Leaching of dissolved organic matter from seagrass leaf litter and its biogeochemical implications

Dissolved organic matter（DOM） represents a significant source of nutrients that supports the microbial-based food web in seagrass ecosystems. However, there is little information on how the various fractions of DOM from seagrass leaves contributed to the coastal biogeochemical cycles. To address this gap, we carried out a 30-day laboratory chamber experiment on tropical seagrasses Thalassia hemprichii and Enhalus acoroides. After 30 days of incubation, on average 22% carbon（C）, 70% nitrogen（N） and 38% phosphorus（P） of these two species of seagrass leaf litter was released. The average leached dissolved organic carbon（DOC）, dissolved organic nitrogen（DON） and dissolved organic phosphorus（DOP） of these two species of seagrass leaf litter accounted for 55%, 95% and 65% of the total C, N and P lost, respectively. In the absence of microbes, about 75% of the total amount of DOC, monosaccharides（MCHO）, DON and DOP were quickly released via leaching from both seagrass species in the first 9 days. Subsequently, little DOM was released during the remainder of the experiment. The leaching rates of DOC, DON and DOP were approximately 110, 40 and 0.70 μmol/（g·d）. Leaching rates of DOM were attributed to the nonstructural carbohydrates and other labile organic matter within the seagrass leaf. Thalassia hemprichii leached more DOC, DOP and MCHO than E. acoroides. In contrast, E. acoroides leached higher concentrations of DON than T. hemprichii, with the overall leachate also having a higher DON： DOP ratio. These results indicate that there is an overall higher amount of DOM leachate from T. hemprichii than that of E. acoroides that is available to the seagrass ecosystem. According to the logarithmic model for DOM release and the in situ leaf litter production（the Xincun Bay, South China Sea）, the seagrass leaf litter of these two seagrass species could release approximately 4×10~3 mol/d DOC, 1.4×10~3 mol/d DON and 25 mol/d DOP into the seawater. In addition to providing readily available nutrients for the microbial food web, the remaining particulate organic matter（POM）from the litter would also enter microbial remineralization processes. What is not remineralized from either DOM or POM fractions has potential to contribute to the permanent carbon stocks.

Migration departure strategies of shorebirds at a final pre-breeding stopover site

Background: Departure decisions and behaviors of migratory birds at stopover sites are expected to maximize fit?ness by trade?offs among avoiding predators, optimizing refueling(energy) capacity, and matching other life?history events. We predict that species with different body sizes and migratory destinations will exhibit different behaviors when departing from the same stopover site. We also predict that with strong time constraint at the final pre?breed?ing stopover site, departure decisions may be less sensitive to exogenous factors, such as wind condition, compared to other stopover or nonbreeding sites.Methods: We recorded migratory departures of four shorebird species, i.e. Eurasian Curlew(Numenius arquata), Bar?tailed Godwit(Limosa lapponica), Great Knot(Calidris tenuirostris), and Grey Plover(Pluvialis squatarola), at Yaluji?ang Estuary Wetlands in China, a final pre?breeding stopover site in the northern Yellow Sea, from 2011 to 2014. We compared flock sizes, departure time and departure directions between species, and investigated the effects of tide and weather conditions(rain and ground wind speed and direction) on the departure decision of shorebirds.Results: We found that larger species departed in smaller flocks and were more variable in daily departure time. Departure trajectory of all four species appeared to be influenced by coastal topography. With the east–west coast?line and intertidal mudflat on the south, birds exhibited westward or eastward deflection from the shortest migra?tory routes. Bar?tailed Godwit was the only species that deviated to the southeast and did not climb over the land. Birds avoided departure during precipitation, while their departure was not related to ground wind benefit or tidal condition.Conclusions: Body size among species, which influences their vulnerability to predators, might be important in shaping shorebird departure strategies. Diverse departure directions could be the result of different wind use tac?tics in climbing stage. Narrow optimal time window of breeding might lead to reduced flexibility in departure date at a final pre?breeding site. Both endogenous and exogenous are important in shaping departure behaviors and decisions.

Plant growth in a fragmented forest is a consequence of top-down and bottom-up processes, but not their interaction

Aims Habitat loss and fragmentation are the leading causes of global biodiversity decline.How fragmentation(leading to edge effects,increased isolation and declining habitat size)interacts with top-down processes like vertebrate herbivory,an important driver of vegetation structure and composition in many ecosystems,is poorly quantified.Interactions between fragmentation and changes in her-bivory may exacerbate their individual influences on plant growth,with implications for management of native plant communities within fragmented landscapes.We examined the effects of habitat fragmentation on herbivore activity,and also how both fragmen-tation and mammalian herbivory influence growth of understorey plant species.Methods This study was conducted at the Wog Wog habitat fragmentation experiment,located in south-eastern New South Wales,Australia.We use herbivore exclusion plots across an experimentally frag-mented landscape to assess the interactive effects of fragmenta-tion and herbivory on the growth of four plant species that vary in growth form and rarity in the landscape.Important Findings We observed species-specific responses to both herbivory and fragmentation,but no additive or interactive effects between these drivers.We show that a reduction in herbivore activity within frag-ments does not correspond with an increase in plant growth,even for the most palatable species.Rather,top-down processes continue to operate across the fragmented landscape.Although changes in habitat conditions within fragments appear to negatively influence both plant growth and mammalian herbivore activity,it is likely that alterations to bottom-up effects(i.e.fragmentation)may be more important than top-down effects(i.e.herbivores)for the spe-cies under investigation.The species-specific response of plants to herbivory or fragmentation may have implications for temporal and spatial population persistence in fragmented landscapes and ulti-mately fragment vegetation structure.

The first draft genome assembly and data analysis of the Malaysian mahseer (Tor tambroides)

The Malaysian mahseer(Tor tambroides),one of the most valuable freshwater fish in the world,is mainly targeted for human consumption.The mitogenomic data of this species is available to date,but the genomic information is still lacking.For the first time,we sequenced the whole genome of an adult fish on both Illumina and Nanopore platforms.The hybrid genome assembly had resulted in a sum of 1.23 Gb genomic sequence from the 44,726 contigs found with 44 kb N50 length and BUSCO genome completeness of 87.6%.Four types of SSRs had been detected and identified within the genome with a greater AT abundance than that of GC.Predicted protein sequences had been functionally annotated to public databases,namely GO,KEGG and COG.A maximum likelihood phylogenomic tree containing 52 Actinopterygii species and one Sarcopterygii species as outgroup was constructed,providing first insights into the genome-based evolutionary relationship of T.tambroides with other ray-finned fish.These data are crucial in facilitating the study of population genomics,species identification,morphological variations,and evolutionary biology,which are helpful in the conservation of this species.

Is there evidence of selection in the dopamine receptor D4 gene in Australian invasive starling populations？

Although population genetic theory is largely based on the premise that loci under study are selectively neutral, it has been acknowledged that the study of DNA sequence data under the influence of selection can be useful. In some circumstances, these loci show increased population differentiation and gene diversity. Highly polymorphic loci may be especially useful when studying populations having low levels of diversity overall, such as is often the case with threatened or newly established inva- sive populations. Using common starlings Sturnus vulgaris sampled from invasive Australian populations, we investigated se- quence data of the dopamine receptor D4 gene （DRD4）, a locus suspected to be under selection for novelty-seeking behaviour in a range of taxa including humans and passerine birds. We hypothesised that such behaviour may be advantageous when species encounter novel environments, such as during invasion. In addition to analyses to detect the presence of selection, we also esti- mated population differentiation and gene diversity using DRD4 data and compared these estimates to those from microsatellite and mitochondrial DNA sequence data, using the same individuals. We found little evidence for selection on DRD4 in starlings. However, we did find elevated levels of within-population gene diversity when compared to microsatellites and mitochondrial DNA sequence, as well as a greater degree of population differentiation. We suggest that sequence data from putatively non- neutral loci are a useful addition to studies of invasive populations, where low genetic variability is expected

A perspective on sensory drive

In 1992, The American Naturalist published a special supplement entitled： ＂Sensory Drive. Does Sensory Drive Biology Bias or Constrain the Direction of Evolution？＂ organized by John Endler. The supplement contained a seminal paper on ＂sensory drive＂ by Endler （1992a） as well as several other well-cited papers on sensory exploitation （Ryan and Keddy-Hector 1992）.

Spatiotemporal patterns and trends of community transmission of the pandemic COVID-19 in South Asia: Bangladesh as a case study

South Asian(SA)countries have been fighting with the pandemic novel coronavirus disease 2019(COVID-19)since January 2020.Earlier,the country-specific descriptive study has been done.Nevertheless,as transboundary infection,the border sharing,shared cultural and behavioral practice,effects on the temporal and spatial distribution of COVID-19 in SA is still unveiled.Therefore,this study has been revealed the spatial hotspot along with descriptive output on different parameters of COVID-19 infection.We extracted data from theWHO and the worldometer database from the onset of the outbreak up to 15 May,2020.Europe has the highest case fatality rate(CFR,9.22%),whereas Oceania has the highest(91.15%)recovery rate from COVID-19.Among SA countries,India has the highest number of cases(85,790),followed by Pakistan(38,799)and Bangladesh(20,065).However,the number of tests conducted was minimum in this region in comparison with other areas.The highest CFR was recorded in India(3.21%)among SA countries,whereas Nepal and Bhutan had no death record due to COVID-19 so far.The recovery rate varies from 4.75%in the Maldives to 51.02%in Sri Lanka.In Bangladesh,community transmission has been recorded,and the highest number of cases were detected in Dhaka,followed by Narayanganj and Chattogram.We detected Dhaka and its surrounding six districts,namely Gazipur,Narsingdi,Narayanganj,Munshiganj,Manikganj,and Shariatpur,as the 99%confidence-based hotspot where Faridpur and Madaripur district as the 95%confidence-based spatial hotspots of COVID-19 in Bangladesh.However,we did not find any cold spots in Bangladesh.We identified three hotspots and three cold spots at different confidence levels in India.Findings from this study suggested the“Test,Trace,and Isolation”approach for earlier detection of infection to prevent further community transmission of COVID-19.