María E. Seuffert

Insights from an Integrated View of the Biology of Apple Snails (Caenogastropoda: Ampullariidae)

ABSTRACT Apple snails (Ampullariidae) are among the largest and most ecologically important freshwater snails. The introduction of multiple species has reinvigorated the field and spurred a burgeoning body of research since the early 1990s, particularly regarding two species introduced to Asian wetlands and elsewhere, where they have become serious agricultural pests. This review places these recent advances in the context of previous work, across diverse fields ranging from phylogenetics and biogeography through ecology and developmental biology, and the more applied areas of environmental health and human disease. The review does not deal with the role of ampullariids as pests, nor their control and management, as this has been substantially reviewed elsewhere. Despite this large and diverse body of research, significant gaps in knowledge of these important snails remain, particularly in a comparative framework. The great majority of the work to date concerns a single species, Pomacea canaliculata, which we see as having the potential to become a model organism in a wide range of fields. However, additional comparative data are essential for understanding this diverse and potentially informative group. With the rapid advances in genomic technologies, many questions, seemingly intractable two decades ago, can be addressed, and ampullariids will provide valuable insights to our understanding across diverse fields in integrative biology.

Influence of Temperature, Size and Sex on Aerial Respiration of Pomacea canaliculata (Gastropoda: Ampullariidae) from Southern Pampas, Argentina

Pomacea canaliculata (Lamarck 1822) is a freshwater snail belonging to the family Ampullariidae, whose natural distribution comprises most of the Plata river Basin and extends southwards to Tandilia and Ventania mountains in southern Pampas, Buenos Aires Province, Argentina (Martin et al., 2001). International concern about this voracious macrophytophagous snail rose when it, and other related species, became established as a serious pest of aquatic crops, including rice and taro, in South and East Asia (Cowie et al., 2006). In addition, the role of invading ampullariids as promoters of ecosystemic changes in invaded natural wetlands has been recently highlighted (Carlsson et al., 2004). Nowadays, P. canaliculata is listed among the top 100 worst invasive alien species of the world (Lowe et al., 2000), being the only freshwater snail included and probably the species with the greater potential for spread in North America (Rawlings et al., 2007). Ampullariids or apple snails have both a welldeveloped gill and a pulmonary sac or lung, and are commonly considered as “amphibious” snails (Andrews, 1965; Berthold, 1991). Water

THRESHOLD TEMPERATURES AND DEGREE-DAY ESTIMATES FOR EMBRYONIC DEVELOPMENT OF THE INVASIVE APPLE SNAIL POMACEA CANALICULATA (CAENOGASTROPODA: AMPULLARIIDAE)

ABSTRACT Pomacea canaliculate is a freshwater snail native to subtropical-temperate South America that has invaded several countries around the world. Temperature is probably one of the main limitations to the expansion of this and other apple snails to higher latitudes in invaded regions. Egg masses are aerial, and the duration of embryonic development varies greatly with air temperature. We compared different methods for determining the lower temperature thresholds and the cumulative degree-days (DD) required for the completion of the embryonic development of P. canaliculate. The lower temperature threshold was estimated with four methods: the least standard deviation from the mean of degree-days, the least standard deviation from the mean of days, the coefficient of variation in days and the linear regression coefficient method. The cumulative degree-days were estimated using hourly records and daily averages (calculated according to the single triangle and the single sine methods) of air temperature. The lower temperature thresholds ranged between 15.8°C and 18.3°C and the cumulative DD between 88.8°C.d and 133.8°C.d. The estimations obtained with the single triangle and the single sine methods were exactly the same. The values obtained with the method of the least standard deviation in degree-days and the corresponding cumulative DD were the poorest estimations. The estimates obtained with daily mean temperatures were close to those obtained with hourly records, indicating that recording only maximum and minimum temperatures should be sufficient. The use of degree-day models for egg development in Pomacea will serve to increase the effectiveness and efficacy of control measures targeted to egg masses through a better timing in their application, especially in localities with highly variable temperatures.

Thermal Biology of the South American Apple Snail Asolene platae (Caenogastropoda: Ampullariidae)

ABSTRACT 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.

First record of the freshwater snail Pseudosuccinea columella (Gastropoda: Lymnaeidae) in southern Pampas (Argentina) and assessment of future spread

ABSTRACT The freshwater snail Pseudosuccinea columella was recorded for the first time in Argentina more than 60 years ago. Since then its distribution in the wild has been restricted to the northeastern provinces. Here we record the presence of P. columella in southern Pampas for the first time, extending its distribution more than 500 km southwards. The climatic suitability of this and other areas of South America for its establishment and spread was analysed using habitat modelling software. Hitherto its spread within and between watercourses in southern Pampas has been very limited, probably through a combination of low climatic suitability, recent introduction and low connectivity of the drainage basins. The suitability of other areas where it has been recently recorded indicates a moderate risk of further spread in central and northwestern Argentina and in coastal areas of the Pacific rim of South America (southern Perú and northern Chile). The recent spread of P. columella in the wild in Argentina may be the result of an increase in the trade in aquarium plants or of the evolution of a new lineage with different ecological capabilities.

Life Table and Demographic Parameters of the Neotropical Apple Snail Asolene platae (Caenogastropoda, Ampullariidae)

Abstract: Apple snails are regarded as invasive or potentially problematic species but some species may be under threat. Life tables are a useful tool to understand the growth potential of freshwater snail populations. Our aim was to estimate the demographic parameters of the Neotropical apple snail Asolene platae (Maton, 1811) to allow a quantitative comparison with invasive apple snails like Pomacea canaliculata (Lamarck, 1822). Life tables were calculated for three laboratory cohorts bred at 25 °C. Life expectancy rises abruptly up to 32–37 months after a period of high post-hatching mortality of one month. The reproductive value peaked at 15–19 months for two cohorts and at 33 months in the other one. The net reproductive rates (R0), generation times (GT) and intrinsic rates of increase (r) were as 55.86 hatchlings, 25.7 months, and 0.188 individuals per individual per month on average, respectively. Among freshwater snails there is a clear inverse relationship between r and GT while R0 has a minor positive influence. The values of GT and r for A. platae are among the highest and lowest, respectively, calculated for freshwater snails at 24–26 °C. These low values of r under optimum conditions indicate a relatively low potential of A. platae populations to increase in new habitats or to recover from disturbances.

Temperature-induced plasticity in morphology and relative shell weight in the invasive apple snail Pomacea canaliculata

Temperature has a great influence on the life-history traits of freshwater snails. In this study we investigated the long term effects of a range of temperatures on shell morphology of the apple snail Pomacea canaliculata, a highly invasive species and an important pest of rice. Analysis of shells using geometric morphometrics showed that the main source of morphological variation was allometry, which was detected in males but not in females. This intersexual divergence in allometric trajectories generates much of the morphological variation evidenced. In females, the monotonic relationship with temperature produced narrower shells in the snails reared at lower temperatures, and more expanded apertures, relatively bigger than the body whorl, at higher temperatures. We also found an inverse relationship between relative shell weight, a proxy for shell thickness, and temperature. The differences in shape and relative shell weight are attributable to the different growth rates associated with different temperatures. Temperature fluctuation around a mean of 23.2 °C seemed to have no influence in shell shape and relative weight when is compared with a constant temperature of 25 °C. Information on the influence of temperature on freshwater snails is important for understanding and predicting changes in the face of global climatic change, especially in traits exhibiting great plasticity, such as shell shape and thickness. This work showed that higher temperatures could result in a relatively thinner shell, implying a greater significance of corrosion in flowing waters and a lower resistance to crushing by predators, especially in low latitude areas.