Variation in the distribution of Corbicula species (Mollusca: Bivalvia: Corbiculidae) after 25 years of its introduction in the Río de la Plata, Argentina

In 1981, Corbicula fluminea (Müller, 1774) and C. largillierti (Philippi, 1844) were recorded at the Río de la Plata River. During the 1980?s, C. largillierti was found on a continuous fringe in the shore of that river, while C. fluminea was only found North of Buenos Aires? harbor. Ten years later, C. fluminea spread to Punta Indio, while C. largillierti remained restricted to tributary streams. The density and size frequency distribution of both species were compared with previous data from samples performed in the same area in 1985?1989. The aim of this research was to determine whether the densities of both species decreased; whether C. fluminea is still more abundant than C. largillierti; and whether the size frequency distributions indicate different population structures from those observed in the end of the 1980?s. Nine localities from the river shore were sampled, and each individual was identified and measured. The size of C. fluminea varied between 2 and 39 mm, showing the highest frequency of individuals between 20 and 25 mm; furthermore the density decreased 90% in 2015/2016. No speci-mens of C. largillierti were found. In conclusion, the populations of Corbicula inhabiting the Río de la Plata River are retracting.Fil: Reshaid, Yamila Veronica. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Cao, Luciana Marina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Brea, Francisco. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Blanche, María Ortiz. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Torres, Santiago Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia Austral. Unidad Académica San Julián; ArgentinaFil: Darrigran, Gustavo Alberto. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentin

Conservación de las poblaciones de bivalvos nativos (Mollusca: bivalvia: unionoida) en Argentina : Variabilidad morfológica y molecular y distribución de Diplodon delodontus (Lamarck, 1819) (Hyriidae)

Sobre la base de los conocimientos previos, los bivalvos dulciacuícolas unionoideos conforman uno de los grupos en mayor peligro de extinción, por lo cual los estudios sobre su distribución y sistemática son importantes para su conservación. A pesar de esto, se han llevado a cabo pocos estudios en Argentina. El objetivo del siguiente Trabajo de Tesis Doctoral fue realizar aportes al conocimiento de la taxonomía y distribución del género Diplodon Spix in Wagner, 1827 (Bivalvia: Unionoida: Hyriidae) y más específicamente de Diplodon delodontus (Lamarck, 1819) en Argentina, abordando los siguientes objetivos específicos: 1) analizar si las variaciones morfométricas de las valvas de ejemplares adultos del género Diplodon apoyan las agrupaciones D. (Rhipidodonta), D. (Diplodon) y D. (Australis) y establecer su estatus taxonómico; 2) identificar los caracteres de la conchilla que permitan la identificación de las especies de Diplodon y, a su vez, poner aprueba la validez de dichas especies en Argentina; 3) establecer la variabilidad genética de ejemplares de Diplodon sp. del balneario El Retobado, arroyo Yuquerí Grande, Entre Ríos, y contrastar las agrupaciones de los análisis moleculares con el estudio de la morfometría geométrica; 4) determinar si existen diferencias morfométricas entre poblaciones de Diplodon delodontus de Argentina, y si las mismas, presentan relación con regiones biogeográficas. Utilizando herramientas bioinformáticas se combinó la ejecución de estudios moleculares con análisis de morfometría geométrica y distribución. El análisis molecular incluyó la comparación de las secuencias de bases del fragmento de ADN mitocondrial que codifica para la enzima Citocromo Oxidasa I (COI). Para la obtención de las secuencias de interés se utilizó la técnica de amplificación por PCR y secuenciación. En los estudios de morfometría geométrica se utilizó el análisis de la variación en la disposición de landmarks. Se realizaron ajustes de Procrustes, se calculó la forma consenso entre las muestras y se realizaron Análisis de Componentes Principales y Análisis Discriminantes. A pesar de que se observaron diferencias en la morfología de la conchilla entre Diplodon (Diplodon) y Diplodon (Rhipidodonta), los resultados estadísticos no mostraron una agrupación robusta ni tampoco una función discriminante confiable para separar ambos subgéneros. El método utilizado no permitió corroborar la validez de D. (Australis) (p>0,05). El análisis comparativo entre las especies del género Diplodon de Argentina permitió delimitar a la mayoría en forma significativa. Los resultados apoyaron la sinonimización de D. fortis con D. chilensis y D. piceus con D. rhuacoicus. No hubo diferencias significativas entre los ejemplares de D. chilensis y los de D. patagonicus (p=0,79). La especie mejor delimitada fue D. parallelopipedon (p<0,01 en todas las comparaciones). Los resultados del análisis morfométrico de los ejemplares del arroyo Yuquerí Grande indicaron la presencia de al menos tres especies simpátricas del género Diplodon: D. parallelopipedon, D. wymanii, D. rhuacoicus y D. burroughianus (p<0,01). El análisis molecular también las separó de manera robusta, relacionando a D. rhuacoicus con D. wymanii y, en última instancia, con D. burroughianus. D. parallelopipedon fue la especie más diferenciada en ambos análisis. El análisis de la variabilidad morfométrica de Diplodon delodontus corroboró las diferencias entre regiones malacológicas. Se identificaron tres morfotipos: 1) Río Uruguay, 2) Paraná Medio y 3) Paraná Inferior y Río de la Plata. El análisis apoyó la agrupación de los ejemplares del Río Uruguay en un morfotipo más diferenciado morfológicamente (p<0,01), manteniéndose más relacionados aquellos ejemplares localizados en el Río Paraná y en el Río de la Plata. Del Trabajo de Tesis Doctoral expuesto, se pudieron extraer las siguientes conclusiones finales sobre la taxonomía del género Diplodon: 1) Si bien los estudios mostraron tendencias en la variación morfométrica dentro del género Diplodon, no se observaron diferencias en la morfología de la conchilla que permitan justificar la separación de las especies del género Diplodon en grupos distintos; 2) debido a la metodología aplicada, no fue posible contrastar la validez del subgénero Diplodon (Australis); 3) se sustentó la sinonimización de D. fortis con D. chilensis y D. piceus con D. rhuacoicus; 4) los resultados del análisis de morfometría geométrica no apoyaron la separación entre D. chilensis y D. patagonicus. Los ejemplares de ambos conjuntos deberán denominarse como D. chilensis (Gray, 1828) de acuerdo con el Principio de Prioridad de la Nomenclatura Zoológica. Del estudio comparativo entre datos morfométricos y moleculares, en ejemplares de Diplodon sp. del arroyo Yuquerí Grande, se concluyó la separación de los individuos en al menos especies: D. parallelopipedon, D. wymanii, D. rhuacoicus y D. burroughianus, siendo D. parallelopipedon la especie más diferenciada en ambos análisis. La separación entre D. wymanii y D. rhuacoicus no fue robusta, pudiendo tratarse de subespecies de la misma especie o de especies estrechamente cercanas. El estudio de la distribución y de la morfometría geométrica de los ejemplares de Diplodon delodontus de Argentina, permitió concluir lo siguiente: 1) se identificaron tres morfotipos correspondientes a: 1) Río Uruguay, 2) Paraná Medio y 3) Paraná Inferior y Río de la Plata; 2) Diplodon delodontus se localiza en el Río Paraná y en el Río de la Plata. A su vez, D. delodontus incluyó una población ubicada en el Paraná Medio y otra distribuída en el Paraná Inferior y Río de la Plata. Los resultados de este análisis no fueron robustos, por lo que deben ser contrastados con otras evidencias. Por último, se establecieron afirmaciones sobre la metodología y objetivos a futuro: 1) es necesario un estudio filogeográfico que incluya toda la Cuenca del Plata; 2) los resultados obtenidos en este Trabajo de Tesis son base para establecer el estado de conservación de Diplodon delodontus en la región; 3) este Trabajo de Tesis Doctoral remarcó la importancia de la combinación de estudios morfológicos con datos de análisis moleculares para el estudio taxonómico de un grupo.Based on previous knowledge, Unionoida freshwater mussels are one of the most endangered groups, whereby research about their distribution and systematics are important for their conservation. Nevertheless, research on this topic in Argentina is scarce. The main purpose of the following PhD Thesis was to make contributions on the knowledge about taxonomy and distribution of the genus Diplodon Spix in Wagner, 1827 (Bivalvia: Unionoida: Hyriidae) and more specifically of Diplodon delodontus (Lamarck, 1819) in Argentina, assessing the following specifical aims: 1) to analyze if morphometric variability in valves of Diplodon adults support D. (Rhipidodonta), D. (Diplodon) and D. (Australis) groups and establish their taxonomic status; 2) to identify features in valves that allow identification of Diplodon species and, at the same time, to test the validity of the taxonomical species in Argentina; 3) to establish genetic variability of Diplodon specimens from El Retobado shore in Yuquerí Grande Stream, Entre Ríos Province, to then contrast groups of molecular analysis with groups obtained by morphometric analysis; 4) to determine if different populations of Diplodon delodontus from Argentina show morphometric differences, and if those differences match with biogeographical regions. A molecular study with geometric morphometrics and distribution analysis was combined applying bioinformatic tools. Molecular analysis included a comparison of sequences of Citocrome Oxidasa I (COI) mitochondrial DNA fragment. Sequences were obtained by PCR amplification and sequenciation techniques. For geometric morphometric studies, variation in landmark positions were analysed. Procrustes adjustments were made, consensus shape between samples was calculated and Principal Component Analysis and Discriminant Analysis were performed. Despite of the differences found between Diplodon (Diplodon) y Diplodon (Rhipidodonta) shells, statistical results neither show a robust grouping nor a reliable discriminant function para separar ambos subgéneros. The method applied did not support D. (Australis) as valid (p&gt;0,05). Comparative analysis between species of Diplodon from Argentina allowed significant delimitations for most of the species. Results supported synonimyzation of D. fortis within D. chilensis and D. piceus within D. rhuacoicus. There were not significant differences between D. chilensis and D. patagonicus specimens (p=0,79). Best delimited species was D. parallelopipedon (p&lt;0,01 in all comparissons). Morphometric analysis of the specimens of Diplodon sp. from Yuquerí Grande Stream indicated the presence of at least three different species of Diplodon: D. parallelopipedon, D. wymanii, D. rhuacoicus and D. burroughianus (p&lt;0,01). Molecular study also showed robust groups, relating D. rhuacoicus more closely with D. wymanii, and with D. burroughianus in last. D. parallelopipedon species was the less morphologically and genetically related. Morphometric analysis of Diplodon delodontus confirmed the differences between malacological regions. Three morfotypes were identified: 1) Uruguay River; 2) Middle Paraná and 3) Lower Paraná and Río de la Plata River (p&lt;0,01). Analysis of D. delodontus specimens supported the presence of a less related morphotype includying Uruguay River specimens, showing a closer relationship for those specimens from Paraná River and Río de la Plata River. From the PhD Thesis exposed, the following final conclusions about the taxonomy of Diplodon were extracted: 1) Even though morphometric variation within Diplodon was observed, the differences in shell morphology did not justify a division in subgenra; 2) the method applied did not support D. (Australis) as a valid subgenus; 3) morphometric analysis sustained synonimyzation of D. fortis within D. chilensis and D. piceus within D. rhuacoicus; 4) D. chilensis specimens did not show significative differences with D. patagonicus specimens, hence they must be called as D. chilensis (Gray, 1828) by the Priority Principle of Zoological Nomenclature. Comparative analysis of morphometrics and molecular data in specimes of Diplodon sp. from Yuquerí Grande stream concluded in classification of individuals into al least three species: Diplodon parallelopipedon, D. wymanii, D. rhuacoicus and D. burroughianus, with D. parallelopipedon as the most diferent species by both analyses. D. wymanii and D. rhuacoicus species were not strongly diferenciated. The study of distribution and geometric morphometrics in specimens of Diplodon delodontus from Argentina allowed to conclude the following: 1) three morphotypes of D. delodontus were identified: 1) Uruguay River; 2) Middle Paraná and 3) Lower Paraná and Río de la Plata River; 2) D. delodontus included one population located in Middle Paraná and other one distributed along Lower Paraná and Río de la Plata River. Results from this analysis were not robust. Ultimately, affirmative propositions about methodology and future aims were stablished: 1) a phylogeografic study including exhaustive molecular sampling along the whole extension of la Plata Basin is necessary; 3) results obtained in this PhD Thesis are basic to establish the conservation status of D. delodontus in the region; 4) the importance of combining morphological and molecular studies in taxonomic research is remarkable.Facultad de Ciencias Naturales y Muse

Gonadal cycle of Corbicula fluminea (Bivalvia: Corbiculidae) in Pampean streams (Southern Neotropical Region)

Corbicula fluminea is an aggressive invasive species of bivalve that arrived into the Río de la Plata River between the late 60’s and early 70’s, and dispersed widely throughout the Neotropical region, evidencing a great adaptive flexibility to different environmental conditions. This species is a functional hermaphrodite with larval incubation inside the inner demibranch. Despite its widespread distribution, there are no previous studies of complete gonadal histology and reproductive cycle for this species in the Neotropical region. In this study, the reproductive dynamics of C. fluminea in a temperate region, the Santa Catalina Pampean stream, Argentina, is described. Samples of 20–30 individuals were collected monthly from April 2003-April 2005 and processed using traditional histological techniques. During the two years of this study, seven spawning events were recognized. Three major spawns occurred in spring and summer, and other four minor ones during summer and autumn. Events of oocyte recovery were observed after spawning. A high number of incubating individuals was detected. The results stressed the difficulty of identifying a particular pattern of gamete release and of spawning behaviour in this invasive species, especially when inhabiting an unstable environment.Facultad de Ciencias Naturales y Muse

Gonadal cycle of Corbicula fluminea (Bivalvia: Corbiculidae) in Pampean streams (Southern Neotropical Region)

Corbicula fluminea is an aggressive invasive species of bivalve that arrived into the Río de la Plata River between the late 60’s and early 70’s, and dispersed widely throughout the Neotropical region, evidencing a great adaptive flexibility to different environmental conditions. This species is a functional hermaphrodite with larval incubation inside the inner demibranch. Despite its widespread distribution, there are no previous studies of complete gonadal histology and reproductive cycle for this species in the Neotropical region. In this study, the reproductive dynamics of C. fluminea in a temperate region, the Santa Catalina Pampean stream, Argentina, is described. Samples of 20–30 individuals were collected monthly from April 2003-April 2005 and processed using traditional histological techniques. During the two years of this study, seven spawning events were recognized. Three major spawns occurred in spring and summer, and other four minor ones during summer and autumn. Events of oocyte recovery were observed after spawning. A high number of incubating individuals was detected. The results stressed the difficulty of identifying a particular pattern of gamete release and of spawning behaviour in this invasive species, especially when inhabiting an unstable environment.Fil: Cao, Luciana Marina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Damborenea, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; ArgentinaFil: Penchaszadeh, Pablo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; ArgentinaFil: Darrigran, Gustavo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Zoología Invertebrados; Argentin

Variation in the distribution of Corbicula species (Mollusca: Bivalvia: Corbiculidae) after 25 years of its introduction in the Río de la Plata, Argentina

In 1981, Corbicula fluminea (Müller, 1774) and C. largillierti (Philippi, 1844) were recorded at the Río de la Plata River. During the 1980’s, C. largillierti was found on a continuous fringe in the shore of that river, while C. fluminea was only found North of Buenos Aires’ harbor. Ten years later, C. fluminea spread to Punta Indio, while C. largillierti remained restricted to tributary streams. The density and size frequency distribution of both species were compared with previous data from samples performed in the same area in 1985–1989. The aim of this research was to determine whether the densities of both species decreased; whether C. fluminea is still more abundant than C. largillierti; and whether the size frequency distributions indicate different population structures from those observed in the end of the 1980’s. Nine localities from the river shore were sampled, and each individual was identified and measured. The size of C. fluminea varied between 2 and 39 mm, showing the highest frequency of individuals between 20 and 25 mm; furthermore the density decreased 90% in 2015/2016. No specimens of C. largillierti were found. In conclusion, the populations of Corbicula inhabiting the Río de la Plata River are retracting.Facultad de Ciencias Naturales y Muse

Distribution of the Unionida (Bivalvia, Paleoheterodonta) from Argentina and its conservation in the Southern Neotropical Region

Bivalves are one of the most representative groups in the Phylum Mollusca, with over 1,100 freshwater species around the world except Antarctica. About 900 of these species belong to the Order Unionida Gray, 1854. In South America, the distributional range of the Unionida includes all countries in the region and extends as far south as the lakes and rivers of Argentinean- Chilean Patagonia. With the aim of generating distribution maps for the different genera of Unionida in Argentina, we consulted the databases of the nation’s main official malacological collections. The data were analyzed and georeferenced using the point-radius method. Spatial analyses were performed with the software Q-GIS 2.16.3 Nødebo using vector layers under the 2007 Argentinean Geodesic Positions reference system. A total 1,833 lots were analyzed, of which it was possible to georeference 1,503. The distribution of Unionida in Argentinean territory was analyzed according to political provinces, Surface Drainage Basins and the Argentinean Protected Areas. Species richness was analyzed using the surface drainage basins of Argentina. We generate distribution maps for each genus and discuss the species threat status and conservation degree in the region. Only six (18%) of the Unionida present in Argentina have been classified by the IUCN, four are Least Concern and two are Data Deficient. This pattern is also valid for all of South America. More than 95% of the distributional range of the Unionida has no protected area. Conservation management is necessary for the preservation of Unionida diversity in southern South America.Facultad de Ciencias Naturales y Museo (FCNM

Estrategias reproductivas en Unionoideos

El objetivo de esta contribución es exponer, a modo de breve reseña, las particularidades del ciclo de vida, estrategias reproductivas y desarrollo de las almejas de agua dulce del orden Unionoida (Mollusca: Bivalvia), así como la importancia de estos conocimientos para la conservación del grupo.Facultad de Ciencias Naturales y Muse

Estrategias reproductivas en Unionoideos

El objetivo de esta contribución es exponer, a modo de breve reseña, las particularidades del ciclo de vida, estrategias reproductivas y desarrollo de las almejas de agua dulce del orden Unionoida (Mollusca: Bivalvia), así como la importancia de estos conocimientos para la conservación del grupo.Facultad de Ciencias Naturales y Muse

Estrategias reproductivas en Unionoideos

El objetivo de esta contribución es exponer, a modo de breve reseña, las particularidades del ciclo de vida, estrategias reproductivas y desarrollo de las almejas de agua dulce del orden Unionoida (Mollusca: Bivalvia), así como la importancia de estos conocimientos para la conservación del grupo.Facultad de Ciencias Naturales y Muse

Gonadal cycle of Corbicula fluminea (Bivalvia: Corbiculidae) in Pampean streams (Southern Neotropical Region)

Corbicula fluminea is an aggressive invasive species of bivalve that arrived into the Río de la Plata River between the late 60’s and early 70’s, and dispersed widely throughout the Neotropical region, evidencing a great adaptive flexibility to different environmental conditions. This species is a functional hermaphrodite with larval incubation inside the inner demibranch. Despite its widespread distribution, there are no previous studies of complete gonadal histology and reproductive cycle for this species in the Neotropical region. In this study, the reproductive dynamics of C. fluminea in a temperate region, the Santa Catalina Pampean stream, Argentina, is described. Samples of 20–30 individuals were collected monthly from April 2003-April 2005 and processed using traditional histological techniques. During the two years of this study, seven spawning events were recognized. Three major spawns occurred in spring and summer, and other four minor ones during summer and autumn. Events of oocyte recovery were observed after spawning. A high number of incubating individuals was detected. The results stressed the difficulty of identifying a particular pattern of gamete release and of spawning behaviour in this invasive species, especially when inhabiting an unstable environment.Facultad de Ciencias Naturales y Muse