First field observations on the aestivation of Omphiscola glabra (Gastropoda, Lymnaeida) uninfected or infected with Fasciola hepatica in central France

Rondelaud

2018

-Field investigations in habitats colonized by Galba truncatula or Omphiscola glabra were carried out to determine if the number of habitats, their area and the number of overwintering snails had not changed over the past 20 years. These habitats were studied in 57 cattle-or sheep-breeding farms located in three French natural regions on sedimentary soils. Compared to the numbers of snail habitats recorded before 1998, the values observed in 2016-2017 were significantly lower, with an overall decline rate of 30% for G. truncatula and 38% for O. glabra. Variations in this decline rate were noted with the type of snail habitat and the largest decreases were observed for vernal pools in meadows. Significantly lower areas in 2016-2017 were noted in two habitat types (drainage furrows, road ditches) for G. truncatula and two other habitat types (drainage furrows, pond banks) for O. glabra. Significantly lower densities of overwintering snails were observed in 2016-2017 in G. truncatula habitats located in drainage furrows and road ditches, while no significant difference was noted for O. glabra, whatever the habitat type. Several causes were at the origin of this population decline and the most important were the present development of mechanical cleaning in road ditches, that of subsurface drainage in meadows and regular gyro-crushing of vegetation around pools in meadows. The data reported in this study confirm the decline that several authors have already noted for O. glabra in Western Europe. The results obtained for G. truncatula require reviewing the biogeographical status of this species and taking possible measures to ensure its conservation while taking into account its role as intermediate host in the F. hepatica cycle.

Section: Number Of Overwintering Snailssupporting

confidence: 89%

Galba truncatula and Omphiscola glabra (Gastropoda, Lymnaeidae): present decline in populations living on sedimentary soils in central France

Dreyfuss

Rondelaud

2018

“…Secondly, two snail categories, i.e., juveniles measuring 3.1-3.4 mm in shell height and adults greater than 15 mm at the beginning of July, were subject to summer drying of their habitats. Owing to their burrowing into the soil during aestivation, the mortality of adult snails on marl was lower than that of adults on granite (Rondelaud et al, 2003). In both types of habitats, the small size of juvenile snails allowed them to better resist aestivation effects, whatever the soil geology, as already reported for G. truncatula (Taylor, 1965).…”

Section: Discussionsupporting

confidence: 55%

“…In each habitat, monthly samples of 100 snails each were randomly collected from January to June and from September to December 2015, whatever their shell height. No sampling was performed in July and August 2015 because of summer drying of habitats and aestivation of snails into marl (Chitray, Thenay) or among the nearest vegetation on ditchsides in the other two habitats (Rondelaud et al, 2003). The shell height of collected O. glabra was measured using electronic callipers.…”

Section: Second Series Of Investigationsmentioning

confidence: 99%

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Insights into the reproductive activity ofOmphiscola (Lymnaea) glabra(Gastropoda: Lymnaeidae) in relation to soil geology in Central France

Titi

Mekroud

et al. 2017

-Transplantations of Omphiscola glabra from granite to marl, or vice versa, between farms known for cases of fasciolosis have shown differences in the maximum shell height of adult snails. To determine whether these differences were due to parasitism, soil geology, or a combination of both factors, four snail populations living on marl or granite were investigated over 12 months to specify the characteristics of egglaying in spring, and to follow the shell growth of both snail generations. In both types of habitats, the number of egg-masses per adult snail and their size significantly decreased during the 7 weeks of snail egg-laying. During this period, each adult snail on marl laid a mean of 6.4 masses and 93.3 eggs. On granite, the mean values were 5.7 masses and 69.1 eggs, respectively. Two annual generations, the first in spring and the other in autumn, were noted in these habitats. The maximum shell height of adults was different: a mean of 19.8 and 20.5 mm on marl compared with 17.2 and 18.2 mm on granite. Soil geology thus plays a role in the egg-laying and shell growth of O. glabra.

“…In contrast, the eggs of both lymnaeids did not withstand summer drying. Juvenile and pre-adult O. glabra burrowed into the soft mud at the beginning of summer drying and aestivated at a depth of 1-6 cm when the bottom sediment was marl (Rondelaud et al, 2003). In the same way, the juvenile and pre-adult G. truncatula could also burrow into the upper layers of the soil, mainly at altitude (Goumghar et al, 2001) or settle on a support structure that varies in nature depending on the type of habitat (Rondelaud et al, 2009).…”

Section: Discussionmentioning

confidence: 99%

Aplexa hypnorum(Gastropoda: Physidae) exerts competition on two lymnaeid species in periodically dried ditches

Rondelaud

Dreyfuss

2016

-Samples of adult Aplexa hypnorum were experimentally introduced into periodically dried ditches colonized by Galba truncatula or Omphiscola glabra to monitor the distribution and density of these snail species from 2002 to 2008, and to compare these values with those noted in control sites only frequented by either lymnaeid. The introduction of A. hypnorum into each ditch was followed by the progressive colonization of the entire habitat by the physid and progressive reduction of the portion occupied by the lymnaeid towards the upstream extremity of the ditch. Moreover, the size of the lymnaeid population decreased significantly over the 7-year period, with values noted in 2008 that were significantly lower than those recorded in 2002. In contrast, the mean densities were relatively stable in the sites only occupied by G. truncatula or O. glabra. Laboratory investigations were also carried out by placing juvenile, intermediate or adult physids in aquaria in the presence of juvenile, intermediate or adult G. truncatula (or O. glabra) for 30 days. The life stage of A. hypnorum had a significant influence on the survival of each lymnaeid. In snail combinations, this survival was significantly lower for adult G. truncatula (or O. glabra) than for intermediate snails. In contrast, the survival of juveniles was similar to that noted in the corresponding controls. This interspecific competition between the physid and either lymnaeid may not be due to food present in their habitat, but might be due to the toxicity of mucus secreted by intermediate and adult A. hypnorum.