Two new species of Mesozoic tree ferns(Osmundaceae:Osmundacaulis)in Eurasia as evidence of long-term geographic isolation

The fossil trunks and rhizomes of Osmundaceae provide important information about its evolutionary history.Due to limited records of the Mesozoic trunks and rhizomes in the Eurasia of the Northern Hemisphere,our understanding on the fossil diversity of the Osmundaceae is hindered.Two new species of the Osmundaceae trunks,Osmundacaulis asiatica sp.nov.and Osmundacaulis sinica sp.nov.representing the first discovery of the Mesozoic tree fern genus Osmundacaulis in Eurasia,are described from Wudalianchi and Qiqihar,Heilongjiang Province,Northeast China,which enriches the plant diversity of the Osmundaceae in the Eurasia,and provides vital evidence for studying the distribution,radiation and evolution of the genus during the Cretaceous.The fossil records suggest that Osmundacaulis species may have evolved from a common ancestor,which first appeared in the Australian portion of Pangaea,and then spread to ancient northern North America and ancient East Asia.Since then,they developed into different species through their own evolutionary lines.The Chinese species have a special local feature that the outer cortex is thicker than the inner cortex,in contrast with reported Osmundacaulis species having thinner outer cortex and thicker inner cortex.Long-term geographic isolation may have led to the radiation of diverse Osmundacaulis species and the appearance of region-specific features,such as the thick outer cortex and the thin inner cortex of the Chinese species.Among all reported Osmundacaulis species,the two new species found in China,O.nerii from the Jurassic of Australia and the O.lemonii from the Jurassic of the USA,have special groups of mucilage-sacs inside sclerenchyma ring of petiole base.Mucilage sacs probably originated independently among taxonomic groups,representing convergent adaptations to similar habitats,rather than indicating genetic inheritance from a common ancestor.

Phylogenetic pattern of alpine plants along latitude and longitude in Hengduan Mountains Region

To detect the horizontal pattern of phylogenetic structure shown by alpine plants, we measured phylogenetic structure using net related index(NRI) and net nearest taxon index(NTI), and analyzed the phylogenetic structure patterns of alpine plants along longitude, latitude and environmental gradients in the Hengduan Mountains Region(HDMR). Our results show that: 1) the phylogenetic structure tended to cluster with increasing latitude and longitude; 2) for NRI, latitude was closer related than longitude,while for NTI, longitude was closer related than latitude, though they both not significantly relate to NTI.The phylogenetic structure tended towards overdispersion in the southern HDMR, with good climate conditions of higher mean annual temperature and more mean annual precipitation. In contrast, with harsh climate conditions of lower mean annual temperature and less mean annual precipitation, the increasing environmental stress led to phylogenetic clustering in the northern HDMR. The results highlighted that in the alpine region of HDMR, environmental filters and geographical isolation had a great effect on the latitudinal and longitudinal alpine species distribution, respectively.

Morphological Comparison between Chinese Ayu and Japanese Ayu and Establishment of Plecoglossus altivelis chinensis Wu&Shan subsp.nov.

The countable characters of Qingdao, Zhejiang, Liaoning and Japanese Ayu arecompared. There are no substantial different characters among the former three Ayu, so thecomprehensive values of them are taken as representative of Chinese Ayu, which is in turn comparedwith Japanese Ayu ( Plecoglossus altivelis altivelis and Plecoglossus altivelis ryukyuensis). By thecoefficient of difference test, 3 and 4 characters are found to be beyond the subspecies levelbetween Chinese Ayu and nominate subspecies (Plecoglossus altivelis altivelis) and between ChineseAyu (Plecoglossus altivelis chinensis) and Ryukyus subspecies (Plecoglossus altivelis ryukyuensis),respectively, which shows that they belong to different subspecies. The China mainland Ayu is a newsubspecies, Plecoglossus altivelis chinensis Wu and Shan, the establishment of which and its formingcauses are discussed.

Genetic structure and demographic histories of two sympatric Culter species in eastern China

Geographic isolation is a key factor in shaping the genetic structure of many fish species.Two sympatric species,Culter alburnus and C.mongolicus,are economically important fish that are widely distributed in China and have been recently used as new aquaculture species.We used the mitochondrial DNA control region(CR)as a marker to investigate the genetic structure of the two species.Phylogenetic analysis revealed two major lineages(Lineages I and II)that were highly consistent with geographical patterns for C.alburnus and C.mongolicus.Based on genetic distance,the Zhujiang(Pearl)River Basin(ZRB)populations potentially represented a cryptic subspecies,which might be differentiated as the result of strict geographic isolation,an earlier diverged event,or peripheral areas.Genetic diversity analysis suggested that the Changjiang(Yangtze)River Basin(CRB)populations are located at,or near the core region of their origination,not only due to the larger population size at the CRB,but also their habitat diversity and suitability for its survival,and the genetic diversity dif ferences among basin populations were significant for the two species.Moreover,demographic analysis indicated that the two Culter species and most populations had undergone a period of population expansion during warm interglacial periods.However,the C.alburnus population of Huaihe River Basin(Weishan Lake)exhibited different patterns during the interglacial period,which may due to the latest diverged time of HRB and Weishan Lake located at the permafrost.Notably,the ZRB(in Songtao Reservoir)C.mongolicus population showed no genetic diversity and had a unique haplotype,which could be treated as a special gene pool for species conservation.In summary,geographic isolation is most likely responsible for the two Culter species distribution patterns.

The frontier evolution and emerging trends of hydrological connectivity in river systems:a scientometric review

With the intensification of climate change and human activities,the watershed ecosystem is seriously fragmented,which leads to the obstruction of hydrological connectivity,and further causes the degradation of the ecosystem.As the value of wetlands continues to be exploited,hydrological connectivity becomes increasingly significant.In this paper,the characteristics and development of hydrological connectivity research from 1998 to 2018 were analyzed through the scientometric analysis based on Web of Science database.CiteSpace,an analytical software for scientific measurement,is used to visualize the results of the retrieval.The analysis results of co-occurrence,co-operative and co-cited network indicate that the hydrological connectivity is a multidisciplinary field which involves the Environment Science and Ecology,Water Resources,Environmental Sciences,Geology and Geosciences.According to Keyword cooccurrence analysis,ecosystem,floodplain,dynamics,climate change and management are the main research hotspots in each period.In addition,the co-cited analysis of references shows that“amphibians”is the largest cluster of hydrological connectivity,and the“channel network”is the most important research topic.It is worth noting that the“GIWS”(Geographically Isolated Wetlands)is the latest research topic and may be a major research direction in the future.