The exotic land gastropod Ovachlamys fulgens (Gude, 1900), aka the jumping snail, was registered in Eldorado city, Misiones province, constituting the first documented record of that species in Argentina-and for all of South America as well. Identities of the individuals were confirmed through morphological examination, and by a DNA sequencing of the cytochrome oxidase subunit I gene. DNA sequences for the mitochondrial 16S-rRNA and the nuclear 18S-rRNA genes were also obtained from the morphologically-confirmed specimens to gain insights into the genetic background of this species in Argentina, and as additional markers for enhancing the rapidity of identification by governmental authorities who are responsible for managing the presence of exotic species. Different size classes suggested that the species had successfully reproduced and become established in the locality. Ovachlamys fulgens is emphasized in the literature as being a serious pest to orchids. Misiones province harbors a high species richness of orchids, representing about one half of the known species in Argentina. Owing to the use of the orchid as an ornamental plant, the commercial trade could have facilitated the introduction of the species into Argentina. Control measures, preventive education, and surveillance are needed to prevent the further spread of this snail.
The genus Aylacostoma Spix, 1827, is mainly endemic to South America, and comprises about 30 nominal species, most of which were described based solely on conchological features following the typological approaches of most of the 19 th and the mid-20 th century authors. Here, we redescribe Aylacostoma chloroticum Hylton Scott, 1954, and describe Aylacostoma brunneum sp. nov. from the High Paraná River (Argentina-Paraguay) by means of morphological and molecular characters. Both are threatened species currently included into an ongoing ex situ conservation programme, as their habitats have disappeared because of damming and the filling up of the Yacyretá Reservoir in the early 1990s. We used DNA sequences from cytochrome b and cytochrome oxidase subunit I (COI) genes to estimate their genetic distances, and the COI sequences were also used to assess their specific status under the evolutionary genetic species concept by means of the K/θ method. Our results clearly demonstrate that both must be recognized as evolutionary genetic species, despite only minor differences in morphological characters other than in the shells.
a b s t r a c tThis article reviews the spread and current distribution of the invasive snail Melanoides tuberculata in Argentina and Paraguay based on data from specimens deposited in museums, published reports and field collections. Field collections were made between April 1999 and May 2010. Snails were searched for using different collecting methods in a variety of habitats. Specimens were identified according to a categorical scoring system based on shell traits and anatomy was compared with published descriptions. Only five records for Argentina and none for Paraguay were found in published reports. The first report of M. tuberculata in Argentina was in 1999. Neither specimens from Argentina nor Paraguay were found in the Argentine Museum of Natural Sciences (MACN). In La Plata Museum (MLP) the only material from these countries was that associated with the published reports. During the course of surveys undertaken since 1999, M. tuberculata was recorded at 19 sampling locations. The presence of this species in Paraguay is reported here for the first time. Since its discovery in Argentina and Paraguay, the snail has colonized both lotic and lentic habitats with a variety of substrata. The records suggest that the species is established and that its introduction resulted from passive dispersal. Actually, spreading is believed to occur by active dispersal (i.e. active migration) from established populations and impact in native communities is expected.
Variation in shape among a living and 2 extinct aquatic snails of the genus Aylacostoma, using a geometric morphometric method of thin plate splines and multivariate analysis was investigated. The analysis was performed to evaluate the diagnostic capability of this method and to explore shell shape differences, due to the lack of other data, in an attempt to answer why only 1 of the species persisted in the wild. Sixteen landmarks in a bi-dimensional space for 32 shells of type, paratype and reference specimens deposited in museums of Argentina were defined. Analysis was successful in assigning individual specimens to particular species. Statistically significant differences in last whorl, aperture, and spire were found for the first 4 non-uniform components explaining an 85% of local variation observed. Differences could be related to a differential use of habitat and/or to the degree of exposure to water current. More globose shell found in the extinct species could be associated to habitats and substrata with the highest water currents, whereas the more stylized shell in the third species could be related to a preference for more protected habitats, like those where it presently occurs.
Highly oxygenated freshwater habitats in the High Paraná River (Argentina–Paraguay) were home to highly endemic snails of the genus Aylacostoma, which face extinction owing to the impoundment of the Yacyretá Reservoir in the 1990s. Two species, A. chloroticum and A. brunneum, are currently included in an ongoing ex situ conservation programme, whereas A. guaraniticum and A. stigmaticum are presumed extinct. Consequently, the validity and affinities of the latter two have remained enigmatic. Here, we provide the first molecular data on the extinct A. stigmaticum by means of historical DNA analysis. We describe patterns of molecular evolution based on partial sequences of the mitochondrial 12S ribosomal RNA gene from the extinct species and from those being bred within the ex situ programme. We further use this gene to derive a secondary structure model, to examine the specific status of A. stigmaticum and to explore the evolutionary history of these snails. The secondary structure model based on A. stigmaticum revealed that most polymorphic sites are located in unpaired regions. Our results support the view that the mitochondrial 12S region is an efficient marker for the discrimination of species, and the extinct A. stigmaticum is recognized here as a distinct evolutionary genetic species. Molecular phylogenetic analyses revealed a sister group relationship between A. chloroticum and A. brunneum, and estimated divergence times suggest that diversification of Aylacostoma in the High Paraná River might have started in the late Miocene via intra-basin speciation due to a past marine transgression. Finally, our findings reveal that DNA may be obtained from dried specimens at least 80 years after their collection, and confirms the feasibility of extracting historical DNA from museum collections for elucidating evolutionary patterns and processes in gastropods.
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