Browsing by Author "Pappalardo, Paula"

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    EMBRYONIC DEVELOPMENT, FEEDING AND INTRACAPSULAR OXYGEN AVAILABILITY IN TROPHON GEVERSIANUS (GASTROPODA: MURICIDAE)
    (OXFORD UNIV PRESS, 2011) Cumplido, Mariano; Pappalardo, Paula; Fernandez, Miriam; Averbuj, Andres; Bigatti, Gregorio
    Large-scale patterns of encapsulated embryo development and causal factors determining developmental success in the marine environment have been relevant issues of research for decades. We studied the embryonic development and intracapsular oxygen availability of Trophon geversianus in egg capsules from northern Patagonia (Golfo Nuevo, Argentina). The intracapsular embryonic development had a mean duration of 112 days (at 12-14 degrees C). The initial number of eggs per capsule was 197 (mean diameter 270 mu m), but on average only four embryos per capsule reached the juvenile stage. Embryos fed on nurse eggs (which disintegrated spontaneously 48 h after oviposition). The sequence of intracapsular developmental stages was recorded from egg to hatching occurred at the crawling stage (mean shell length 2.8 mm). Maximum growth rate was observed at the 'veliger' stage, while nurse eggs were consumed. A decrease in embryo number was observed between prehatching and hatching. Cannibalism was recorded in an egg capsule containing a prehatching embryo, which showed signs of shell drilling by the accessory boring organ. Intracapsular oxygen availability decreased from 90% during the cleavage stage to 45% of air saturation in the final stages of development (at 13 degrees C). Abnormal embryos were recognized in egg capsules, probably associated with food competition or oxygen limitation.
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    Growth compensation as a regulatory mechanism of purple clam Amiantis purpurata population dynamics in Patagonia
    (2011) Morsan, Enrique M.; Pappalardo, Paula; del Socorro Doldan, Maria
    Density-dependent processes may drive the population dynamics in marine species through intraspecific competition for food or space. We examined processes controlling population dynamics in the purple clam Amiantis purpurata population of Playa Villarino (north of San Matias Gulf, Argentina) at the southernmost limits of its distribution. Population structure at this location has been dominated for more than 2 decades by 3 consecutive cohorts settled in 1978-1980. We used data on mean size and mass, growth rate, area covered by residents, density and biomass collected at 2 sites between 1982 and 2003, and a survey performed in 1995 over the whole population, to explore density dependence. The spatial pattern showed that: (1) whereas density was heterogeneous with highest values at the western side of the ground, biomass was more uniform, and the relationship between biomass and density was non-linear, becoming asymptotic at a density of 200 clams m(-2); (2) body size and density decreased over time; and (3) the substrate area used by clams was less than 35% of the available substrate. Temporal patterns showed that (1) density decreased with time but biomass was almost constant, and (2) growth curves were indicative of a density-dependent effect: individuals at low-density sites grew faster than individuals at high-density sites. Differences were strong between sites and slight (or absent) between cohorts. Natural mortality, which did not differ between cohorts, was estimated by the decrease in density over time as M = 0.126. We propose that the purple clam population is regulated by a compensatory effect whereby losses due to mortality are compensated by increased growth rate, and therefore enhancement of local biomass.
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    The effects of temperature and oxygen availability on intracapsular development of Acanthina monodon (Gastropoda: Muricidae)
    (2006) Fernandez, Miriam; Pappalardo, Paula; Jeno, Katherine
    Freshwater and marine organisms show similar models of parental care and are faced with similar constraints to brood, which suggest that comparable environmental limits drive the evolution of parental care in aquatic systems. In fact, the low diffusion coefficient and solubility of oxygen in aquatic environments affect oxygen acquisition and therefore the capacity to aggregate embryos. The effect of other critical environmental variables, such as temperature, is less clear. We assessed the effects of temperature and oxygen availability on (1) the number of developed and undeveloped encapsulated embryos, (2) the proportion of embryos reaching advanced stages during intracapsular development (counting not only developed and undeveloped embryos but also abnormal embryos), (3) asynchrony in development (estimated only in capsules in which development occurred), and (4) final embryo size, as the first step toward identifying the main factors constraining parental care in the ocean. We used the gastropod Acanthina monodon as a model because it has an extended latitudinal range of distribution and exhibits feeding larvae during intracapsular development. The latter factor is relevant because previous studies have suggested that sibling cannibalism could be triggered by intracapsular competition for oxygen. Freshly laid egg capsules were collected and incubated until embryos hatched under different experimental temperatures (7, 11, 15 and 19 degrees C) and oxygen conditions (hypoxia: 50-60 % air saturation; normoxia; and hyperoxia: 150-160 %). More embryos remained in early stages at the end of the experimental period under hypoxia and at the highest experimental temperature. The mean number of developed embryos was significantly lower under hypoxia conditions than under normoxia and hyperoxia, but was not influenced by temperature. However, temperature negatively affected embryo size of developed embryos and the level of asynchrony (number of different developmental stages per capsule). This suggests that even when a comparable number of embryos develops at high temperature, subsequent survival may be affected, since developed embryos attained smaller sizes. The negative effect of high temperature on embryo aggregation has also been reported for Brachyuran crabs, affecting female patterns of oxygen provision and brooding costs. This evidence suggests that aggregating embryos in the ocean, even under optimum oxygen conditions, may be negatively affected at high temperatures. Spatial patterns of distribution of brooding species in the ocean tend to agree with this prediction. Our analysis is particularly relevant given the current increase in temperature and the proportion of anoxic areas in the world's oceans.