Genetic variants of mitochondrial DNA (mtDNA) at the individual (heteroplasmy) and population (polymorphism) levels provide insight into their roles in multiple cellular and evolutionary processes. However, owing to the paucity of genome-wide data at the within-individual and population levels, the broad patterns of these two forms of variation remain poorly understood. Here, we analyze 1,804 complete mitochondrial genome sequences from Daphnia pulex, D. pulicaria, and D. obtusa. Extensive heteroplasmy is observed in D. obtusa, where the high level of intraclonal divergence must have resulted from a biparental-inheritance event, and recombination in the mitochondrial genome is apparent, although perhaps not widespread. Global samples of D. pulex reveal remarkably low mitochondrial effective population sizes, < 3% of those for the nuclear genome. In addition, levels of population diversity in mitochondrial and nuclear genomes are uncorrelated across populations, suggesting an idiosyncratic evolutionary history of mitochondria in D. pulex. These population-genetic features appear to be a consequence of background selection associated with highly deleterious mutations arising in the strongly linked mitochondrial genome, which is consistent with polymorphism and divergence data suggesting a predominance of strong purifying selection. Nonetheless, the fixation of mildly deleterious mutations in the mitochondrial genome also appears to be driving positive selection on genes encoded in the nuclear genome whose products are deployed in the mitochondrion.

Whole-genome duplications (WGDs) have shaped the gene repertoire of many eukaryotic lineages. The redundancy created by WGDs typically results in a phase of massive gene loss. However, some WGD-derived paralogs are maintained over long evolutionary periods, and the relative contributions of different selective pressures to their maintenance is still debated. Previous studies have revealed a history of three successive WGDs in the lineage of the ciliate Paramecium tetraurelia and two of its sister species from the P. aurelia complex. Here, we report the genome sequence and analysis of 10 additional P. aurelia species and one additional outgroup, revealing aspects of post-WGD evolution in 13 species sharing a common ancestral WGD. Contrary to the morphological radiation of vertebrates that putatively followed two WGD events, members of the cryptic P. aurelia complex have remained morphologically indistinguishable after hundreds of millions of years. Biases in gene retention compatible with dosage constraints appear to play a major role opposing post-WGD gene loss across all 13 species. In addition, post-WGD gene loss has been slower in Paramecium than in other species having experienced genome duplication, suggesting that the selective pressures against post-WGD gene loss are especially strong in Paramecium. A near complete lack of recent single-gene duplications in Paramecium provides additional evidence for strong selective pressures against gene-dosage changes. This exceptional dataset of 13 species sharing an ancestral WGD and two closely related outgroup species will be a useful resource for future studies on Paramecium as a major model organism in the evolutionary cell biology.

Chinese online shopping industry has grown dramatically in recent decades. The purpose of this study is to investigate the key factors that affect the operating performance of online shopping companies in China. In particular, the study examines the three features of Chinese online shopping companies: (i) Multi-complex products/a single-special product, (ii) online store only/online and offline stores, (iii) US-listed/China-listed. The tests are leveraged by applying DuPont analysis which is widely used for identifying the sources of operating performance. DuPont analysis decomposes ROA (return on assets) into ATO (asset turnover) and PM (profit margin). A higher ATO represents efficient use of assets while a higher PM indicates efficient cost structure. By using seven Chinese online shopping companies, we find that companies selling multi-complex products have a higher ATO than companies selling a single-special product. However, multi-complex companies’ PM is lower than that of single-special companies, with no difference in ROA between those two groups. Second, online shopping companies with offline stores have a lower PM and ROA than online store only companies. Lastly, we document that US-listed online shopping companies have a higher ATO, PM, and ROA than China-listed companies. The results of this study provide important implications for the future development of the Chinese shopping industry. The findings may present the current situation and shortcomings of the companies, thereby playing a guiding role in the management and development of online shopping companies in China.

During the survey of pathogenic fungi on medicinal plant leaves in Yunnan Province, China, two Cladosporium-like taxa were isolated from leaf spots of Paris polyphylla. Based on morphological characteristics and phylogenetic analysis of combined ITS, TEF1-α and ACT genes, two new species were discovered. Two new species Cladosporium yunnanensis and C. paris are introduced, the detailed descriptions and illustrations are provided. Morphology of the two new species is compared with other related Cladosporium species. This study widens the host diversity of the genus Cladosporium.