Fine-scale genetic structure of the freshwater snail Promenetus exacuous in the New York State region: the influences of historical colonization, habitat connectivity and dispersal ability
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ABSTRACT The pulmonate freshwater snail Promenetus exacuous (Planorbidae) has a widespread patchy distribution throughout much of North America, including New York State and the surrounding areas. Minimal life history information exists for the species in this region and information on its genetic diversity and structure is currently lacking for any portion of its range. We examined the species’ reproductive behaviour, genetic diversity and population structure throughout New York and western Connecticut using cytochrome c oxidase subunit I (COI) haplotypes (241 snails) and 10 microsatellite loci (312 snails). Throughout the region, P. exacuous is a single, primarily outcrossing species with relatively high within-population genetic diversity. Populations are genetically differentiated and composed of divergent COI lineages. The region was colonized after the Wisconsin glacial retreat by snails from multiple, historically isolated populations and Pleistocene events played a major role in the historical diversification of lineages. Subsequent dispersal has likely been facilitated by birds and humans, but contemporary gene flow is low, resulting in genetic differentiation even among geographically proximate sites. Our data reveal that complex interactions between historical and contemporary processes contribute to the overall patterns of genetic diversity in freshwater snails.Keywords:
Freshwater snail
Lymnaea stagnalis
Freshwater snail
Lymnaea
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Lymnaea stagnalis
Lymnaea
Freshwater snail
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Parasitism often influences the phenotype of individuals. Many of the resulting changes are due to changes in resource allocation that come with infection. Here we examine the effect of a trematode parasite on the shape and defence morphology of a New Zealand freshwater snail, Potamopyrgus antipodarum . The trematode Microphallus sp. asexually produces hundreds of metacercarial cysts in the snail. The length, width and 2-dimensional area of each snail were measured. Snails were also assessed for their degree of spininess. Snails were dissected to determine gender, brooding condition and parasitism. Snails infected with Microphallus sp. were found to be significantly less spiny than uninfected snails. Microphallus -infected snails were also found to have a significantly greater width to length ratio at larger sizes than their uninfected counterparts. These trends could be explained in at least 3 ways. (1) Infection causes the snails to not produce spines and to become wider. (2) Spiny and narrower snails are more likely to die when they become infected. (3) Spiny and narrower snails are more resistant to infection. The changes in phenotype observed are unlikely to be adaptive for either the host or parasite and probably represent physiological by-products of the host-parasite relationship.
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Two Local Government Areas in Bauchi State, Nigeria, harboring many snail infested water bodies were surveyed for the presence of intermediate host snail vector species for a period of 13 months. This study revealed five medically important snail species which were comprised of Bulinus (Physopsis) globosus, Bulinus (Bulinus) truncatus, Bulinus (Bulinus) forskalii, Biomphalaria pfeifferi, and Lymnaea natalensis. A significant fluctuation in relative abundance of these snails was observed with a peak at the beginning of the dry season. This peak was then followed by a decline during the rainy season resulting in almost the elimination of the snails in some sites and low numbers in others. It was equally observed that the snails had a water velocity, rainfall and temperature-dependent seasonal cycle with rapid increases in abundance during periods of favorable conditions. Snail-plant relationships and preferred substratum were also evaluated. Results obtained from this study are very vital for the planning of snail control in Bauchi State.International Journal of Biological & Chemical Sciences Vol. 1 (2) 2007: pp. 121-127
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Phasmarhabditis hermaphrodita is a lethal parasite of several slug and snail species that has been formulated into a biological control agent. However, the complete host range of this nematode is poorly understood, in particular its potential to affect non-target aquatic snail species. Here we exposed three species of juvenile and adult freshwater snail ( Lymnaea stagnalis , Planorbarius corneus and Bithynia tentaculata ) to 30 and 150 P. hermaphrodita cm −2 and assessed survival, as well as differences in weight for 66 days. We show that P. hermaphrodita has no effect on the survival of L. stagnalis , P. corneus and B. tentaculata after 66 days of exposure. In summary, we found little evidence of P. hermaphrodita causing mortality to three freshwater snail species at two different life stages and believe that P. hermaphrodita would have little effect on non-target snail species in the wild.
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The mineralized shell (consisting of calcium carbonate) of the tropical freshwater snail Biomphalaria glabrata was investigated with high resolution synchrotron X-ray powder diffractometry and X-ray absorption spectroscopy (EXAFS). Parts from different locations of the snail shell were taken from animals of different age grown under various keeping conditions. Additionally, eggs with ages of 60, 72, 120, and 140 hours were examined. Traces of aragonite were found as first crystalline phase in 120 h old eggs, however, Ca K-edge EXAFS indicated the presence of aragonitic structures already in the X-ray amorphous sample of 72 h age. The main component of the shell of adult animals was aragonite in all cases, but in some cases minor amounts of vaterite (below 1.5%) are formed. The content of vaterite is generally low in the oldest part of the shell (the center) and increases towards the mineralizing zone (the shell margin). In juvenile snails, almost no vaterite was detectable in any part of the shell.
Biomphalaria glabrata
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Lymnaea stagnalis
Digenea
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Helix pomatia
Lymnaea stagnalis
Freshwater snail
Helix (gastropod)
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The acanthocephalan Neoechinorhynchus emydis has a complex life cycle and infects turtle, ostracod, and snail hosts. However, little information is available on the seasonal distribution or the effects of N. emydis on freshwater snail hosts. To address this, we examined the seasonal distribution and melanization of acanthocephalans in Planorbella cf. Planorbella trivolvis snails from a single location in north-central Oklahoma. Seasonally, prevalence of N. emydis was 0% during the winter, increased to 50% during the summer, and declined to 17% in the fall. Mean abundance exhibited more variation but generally followed a similar pattern as prevalence. More important, all acanthocephalans located within the head/foot region of snail hosts contained melaninlike pigment surrounding each worm, suggesting that snails were mounting an immunological reaction to infections with N. emydis. Snail shell diameter was greatest during the fall and decreased during the winter, indicating that larger or older snails were dying during the winter. However, because field-collected snails were commonly infected with trematodes, and snail size varied significantly with season, it was unclear whether the observed seasonal dynamics of acanthocephalan infections were a result of snail mortality resulting from snail age, parasitic infections, or a combination of factors. To control for these factors, we exposed laboratory-reared Planorbella cf. P. trivolvis snails to naturally infected ostracods in field cages for 5-wk intervals during the winter, spring, and summer. Data from snail-cage infections were consistent with the seasonal field survey such that N. emydis infections were highest in the summer (20%) and lowest (0%) in the winter, suggesting that snails were not ingesting infected ostracods during the winter. However, fewer of our laboratory-reared snails survived in field cages during winter than during spring and summer, suggesting that snails may die more often during harsh winter conditions. Finally, we conducted a laboratory survival experiment by testing the life span and egg production of field-collected snails of various sizes that were naturally infected with acanthocephalans or trematodes or both. Our snail-survival experiment indicated that snail size but not infection status with acanthocephalans or trematodes affected snail survival, with larger snails surviving a shorter amount of time than smaller snails. In addition, snails infected with trematodes laid significantly fewer eggs compared with uninfected snails or snails infected with acanthocephalans. However, we found no significant difference in the number of eggs laid by acanthocephalan-infected and uninfected snails. Although other abiotic factors still need evaluation, we suggest that the occurrence of acanthocephalans in snails throughout the year may be partially influenced by the abundance of infected ostracods that snails may be ingesting and snail population fluctuations during the year.
Freshwater snail
Acanthocephala
Seasonality
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