Verónica Núñez

FRESHWATER GASTROPODA FROM ARGENTINA: SPECIES RICHNESS, DISTRIBUTION PATTERNS, AND AN EVALUATION OF ENDANGERED SPECIES

Few studies have dealt with the geographic distribution of freshwater snails in Argentina. The objectives of this study were to: (1) determine species and family richness and diversity patterns; (2) verify if species richness behaves according to Rapoports rule; (3) identify and classify species according to their distributions; and (4) identify endangered species. A grid was applied to a map of Argentina, with each of 340 squares (SUs) representing 10,000 km2. A database of 3,376 records was analyzed. Of the 101 species belonging to ten families recorded in Argentina, four are introduced and 40 are endemic to Argentina. The Lithoglyphidae have the highest number of species (22). The highest species richness/SU was recorded in the Brazilic subregion at Salto Grande (32 species) on Uruguay River, and parts of the Río de la Plata (31). In this subregion the species richness values increase from west to east. The highest richness in the Chilean-Patagonian subregion was detected at San Carlos de Bariloche, Río Negro province (9), and the Chilinidae contained the largest number of species. In Argentina, the north-south decline species pattern could be explained through Rapoports rule. In Patagonia, the species richness gradients do not show significant west-east trends. Most of the native species of freshwater molluscs of restricted distribution can be considered endangered (about 45 species) but need further study.

The giant African snail, Achatina fulica (Gastropoda: Achatinidae): Using bioclimatic models to identify South American areas susceptible to invasion

Abstract. The best way to reduce problems related to invasive species is by preventing introductions into potentially susceptible areas. The purpose of this study was to create distribution models for the invasive gastropod Achatina fulica Bowdich, 1822 in South America in order to evaluate its potential geographic distribution and identify areas at potential risk. This mollusc, considered one of the 100 worlds worst invasive alien species, is the focus of intense concern due to its impact on agriculture, human health, and native fauna. We tested two commonly used ecological niche modeling methods: Genetic Algorithm for Rule-Set Prediction (GARP) and Maximum Entropy (MaxEnt). Models were run with occurrence points obtained from several sources, including the scientific literature, international databases, governmental reports and newspapers, WorldClim bioclimatic variables, and altitude. Models were evaluated with the threshold-independent Receiver Operating Characteristic (ROC) and Area Under the Curve (AUC). Both models had consistent performances with similar areas predicted as susceptible, including areas already affected and new potentially susceptible areas in both tropical and temperate regions of South America.

Invasion of the Argentinean Paranense Rainforest by the Giant African Snail Achatina fulica

Abstract: The tropical land snail Achatina fulica Bowdich, 1822, native to Africa, is reported for the first time in Argentina, in Puerto Iguazú City, Misiones Province. This city is surrounded by protected areas. Three randomly selected 1-m2 plots were marked off in private gardens and in the area surrounding an urban stream for snail sampling. The high snail density detected could have ecological, sanitary, and economic consequences which have already been documented in other countries.

Freshwater Gastropod Provinces from Argentina

ABSTRACT Diverse biogeographic regions have been proposed in Argentina using different approaches of biogeography and different criteria. However, none of these proposals has considered freshwater gastropods in estimating biodiversity values, although gastropods from continental waters have great ecological importance and are a useful group to characterize freshwater environments. For this reason, our aim is to define freshwater gastropod provinces and to compare them with the available information on biogeographic regions previously defined using other data sets. The gastropod database comprises approximately 4,000 georeferenced records from museum collections, bibliographic records, and collections of our research team. A similarity analysis among basins was carried out using the species as characters and applying Jaccards coefficient and UPGMA clustering with the MVSP program to obtain the resulting phenogram. Eight provinces were identified: I, Misionerean; II, Middle Paraná; III, Uruguay River; IV, Lower Paraná — Río de la Plata; V, Central; VI, Cuyo; VII, Northern Patagonia; and VIII, Southern Patagonia. Between Provinces V and VI lies a Transitional Zone that shows a higher faunal similarity with the Del Plata basin than with the Patagonian basins. The provinces with the highest diversity were I and IV (H = 1.92 and 1.89 respectively), while Province III shows the highest richness (S = 51) and quantity of endemic and vulnerable species. These provinces are the most densely populated in the country and therefore include the areas with the highest environmental degradation level.

First Records of Four Exotic Slugs in Argentina

Abstract: This paper reports for the first time the occurrence of four exotic terrestrial slug species in Argentina: Lehmannia valentiana (Férussac, 1823) (Limacidae), Deroceras invadens Reise et al. 2011 (Agriolimacidae), Arion intermedius Normand, 1852 (Arionidae) and Meghimatium pictum (Stolyczka, 1873) (Philomycidae). The study is based on specimens deposited in museums in Argentina. Both the morphologic characteristics and the mitochondrial cytochrome oxidase I gene sequences were used to identify the exotic species. Phylogenetic analyses were also carried out in order to explore the location of their origins. Lehmannia valentiana had the oldest records and has been widely distributed in Argentina. Deroceras invadens and A. intermedius were found to be restricted to the southern portion of the country. Meghimatium pictum was recorded in the northwest and northeast Argentina, and the DNA sequences analyzed from this species were more closely related to specimens from the west of the Strait of Taiwan. A determination of the origin of the other species was impossible because either the sequences analyzed grouped with samples from different geographical origins or only few sequences were available for comparison. In view of the invasive potential of these slug species, the present work provides new and potentially useful DNA sequence data obtained from morphologically-confirmed specimens. Information provided from these analyses should assist in making a rapid identification of these exotic slugs by nonspecialists and governmental authorities who are responsible for managing and controlling the presence of exotic species.

Differences on allocation of available resources, in growth, reproduction, and survival, in an exotic gastropod of Physidae compared to an endemic one

Physa acuta Draparnaud, 1805 is an invasive gastropod that can affect local species. In Argentina, it is widespread and abundant, even in environments inhabited by the native species Stenophysa marmorata Guilding, 1828. Its predominance raises the question whether this could be explained by a more successful energy allocation in functional requirements (growth, reproduction and survival) compared to S. marmorata. This study was aimed at comparing growth rates, as well as survival and fecundity, between both species under laboratory conditions. Individuals born on the same day were grouped in four per aquaria and kept under controlled conditions of food, light, and temperature. Snails were weekly measured (maximum shell length), and growth rates were calculated using the Von Bertalanffys equation. The number of eggs and survivors were grouped by week. Stenophysa marmorata was larger at birth than Physa acuta and invested more energy in growth, delaying sexual maturity. This resulted in a disadvantage in fecundity and survival compared to P. acuta, which had a lower growth rate but matured earlier and survived longer. Furthermore, the growth of P. acuta was not affected by reproduction, its reproductive period was longer, consequently with more eggs laid than S. marmorata.

Population Studies of an Endemic Gastropod from Waterfall Environments

Abstract: Chilinidae is a family endemic to South America, ranging from the Tropic of Capricorn to Cape Horn and the Falkland Islands, and includes 32 species. However, there are few population studies on the Chilinidae. We study aspects of the ecology of an endemic species, Chilina megastoma Hylton Scott, 1958, from the Arrechea Falls in the Iguazú National Park, Argentina, such as density and individual annual growth trends. Nine samplings were carried out between December 2003 and December 2005, using two transects that crossed the waterfall. Individual annual growth rate was analyzed according to length, following von Bertalanffys model. Six cohorts were identified, some in the same climatic season but successive years (two in winter and two in summer). The winter and autumn cohorts reached 85% of their last whorl length in the first year. Compared to other families of gastropods from subtropical climates, these populations have several recruitment events per year, but never in winter.

Fecundity and survival advantages of an exotic gastropod compared to a native species

Abstract: In Argentina the exotic snail Physa acuta Draparnaud, 1805 is predominant in environments previously inhabited by the native species Stenophysa marmorata Guilding, 1828, raising the question of whether this could have occurred because of differences in survival or reproductive strategies. To analyze the life cycle of these two species, I used the horizontal—life-table method and considered the number and proportion of viable of eggs per oviposition. Although both species suffered a high degree of mortality during the first weeks after oviposition, both the rate and the force of mortality was much greater during the reproductive period, so that the survival curve was not as markedly concave as with other gastropods. Physa acuta survived longer than S. marmorata, began its reproductive period earlier, and had a longer and more continuous reproductive stage. The number of ovipositions per snail was not different between the two species; but since the mean number of eggs per oviposition was higher in P. acuta, fecundity was likewise higher. The increase in fecundity was accompanied by an enhancement of the mortality rate in S. marmorata. The percentage of viable eggs was higher in P. acuta than in S. marmorata, but fecundity increased with age in both species. Life expectancy, reproductive value, and net reproductive rate were higher in P. acuta. The success of the exotic species P. acuta in the native habitat of S. marmorata could be explained in part by the formers earlier sexual maturation, higher reproductive potential, and greater longevity. Further field and laboratory studies are needed to demonstrate the existence of interspecific competition between these two gastropods.

Redescription of Potamolithus paranensis (Pilsbry, 1911) and Potamolithus simplex (Pilsbry, 1911) (Gastropoda: Tateidae)

ABSTRACT Potamolithus Pilsbry & Rush, 1896 is a species-rich genus, endemic to South America, with many of its species considered Vulnerable due to a restricted distribution; half of them are called into question, since they are known only from their shells. The purpose of this article is to describe the anatomy of P. paranensis (Pilsbry, 1911) and P. simplex (Pilsbry, 1911) from the Argentinean Misiones province, and to evaluate the value of anatomical features in this genus. These two species differ in penis morphology and pigmentation, ctenidium length, and relative position of the opening of the pallial oviduct, seminal receptacle and bursa copulatrix. Consequently, it appears that anatomical data could help solve taxonomic conflicts that are currently unresolved by shell morphology alone.

Strigeid parasites of Circus buffoni from Argentina, with the description of a new species of Parastrigea Szidat, 1928

Studying the Helminthological Collection of Museo de La Plata (MLP-He), several specimens of digeneans, recovered parasitizing a long-winged harrier, Circus buffoni (Accipitridae) from Buenos Aires Argentina, were analysed. The morphological and morphometric analysis of these specimens revealed the presence of two strigeid species, one of them new for science. Parastrigea buffoni n. sp. is characterised by a forebody differentiated in a retractile cephalic region with a large opening and a balloon-shaped collar region or collerette, suckers located in cephalic region, holdfast organ with well development dorsal and ventral lips that can emerge through opening, a claviform hindbody, a large copulatory bursa with muscular ring (Ringnapf) and a genital cone well delimited, crossed by a sinuous hermaphroditic duct with internal rugae. The euryxenous parasite, Strigea falconis brasiliana, is briefly described, parasitizing a new host. This is the first record of helminths parasitizing long-winged harrier.