Using eDNA to detect the distribution and density of invasive crayfish in the Honghe-Hani rice terrace World Heritage site

The Honghe-Hani landscape in China is a UNESCO World Natural Heritage site due to the beauty of its thousands of rice terraces, but these structures are in danger from the invasive crayfish Procambarus clarkii. Crayfish dig nest holes, which collapse terrace walls and destroy rice production. Under the current control strategy, farmers self-report crayfish and are issued pesticide, but this strategy is not expected to eradicate the crayfish nor to prevent their spread since farmers are not able to detect small numbers of crayfish. Thus, we tested whether environmental DNA (eDNA) from paddy-water samples could provide a sensitive detection method. In an aquarium experiment, Real-time Quantitative polymerase chain reaction (qPCR) successfully detected crayfish, even at a simulated density of one crayfish per average-sized paddy (with one false negative). In a field test, we tested eDNA and bottle traps against direct counts of crayfish. eDNA successfully detected crayfish in all 25 paddies where crayfish were observed and in none of the 7 paddies where crayfish were absent. Bottle-trapping was successful in only 68% of the crayfish-present paddies. eDNA concentrations also correlated positively with crayfish counts. In sum, these results suggest that single samples of eDNA are able to detect small crayfish populations, but not perfectly. Thus, we conclude that a program of repeated eDNA sampling is now feasible and likely reliable for measuring crayfish geographic range and for detecting new invasion fronts in the Honghe Hani landscape, which would inform regional control efforts and help to prevent the further spread of this invasive crayfish

Capture efficiency and size selectivity of sampling gears targeting red-swamp crayfish in several freshwater habitats

The ecological importance of the red-swamp crayfish (Procambarus clarkii) in the functioning of freshwater aquatic ecosystems is becoming more evident. It is important to know the limitations of sampling methods targeting this species, because accurate determination of population characteristics is required for predicting the ecological success of P. clarkii and its potential impacts on invaded ecosystems. In the current study, we addressed the question of trap efficiency by comparing population structure provided by eight trap devices (varying in number and position of entrances, mesh size, trap size and construction materials) in three habitats (a pond, a reed bed and a grassland) in a French marsh in spring 2010. Based on a large collection of P. clarkii (n = 2091, 272 and 213 respectively in the pond, reed bed and grassland habitats), we found that semi-cylindrical traps made from 5.5 mm mesh galvanized steel wire (SCG) were the most efficient in terms of catch probability (96.7–100% compared to 15.7–82.8% depending on trap types and habitats) and catch-per-unit effort (CPUE: 15.3, 6.0 and 5.1 crayfish·trap-1·24 h-1 compared to 0.2–4.4, 2.9 and 1.7 crayfish·trap-1·24 h-1 by the other types of fishing gear in the pond, reed bed and grassland respectively). The SCG trap was also the most effective for sampling all size classes, especially small individuals (carapace length \hbox{$\leqslant 30$} ⩽ 30 mm). Sex ratio was balanced in all cases. SCG could be considered as appropriate trapping gear to likely give more realistic information about P. clarkii population characteristics than many other trap types. Further investigation is needed to assess the catching effort required for ultimately proposing a standardised sampling method in a large range of habitats

FISH COMMUNITY STRUCTURE IN TEMPORARY LOWLAND FLOODED GRASSLANDS

In the context of a clear-cutting experiment of sedge areas on seasonally flooded grasslands, we described the fish community structure and the relationships between its spatial organisation and some environmental variables in early spring in 2000. A confinement gradient related to an increase in macrophyte density and determined by the nearest distance from permanent waters seemed to be a key factor in structuring the fish community in the flooded grasslands. Along this gradient, Cyprinids (essentially 0+) dominated near permanent water bodies (95% in abundance) but were substituted further by more tolerant species (Anguilla anguilla and Lepomis gibbosus) and mainly Ameiurus melas (age > 1, 40% in abundance). Although most species (10/13) present in the main permanent channels have been found in flooded grasslands, the efficiency of these grasslands as fish habitat was low compared to other similar sites from literature. We concluded on the importance of a confinement gradient and the water regime, isolating grasslands during summer and responsible of the scarce presence of fish

Presence of two independent chromosomes in the Brucella melitensis 16M genome.

Mapping the restriction fragments of the Brucella melitensis 16M genome with a new restriction endonuclease, PacI, which cut the DNA into only eight fragments, indicated that this species contains two unique and independent replicons of about 2,100 and 1,150 kb. Pulsed-field gel electrophoresis of intact DNA revealed two bands migrating the expected distances. These replicons were identified as two unique and independent chromosomes by the presence of rRNA operons and genes for heat shock proteins mapping to separate replicons

Análise morfológica de Sagittaria montevidensis desenvolvida em diferentes condições de inundação Morphological analysis of Sagittaria montevidensis developed under different flooding conditions

O cultivo de arroz irrigado em sistema pré-germinado tem permitido o desenvolvimento de plantas daninhas aquáticas, como as da espécie Sagittaria montevidensis (sagitária), a qual desenvolveu biótipos resistentes a herbicidas inibidores de ALS, no Estado de Santa Catarina. No presente trabalho, objetivou-se examinar as respostas morfológicas de sagitária quanto à variação da lâmina d'água, crescendo sob condições ambientais controladas. Os tratamentos foram representados pelas seguintes condições de inundação: solo saturado, 5, 10 e 20 cm de submersão, em delineamento experimental completamente casualizado, com cinco repetições. A presença de lâmina d'água favoreceu a germinação das sementes de sagitária. O aumento da profundidade de submersão incrementou a estatura da planta por meio do alongamento dos pecíolos das folhas espatuladas e sagitadas. Variação na profundidade da lâmina d'água não modificou o número de plantas, a massa seca, o número de folhas e de raízes, o tamanho da folha linear, o tamanho da lâmina foliar espatulada e sagitada e do escapo floral das plantas de S. montevidensis. As folhas de sagitária de mesmo tipo morfológico, quando desenvolvidas nas profundidades de água testadas, não diferiram histologicamente.<br>The cultivation of irrigated rice under water-seeded rice system has allowed the development of aquatic weed plants such as Sagittaria montevidensis (giant arrowhead), which has developed biotypes resistant to ALS-inhibiting herbicides in the state of Santa Catarina. This research aimed to investigate the morphologic responses of giant arrowhead to water level variation, under controlled environmental conditions. The treatments were represented by the following flood conditions: saturated soil, 5, 10 and 20 cm of water submersion, arranged in a completely randomized design, with five repetitions. Seed germination was promoted by the presence of water. Submersion depth increased plant height through petide lengthening of the spatulate and sagittate foliar blade size leaves. Water sheet depth variation did not modify the number of plants, dry mass, the number of leaves and roots, linear leaf size, spatulate and sagittate foliar blade size and the inflorescence axis of the S. montevidensis plants. The giant arrowhead leaves of the same morphological type did not differ histologically when developed under the tested water depths