Insights into the natural history of Ampullariids from the Lower Río de la Plata Basin, Argentina.

MARTÍN, PABLO RAFAEL; BURELA, SILVANA; TIECHER, MARÍA JOSÉ

Tentacle (The Newsletter of the Mollusc Specialist Group of the Species Survival Commission of the International Union for the Conservation of Nature and Natural Resources)

IUCN-The World Conservation Union

Año: 2013 vol. 21 p. 11 - 13

0958-5079

Apple snails (Ampullariidae) are renowned globally as successful invaders, as voracious pests of aquatic crops and as promoters of ecosystem changes in natural wetlands. However, a recent review highlighted that only 14 species of apple snails have been translocated beyond their native areas and less than half of them have caused ecological or economical impacts (Horgan et al., 2012). Most of their reputation is attributable to a few New World species of the genus Pomacea (in particular P. canaliculata) and to the ramshorn apple snail, Marisa cornuarietis. This prompted the IUCN Invasive Species Specialist Group to include Pomacea canaliculata in the list of 100 of the World?s Worst Invasive Alien Species, although at least one other species of the genus, Pomacea maculata, could probably be included in the list. The apple snails that have received most attention from the scientific community and the public during the last few decades are mainly the invasive ones such as M. cornuarietis, P. canaliculata and P. maculata. The Florida apple snail, Pomacea paludosa, a non-invasive species with a limited Caribbean distribution, is a remarkable exception although in this case most of the interest comes from being the staple food of the specialized apple snail predator Rostrhamus sociabilis, an endangered raptor in Florida. Other Pomacea species such as P. patula and P. urceus have also raised some conservation concern because they are overexploited for human consumption in Central and South America. The aforementioned apple snail species are just the emerging tip of the apple snail diversity ?iceberg? the underwater part of which is the large number of species still living beyond the reach of scientific inquiry in tropical and subtropical areas around the world. Many of them inhabit inland waters of the Neotropics (Central and South America), where four genera are recognised (Pomella has been recently synonymised with Pomacea) and dozens of species have been described, although only a few of them have received more than a name, a brief description of the shell and an imprecise type locality. The Lower Río de la Plata basin hosts representatives of all the genera of Neotropical apple snails, including some endemic genera and species , but is also the source of the three Pomacea species introduced into Asia, North America, Pacific islands and, recently, Europe. The fame of their invasive relatives probably leads to the conservation of these non-invasive apple snails being of least concern but in fact little is known about their natural history, distribution, demography and conservation status. The large number of genera and species in the area almost certainly reflects a high diversity of life history strategies and degrees of habitat specialization. Probably many of these species are not as flexible and adaptable as the invasive representatives. The apple snails inhabiting the Río de la Plata basin, the main hydrographic drainage in southern South America, face the impacts of habitat modifications resulting from the construction and operation of several very large dams as well as the impacts of invasive species. Beyond changing the nature of the habitat from lotic to lentic over large distances, these dams have disrupted the naturally variable hydrological regime of these rivers and hence affected the cycle of high and low waters in their flood plains. Deforestation, reforestation and land use intensification may provoke changes in detrital inputs, water quality and aquatic communities. Furthermore, the Paraná river has become a major ?hydroway? and is one of the main routes for transporting cargo among the various countries of the region (Argentina, Brazil, Paraguay and Uruguay). The Uruguay river, which supports the highest diversity of apple snail genera in the world, serves as the border between Argentina, Uruguay and Brazil and has been the focus of recent environmental concerns related to the installation of paper mill industries. Only five out of twelve species of apple snails inhabiting Argentinean waterbodies have been included in the IUCN Red list of Threatened Species database (IUCN, 2012), and none of them was considered as endangered. Pomacea canaliculata was categorized as of Least Concern because of its wide distribution and positive population trend. Pomacea megastoma, Felipponea neritiformis and Asolene pulchella were also considered as of Least Concern because of their wide distributions although their population trends were unknown. Felipponea iheringi was categorized as Data Deficient because of the lack of reliable information on its distribution. The status of the only species of Marisa, M. planogyra, which is restricted to the Middle Paraná river, has not been evaluated. Some of these species were considered as widely distributed and hence of Least Concern because of their presence in three countries (Argentina, Brazil and Uruguay), although in fact they inhabit only a single drainage basin or part of it (e.g. Uruguay river basin or Paraná river basin). However, considered that Asolene platae, Felipponea elongata and F. iheringi were endangered on the basis of their ?continuous restricted distribution?. Some species such as P. megastoma and Felipponea neritiformis, apparently restricted to places with bedrock and running water, seem to be especially prone to reductions in habitat extent by the impoundment of sections of the rivers. Moreover, P. megastoma seems to be mostly restricted to the left bank of the Uruguay river and Río de la Plata because of this habitat requirement. The fouling of apple snail shells and hard substrates by the invasive golden mussel, Limnoperna fortunei, has raised some concern especially regarding these apples snails associated with rocky bottoms. During the last decade there have been important advances in knowledge of the distribution of Argentinean apple snails. However, there were almost no studies concerning the natural history of apple snails other than Pomacea spp. Even information about the basic aspects of the anatomy and biology of very conspicuous species such as P. megastoma has emerged only in the last few years. For instance, the left nuchal lobe, used for aerial respiration in apple snails, was described as rudimentary and almost absent but our observations showed that it can be used as a snorkel to reach the surface in the same way as in Pomacea. Only recently the egg masses of this species have been reported (Hayes et al., 2009) and they are aerial and calcareous, as in Pomacea, and not gelatinous and subaquatic like those of the genus Asolene in which it was placed until recently. Presently there are two ongoing projects funded by the Universidad Nacional del Sur (UNS, PGI24/B185) and the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, PIP11220090100473) on the biology and ecology of Argentinean apple snails. Our aims in the short term are to study the natural history of at least one of the non-invasive species of each genus of apple snails with the goal of achieving a better comprehension of the evolution of their behavioral and physiological adaptations. The apple snails are collected with the required legal permissions, and then taken to the laboratory to establish populations that are maintained under controlled water temperature, light and food. All possible aspects of the life history of the snails are studied, including life span, egg-laying behaviour, fecundity, thermal limits, and other habitat requirements. Our experience indicates that P. canaliculata, P. maculata and Asolene pulchella readily grow and reproduce under laboratory conditions, but some species of Pomacea (P. megastoma and P. americanista) and Felipponea at first proved to be difficult to maintain in laboratory cultures even under carefully controlled conditions. Most species do not thrive in tap water, unlike P. canaliculata. Asolene pulchella preys readily on its own egg masses and hence requires special care; in individual aquaria females frequently deposits an egg mass and eat it in the course of a single night, even with lettuce provided ad libitum. Some species are slow growing and long lived, apparently maturing in their second year of life at 25 ºC, which makes demographic studies difficult. It is common sense that we cannot conserve what we do not know. We hope that the information that we are gathering in our projects will help to categorize the different species of apple snails from the Lower Río de la Plata Basin and hence to preserve as much as possible of the Neotropical ampullariid diversity.