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International audienceCopper is an essential element for the function of metabolic pathways in many living organisms like photosynthesis in plants. But, for the last decades, anthropogenic sources and release of Cu lead to environmental pollution particularly in aquatic ecosystems. The aquatic plant, Myriophyllum alterniflorum, known as a bioindicator of metal pollution, could be used as biomonitor. The aim of this study is to evaluate biomarkers responses of watermilfoil during Cu pollution at high environmental levels (100 μg l−1 CuSO4) in controlled conditions. Morphological and anatomical features like a new double endodermis (DE) layer were evidenced in response to Cu treatment. Moreover, physiological parameters like pigments contents, osmotic potential and proline content present a differential response to Cu stress in young and old leaves of watermilfoil. Finally, despite a rapid and strong phytoaccumulation of Cu, only young leaves are slightly affected in their cell membrane integrity as indicated by MDA content. In comparison with the Cu effect on other aquatic macrophytes, M. alterniflorum develops particular protection mechanisms like the ROS scavenging using proline rather than carotenoids, the reduction of water loss with the DE and the heavy metal elimination through senescence to protect preferentially the photosynthetic components of the young leaves and the main-stem elongation. Due to its Cu sensitivity, M. alterniflorum appears as important in the field of environmental studies using plant biomarkers

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Lymnaea truncatula, 4 mm in height, were subjected to infection by a single miracidium of Fasciola gigantica, then raised at 23°C until day 60 of the experiment. Histological study of these snails demonstrated a mean redial burden of 34 parasites at day 60, of which one third were degenerating forms. The mean number of living independent rediae did not exceed 5 for the first and second generations. Conversely, in subsequent generations there were as many as 18 rediae per snail at day 60. The first living redia of the first generation in particular gave rise to daughter rediae. Mature rediae appeared at day 35 and especially concerned the first and second generations at day 60. The authors conclude that development of the first and second redial generations occurs during the same period, and that the forms of the first cohort of the second generation are produced from the first redia of the first generation which originated from the sporocyst.

As most natural watercress beds in central France are located upstream of the permanent habitats of two lymnaeid species, Galba truncatula and Omphiscola glabra, field investigations were made from 1999 to 2004 on 67 beds to determine why the contamination of watercress with Fasciola hepatica is irregular over time in these sites, while definitive hosts, especially lagomorphs, are regularly found infected around them. Snails are able to migrate upstream in winter and spring towards the beds, and a 4-year survey demonstrated the existence of annual variation in the colonization of these sites by snails. In the 45 beds irregularly contaminated with F. hepatica over time, 37.7-62.2%, according to the year, were not populated by lymnaeids, in spite of the presence of snail populations downstream. G. truncatula was found alone in 8.8-13.3% of sites and was the first colonizing snail in 24.3-33.3% when the two lymnaeid species successively settled in these waterholes. The colonizing ability of O. glabra was more limited, as it was observed alone in 2.2% of beds and was the first colonizing snail in only 2.2-20% of them. The distances covered by these snails significantly increased with increasing migration time. After migration, a few overwintering snails (3.8% of G. truncatula and 6.8% of O. glabra) are able to colonize the beds, but their numbers decreased when the distance of migration was greater. O. glabra migrated more quickly and reached more watercress beds than G. truncatula. However, this did not influence the natural infections of snails, which were more frequent in the F1 of G. truncatula. The variability observed in the colonization of beds by snails might explain the regular or irregular contamination of wild watercress by metacercariae of F. hepatica. One of the factors which may explain this variability is the occurrence of showers in spring, so that a few snails are able to reach watercress beds after their upstream migration.