Effect of temperature on the duration of larval and pupal stages of two species of sciomyzid flies, predators of the snail Lymnaea truncatula

The duration of larval and pupal stages of two species of predatory flies was investigated at five constant temperatures. Ilione albiseta (Scopoli): Mean duration of first and second instars was shortest at 23°C and there was 100% survival of first instar larvae at all temperatures. Mean third instar larval duration decreased from 104 days at 17°C to 27.5 days at 26°C. Total percentage larval survival was greatest at 17°C and least at 26°C. Mean pupal duration decreased as temperature increased and this occurred also under outdoor conditions. Pherbellia cinerella (Fallén): As temperature increased mean larval duration decreased but the percentage of larvae pupating also decreased (100% at 14°C, 33.3% at 26°C). There was a trend for shorter mean pupal durations at higher temperatures.

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Résumé L'action de la température a été examinée à 14, 17, 20, 23 et 26°C. Les 2 espèces sont prédatrices de L. truncatula, vecteur de la douve du foie en Irlande, où elle provoque à l'àgriculture une perte évaluée à 10 millions de livres par an. Les données recuellies en conditions contrôlées du laboratoire doivent permettre de définir les conditions optimales pour l'élevage continu de ces espèces. Ceci est indispensable pour évaluer, dans la nature leurs potentialités pour la lutte biologique. Ilione albiseta: C'est à 23°C que le développement des larves de premier et second stades sont les plus brefs; la survie du premier stade est totale à toutes les températures constantes examinées. La durée moyenne du 3ème stade décroît de 104 jours à 17°C jusqu'à 27,5 jours à 26°C. Le taux de survie total est plus élevé à 17°C qu'à 26°C. La durée moyenne de la nymphose diminue quand la température croît, et ceci se produit aussi à la température ambiante extérieure. On réduit de moitié la durée du développement de l'éclosion de l'oeuf à l'apparition de l'adulte, entre la nature et le laboratoire, en utilisant respectivement: 23°, 17° et 26°C pour les premier et second stades, le troisième stade, la nymphé. Cela devrait aider à multiplier la souche pour la lutte biologique. Pherbellia cinerella: Avec élévation de la température la durée du développement larvaire diminue, mais aussi le nombre de larves parvenant à la pupaison (100% à 14° et 33,3% à 26°C). La nymphose tendait à être plus brève aux températures les plus élevées.

     

Survivorship of geographic Pomacea canaliculata populations in responses to cold acclimation

1. Pomacea canaliculata, a freshwater snail from South America, has rapidly established natural populations from south to north subtropical region in China, since its original introductions in the 1980s. Low temperature in winter is a limiting factor in the geographic expansion and successfully establishment for apple snail populations. There have been some studies on population level of low temperature tolerance for P. canaliculata, yet little is quantified about its life‐history traits in responses to cold temperatures. Whether these responses vary with the acclimation location is also unclear. We investigated the survivorship and longevity of P. canaliculata in responses to cold temperatures and examine whether these responses vary with the location and snail size. We hypothesized that survival of the snails depends on their shell height and the level of low temperature, and P. canaliculata population from the mid-subtropical zone may exhibit the highest viability over the cold thermal range.
2. We sampled P. canaliculata populations from five latitude and longitude ranges of subtropical China: Guangzhou population in southernmost (SM‐GZ), three populations of Yingtan (MR‐YT), Ningbo (MR‐NB), Ya'an (MR‐YA) in midrange, and Huanggang population in northernmost (NM‐HG) subtropical zone. For each P. canaliculata population, survival and longevity at six cold acclimation temperature levels (12, 9, 6, 3, 0, and ?3°C) were quantified, and the effects of location and shell height were examined.
3. The MR‐YA population from mid-subtropical zone of China exhibited the highest survival rate and prolonged survival time regardless of the temperature acclimation treatments, whereas the SM‐GZ population from southern subtropical was the most sensitive to cold temperatures, particular temperatures below 9°C. No individuals of the SM‐GZ population could survive after stressed for 30 days (3°C), 5 days (0°C) and 2 days (?3°C), respectively. For each experimental P. canaliculata population held at 3, 0, and ?3°C, individuals with intermediate shell height of 15.0–25.0 mm had significantly higher survivals.
4. The results highlight a request of a more thorough investigation on acclimation responses in each of the life table demographic parameters for P. canaliculata, and pose the question of whether natural selection or some genetic changes may have facilitated adaptation in invasive locations.

     

Response of grazing snails to phosphorus enrichment of modern stromatolitic microbial communities

1. The effects of added phosphorus (P) on the growth, P and RNA : DNA contents, and survivorship of snails grazing on laminated microbial mats (living ‘stromatolites’) were examined in the Rio Mesquites at Cuatro Ciénegas, Mexico (total P, c. 0.60 μmol L^?1) to test the hypothesis that strong P‐limitation of microautotroph growth produces a stoichiometric constraint on herbivores because of mineral P‐limitation. 2. In a 3‐week experiment performed in summer 2001, addition of phosphorus (+15 μmol L^?1) resulted in a strong decline in stromatolite biomass C : P ratio from very high levels (c. 2300 : 1 by atoms) to moderate levels (c. 550 : 1). The endemic hydrobiid snail Mexithauma quadripaludium responded to P‐enrichment with elevated body P content and higher RNA : DNA ratios, especially for small animals likely to be actively growing. This positive response is consistent with the existence of a stoichiometric constraint on snail growth. 3. In a longer experiment (8 weeks) involving a more moderate P enrichment (+5 μmol L^?1) in summer 2002, P enrichment reduced stromatolite C : P ratio from moderate values in control treatments (c. 750) to very low values (<100 : 1). Snails responded to stromatolite P‐enrichment with increased body P content but, in contrast to the first experiment, with lower RNA : DNA ratio, lower growth rates, and higher mortality. 4. These contrasting results suggest that both very high and very low biomass C : P ratios in stromatolites are detrimental to M. quadripaludium performance, leading us to hypothesise that these herbivores live on a ‘stoichiometric knife edge’.     

Macroinvertebrate succession during leaf litter breakdown in a perennial karstic river in Western Brazil

Leaf litter is a major basal resource to stream ecosystems, but few studies addressed their role in karst systems, mainly in intermittent springs and lakes. Patterns of resource use in perennial rivers are poorly known, although the input of leaf litter strongly influences macroinvertebrate assemblage structure. In this study, we evaluated the structure of macroinvertebrate assemblages along the decomposition of leaf litter in a tropical karst river, using leaf litter cages made of coarse nylon mesh (25 mm) to allow colonization by macroinvertebrates. The experiment was followed weekly for 10 weeks. The assemblages were dominated by snails (90.5% of total fauna), hyalellid amphipods, and larval chironomid midges, with highest abundances in the intermediate stages of the experiment, resulting in a gradient in assemblage structure. The large abundance of snails, which are common in other karst systems, suggest that this group may have an important role in decomposer food webs, facilitating or directly contributing to leaf breakdown. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Chemical analysis of mucus from certain land snails under Egyptian conditions

Abstract

The present investigation was carried out to study the chemical analysis of the mucus of three common land snails, Eobania vermiculata, Theba pisana and Monacha obstructa, and identification of the chemical compositions by using GC-MS. Results revealed that several variations in composition were observed between all species. Oxime, methoxy-phenyl and cyclotrisiloxane, hexamethyl were major components found that in three species, the total areas detected were 86.23, 76.83 and 70.83, respectively. This different composition of mucus may be due to differences from one species to another; different mechanical properties (function) are influenced by external factors such as temperature, humidity, light intensity, soil conditions and food supply.     

Experimental hybridization between two sub-species of snails (Helix aspersa aspersa and Helix aspersa maxima): consequences for fertility,survival and growth

Summary

The experimental laboratory pairing of hermaphroditic snails of different sub-species, Helix aspersa aspersa (H.a.a) and H. aspersa maxima (H.a.m.), made it possible to obtain both reciprocal hybrids for the first time and to describe their growth. The relatively small number of matings observed (20–25%) was partly responsible for the small number of clutches obtained (10–13%). The cross H.a.a.M × H.a.m.F is more fertile than the reciprocal. The observed tendency to reproductive isolation (behavioural and anatomical) suggests that H.a.a. and H.a.m. should be considered as two sub-species. Hybridization is not accompanied by a beneficial heterosis effect since significant juvenile mortality and an increased variation in growth were observed. The small size of H.a.a. is a dominant characteristic, whereas the colour of the mantle edge in the Fl individuals is intermediate between the black of H.a.m. and the white of H.a.a. The Fl generation is fertile and gives F2 snails with an adult size close to that of H.a.a. but slower growing. This approach allows investigations into the mechanisms underlying the reproductive isolation of parental sub-species.     

Three new species of the carnivorous snail genus Perrottetia Kobelt, 1905 from Thailand (Pulmonata,?Streptaxidae)

Three new species of the streptaxid snail genus Perrottetia are described from north and northeastern Thailand, Perrottetia aquilonaria sp. n., Perrottetia dermapyrrhosa sp. n. and Perrottetia phuphamanensis sp. n. Each species is endemic to a single or a few limestone mountain ranges. The species are characterized by the morphology of their genital organs, as well as by shell characters. Perrottetia aquilonaria sp. n. has a club shaped distal penis and large penial hooks are present and penial papillae cover almost the entire penial hook portion; adjacent areas possess low reticulated folds. Perrottetia dermapyrrhosa sp. n. has a long genital atrium and the penial sheath is about two-thirds of the penis length. Penial hooks are long, scattered and sunken into deep ovate hollows; vaginal hooks are present. Perrottetia phuphamanensis sp. n. has a rounded and protruded shell periphery. The aperture is subcircular, peristome is thick and the second parietal lamella is adjacent to the first parietal lamella; a basal lamella is the smaller than in the other Thai species.     

Scale-dependence in geographic variation in a freshwater gastropod across the Palearctic

ABSTRACT

The reality of spatial clinal variation in morphological traits of freshwater pulmonate snails (Gastropoda: Pulmonata) has repeatedly been questioned or totally discounted. There is a lack of sound statistical evidence in the articles hitherto published on this subject supporting these claims. Here, by means of different analytical methods (analysis of spatial autocorrelation, linear regression analysis, canonical correlation analysis and others), we demonstrate that shell variation in the dwarf pond snail, Galba truncatula, is patterned in space throughout the northern and central Palearctic, with latitudinally-oriented clines in body size and in some shell proportions. Shell size in G. truncatula decreases with latitude and temperature, representing a special case of converse Bergmann cline. However, the temperature itself is hardly the main driver of shell size variation. It is argued that the shorter growing seasons at high latitudes may represent a better explanation for the observed trend. Shell proportions in the dwarf pond snails vary weakly at the macrogeographic scale, being spatially patterned at lower (mesogeographic) scales around 1200–1500?km. In general, spatial variation in G. truncatula shell size is decoupled from variation in shell shape, demonstrating clear scale-dependence similar to that found in different species of terrestrial (non-aquatic) pulmonate snails.     

High resilience of Mediterranean land snail communities to wildfires

In the Mediterranean region, wildfires have devastating effects on animals with limited mobility. With their poor dispersal abilities, their habitats on vegetation and in litter, and their sensitivity to humidity and shade, we expected land snails to be an interesting model to assess short, medium and long-term impact of fires on fauna biodiversity and their resilience. Stratified sampling was carried out on 12 sampling sites in garrigues and forests of Provence (southeastern France), according to fire regime (number of fires, fire intervals and age of the last fire) over the past 30 years. Data were investigated using diversity indexes, Kruskal–Wallis test, dendrogram of affinities and Correspondence Analysis (CA). We found, however, that Mediterranean land snail communities are particularly resilient to fires. Although abundance is drastically reduced in the short-term, species richness and community diversity are preserved provided that the time lapse between two successive fires is longer than the time required for recovery (i.e. around 5 years). This high community resilience in the short-term may be partly due to ecological and ethological aptitudes of land snails. However, these astonishing results, which have implications for conservation biology, are mainly due to the presence, within burned areas, of cryptic refuges that allow initial land snail survival, malacofauna persistence after successive fires and consistent biogeographical patterns in the long-term.