Carolina Briones

Ciclo gonadal del chorito Mytilus chilensis (Bivalvia: Mytilidae) en dos localidades del sur de Chile

A qualitative and quantitative analysis was carried out of the gonadal cycle of the bivalve Mytilus chilensis from Chaihuin and Yal bay, southern Chile, between October 2007 and June 2008. Four gametogenic stages were determined using histological analysis of the gonads, and quantitative estimates were made of the Gametic Volume Fraction (VFG), percentage of inter follicular connective tissue, and the Gonadosomatic Index (IG). The quantitative analysis (VFG) was the best indicator of spawning. Two spawning events, one in October and one in March, were observed simultaneously in both sexes of mussels from Chaihuin. However, for specimens from bahia Yal, four spawning events were registered, principally from March to June (autumn), when the water temperature decreased. The relationship between the IG and the gametogenic stages was very low, as was that between the IG and the percentage of mature oocytes. Therefore, the IG is not a good indicator of spawning in this species. A re-evaluation of the ban period established for Mytilus chilensis (1 November to 31 December) is suggested since most individuals from the populations studied mature mainly in October. At both sites, the percentage of connective tissue for the analyzed mussel individuals ranged between 15 and 70% of gonadal coverage. The results obtained in the present study showed differences in the reproductive cycles of Mytilus chilensis between the sites sampled.

Geographical Variation of Shell Thickness in the Mussel Perumytilus purpuratus Along the Southeast Pacific Coast

At broad geographical scales, the variation in bivalve shell thickness can be modulated by environmental factors that vary with latitude, such as sea surface temperature (SST), seawater pH, or calcium carbonate availability. Mussels usually form multilayered beds, and shell thickness is also expected to be affected by density and layering due to intraspecific competition. In this work, we explored the geographical variation of shell thickness in the intertidal mussel Perumytilus purpuratus between 18° and 42°S along the southeastern Pacific coast. We tested the hypothesis that there was a positive relationship between shell thickness and SST, and then we explored other variables that could have an effect on thickness, such as density, number of layers, and others environmental variables (pH and calcite concentration). The expected positive linear relationship between shell thickness and sea surface temperature was not found, but when the other population variables were included in the analysis, an unexpected inverse SST-thickness relationships appeared as significant, probably because this species could be adapted to colder and more acid seawater as are those of the tips of South America. Thickness was also negatively affected by density, which was expected for a gregarious species showing high intraspecific competition. Finally, our results highlight the importance of including density and crowding effects when macroscale patterns are explored, particularly in gregarious species, since these patterns could also be modulated by density-dependent processes, which might then override latitudinal trends of shell thickness when they are not included in the analyses.

Análisis comparativo del ciclo gametogénico de Perumytilus purpuratus (Bivalvia: Mytilidae), en las localidades de Taltal y Huasco, norte de Chile

A qualitative and quantitative study of the gametogenic cycle from natural populations of Perumytilus purpuratus at the localities of Taltal and Huasco was carried out between October 2007 and October 2008. By means of histological analysis a gonadal maturation table was constructed according to the microscopic characteristics. Also the Gametic Volume Fraction (GVF) (% of previtelogenic oocytes, vitelogenic oocytes and mature oocytes), percentaje of interfolicular connective tissue and Gonadic Index (GI) were determined. According to the qualitative analysis, P. purpuratus has a semiannual reproductive cycle starting in January with spawning mainly during spring-summer, even do some winter spawning were detected. However, the quantitative analysis of mature oocytes percentajes found that at Taltal population four spawnings were detected (December, March, July and October) while in Huasco population three spawnings were detected (December, February and September). The relationship between GI with the gametogenic stages and the mature oocyte percentajes were significant at the localities studied. Also significant differences of the condition index between males and females were observed. Along the latitudinal gradient the reproductive cycle of P. purpuratus showed variations according to the timing and synchrony.

Una revisión de la asimetría bilateral en bivalvos

During the last years, studies on bilateral asymmetry have substantially increased. However, in the literature exists a clear trend toward the study of the f...