Santiago Peredo

Bivalve distribution in hydrographic regions in South America: historical overview and conservation

Based on literature review and malacological collections, 168 native freshwater bivalve and five invasive species have been recorded for 52 hydrographic regions in South America. The higher species richness has been detected in the South Atlantic, Uruguay, Paraguay, and Amazon Brazilian hydrographic regions. Presence or absence data were analysed by Principal Coordinate for Phylogeny-Weighted. The lineage Veneroida was more representative in hydrographic regions that are poorer in species and located West of South America. The Mycetopodidae and Hyriidae lineages were predominant in regions that are richest in species toward the East of the continent. The distribution of invasive species Limnoperna fortunei is not related to species richness in different hydrographic regions there. The species richness and its distribution patterns are closely associated with the geological history of the continent. The hydrographic regions present distinct phylogenetic and species composition regardless of the level of richness. Therefore, not only should the richness be considered to be a criterion for prioritizing areas for conservation, but also the phylogenetic diversity of communities engaged in services and functional aspects relevant to ecosystem maintenance. A plan to the management of this fauna according to particular ecological characteristics and human uses of hydrographic regions is needed.

Spermiogenesis and sperm ultrastructure in the freshwater mussel Diplodon chilensis chilensis (Mollusca: Bivalvia)

Summary Spermiogenesis and sperm ultrastructure of Diplodon chilensis chilensis have been studied. Early spermatids show some peculiar characteristics which include scanty cytoplasm mitochondria restricted to a juxtanuclear region and a poorly developed Golgi complex, a feature present throughout spermiogenesis. Mid and late spermatids show an elongated nucleus and a granular pattern of chromatin condensation. The Golgi complex does not show changes associated to the formation of structures of the acrosomal complex. The mature spermatozoon agrees in all main features with those of bivalves with external fertilization. It is thus of the primitive type with bullet-shaped nucleus and five mitochondrial spheres in the middle piece. The head of the mature sperm lacks acrosomal structures. Previously reported modifications in the reproductive biology of D. ch. chilensis with respect to aspects considered representative of bivalves, have not brought about major modifications in sperm morphology.

Estado de conocimiento de los Bivalvos dulceacuícolas de Chile

Se presenta el estado actual del conocimiento de los bivalvos dulceacuicolas chilenos. Las especies descritas a la fecha, pertenecen a las familias Hyriidae, representada solo por el genero Diplodon con dos especies (D. chilensis y D. solidulus) y Sphaeriidae con tres generos: Pisidium con siete especies (P. chilense, P. magellanicum, P. lebruni, P. observationis, P. meierbrooki, P. huillichum y P. llanquihuense), Sphaerium con dos especies (S. lauricochae y S. forbesi) y Musculium con dos especies (M. argentinum y M. patagonicum). Entidades subgenericas y subespecificas son reconocidas solo para Hyriidae. Se propone a Pisidium chilense, P. huillichum, P. llanquihuense, P. lebruni y D. solidulus como especies endemicas de Chile. Se senala la distribucion geografica de las especies, se analizan las implicancias que generan para la taxonomia, las variaciones fenotipicas experimentadas por los hiridos, las causas de la declinacion de las poblaciones y los vacios de conocimiento en ambas familias. Se reportan los especialistas en el tema y las colecciones existentes.

ALIMENTACION Y CONDUCTA ALIMENTARIA DE LA ALMEJA DE AGUA DULCE DIPLODON CHILENSIS (BIVALVIA: HYRIIDAE)

Con el proposito de conocer cualitativamente la alimentacion y la conducta alimentaria de la almeja de agua dulce Diplodon chilensis, se analizo mediante estudios de laboratorio y de campo el comportamiento alimentario y el contenido digestivo de especimenes procedentes de sustratos areno-pedregosos y arenosos del Lago Panguipulli y se relaciono con la oferta ambiental existente en el sustrato (fitobentos) y en el agua (fito-plancton). El analisis del contenido digestivo de los especimenes y los resultados experimentales, indican que Diplodon chilensis tiene una alimentacion mixta en base a fitoplancton, fitobentos y materia organica existente en el plancton y en el bentos

Evidencia de solapamiento de micro-hábitat entre juveniles del salmón introducido Oncorhynchus tshawytscha y el pez nativo Trichomycterus areolatus en el río Allipén, Chile

Introduced juvenile Chinook salmon (Oncorhynchus tshawytscha) have been found co-occurring with native fishes in the Allipen River, Chile. Due to this co-occ...

LA RELOCALIZACION COMO UNA HERRAMIENTA DE CONSERVACION Y MANEJO DE LA BIODIVERSIDAD: LECCIONES APRENDIDAS CON DIPLODON CHILENSIS (GRAY 1828) (BIVALVIA, HYRIIDAE)

Entregamos las lecciones aprendidas de un proyecto de relocalizacion de largo plazo llevado a cabo con el hirido Diplodon chilensis. El documento analiza las causas de la declinacion de las poblaciones en Chile y el uso de la relocalizacion como una herramienta de conservacion y manejo de la biodiversidad acuatica. Las lecciones aprendidas analizan las consideraciones que deben cautelarse antes, durante y despues de llevado a cabo el proceso de relocalizacion y las implicancias ecologicas, sanitarias y evolutivas de los programas de relocalizacion. Concluimos que la relocalizacion es una herramienta adecuada para la conservacion y manejo de las poblaciones de almejas de agua dulce y que se puede llevar a cabo exitosamente tomando las consideraciones antes senaladas

Life Histories and Dynamics of Stream and Lacustrine Populations of Musculium argentinum (D'Orbigny, 1842) (Bivalvia: Sphaeriidae) from Southern Chile

ABSTRACT Life histories and population dynamics of two populations of Musculium argentinum, one inhabiting a fluvial environment and the other a lacustrine one, are compared. Musculium argentinum is oviparous, iteroparous, and sequential incubator, reproducing throughout the year. The life cycle pattern of the fluvial population, unlike the lacustrine one, is characterized by seasonal reproductive variations, more marked in spring and summer, higher fertility and population reproductive productivity (potential recruitment), higher number of marsupial sacs per hemibranch, and smaller size of first reproduction. The content of organic matter and water flow would be the main factors determining the higher population density observed in the fluvial population.

Some Aspects of the Reproductive Biology of Two Populations of Musculium argentinum (D'Orbigny, 1835) (Bivalvia: Sphaeriidae) from Southern Chile

ABSTRACT Sphaerids have adopted a variety of life strategies that have allowed them to show a cosmopolitan distribution. Among these strategies, those related to reproduction, such as sexuality (hermaphroditism), offspring incubation, fertility, number of generations per year, times an individual reproduces during its lifespan, among others, have been decisive with regard to its permanence in time and space, and to colonize and maintain populations in permanent or temporary freshwater bodies. The aim of the current study is to compare reproductive traits of 2 Musculium argentinum populations inhabiting different environments (stream and lake) to determine the potential influence of the environment on reproduction of these populations. During 1 y (October 2006 to 2007) monthly samples were taken at 2 study sites: Lautaro stream (38°32′ S, 72°27′ W) and La Poza, Villarrica Lake (39°16′27″ S, 71°58′54″ W). Sixty specimens were collected monthly from each population. Valve length of each specimen of the sample was registered to determine the size structure of each population. Fifty animals of known valve length were dissected to determine presence and number of brooding sacs in the inner hemibranches, number of embryos in each sac, and number of newly hatched clams. Ten specimens were processed for optical microscopy with routine histological techniques to characterize the gonad activity pattern. Results indicate that M. argentinum is hermaphroditic in both populations, with gonadal activity throughout the year, iteroparous, and with embryos in brooding sacs and newly hatched clams present year-round. These results indicate that differences in the environment did not produce major changes in reproductive strategies in both M. argentinum populations studied.

Nuclear DNA content in two Sphaeriidae species from Southern Chile (Bivalvia: Veneroida)

ABSTRACT The family Sphaeriidae is a group of cosmopolitan freshwater clams that inhabit temporary and permanent fluvial and lacustrine environments around the world. In Chile, Sphaeriidae is represented by 11 species belonging to the genera Musculium, Pisidium and Sphaerium. In this study, the nuclear DNA content (or 2C-value) of Musculium argentinum (d’Orbigny, 1835) and Pisidium llanquihuense Ituarte, 1999 was estimated for the first time. Musculium argentinum showed a 2C-value of 3.7 ± 0.38 pg, whereas P. llanquihuense showed a 2C-value of 3.57 ± 0.36 pg. These 2C-values are within the range previously reported for Sphaeriidae (2.35–5.7 pg), which includes diploids and polyploids, amounting to 13 of the species examined around the world. Of the cytological data available for the family, the nuclear DNA content can have a unifying role in understanding the magnitude of the chromosome polymorphisms within this polyploid complex.