Núria Garriga

Food availability determines the response to pond desiccation in anuran tadpoles

Food availability and pond desiccation are two of the most studied factors that condition amphibian metamorphosis. It is well known that, when food is abundant, organisms undergo metamorphosis early and when they are relatively large. The capability of anurans to accelerate their developmental rate in response to desiccation is also common knowledge. These two variables must act together in nature, since we know that, as a pond dries, the per capita resources decrease. We conduct an experiment to evaluate the effects of desiccation and food availability separately and in combination in tadpoles of the painted frog (Discoglossus pictus). We demonstrate that food deprivation leads to slow growth rates, which delay metamorphosis and produce smaller size and weight. The capability to accelerate metamorphosis when facing a drying pond is also confirmed, but, nevertheless, with factor interaction (when the pool is drying and resources are scarce) the capacity to respond to desiccation is lost. In addition, slow drying rates are shown to be stressful situations, but not enough to provoke a shortening of the larval period; in fact, the larval period becomes longer. We also demonstrate that the interaction of these factors changes the allometric relationship of different parts of the hind limb, which has implications for the biomechanics of jumping. Due to low mortality rates and an adequate response to both environmental factors, we expect D. pictus to have a great invasive potential in its new Mediterranean distribution area, where lots of temporary and ephemeral ponds are present.

Formation constants for the complexes of 2-mercapto-3-phenylpropanoate with nickel(II) and hydrogen ions

The system formed by 2-mercapto-3-phenylpropanoate (MPP), nickel(II) and hydrogen ions in 30% (v/v) ethanol-water at 25 degrees and I = 100mM (nitrate) has been characterized by means of glass-electrode potentiometry. Protonation constants for 2-mercapto-3-phenylpropanoate and formation constants for the complexes Ni(3)(MPP)(2-)(4) and Ni(MPP)(2-)(2) are reported.

Dissociation constants and reactions of 3-phenyl and 3-cyclohexyl-2-mercaptopropenoic and 3-phenyl-2-mercaptopropanoic acids.

The dissociation constants of 3-phenyl- and 3-cyclohexyl-2-mercaptopropenoic acids have been determined spectrophotometrically (I = 0.01M) in aqueous medium, and potentiometrically for both reagents and for 3-phenyl-2-mercaptopropanoic acid in water-ethanol medium. The analytical properties of the three compounds have been studied and also the compositions of some of their insoluble metal chelates.

Growth strategies of tadpoles along the pond permanency gradient

The preference for particular features of water bodies for reproduction is one of the most important aspects of anuran ecology, affecting key aspects of both tadpole and adult life. The use by species of different habitats along the pond permanency gradient has been already studied, noting conflicting selective pressures from predation and desiccation risk. Here, we aim to discover physiological patterns related with this gradient. As a study system, we used the full anuran community of the NE Iberian Peninsula. We quantified growth rate, consumption rate, food assimilation and the proportion of energy allocated to growth, as well as gut length, for all species. Food consumption rate and growth allocation were the variables that defined tadpole growth, while food assimilation abilities and gut length seem to have a secondary or cryptic role in growth. More interestingly however, our data suggests a labile continuum of consumption-based versus allocation/assimilation-based growth strategies differentiating species. Differences among species follow predictions of adaptation to the pond permanency gradient selective pressures. Species from ephemeral ponds are more prone to use consumption-related growth tactics while species inhabiting ponds with longer hydroperiods are more efficient retaining and allocating energy into growth, although results seem partly shaped by strong interspecific competition. Physiological differences in growth and the usage of the assimilated energy could be an additional factor to understand how tadpoles adapt to the features of ponds they inhabit, as well as how they compete and coexist.

A potentiometric study of the complexation of manganese(II) by 2-mercapto-3-phenylpropenoate in solution

Abstract Complex formation between manganese(II) and 2-mercapto-3-phenylpropenoate (MPP) has been studied at 25°C and 100 mmol dm−3 NO3− in 30% (v/v) ethanol-water using glass electrode potentiometry. The titration data can be explained by the formation of the complex MnMPP, log β110 = 5.407.

Impact of ammonium nitrate and sodium nitrate on tadpoles of Alytes obstetricans

The presence of pesticides, herbicides and fertilisers negatively affect aquatic communities in general, and particularly amphibians in their larval phase, even though sensitivity to pollutants is highly variable among species. The Llobregat Delta (Barcelona, Spain) has experienced a decline of amphibian populations, possibly related to the reduction in water quality due to the high levels of farming activity, but also to habitat loss and alteration. We studied the effects of increasing ammonium nitrate and sodium nitrate levels on the survival and growth rate of Alytes obstetricans tadpoles under experimental conditions. We exposed larvae to increasing concentrations of nitrate and ammonium for 14 days and then exposed them to water without pollutants for a further 14 days. Only the higher concentrations of ammonium (>33.75 mg/L) caused larval mortality. The growth rate of larvae was reduced at ≥22.5 mg/L NH4+, although individuals recovered and even increased their growth rate once exposure to the pollutant ended. The effect of nitrate on growth rate was detected at ≥80 mg/L concentrations, and the growth rate reduction in tadpoles was even observed during the post-exposure phase. The concentrations of ammonium with adverse effects on larvae are within the range levels found in the study area, while the nitrate concentrations with some adverse effect are close to the upper range limit of current concentrations in the study area. Therefore, only the presence of ammonium in the study area is likely to be considered of concern for the population of this species, even though the presence of nitrate could cause some sublethal effects. These negative effects could have an impact on population dynamics, which in this species is highly sensitive to larval mortality due to its small clutch size and prolonged larval period compared to other anuran amphibians.

Extraction-spectrophotometric determination of manganese with 3-phenyl-2-mercaptopropenoic acid

An extraction-spectrophotometric procedure for the determination of manganese(II) based on the formation of a chelate with 3-phenyl-2-mercaptopropenoic acid is described. The 1:2 manganese complex is quantitatively extracted into isoamyl alcohol (2-methylbutan-1-ol) in the pH range 6.3–9.4. The extract shows maximum absorbance at 625 nm (Iµ= 7.3 × 103 l mol–1 cm–1) and obeys Beers law up to 20 µg ml–1 of manganese. The method is selective and has been applied successfully to the determination of manganese in standard samples.