Asolene platae is a freshwater snail of the Ampullariidae native from La Plata River basin in Sou... more Asolene platae is a freshwater snail of the Ampullariidae native from La Plata River basin in South America. Water temperature has an overwhelming influence on the biology of apple snails, though there are no systematic studies related to the thermal biology of this species. The effect of temperature on the activity, growth and mortality of A. platae was studied through laboratory experiments using constant temperatures of 15, 20, 25, 30 and 35°C. The lower threshold and cumulative degree-days for the embryonic development were estimated under fluctuating temperature. Water temperature had a significant effect on the activity of A. platae, being almost null at 15°C, reaching its maximum in the range 25-30°C and decreasing above 30°C. Regardless of temperature, snails remained resting nearly half of the time, exhibiting less activity than other apple snails across similar temperatures. Mortality was higher for hatchlings than for adults at all temperatures with the exception of 35°C, which resulted in high levels of mortality for both groups. Growth of hatchlings was significantly affected by temperature, being highest between 25 and 35°C. The lower temperature threshold for the embryonic development was around 16°C and the cumulative degree-days to complete development were estimated between 107.5 and 120.5°C.d. The optimum temperature for A. platae would be 25-30°C. Temperatures of 35°C and above would be harmful, while temperatures below 20°C resulted in rapid decreasing in activity and slower growth rates. The information about the thermal requirements of A. platae will be useful optimizing rearing conditions and developing predictive models of the potential distribution of A. platae in scenarios where it is introduced outside of its native range.
Pomacea canaliculata is a freshwater snail that cultured under certain conditions could provide i... more Pomacea canaliculata is a freshwater snail that cultured under certain conditions could provide interesting rewards in research and aquaculture. P. canaliculata is usually reared at 25°C, though the optimal temperature for culturing this species, that balances growth and survival rates, is so far unknown. In this work we present results of growth and survival of cohorts reared in the laboratory at different constant water temperatures (15, 20, 25, 30 and 35°C) during the pre-reproductive period. Two different groups were recognized among the five treatments: the two lower temperatures (15 and 20°C) that showed no mortality but with very low growth rates and the treatments of 25, 30 and 35°C in which snails grew faster but displayed a reduction in survival as temperature increases. After 10 weeks, the mean shell lengths attained at 30 and 35°C were only 2-3 mm higher than that of the treatment of 25°C and were not statistically different. Our results support using water temperatures ...
Limnologica - Ecology and Management of Inland Waters, 2013
Studies dealing with the distribution of freshwater mollusks in the Pampean plains are very scarc... more Studies dealing with the distribution of freshwater mollusks in the Pampean plains are very scarce and have all focused on the determinants of their presence among different waterbodies. The aims of this study were to investigate the distribution of the apple snail Pomacea canaliculata among and within Pampean streams. The main sampling scheme included heterogeneous sections within different sites belonging to all the streams of the Encadenadas del Oeste basin (Buenos Aires Province), in which apple snails' presence and abundance as well as several environmental variables were recorded. P. canaliculata was present in long streams originating in the Piedmont area, with the exception of one that suffered extensive dredging works but it was absent in short streams originating in the plains. Lower altitudes and higher organic matter contents characterized the inhabited sites among the long streams. At a smaller scale, higher concentrations of Na + and lower levels of organic suspended matter characterized the inhabited sections. Within the short streams P. canaliculata was only found at sites located downstream from a connection to an inhabited long stream and hence constituted sink populations; short streams presented alkaline waters with high conductivity, very slow currents and no trees. The microhabitat of P. canaliculata was investigated at two sites from two different streams in which environmental variables were registered at individual snails' locations and at systematically distributed points. Apple snails were more frequently found in places located close to the shore, where current velocity was usually low, sediments fine and rich in organic matter, and macrophytes abundant. These variables were all correlated at this small scale thus making their individual interpretation difficult. All the streams in this basin appear to be habitable for P. canaliculata, but the populations would only persist autonomously in the medium and low reaches on the long streams. The distribution within long streams is probably governed by stochastic patterns of extinction-colonization as a consequence of the variability of the climatic and hydrological conditions in this region.
a b s t r a c t 1. The effect of temperature on the activity of the freshwater snail Pomacea cana... more a b s t r a c t 1. The effect of temperature on the activity of the freshwater snail Pomacea canaliculata was investigated through field surveys and laboratory trials. 2. During winter most snails in the field were inactive but not in a deep lethargic state; the temperature at which half of the snails were active was 13-15 1C. 3. The time spent active and feeding increased with temperature between 10 and 30 1C, exposure time being unimportant except in foul water at 35 1C, while time spent crawling remained constant above 10 1C. 4. Activity decreased above 30 1C but no heat coma was observed with temperatures raised to 36.2 1C. 5. Under fluctuating temperatures, the rate of change in the percentage of active snails during cooling was higher than during warming, whereas the temperature at which half of the snails were active was lower.
The invasive Neotropical snail Pomacea canaliculata is usually regarded as amphibious, although t... more The invasive Neotropical snail Pomacea canaliculata is usually regarded as amphibious, although the relative significance of aerial and aquatic respiration is unknown. To investigate the degree of dependence on aerial respiration and its influences on microdistribution, experiments were performed in the laboratory and under seminatural and natural conditions. Restriction of aerial respiration negatively affected survivorship, activity and feeding, its effects worsening with temperature and water fouling; females were more seriously affected than males although the effect depended on reproductive effort. Snails were unevenly distributed relative to the access to air, both in a stream and in an outdoor tank, being concentrated less than 2-4 m from the nearest emergent substratum. Accessibility to air would be an important trait of waterbodies prone to invasions of P. canaliculata, especially in tropical areas. The effectiveness of some control measures could be increased by focusing on areas where snails are concentrated due to their dependence on air.
The aim of this study was to test the hypothesis that positive rheotaxis and anti-detachment beha... more The aim of this study was to test the hypothesis that positive rheotaxis and anti-detachment behaviors contribute to the persistence of Pomacea canaliculata in lotic environments. This invasive apple snail is commonly considered a lentic dweller. In a first series of trials in a laboratory flume, current velocity was gradually increased until snails' detachment. Detachment velocity was highly variable, with some snails able to withstand strong currents during short periods. Sexually undifferentiated snails were the most resistant to detachment; most of the snails that resisted high velocities were facing flow before detachment. In a second series of trials, snails' net displacement was estimated at three fixed velocities (0, 0.15, and 0.30 m s -1 ). Current velocity did not influence mean net displacement, which was not different from zero. Marked snails were released in a stream and recaptured 24 h later estimating their net displacement. Most recovered snails dispersed a short distance from the release point and crawled through sites with very low current velocities. A small proportion of snails drifted downstream, indicating the existence of different dispersal mechanisms. Snails were able to resist current velocities that are among the highest recorded in streams in the Pampas region. P. canaliculata did not show a positive rheotactic response; in flowing water, snails crawl more often upstream, but at a slower pace than downstream. At the population level, a slow upstream spread seems possible in plain's streams, probably being enough to compensate drift, but not to colonize headwaters. Irrigation systems are feasible pathways for the spread of this species in invaded regions.
Asolene platae is a freshwater snail of the Ampullariidae native from La Plata River basin in Sou... more Asolene platae is a freshwater snail of the Ampullariidae native from La Plata River basin in South America. Water temperature has an overwhelming influence on the biology of apple snails, though there are no systematic studies related to the thermal biology of this species. The effect of temperature on the activity, growth and mortality of A. platae was studied through laboratory experiments using constant temperatures of 15, 20, 25, 30 and 35°C. The lower threshold and cumulative degree-days for the embryonic development were estimated under fluctuating temperature. Water temperature had a significant effect on the activity of A. platae, being almost null at 15°C, reaching its maximum in the range 25-30°C and decreasing above 30°C. Regardless of temperature, snails remained resting nearly half of the time, exhibiting less activity than other apple snails across similar temperatures. Mortality was higher for hatchlings than for adults at all temperatures with the exception of 35°C, which resulted in high levels of mortality for both groups. Growth of hatchlings was significantly affected by temperature, being highest between 25 and 35°C. The lower temperature threshold for the embryonic development was around 16°C and the cumulative degree-days to complete development were estimated between 107.5 and 120.5°C.d. The optimum temperature for A. platae would be 25-30°C. Temperatures of 35°C and above would be harmful, while temperatures below 20°C resulted in rapid decreasing in activity and slower growth rates. The information about the thermal requirements of A. platae will be useful optimizing rearing conditions and developing predictive models of the potential distribution of A. platae in scenarios where it is introduced outside of its native range.
Pomacea canaliculata is a freshwater snail that cultured under certain conditions could provide i... more Pomacea canaliculata is a freshwater snail that cultured under certain conditions could provide interesting rewards in research and aquaculture. P. canaliculata is usually reared at 25°C, though the optimal temperature for culturing this species, that balances growth and survival rates, is so far unknown. In this work we present results of growth and survival of cohorts reared in the laboratory at different constant water temperatures (15, 20, 25, 30 and 35°C) during the pre-reproductive period. Two different groups were recognized among the five treatments: the two lower temperatures (15 and 20°C) that showed no mortality but with very low growth rates and the treatments of 25, 30 and 35°C in which snails grew faster but displayed a reduction in survival as temperature increases. After 10 weeks, the mean shell lengths attained at 30 and 35°C were only 2-3 mm higher than that of the treatment of 25°C and were not statistically different. Our results support using water temperatures ...
Limnologica - Ecology and Management of Inland Waters, 2013
Studies dealing with the distribution of freshwater mollusks in the Pampean plains are very scarc... more Studies dealing with the distribution of freshwater mollusks in the Pampean plains are very scarce and have all focused on the determinants of their presence among different waterbodies. The aims of this study were to investigate the distribution of the apple snail Pomacea canaliculata among and within Pampean streams. The main sampling scheme included heterogeneous sections within different sites belonging to all the streams of the Encadenadas del Oeste basin (Buenos Aires Province), in which apple snails' presence and abundance as well as several environmental variables were recorded. P. canaliculata was present in long streams originating in the Piedmont area, with the exception of one that suffered extensive dredging works but it was absent in short streams originating in the plains. Lower altitudes and higher organic matter contents characterized the inhabited sites among the long streams. At a smaller scale, higher concentrations of Na + and lower levels of organic suspended matter characterized the inhabited sections. Within the short streams P. canaliculata was only found at sites located downstream from a connection to an inhabited long stream and hence constituted sink populations; short streams presented alkaline waters with high conductivity, very slow currents and no trees. The microhabitat of P. canaliculata was investigated at two sites from two different streams in which environmental variables were registered at individual snails' locations and at systematically distributed points. Apple snails were more frequently found in places located close to the shore, where current velocity was usually low, sediments fine and rich in organic matter, and macrophytes abundant. These variables were all correlated at this small scale thus making their individual interpretation difficult. All the streams in this basin appear to be habitable for P. canaliculata, but the populations would only persist autonomously in the medium and low reaches on the long streams. The distribution within long streams is probably governed by stochastic patterns of extinction-colonization as a consequence of the variability of the climatic and hydrological conditions in this region.
a b s t r a c t 1. The effect of temperature on the activity of the freshwater snail Pomacea cana... more a b s t r a c t 1. The effect of temperature on the activity of the freshwater snail Pomacea canaliculata was investigated through field surveys and laboratory trials. 2. During winter most snails in the field were inactive but not in a deep lethargic state; the temperature at which half of the snails were active was 13-15 1C. 3. The time spent active and feeding increased with temperature between 10 and 30 1C, exposure time being unimportant except in foul water at 35 1C, while time spent crawling remained constant above 10 1C. 4. Activity decreased above 30 1C but no heat coma was observed with temperatures raised to 36.2 1C. 5. Under fluctuating temperatures, the rate of change in the percentage of active snails during cooling was higher than during warming, whereas the temperature at which half of the snails were active was lower.
The invasive Neotropical snail Pomacea canaliculata is usually regarded as amphibious, although t... more The invasive Neotropical snail Pomacea canaliculata is usually regarded as amphibious, although the relative significance of aerial and aquatic respiration is unknown. To investigate the degree of dependence on aerial respiration and its influences on microdistribution, experiments were performed in the laboratory and under seminatural and natural conditions. Restriction of aerial respiration negatively affected survivorship, activity and feeding, its effects worsening with temperature and water fouling; females were more seriously affected than males although the effect depended on reproductive effort. Snails were unevenly distributed relative to the access to air, both in a stream and in an outdoor tank, being concentrated less than 2-4 m from the nearest emergent substratum. Accessibility to air would be an important trait of waterbodies prone to invasions of P. canaliculata, especially in tropical areas. The effectiveness of some control measures could be increased by focusing on areas where snails are concentrated due to their dependence on air.
The aim of this study was to test the hypothesis that positive rheotaxis and anti-detachment beha... more The aim of this study was to test the hypothesis that positive rheotaxis and anti-detachment behaviors contribute to the persistence of Pomacea canaliculata in lotic environments. This invasive apple snail is commonly considered a lentic dweller. In a first series of trials in a laboratory flume, current velocity was gradually increased until snails' detachment. Detachment velocity was highly variable, with some snails able to withstand strong currents during short periods. Sexually undifferentiated snails were the most resistant to detachment; most of the snails that resisted high velocities were facing flow before detachment. In a second series of trials, snails' net displacement was estimated at three fixed velocities (0, 0.15, and 0.30 m s -1 ). Current velocity did not influence mean net displacement, which was not different from zero. Marked snails were released in a stream and recaptured 24 h later estimating their net displacement. Most recovered snails dispersed a short distance from the release point and crawled through sites with very low current velocities. A small proportion of snails drifted downstream, indicating the existence of different dispersal mechanisms. Snails were able to resist current velocities that are among the highest recorded in streams in the Pampas region. P. canaliculata did not show a positive rheotactic response; in flowing water, snails crawl more often upstream, but at a slower pace than downstream. At the population level, a slow upstream spread seems possible in plain's streams, probably being enough to compensate drift, but not to colonize headwaters. Irrigation systems are feasible pathways for the spread of this species in invaded regions.
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