Silvina Van der Molen

Shell shape variation in the Nassariid Buccinanops globulosus in northern Patagonia

Morphological variation among natural populations is a phenomenon commonly observed in marine invertebrates and well studied, particularly, in shelled gastropods. The nassariid Buccinanops globulosus is interesting to study shell shape variation because it exhibits strong interpopulation differences in life history features, including maximum size, fecundity and growth rate. In this study, we examined the pattern of variation in size and shell shape among populations and between sexes of B. globulosus (Bahía San Antonio 40°29′S 63°01′W, Playa Villarino 40°45′S 64°40′W and Bahía Nueva 42°46′S 65°02′W). In particular, we used geometric morphometric techniques to test: (1) whether the two components of shell morphology (size and shape) are independent and (2) whether shape differences between sexes are consistently found among populations, regardless of their body sizes. Our results show shell shape variation between the populations of B. globulosus of northern Patagonia. Intra-specific shell shape variation is affected by body size, indicating allometry. Regardless of the size differences, individuals from Playa Villarino have high-spired shells, and shorter apertures and wider columellar area than individuals from the other populations. Also, sex-related shape differences were consistently found at each population, thus suggesting a common sexual dimorphism in shell morphology for this species. The functional significance of the variability found is discussed in terms of the flexibility of developmental programmes for morphology as well as the evolution of phenotypic plasticity.

Use of shell-shape to discriminate between Brachidontes rodriguezii and Brachidontes purpuratus species (Mytilidae) in the transition zone of their distributions (south-western Atlantic)

Fil: Van Der Molen, Silvina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Nacional Patagonico; Argentina

Reproductive cycle of the southern geoduck clam, Panopea abbreviata (Bivalvia: Hiatellidae), in north Patagonia, Argentina

Summary On the basis of histological examination, we present the first description of gametogenesis in Panopea abbreviata. Six stages of gonad development were identified using morphological and histochemical criteria. The gonads are diffuse and cannot be sexed with the naked eye. The analyses of gonad tissues showed that the gametogenic cycle is continuous with no resting period. Ripe individuals of both sexes were found for most of the year, and the spawning season seems to be protracted. The application of histological techniques to individuals collected monthly revealed a bias in the sex ratio depending on the body length. Even when the sex ratio was balanced in large clams, for small individuals, the sex ratio was biased in favour of the males. Although no hermaphroditic individuals were found in our samples, the possibility of protandry should be examined further.

A histopathological survey of the razor clam Ensis macha (Pharidae) along the Patagonian Argentina coast

This is the first study performed to determine the health status of the razor clam, Ensis macha, including six different populations along Argentina Patagonian coast and one of Chile. The parasites and pathologies affecting E. macha were analyzed and their prevalence and mean intensity values were calculated. To establish which factors affect the presence and intensity of infection, Generalized Linear Models (GLMs) were applied. Basophilic inclusions, ciliates, coccidians protozoans and turbellarians were found. We report an Aporocotylidae digenean and hemocyte infiltrations. None of the parasites is OIE (World Organisation for Animal Health) notifiable, and none seemed to be pathogenic, with the exception of the digenean. The prevalence of the parasites was affected mainly by environmental factors (such as site of sampling and season) instead of intrinsic conditions of the clam (such as size, condition index, sex and gonadal stage). On the other hand, the maximum intensity of parasites was not only related with cold seasons but also with the partially spawned gonadal stage of E. macha. During this stage, the clams would need to store energy for the next gametogenesis cycle, might be more susceptible to infection by the parasites.

Analysis of the morphological variation of Doryteuthis sanpaulensis (Cephalopoda: Loliginidae) in Argentinian and Brazilian coastal waters using geometric morphometrics techniques

Shape variation of individuals from three locations, two from Argentina and one from Brazil, was analysed by geometric morphometrics techniques. Individuals were weighed, measured, sexed, assigned to a maturity stage and photographed. For the analysis, two landmark configurations were used: one of nine landmarks (9L) and another of 25 landmarks (25L). To visualise shape variation, a principal component analysis (PCA) on Procrustes coordinates was conducted. The percentage of total shape variation explained by the 9L configuration was 80.5% (PC1: 61% and PC2: 19.5%), while the percentage for the 25L configuration was 76.4% (PC1: 54.8% and PC2: 21.6%). Based on this, shape analyses were performed using only the 9L configuration. The PCA results indicated that specimens show a large overlap between the categories based on sex and maturity stage. When location is considered, squid shape from São Sebastião and Rawson Port were very similar, while in Nuevo Gulf, the presence of two different morphological groups were observed: one similar to São Sebastião and Rawson Port, and the other with a morphology typical of Nuevo Gulf. Thus, two different morphotypes were defined: (i) morphotype of the continental shelf and (ii) morphotype typical of the gulf. The continental shelf morphotype is characterised by larger fins and wider mantle than the gulf morphotype. These results suggest that the morphotypes of Doryteuthis sanpaulensis are adaptations to oceanographic regimens.

Fluctuating asymmetry in the shell shape of the Atlantic Patagonian mussel, Mytilus platensis, generated by habitat-specific constraints

Fluctuating asymmetry (FA) consists of random deviations from perfect symmetry, and it is a useful trait to monitor developmental stability and ecological stress. The principal goal in this work was to study shell shape FA in Mytilus platensis as a measure of stress of living in intertidal wild areas compared to subtidal cultured ones. Shell shape asymmetry was studied by geometric morphometrics using landmarks and semilandmarks from internal and external anatomical structures. We analyzed FA comparing shell shape from 452 individuals living at different habitats (intertidal rocky shores vs. subtidal longlines) in two Patagonian sites. We predict that mussels living in the intertidal present higher levels of morphological alterations (i.e., FA) than those from the subtidal, where the environmental stress is lower. We based the asymmetry analysis on the FA scores from Procrustes ANOVA; all effects of the model were statistically significant. The Procrustes FA scores differed significantly between habitats: intertidal populations presented higher FA scores than subtidal ones. As predicted, shell shape in Mytilus platensis is influenced by the habitat and these differences add evidence to the fact that FA is a suitable measure of developmental instability, indicating the inability of species to buffer stress in its developmental pathways.

Local scale variation in the reproductive pattern of the southern geoduck, Panopea abbreviata (Bivalvia: Hiatellidae), in Patagonia

espanolDurante el 2007 se realizaron estudios para explorar la variabilidad espacial a escala local, del ciclo reproductivo de Panopea abbreviata en 3 poblaciones presentes en los golfos Nord-patagonicos (El Sotano y Puerto Lobos, en el Golfo San Matias, y Punta Conos en el Golfo San Jose), Argentina. Estudios previos determinaron que P. abbreviata presenta un patron reproductivo, en ambos sexos, caracterizado por una continua proliferacion y evacuacion de gametos durante todo el ano. Sin embargo, el uso de indicadores cuantitativos (distribucion de frecuencia de diametros ovocitarios, ovocitos por campo ocular y area ovocitaria relativa) para las hembras permitio observar una ligera estacionalidad. Las variaciones en el ciclo reproductivo fueron relacionadas con el regimen anual de temperatura de cada sitio. Las hembras de El Sotano y Puerto Lobos muestran una estacionalidad similar en el patron reproductivo: las fases de proliferacion y maduracion predominan cuando la temperatura disminuye durante otono (marzo-mayo); este patron se revierte, cuando las temperaturas comienzan a aumentar durante primavera (septiembre-noviembre). Mientras que, en Punta Conos este patron es mas irregular. Sin embargo, en todas las poblaciones se encontraron individuos de ambos sexos en estadio de madurez durante todo el ano, evidenciando la ausencia de un periodo de inactividad gonadal. En las 3 poblaciones ambos sexos se caracterizan por multiples pulsos cortos de evacuacion de gametos. Este mismo patron se encontro en otras poblaciones de P. abbreviata y es unico para el genero Panopea. Los 3 sitios estudiados presentaron un patron reproductivo similar. EnglishDuring 2007 was carried out studies to explore local scale spatial variability in the reproductive cycle of Panopea abbreviata in 3 sites of the northern Patagonian gulfs (El Sotano and Puerto Lobos, in San Matias Gulf, and Punta Conos in San Jose Gulf), Argentina. Previous reports have revealed that P. abbreviata exhibits a reproductive pattern characterized, in both sexes, by continuous proliferation of gametes and spawning throughout the year. However, the use of quantitative indicators for females has shown a slight seasonality to this pattern. Local spatial variability in the reproductive cycle of P. abbreviata was observed at 3 sites and related to variation in the annual temperature regime at each locality. The females of El Sotano and Puerto Lobos showed similar seasonality in the reproductive pattern: proliferation and maturation phases prevailed over spawning stages when temperature decreased during autumn (March-May); this pattern was reversed when temperatures began to increase during spring (September-November). At Punta Conos this pattern is more irregular. However, at all localities, mature individuals of both sexes were present throughout the year, without a resting period during the reproductive cycle. The reproductive pattern is similar in the 3 sites with many small pulses in reproductive activity that are difficult to detect and characterized by year-round spawning. The same pattern was found in other localities of P. abbreviata and is unique in the genus Panopea.