Studies on the ecology and reproductive biology of ampullariids from southern pampas.

- MARTÍN P. R., BURELA, S., TAMBURI, N. E., SEUFFERT, M. E., TIECHER, M. J. & SAVEANU, L.

San Miguel de Tucumán, Tucumán

Workshop; 4th International workshop on the Biology of Ampullariidae.; 2010

STUDIES ON THE ECOLOGY AND REPRODUCTIVE BIOLOGY OF AMPULLARIIDS FROM SOUTHERN PAMPAS Pablo R. Martín, Silvana Burela, Nicolás E. Tamburi, María Emilia Seuffert, María José Tiecher, Lucía Saveanu & Martín Carrizo Pomacea canaliculata exhibits a peculiar suite of morpho-physiological and behavioural adaptations and besides it can alter the functioning of invaded natural wetlands; likewise, it probably plays an important ecological role in many waterbodies in its native range. We are following three main lines of research on this interesting snail: reproductive biology and life-history strategy, trophic ecology and determinants of its distribution at different scales. Experimental studies addressing the significance of the lengthy copulations of P. canaliculata showed that most of the copulation time is necessary to transfer enough sperm to assure the fertilization of all the female?s ova while genital connection or mate guarding can only account for 20% of its duration. A still puzzling component of the mating behaviour are the oral nuptial gifts produced by the males and eaten by the females; several functional explanations have been tested (to repel prowler males, to entice the female to remain in copulation or to manipulate her reproductive output to raise paternity ratio) but the results provided only new questions. A comparative approach to the significance of nuptial oral gifts lead us to initiate the investigation of apple snails with different reproductive strategies. Our observations on Asolene pulchella, which lays gelatinous egg masses under water, suggest that the details of both the structure of egg masses and the development of this group may constitute a rich source of traits for comparative and taxonomic studies. Our studies showed that P. canaliculata is able to complete its life cycle despite strong chronic limitations in food availability and that the life history strategy is sexually dimorphic relative to this factor. Females mature at similar sizes irrespective of food availability but, under the poorest conditions, at the expense of a delayed maturity and a reduction in fecundity; egg size and viability are not affected but hatchlings? survivorship increases with maternal deprivation. Contrarily, males mature as soon as possible regardless of the size attained, but this has no effect on their reproductive success. Confronted to sudden interruptions of food availability, females showed a higher survivorship than males. Best known for its macrophytophagous habit and its negative consequences on aquatic crops and macrophyte communities, P. canaliculata also uses alternative feeding mechanisms whose ecological significance is still poorly understood; the most peculiar among these is ciliary feeding. Our results showed that snail size, but not sex, is an important factor determining the use of this mechanism and capture rates. The spectrum of materials that can be captured by this mechanism seems wider than previously recognized. The natural diet of this polyphagous species in Southern Pampas is the next step in our research. Typically considered as a lentic species, our surveys in Southern Pampas showed that P. canaliculata also thrives in lotic waterbodies. We tried to characterize its hydrodynamic microhabitat and to understand its dispersal in these streams. In field surveys all the snails were found at current velocities below 0.3 m.s-1. However, open flume trials showed that snails can withstand strong currents (up to 1.64 m.s-1) during short periods although even slow currents interfere with routine activities like crawling and lung ventilation. In 2 h-trials in the flume the net displacement at low current velocities was similar downstream and upstream; however, in an mark-recapture experiment, most of the snails recovered 24 h later dispersed short distances downstream. Future efforts will focus on mechanistic niche models that should be able to explain and predict the distribution and dispersal of this species.