,880 bp was identified for the chloroplast, and the mitochondrial genome was assembled as a circle with 43,657 bp in length. This study provides the first and only record of organelle genomic information of the freshwater Phaeophyceae, which are important for understanding the endosymbiosis theories. Concatenated (Bayesian inference, maximum likelihood under MFP and GHOST models) and coalescent methods were used to construct the phylogenetic relationship among secondary plastidbearing lineages based on organelle genomes. Obvious conflicts were observed in grouping relationships of chloroplast and mitochondrial genomes, even among different evolutionary models and tree-constructing methods. The transcriptome of H. fluviatilis was sequenced and used to construct the phylogenetic relationship among secondary plastid-bearing lineages. The phylogenetic relationships in nuclear and mitochondrial genomes were consistent in grouping CHSR taxa (cryptophytes, haptophytes, stramenopiles and rhizarians) in an independent branch. The phylogenetic relationship constructed from nuclear transcriptomes was highly reliable by owning robust supporting values on each node and was consistent with the serial endosymbiosis theory on evolution of red secondary plastid-derived lineages.

摘要: Life history theory predicts that species-specific life history traits are shaped by variations in environmental conditions. Understanding the key environmental factors determining life history strategies can provide insights into the mechanisms of community assembly and identify potential biodiversity threats by predicting selective responses to environmental perturbations. We collected life history traits for fish species from 14 river basins across 5 continents to identify their life history strategies and explore the related key environmental factors. Our results showed that fishes from all the river basins conformed to a triangular life history strategy model including periodic, opportunistic, and equilibrium endpoints. However, the proportions of these three strategies varied significantly amongst river basins. For example, the Rhine River basin had a high proportion of fish with the periodic strategy and a low proportion of fish with the opportunistic strategy, whereas the Mississippi River basin displayed the opposite pattern. At the river basin extent, linear regression analysis revealed that the proportion of species with the opportunistic strategy increased with mean annual temperature, annual variation in river discharge, and annual precipitation, and was negatively associated with latitude. In contrast, species with the periodic strategy were negatively related to annual variation in river discharge and positively with latitude. These findings corroborate that opportunistic species are adapted to unpredictable environments, whereas periodic species are adapted to predictable environments. We then used molecular phylogeny to reconstruct the ancestral state of Yangtze fishes and analyzed the percentage composition of the three life history strategies across geological times. We found dominance of the equilibrium strategy in the Upper Cretaceous followed by dominance of periodic fishes before the Paleocene. Opportunistic fish species began to dominate the Yangtze River basin after the Miocene, with more than half of the fish species being opportunistic. This implies that the environmental conditions in the Yangtze River basin evolved from stable (low annual variation in river discharge) to unstable (high annual variation in river discharge and high annual precipitation) states, possibly associated with the onset of seasonality expressed as prevalence of a monsoon climate and the overall alteration of precipitation patterns. Life history theory can give hints for assessing river ecological conditions because changes in strategy proportions may indicate the alteration of environmental conditions. Such changes can aid in developing suitable strategies for river ecological protection and fish resource management.

摘要: Given their varied physiological and ecological attributes, phytoplankton frequently exhibit disparate responses to changes in environmental conditions. Therefore, when studying modifications in the structure of a phytoplankton community, it is necessary to consider such differences and investigate the underlying mechanisms. Through a field sampling study of 26 lakes, we found that the differing responses of phytoplankton to changes in environmental factors were partly related to their genome size. The Cyanobacteria and Chrysophyta, which possess smaller genomes, exhibited a relatively low degree of sensitivity to alterations in nutrient concentrations. However, they demonstrated a stronger dependence on the metabolic processes of environmental microorganisms compared to other phytoplankton with larger genomes. Furthermore, the Cyanobacteria and Chrysophyta were more closely associated with environmental nutrients and water chemistry and were more actively involved in interspecific interactions among phytoplankton. By randomly deleting sample points, we verified the generality of the above conclusions. However, more refined grouping analyses indicate that diatoms exhibited different ecological characteristics due to their physiological and morphology. The present study offers new insights into the mechanisms underlying the ecological adaptations of phytoplankton and may provide new guidance for the management of Cyanobacterial blooms. Further studies could take a more refined approach to investigate the effect of phytoplankton effective genome size on their adaptive capacity.