CHOICE OF MACROPHYTE SUBSTRATE IN THE USE OF DIATOMS AS INDICATORS OF POND WATER QUALITY ASSESSMENT: PRELIMINARY DATA ON THE CASE OF ALALAY POND (COCHABAMBA, BOLIVIA)

Alalay Pond is a 230-hectare, shallow aquatic ecosystem within Cochabamba, the third largest city in Bolivia. With the aim to determine the suitability of epiphytic diatoms for water quality assessment in the pond and to choose a substrate that would hold a representative bioindicator epiphytic community, the macrophytes Schoenoplectus californicus subsp. tatora (Kunth) T. Koyama, Typha dominguensis Pers., Myriophyllum verticillatum L. and Azolla filiculoides Lam. were selected and differences in diatom community composition and structure were tested. Diatoms were collected during four sampling campaigns in the March-September, 2011 period, from three stations contiguous to the pelagic zone and prepared for analysis using standard, internationally used protocols. In all, 27 samples were collected from which 28 taxa characteristic of eutrophic environments were identified and 17 others could not be assigned names from the literature. Although many of the species are shared among sampling sites, the epiphytic communities developing at each station were different in structure and composition. Although, there are marked temporal variations in community features on each of the macrophytes, Shannon-Wiener and Pielou indexes, as well as canonical correspondence analysis, showed no marked differences within a single campaign and station among the 4 macrophytes. Shifts in structure and composition are denoted less commonly by species replacement and more often by changes in percent relative abundance of dominant and rare species. Very few species are restricted to a station or seem to show strong preference for a particular substrate. Taking into account growth, structural and ecological characteristics, as well as some phenological features of the macrophytes, S. californicus subsp. tatora and T. dominguensis are the most suitable substrates for water quality assessments in the pond. As demonstrated by multivariate analyses, among-site and time-scale differences in community composition and structure were attributable to alkalinity, chemical oxygen demand (COD), ammonium-nitrogen, conductivity and dissolved oxygen (DO). More frequent sampling, diversification of substrates and extending the study for a longer period are recommended to establish a monitoring program during any future restoration of the pon

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

eDNA metabarcoding from aquatic biofilms allows studying spatial and temporal fluctuations of fish communities from Lake Geneva

International audienceAbstract Fish communities are now studied non‐invasively using environmental DNA (eDNA) recovered from water samples. The objective of this study is to evaluate the possibility of surveying these communities using fish eDNA passively “captured” by aquatic biofilms. To this end, biofilm samples developing on natural and artificial substrates were collected every 2 weeks for a year and a half in a large lake (Lake Geneva). DNA was extracted from biofilms and fish communities were targeted using a standard 12S barcode with a metabarcoding approach. The fish eDNA signal recovered from biofilms revealed temporal and spatial changes in fish communities. These changes were linked to fish habitat preferences and spawning season. Peaks in the eDNA signal of some taxa fitted with their spawning period reported in the literature. We evidenced that the nature of the biofilm's substrate (natural or artificial) does not affect the image obtained of the fish community composition. Furthermore, by using biofilms grown on artificial substrates, the studied temporal window of the eDNA signal can be controlled. With biofilms acting as environmental passive samplers, our results open up the possibility to accurately monitor fish communities and their temporal and spatial changes with eDNA in a faster and less expensive way than with the classical water filtration approach

DNA metabarcoding and microscopic analyses of sea turtles biofilms: Complementary to understand turtle behavior.

Sea turtles are distributed in tropical and subtropical seas worldwide. They play several ecological roles and are considered important indicators of the health of marine ecosystems. Studying epibiotic diatoms living on turtle shells suggestively has great potential in the study of turtle behavior because diatoms are always there. However, diatom identification at the species level is time consuming, requires well-trained specialists, and there is a high probability of finding new taxa growing on turtle shells, which makes identification tricky. An alternative approach based on DNA barcoding and high throughput sequencing (HTS), metabarcoding, has been developed in recent years to identify species at the community level by using a DNA reference library. The suitabilities of morphological and molecular approaches were compared. Diatom assemblages were sampled from seven juvenile green turtles (Chelonia mydas) from Mayotte Island, France. The structures of the epibiotic diatom assemblages differed between both approaches. This resulted in different clustering of the turtles based on their diatom communities. Metabarcoding allowed better discrimination between turtles based on their epibiotic diatom assemblages and put into evidence the presence of a cryptic diatom diversity. Microscopy, for its part, provided more ecological information of sea turtles based on historical bibliographical data and the abundances of ecological guilds of the diatom species present in the samples. This study shows the complementary nature of these two methods for studying turtle behavior

Constraint phylogeny based on <i>Nitzschia inconspicua</i> sensu lato and its neighboring species from R-Syst::diatom sequences and on the neighboring OTU sequences of samples taken from the shells of sea turtles.

<p>This tree was obtained using the rapid bootstrapping option in RaxML and was drawn using MEGA7. Only the OTUs were constrained. Grey squares delimit four groups of OTUs that co-occurred on the same turtles.</p

Constraint phylogeny based on R-Syst::diatom sequences and on the OTU sequences of samples taken from the shells of sea turtles.

<p>This tree was obtained using the fast tree search option in RaxML and was drawn using iTOL [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195770#pone.0195770.ref073" target="_blank">73</a>] <a href="http://itol.embl.de/" target="_blank">http://itol.embl.de</a>.</p

Light and scanning electron microscopy images of <i>Nitzschia inconspicua</i> from each turtle.

<p><b>A―E</b>. Light microscopy. <b>A.</b> Turtle 1. <b>B</b>. Turtle 2. <b>C―D</b>. Turtle 5. <b>E.</b> Turtle 6.<b>F―K</b>. Scanning electron microscopy. <b>F</b>. Turtle 1. <b>G.</b> Turtle 2. <b>H.</b> Turtle 3. <b>I</b>. Turtle 4. <b>J</b>. Turtle 5. <b>K.</b> Turtle 6. Scale bar: 10 μm.</p

NMDS ordination plots and cluster representations.

<p>K-means and NMDSs were calculated based on the Bray-Curtis distances of the species lists and the OTU lists (each expressed in percentages) obtained using microscopy and metabarcoding, respectively.</p

Relationship between the genetic distances of OTUs and their occurrences on sea turtles.

<p><b>Genetic distance is based on the number of base substitutions per site between sequences</b>. Occurrence is based on the Spearman correlation coefficient calculated for the abundance of OTUs in the samples. The relationship is linear and significant (p-value < 0.001).</p

Location of Mayotte Island (France) in the south west Indian Ocean.

<p>The black square indicates where the <i>Chelonia mydas</i> were sampled.</p