Cellular development of the germinal epithelium during the gametogenic cycle of the golden mussel Limnoperna fortunei (Bivalvia: Mytilidae)

AbstractThe golden mussel Limnoperna fortunei is an invasive species that has quickly dispersed and colonized several potential different habitats distributed all over the world, causing environmental and economic impacts. Thus, in order to contribute to a better understanding of the reproductive aspects of L. fortunei, we described the cellular dynamic of the male and female germinal epithelium during the annual reproductive life history of this species, with the use of high resolution histology. An approximate of 1 200 specimens of L. fortunei were sampled periodically on the upper Paraná River floodplain (Brazil), from March 2010 to December 2012. Based on the activity of the germinal epithelium and consequent germ cell development, this study has resulted in the recognition of the following reproductive phases: Developing, Spawning Capable, Regressing and Regenerating. In the characterization of these phases, the following germ cells were described for males: spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa. Cell nests, oogonia, early prophase oocytes, previtellogenic oocytes and vitellogenic oocytes (early vitellogenic oocytes, middle vitellogenic oocytes and full-grown oocytes) were described for females. The morphological data and reproductive parameters obtained, showed the value of the cellular dynamics of the germinal epithelium, for the understanding of the cyclic gonadal events during the adult reproductive life of the mollusk in general. These results on the gametogenesis of this invasive species may be a fundamental tool for the development of control strategies and programs implementation, to reduce their proliferation and impacts in natural local environments. Rev. Biol. Trop. 64 (2): 521-536. Epub 2016 June 01.

ResumenEl mejillón dorado Limnoperna fortunei (Dunker, 1857) es una especie invasora que se ha dispersado rápidamente y ha colonizado diferentes hábitats potenciales distribuidos por todo el mundo, causando impactos ambientales y económicos. El control de esta especie depende del conocimiento de los aspectos reproductivos. Entre marzo 2010 y diciembre 2012 fueron muestreados periodicamente alrededor de 1 200 especímenes de L. fortunei en la planicie de inundación del Alto Rio Paraná, Brasil. Con el fin de contribuir con una mejor comprensión de los aspectos reproductivos de L. fortunei, se describió la dinámica celular del epitelio germinativo masculino y femenino durante la vida reproductiva anual de esta especie, mediante histología de alta resolución basada en la actividad del epitelio germinal y el consecuente desarrollo de las células germinales. En este estudio se reconocieron las siguientes fases reproductivas: desarrollo, capacidad de desove, regresión y regeneración. En los machos se describieron las siguientes células germinales: espermatogonias, espermatocitos primarios y secundarios, espermátidas y espermatozoides. Mientras que en las hembras se estudiaron: nidos celulares, ovogonias, ovocitos profásicos tempranos, ovocitos pre-vitelogénicos y ovocitos vitelogénicos (ovocitos vitelogénicos tempranos, ovocitos vitelogénicos y ovocitos completamente desarrollados).Los datos morfológicos y parámetros reproductivos que se muestran aquí confirman cómo la dinámica celular del epitelio germinal permite la comprensión de los acontecimientos cíclicos gonadales durante la vida reproductiva de adultos del molusco, en general. El conocimiento de la gametogénesis de esta especie invasora puede convertirse en una herramienta fundamental para el desarrollo de estrategias de control y aplicación de programas para disminuir su proliferación en ambientes naturales.

Sperm ultrastructure of Mytella (Bivalvia) populations from distinct habitats along the northern coast of São Paulo State, Brazil

Ultrastructural analyses of bivalve spermatozoa are relevant in studies that aim to identify taxonomic traits for the purposes of discriminating species and conducting phylogenetic studies. In the present work, spermatozoa of mussel specimens of the genus Mytella, collected from two populations living in distinct habitats, were examined by electron microscopy. The objective was to identify sperm ultrastructural taxonomic traits that could be used to differentiate Mytella species. The specimens were from populations that live in intertidal zones on the southeast coast of Brazil, either buried in muddy-sand sediment or anchored to rocky substrates. The acrosomal vesicle was conical and long, the axial rod extended from the nucleus to the acrosome, the nucleus was an oblate spheroid with a condensed chromatin, the intermediate portion contained mitochondria encircling a pair of centrioles, and there was a single flagellum. The sperm was of a primitive type. The spermatozoon ultrastructure did not distinguish the specimens buried in muddy-sand sediment from those anchored to rocky substrates. The data suggest that the specimens analyzed, despite living in distinct habitats, belong to the same species, which conchological analyses identified as M. charruana. The presence of an axial rod in their sperm cells supports the inclusion of M. charruana in the subfamily Mytilinae.

Surface morphology of Mytella falcata gill filaments from three regions of the santos estuary

Bivalves have been extensively used to monitor aquatic habitats because their sedentary filter feeding habit results in the accumulation of elements from the environment. The genus Mytella is of special interest because its habit of burrowing in sediments can provide information about the substrate conditions in estuaries. Gill filaments have a large surface that is in constant contact with the water and therefore are used to monitor aquatic environments. In this study, we used scanning electron microscopy (SEM) to investigate the morphology of Mytella falcata gill filaments and to compare the gill structure in specimens from three sites (A, B and C) of the Santos estuary in southeastern Brazil. Site A presents low levels of pollutants, whereas sites C and B were directly affected by industrial discharges and harbor pollutants. The gill filaments of M. falcata have three types of cilia, namely, lateral cilia, eu-latero-frontal cirri and frontal cilia. Structures joining the inner and outer lamellae were found on the abfrontal surface, in addition to the presence of composite and simple cilia. A comparison of the filaments of bivalves from the three sites revealed no morphological alterations, but there was an accumulation of mucus on the frontal surface of the gill filaments of specimens collected at site B. This mucus may function as a protective barrier against pollutants. Bivalves from site C showed no such alteration, even though this site had the highest levels of pollutants. This lack of alterations may reflect the fact that these specimens were collected from concrete pillars where there would be less contact with pollutants. Our findings may reflect a long-term adaptation of these mollusks to chronic exposure to pollutants.