The apple snail, Pomacea canaliculata has made a tremendous threat to agricultural crops as well as environmental ecology in Taiwan. Although various control methods are available, there are certain limitations in each of the applications. The present study was conducted to evaluate the application potential of food preference in attractant usage to apple snails. It has been found that apple snails actively searched animal materials. Fish blood and egg glair were as attractive as banana (Musa sp.). With equal weight, blood clots from cobia (Rachycentron canadum) and pig (Sus sp.) were more attractive than banana, and cooked pig blood was as attractive as banana. The response of snails to concentrated extracts from fish blood (with molecular weight > 5000) was stronger than banana. There were no significant differences in snails¡¦ responses to blood from pig, cobia, freshwater and seawater milk fish (Chanos chanos). Furthermore, protein was probably the attractive source to apple snails and frozen-treated blood increased attractive response. As expected, blood clots from cobia and pig were more attractive than banana in the field. In summary, the results show that animal protein is potentially applicable as attractive components for apple snails.

The apple snail, Pomacea canaliculata has made a tremendous threat to aquatic agricultural crops for many years. But safe and effective methods to eliminate them are still not available. Traditionally, pesticides are the most common way to kill apple snails. However, the occurrence of drug resistance and drug residual causes even more serious problems. The present study was conducted to evaluate the effectiveness of attractants to apple snails in the fields. The experiments included the effectiveness of different attractants and trap designs under different environmental conditions. It was found that attractants of banana pulp, chicken blood and condensed fish soluble were effective with at least 12-hour trapping time. The sizes of attracted snails were similar to the ambient snails. Snails (Pomacea scalaris, Sinotaia quadrata, Planorbioidae spp.), insects (Sphaerodema rustica, water scorpion),tadpole and fishes (Poecilia reticulate, Trichogaster trichopterus) were also found in the traps. Besides, two-opening traps with funnel entrance were more effective than the traps without funnel entrance. In general, in still water with ambient density of apple snails range from 6.2¡Ó 6.1 to 50.3¡Ó14.2 individual/m2,the relationship between attracted snails and ambient snail density was negative in chicken blood group (p < 0.001), positive in condensed fish soluble (p < 0.05) and no trend in banana group (p > 0.05). The results support the hypothesis that areas with abundant food usually have high snails density and those snails are less attracted by potential food items.

No description available.

Pomacea canaliculata es un gasterópodo de agua dulce perteneciente a la familia Ampullariidae (Architaenioglossa, Caenogastropoda), cuyo rango de distribución natural abarca desde el sur de Brasil hasta el sur Bonaerense. Se lo considera uno de los 100 peores invasores a escala global debido a su voracidad, altas tasas reproductivas y alta plasticidad en su ciclo vital. El objetivo principal de este trabajo de tesis fue estudiar la norma de reacción de diversas características del ciclo vital de P. canaliculata frente a la disponibilidad trófica. Específicamente se estudió cómo afectan distintos niveles de disponibilidad trófica constantes, el crecimiento, la talla y la edad a la que alcanzan la madurez, la cantidad de recursos que destinan a la reproducción y la forma de su conchilla. Finalmente, se estudió el efecto de una interrupción abrupta en la alimentación sobre la reproducción, el crecimiento y la supervivencia. Los resultados mostraron una superioridad en los parámetros específicos de ingestión y eficiencia de crecimiento de las hembras respecto de los machos y en los juveniles respecto de los adultos. P. canaliculata puede completar normalmente su ciclo vital bajo un amplio rango de disponibilidades tróficas. Frente a distintas disponibilidades tróficas la estrategia de las hembras fue madurar a distintas edades y a una talla semejante, mientras que en los machos fue madurar a edades semejantes pero a tallas muy distintas. La disponibilidad trófica no afectó el éxito reproductivo de los machos, mientras que en las hembras las restricciones en la disponibilidad trófica provocaron descensos, principalmente en el número de huevos. En caracoles en reproducción, un corte abrupto de la alimentación redujo la supervivencia más en machos que en hembras, y produjo una caída en el número de cópulas y de puestas. Un efecto maternal en el cual el vigor de la progenie de hembras que crecieron con baja disponibilidad trófica se incrementa respecto de las hembras sin restricciones alimentarias parece indicar una estrategia adaptativa transgeneracional. La forma de la conchilla parece cambiar en algún grado con la disponibilidad trófica pero sin ningún patrón claro y monótono; el dimorfismo sexual no parece verse alterado por la disponibilidad trófica. Aparecen indicios que sugieren que el contenido de nitratos del agua y la materia orgánica del sustrato en ambientes naturales tienen relación con parámetros poblacionales como la densidad de puestas y la talla máxima de P. canaliculata; por el contrario, los iones inorgánicos y los factores fisicoquímicos analizados no mostraron relación con éstos. La estrategia evolutiva de Pomacea canaliculata frente a la disponibilidad trófica parece basarse en una alta plasticidad de su ciclo vital, abarcando el crecimiento, la maduración y el esfuerzo reproductivo, así como en un alto grado de diferenciación sexual en estas características. / Pomacea canaliculata is a freshwater snail belonging to the family Ampullariidae (Architaenioglossa, Caenogastropoda) whose natural range extends from Southern Brazil to Southern Pampas in Argentina. It has been nominated as one of the 100 worst invaders at a global scale, owing to its voracious feeding habits, high reproductive rates and plastic life history traits. The main aim of this Thesis was to study the reaction norms to trophic availability of several life history traits in P. canaliculata. Specifically, the way in which growth, age and size at maturity, reproductive effort and shell shape are affected by different chronic levels of trophic availability was investigated. In addition, the effect of an abrupt shortage of food on reproduction, growth and survivorship was investigated. The results obtained showed higher values of specific parameters of ingestion and growth efficiency in females than in males and in juvenile snails relative to adults. P. canaliculata is able to complete its life cycle under a wide range of trophic availability. Confronted with different trophic availabilities, the strategy of females was to mature at different ages but always at almost the same size, whereas for males it was to mature at the same age but at very different sizes. Trophic availability did not affect the reproductive success of males while for females restricted trophic availabilities caused a drop mainly in the number of eggs laid. For snails which were already in reproductive state, an abrupt shortage of food reduced the survivorship of males in a higher degree than in females and a drop in the number of copulations and egg masses laid. A maternal effect, in which the progeny of females grown under low trophic availabilities showed a higher vigor than those from females fed ad libitum, suggests a transgeneration adaptive strategy. Shell shape seems to be affected by trophic availability though without producing a clear and monotonous pattern; sexual dimorphism seems not to be affected by trophic availability. The nitrate content of water and the organic matter of sediments seem to be related to demographic parameters of P. canaliculata, like density of egg masses and maximum sizes; on the other hand, inorganic ions and physicochemical variables did not show any relation with them. The evolutionary strategy of Pomacea canaliculata relative to trophic availability seems to be based on a high plasticity in life history, including growth, maturity and reproductive effort, and on a high degree of sexual differentiation in these traits.

The Pomacea apple snails are amphibious operculate freshwater gastropods. They exhibit different stress tolerant abilities as some of them are invasive (e.g., Pomacea maculata and Pomacea canaliculata) and others are non-invasive species (e.g., Pomacea diffusa). By using a comparative approach, I have profiled the perivitelline fluid of P. maculata, compared the physiological and proteomic responses of P. canaliculata and P. diffusa to thermal and hypoxic stressors, and examined their sequence divergences. 74 proteins were identified from the PVF of P. maculata. Comparison of gene expression levels between albumen gland (the organ that secrets PVF) and other organs showed that 24 PVF genes were specifically expressed in albumen gland. Base substitution analysis of PVF and housekeeping orthologs between P. maculata and its congener P. canaliculata showed that these reproductive genes have higher evolutionary rate. The LT50 of P. canaliculata was significantly higher than that of P. diffusa. More than 3,350 proteins were identified from the hepatopancreas of the snails exposed to acute and chronic thermal stress using iTRAQ-coupled mass spectrometry. Chronic exposure caused differential expression of more proteins, with many of them related to restoration of damaged molecules, ubiquitinating dysfunctional molecules, and utilization of energy reserves in both species; but only in P. diffusa there was a shift from carbohydrate to lipid catabolism. Analysis of orthologous genes encoding the differentially expressed proteins revealed nine candidate genes may have undergone positive selection (Ka/Ks > 0.5). A 72 h mortality experiment showed that P. canaliculata is much more tolerant to hypoxia than P. diffusa. The two species were then exposed to four levels of dissolved oxygen (6.7, 4.1, 2.0 and 1.0 mg O2 L-1) for 8 h, and their gill proteins were analyzed using iTRAQ-coupled LC-MS/MS. Compared with P. diffusa, P. canaliculata had more up-regulated signal transduction proteins and down-regulated proteins which are involved in glycolysis and the tricarboxylic acid cycle. Evolutionary analysis indicated that selection has acted on some of the hypoxia responsive genes. The comparative method and results provide a framework for studying the genetic basis of species invasion and predicting their further expansion in a changing climate for non-model species.

The distribution of apple snail Pomacea canaliculata is islandwide but Pomacea scalaris is only found in southern Taiwan. In order to gain more information on the not well-known invasive species of P. scalaris, the growth and feeding of P. canaliculata and P. scalaris were studied. The hatching period of P. canaliculata (10.4¡Ó1.3 days) was shorter than that of P. scalaris (12.2¡Ó2.3 days). And, the hatching size of P. canaliculata was also smaller. Two weeks after hatching, a significant higher growth rate in P. canaliculata had been found. The 75-day growth equations for P. canaliculata and P. scalaris were y = 0.29x + 1.09 (p < 0.001) and y = 0.16x + 1.68 (p < 0.001), respectively. Feeding structures of mandible, radulae, central tooth and stomach in P. canaliculata were larger than that of P. scalaris. But, there was no significant difference in the length of gut between the two species. Food passing time in P. canaliculata (1.4¡Ó0.7 days) was less than that of P. scalaris (2.9¡Ó0.7 days). And, the approximate digestibility per day of P. canaliculata (44.41¡Ó24.02%) was higher than that of P. scalaris. Through the analyses of £_13C, £_15N, stomach content and feces, it is known that they have the same trophic level with similar food sources. Additionally, the values of £_13C and £_15N were significantly different between sites of JiouRu and Wugou-shui, Pingtung. In other words, the feeding environments were different between the two sites. Based on the results, it is concluded that the superiority of growth and feeding performance in P. canaliculata is important in shaping its wide distribution in Taiwan.

The apple snail Pomacea canaliculata Lamarck is a native of South America but has invaded Hong Kong since early 1980s. Its feeding has resulted in a tremendous loss in semi-aquatic agriculture, especially rice (Oryza sativa L.) and other aquatic crops such as taro (Colocasia esculenta L.) and water spinach (Ipomoea aquatica Forssk). While spreading to freshwater wetlands, its feeding threatens macrophyte diversity. Owing to its voracious appetite, this invasive snail has also become a competitor of lowland indigenous mollusks. On ecosystem level, over-grazing by high density of apple snails could also induce excessive release of nutrients from macrophytes to water bodies, thus promoting phytoplankton growth and primary production. Measures to control invasive apple snails fall into three categories: mechanical / cultural, chemical, and biological. Among them, biological control methods are appealing because they are usually considered relatively less labor-intensive and more cost-effective. However, both the control efficacy and potential non-target effects should be carefully evaluated before adopting a species in biological control. Although various fish species have been proposed as biological control agents for apple snails, their effectiveness and non-target effects on wetland flora and fauna are largely unknown. This study investigated the feasibility of black carp (Mylopharyngodon piceus Richardson) as bio-control agent for apple snails in both laboratory and field experiments. The laboratory experiment compared the feeding of black carp, common carp (Cyprinus carpio L.) and white-spotted catfish (Clarias fuscus Lacepède) on apple snails. These three species are indigenous and widely aquacultured in southern China. The three species of fish of comparable body length were each offered apple snails of various sizes ad libitum in aquaria. Black carp (fork length: 165 mm; maximum gap width: 16 mm) was the most effective predator, with a predatory rate of 70.5 apple snails in 48 hours. Common carp and white-spotted catfish of similar fork lengths consumed only 58.6 and 15.7 apple snails on average within the same experimental period. Apple snails preyed upon by black carp and common carp were juveniles, with their respective shell length ranged from 3 - 16mm and 3 - 17mm, while that for white-spotted catfish ranged from 3 - 21mm. An 8-week mesocosm experiment was conducted in a constructed wetland during the dry season of 2011 to determine whether black carp (fork length: 170 -185 mm) is as effective as common carp (fork length: 170 - 195 mm) as a bio-control agent for apple snails, but causes less herbivory to macrophytes and predation to non-Pomacea snails. Both species of carp preyed effectively on P. canaliculata, removing almost all apple snail individuals (~ 200 per enclosure) that were small enough to fit into their mouths. The effects of the two fish species on macrophytes were different. Black carp reduced herbivory on macrophytes through reducing apple snail density. However, common carp reduced apple snail density but did not result in a lower level of herbivory because it also grazed on macrophytes. Non-target mollusk density was reduced by both fish species. A one-year whole-pond experiment was also conducted in June 2012 to June 2013 to investigate the applicability of black carp as a biological control agent of apple snails in constructed freshwater wetlands. Three separate constructed freshwater wetlands were used as replicates of the experiment. Each wetland was divided into a control side without black carp and a treatment side with black carp. Four individuals of black carp (fork length 260 - 310 mm) were released to the side of wetland assigned as treatment. Prior to starting the experiment and every three months, density of apple snails and other macro-invertebrates, apple snail egg clutch size and abundance, water quality parameters (total nitrogen, ammonia nitrogen, total phosphorus and reactive phosphorus) were recorded. Black carp was highly tolerant to the low dissolved oxygen in the shallow stagnant waters. It was an effective predator of juvenile apple snails (<5 – 25mm), but it did not result in significant reduction of adult apple snails (shell length >25mm) nor affected their reproduction. In addition, black carp preyed on non-apple snail macro-invertebrates, especially mollusks. In conclusion, our study has shown that juvenile black carp (minimum total length: 300mm) is a suitable bio-control agent of apple snails in shallow water wetlands as it is tolerant of stagnant poor water quality and is an effective predator of apple snails. A major decline of 89.2% in average overall density of apple snail has been recorded in the treatment plots of the three experimental sites after one year. Juvenile snails would be eradicated before they get to mature minimum size (male SL: 25.2 ± 3.3mm; female: 29.8 ± 3.6mm) for reproduction. Given the longevity of black carp, a low stocking density (80-89 individuals ha-1) is sufficient to control apple snail populations. However, black carp reduces the abundance and diversity of non-target macro-invertebrates. Therefore the benefits of the biological control must be weighed against the potential undesirable effects on wetland diversity before adopting in the pest management. To maximize the control efficacy, mechanical methods to eradicate adult snails, for instance hand-picking in the shallow water, should be implemented with biological control effort in an integrated apple snail management program.

Invasive species are detrimental to native biotas worldwide. Recently, Florida was invaded by a freshwater snail (Pomacea canaliculata) native to Argentina. This snail is a serious pest of rice crops in Asia, but little is known about its interactions within Florida ecosystems. Possible competitive exclusion of the native congener (P. paludosa) is a concern because it is the almost exclusive prey of the federally endangered Everglades snail kite (Rostrhamus sociabilis). My research consisted of three parts. First, to identify possible methods to control P. canaliculata in the egg stage, I experimentally evaluated the effects of photoperiod, substrate availability, and food type and availability on hatching success and hatchling survival. None of these factors significantly affected hatching or survival, suggesting that P. canaliculata could invade many water bodies. Second, I used a randomized block design to assess the separate and combined effects of population density and food availability on growth and spawning of P. canaliculata. Food availability but not density significantly affected growth; snails fed less food grew less, but neither factor affected spawning. Third, I used a replacement series design to assess competition between P. canaliculata and P. paludosa under food limitation. For both species, snails fed less grew significantly less, and snails exposed to greater congener densities spawned less than when exposed to conspecifics only. While my results predict that P. paludosa should exclude P. canaliculata, previous literature and current invasions suggest that the exotic snail may co-exist with its North American congener.

The distribution of apple snail Pomacea canaliculata are island-wide but Pomacea scalaris is only found in southern Taiwan. In order to gain more information on the not well-known alien invasive species, comparative studies on the reproduction and thermal tolerance of P. canaliculata and P. scalaris were conducted. Sexual dimorphism in shell morphology has been found in both species, with wider operculum in males. Positive correlation between shell length and penis sheath length or penis length has been observed in male P. canaliculata and P. scalaris, based on the samples collected during the period of December 2004 and March 2006, The width of penis sheath in P. canaliculata was greater than in P. scalaris. Positive correlation between shell length and the height and width of vestigial penis in female P. canaliculata and P. scalaris was also found. The width of vestigial penis in P. scalaris was greater than in P. canaliculata. Gonadosomatic index (GSI) in male P. canaliculata and P. scalaris was 68 and 60% and 31 and 33% in females. Their reproductive cycle was annual without seasonal peaks. Significant difference in thermopreferrenda was found between P. canaliculata and P. scalaris. The 24, 48 and 72-h lethal thermal minima temperatures in P. canaliculata and P. scalaris were similar, i.e. 9.8¡V11.8¢J. And, the 24, 48 and 72-h lethal thermal maxima temperatures were 33.1¡V35.9¢J. Based on the results, it is known that P. canaliculata and P. scalaris reproduce year-round and temperature is not a major factor in shaping the species distribution pattern in Taiwan.

El caracol de agua dulce sudamericano Pomacea canaliculata en un herbívoro generalista con hábitos de alimentación principalmente macrofitófagos. Los impactos más relevantes que este invasor ha producido fuera de su rango de distribución nativo se deben a la erradicación de la vegetación sumergida, que genera cambios en el funcionamiento ecosistémico. El estudio de la dieta natural y de otros aspectos de la alimentación de P. canaliculata son importantes para comprender sus efectos sobre la vegetación y su rol en los humedales naturales en su rango de distribución nativo, que no han sido estudiados aún. Los objetivos de esta tesis fueron analizar los determinantes de la variación en la dieta natural de P. canaliculata en la Cuenca de las Encadenadas del Oeste (Buenos Aires, Argentina), evaluar el efecto de su herbivoría sobre la composición y estructura de las macrófitas sumergidas e investigar si la ingesta de partículas líticas afecta los procesos digestivos. La palatabilidad y preferencia que presentan las diversas macrófitas sumergidas son las que determinan la herbivoría de P. canaliculata. Experimentos de laboratorio mostraron que la palatabilidad está relacionada de forma negativa con las defensas físicas de las mismas y que la preferencia se encuentra determinada por la palatabilidad. A través de experimentos en mesocosmos se demostró que P. canaliculata podría estar afectando la comunidad de macrófitas en su rango de distribución nativo, debido a la erradicación o a la disminución de la biomasa de algunas macrófitas, producido por el efecto de su herbivoría en conjunto con un incremento en la turbidez del agua. A su vez se registraron efectos sobre otros componentes del ecosistema, como el aumento en la productividad del fitoplancton y una disminución en la biomasa de detritos. El análisis de los contenidos del tracto digestivo de P. canaliculata a través de la técnica micrográfica resultó un método adecuado para estudiar su dieta natural. El estudio del contenido del intestino es suficiente para determinar la dieta, aportando la misma o una mayor información que el estómago, que ha sido el órgano usualmente estudiado. El componente principal de la dieta de P. canaliculata en su rango de distribución nativo fueron los detritos, mientras que macrófitas, gramíneas, restos animales y algas filamentosas completaron los ítems más representativos. Los diagramas de Amundsen sugieren que esta especie se comporta como generalista, resaltando la importancia de los detritos en la dieta natural. A pesar de que los ambientes estudiados difieren en la disponibilidad de recursos tróficos potenciales, la dieta estimada a partir de los contenidos digestivos no muestra variación entre ambientes ni a lo largo del año. Con la excepción del arroyo donde P. canaliculata es más frecuente, la frecuencia y abundancia de las macrófitas sumergidas en la Cuenca de las Encadenadas del Oeste no se relacionaron con las de P. canaliculata. Sin embargo, al comparar esta cuenca con otra cercana, donde este caracol está ausente, se encontraron diferencias evidenciando un probable efecto del caracol. La presencia de partículas líticas en el tracto digestivo de P. canaliculata es común en caracoles provenientes de ambientes naturales. La disponibilidad de partículas líticas puede aumentar la eficiencia de crecimiento, permitiendo alcanzar mayores largos y pesos, especialmente en las hembras juveniles. La ingesta de partículas parece ocurrir de forma accidental, pudiendo ingerir partículas que tengan un efecto adverso. Las partículas líticas en el tracto digestivo de P. canaliculata podrían actuar como gastrolitos, aunque esta función dependerá de la forma, tamaño y mineralogía de las mismas. Los resultados de esta tesis sugieren que Pomacea canaliculata tiene un rol como especie clave en su rango de distribución nativo y este rol puede mantenerse en el rango exótico. Los resultados obtenidos, también sugieren que podría tener un rol importante en la resistencia biótica ante macrófitas invasoras y también un uso potencial como agente de control biológico. Sin embargo, la palatabilidad de las macrófitas presentes en los ambientes naturales y sus respectivas abundancias son determinantes del rol de esta especie y de los efectos que puede llegar a producir. / The South American freshwater snail Pomacea canaliculata is a generalist herbivore with macrophytophagous feeding habits. The most relevant impacts that this invasive snail has produced outside of its native range are due to the eradication of submersed vegetation, which generates changes in ecosystem functioning. The study of the natural diet and other aspects of the trophic ecology of P. canaliculata are important to understand its effects on aquatic vegetation and its role in waterbodies in its native range, which have not yet been studied. The objectives of this thesis were to study the determinants of the variation in the natural diet of P. canaliculata in the Encadenadas del Oeste basin (Buenos Aires, Argentina), to evaluate the effect of its herbivory on the composition and structure of submersed macrophyte communities and to investigate if the ingestion of lithic particles affects the digestive processes of the snail. The palatability and preference for the different submersed macrophytes determine the herbivory of P. canaliculata. Laboratory experiments showed that palatability is negatively related to the physical defenses of the submersed macrophytes and that the preference for one or another species depends on their palatability. Mesocosmos experiments demonstrated that P. canaliculata could be affecting the submersed macrophyte communities in its native range, due to the eradication or biomass reduction of some macrophytes, probably as a result of its herbivory together with an increase in water turbidity. At the same time, effects on other ecosystemic components were observed, such as the increase in the productivity of phytoplankton and a decrease in detrital biomass. The micrographic analysis of the digestive contents was an adequate method to study the natural diet of P. canaliculata. The analysis of the intestine content is sufficient to determine the diet, giving the same or even more information than the stomach, which has been the usually studied organ. The main component of the diet of P. canaliculata in its native range was detritus, while macrophytes, grasses, animal remains and filamentous algae completed the most representative items. The Amundsen diagrams suggest that this species behaves as a generalist, and highlights the importance of detritus in its natural diet. Although the environments studied differ in the availability of potential trophic resources, the diet estimated from the digestive contents does not show variation among environments or throughout the year. Exception made of the stream where P. canaliculata was more frequent, the frequency and abundance of submersed macrophytes in the Encadenadas del Oeste basin was not related to the presence and abundance of P. canaliculata. However, when comparing this basin with a nearby one where the snail is naturally absent, differences were found in the frequency of occurrence of the most palatable macrophytes, probably indicating an effect on the part of the snail. The presence of lithic particles in the digestive tract is common in P. canaliculata snails from natural waterbodies. The availability of lithic particles can increase growth efficiency, allowing greater lengths and weights to be reached by the snails, especially by juvenile females. The ingestion of these particles seems to happen accidentally, as the snails may ingest also particles that have noxious effects. The lithic particles in the digestive tract of P. canaliculata could act as gastroliths, although this function would depend on their shape, size and mineralogy. The results of this thesis suggest that Pomacea canaliculata has a role as a keystone species in its native range which may be maintained in the exotic range. Results also indicate this snail could play a role in the biotic resistance against invasive macrophytes in addition to showing a potential as a biological control agent. However, the palatability of the macrophytes present in natural environments and their respective abundances are determinants of the role of this species and the effects it eventually produces.