Genetic diversity analysis of spawner and recaptured populations of Chinese shrimp(Fenneropenaeus chinensis)during stock enhancement in the Bohai Bay based on an SSR marker

Eight microsatellite markers were used to analyze genetic diversity, level of inbreeding, and effective population size of spawner and recaptured populations of Chinese shrimp（Fenneropenaeus chinensis） during stock enhancement in the Bohai Bay in 2013. A total of 254 and 238 alleles were identified in the spawner and recaptured populations, respectively, and the numbers of alleles（N_a） were 8–63 and 6–60, respectively. The numbers of effective alleles（N_e） were 2.52–21.60 and 2.67–20.72, respectively. The polymorphism information content ranged from 0.529 to 0.952. The observed heterozygosity（H_o） values（0.638–0.910 and 0.712–0.927） were lower than the expected heterozygosity（H_e） values（0.603–0.954 and 0.625–0.952）, which indicated that the two populations possessed a rich genetic diversity. In 16 tests（2 populations×8 loci）, 13 tests deviated from the HardyWeinberg equilibrium. F_（is） values were positive at seven loci and the inbreeding coefficients（F） of the two populations estimated by trio ML were 13.234% and 11.603%, suggesting that there was a relatively high degree of inbreeding. A certain level of inbreeding depression had occurred in the Chinese shrimp population. F_（st） values ranged from 0 to 0.059, with a mean of 0.028, displaying a low level of genetic differentiation in the two populations. Effective population sizes（3 060.2 and 3 842.8） were higher than the minimum number suggested for retaining the evolutionary potential to adapt to new environmental conditions. For enhancement activity in 2014,the ideal number of captured shrimp spawners should have ranged from 7 686 to 19 214 to maintain genetic diversity and effective population size. Further strategies to adjust the balance of economic cost, fishing effort and ideal number of shrimp spawners to maintain a satisfactory effective population size for ensuring the sustainability of Chinese shrimp are proposed.

Current plant diversity but not its soil legacy influences exotic plant invasion

Current plant diversity can influence exotic plant invasion,but it is unclear whether there is a legacy effect of plant diversity on exotic plant invasion.As plant diversity can affect soil microbial communities and physio-chemical properties,which may cascade to impact subsequent exotic plant growth,we hypothesize that the soil legacy effect of plant diversity can influence exotic plant invasion.We conducted a plant–soil feedback experiment.In the conditioning phase,we trained soils by monocultures of 12 plant species from three functional groups(4 grasses,3 legumes and 5 forbs)and mixtures of 8 randomly selected species with all three functional groups from this 12-species pool.In the test phase,we grew the invasive plant Bidens pilosa with a co-occurring native grass(Arthraxon hispidus),with a co-occurring native forb(Pterocypsela indica)or with both in each type of the conditioned soils.The performance of B.pilosa relative to its native competitors varied depending on the functional type of both conditioning plant species in the conditioning phase and competing plant species in the test phase.Diversity of the conditioning plants did not influence the growth difference between B.pilosa and its native competitors.However,increasing diversity of the competing plant species reduced the performance of B.pilosa relative to its native competitors.Our results suggest that current plant diversity can reduce exotic plant invasion through increasing growth inequality between invasive and native plants,but the soil legacy effect of plant diversity may have little impact on exotic plant invasion.

Assessing the genetic diversity of the critically endangered Chinese sturgeon Acipenser sinensis using mitochondrial markers and genome-wide single-nucleotide polymorphisms from RAD-seq

As a living fossil, the endangered Chinese sturgeon(Acipenser sinensis) has been considered a national treasure in China. Here,the famous Gezhouba Dam and Three Gorges Dam on the Yangtze River were built in 1988 and 2006, for economic purposes.The natural population of Chinese sturgeon has declined since then, as these dams block its migratory route to the original spawning grounds in the middle reaches of the Yangtze River. In 2013 and 2014, there was an absence of spawning where it typically happened near the Gezhouba Dam. Nevertheless, from April to June in 2015, over 1,000 larvae with different body lengths(10–35 cm) were detected along the Shanghai Yangtze Estuary; but only little is currently known about the population genetic structure of the Chinese sturgeon. Herein, we inferred population genetic parameters from 462 available Chinese sturgeon specimens based on a 421-bp fragment of the mitochondrial DNA(mtDNA) D-loop region and 1,481,620 SNPs(singlenucleotide polymorphisms) generated by restriction site-associated DNA sequencing(RAD-seq). For the D-loop dataset, 15 haplotypes were determined. Randomly picked 23 individuals, representing the 15 D-loop haplotype groups, were subsequently used for further RAD-seq validation. The average nucleotide diversity calculated from the mtDNA and RAD datasets was 0.0086 and 0.000478, respectively. The overall effective female population size was calculated to be 1,255 to 2,607, and the long-term effective population size was estimated to range from 11,950 to 119,500. We observed that the genetic variability and the effective female population size of the current population in the Yangtze River are severely low, which are similar to the data reported over 10 years ago. The deduced relatively small effective population of female fish, limiting the genetic connectivity among Chinese sturgeon, should be considered a serious threat to this endangered species.

Does hydrological fluctuation alter impacts of species richness on biomass in wetland plant communities?

Aims The diversity-productivity relationship is one of the most critical questions in ecology and can be altered by environmental factors.Hydrological fluctuation affects growth of wetland plants,and such effects vary with plant species.Therefore,we hypothesized that hydrological fluctuation changes effects of species richness on productivity of wetland plant communities.Methods We constructed wetland plant communities consisting of three or six wetland plant species and subjected them to hydrological fluctuation(i.e.gradually changing water level)of two frequencies and two ranges,with unchanged water level as the control.We measured height,root and shoot dry mass of each plant at harvest.Important Findings Hydrological fluctuation significantly decreased biomass of wetland plant communities,which was due to impacts of fluctuation range,but not those of fluctuation frequency.Community biomass was significantly higher when species richness was higher,and such an effect did not depend on hydrological fluctuation.Therefore,hydrological fluctuation can decrease the productivity of wetland plant communities but may not alter the diversity-productivity relationship.

Spatial heterogeneity in soil particle size:does it affect the yield of plant communities with different species richness?

Aims Soil heterogeneity is ubiquitous in many ecosystems.We hypothesized that plant communities with higher species richness might be better adapted to soil heterogeneity and produce more biomass than those with lower richness.This is because there is niche differentiation among species and different species can complement each other and occupy a broader range of niches when plant species richness is high.However,no study has tested how soil particle heterogeneity affects the yield of plant communities,and whether such effects depend on the spatial scale of the heterogeneity and the species richness within the communities.Methods In a greenhouse experiment,we sowed seeds of four-species or eight-species mixtures in three heterogeneous treatments consisting of 32,8 or 2 patches of both small(1.5 mm)and large quartz(3.0 mm)particles arranged in a chessboard manner and one homogeneous treatment with an even mixture of small and large quartz particles.Important Findings Biomass production was significantly greater in the communities with high species richness than those with low species richness.However,soil particle heterogeneity or its interactions with patch scale or species richness did not significantly affect biomass production of the experimental communities.This work indicates that plant species richness may have a bigger impact on plant productivity than soil particle heterogeneity.Further studies should consider multiple sets of plant species during longer time periods to unravel the potential mechanisms of soil heterogeneity and its interactions with the impacts of species richness on community yield and species coexistence.