Browsing by Author "Naya, DE"

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    Digestive morphology and enzyme activity in the Andean toad, Bufo spinulosus
    (2005) Naya, DE; Farfán, G; Sabat, P; Méndez, MA; Bozinovic, F
    Gut plasticity is a trait with implications on animal performance. However, and despite their importance as study models in physiology, research on gut flexibility in amphibians is scarce. In the present work, we analyse digestive adjustments of Bufo spinulosus adult individuals to cope with changes in diet quality and quantity at two organizational levels (i.e., digestive morphology and enzymes). We found that changes in gut:size are related to the amount of food ingested, but not to diet composition. This is in agreement with "the gut seasonal change" hypothesis and offers a proximal explanation for this change. Digestive enzymatic activity (maltase and aminopeptidase-N) did not change with diet quality or quantity, which agrees with the hypothesis of "bard-wired physiology in adult amphibians". Both hypotheses are in agreement with the general theoretical framework of gut phenotypic flexibility when interpreted in light of amphibian natural history. In addition, our results indicate that the correlation between feeding frequency and the level of gut up-regulation proposed for interspecific comparisons may also be found at the intraspecific level. (c) 2004 Elsevier Inc. All rights reserved.
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    Dynamic digestive responses to increased energy demands in the leaf-eared mouse (Phyllotis darwini)
    (2005) Naya, DE; Bacigalupe, LD; Bustamante, DM; Bozinovic, F
    A major area of interest in comparative physiology has been to understand how animals cope with changing environmental demands in time and space. The digestive system has been identified as one of the more sensitive systems to changes in environmental conditions. However, most research on this topic has evaluated these effects during peak energetic demands, which do not allow for evaluation of the dynamics of the digestive response along a more natural continuous gradient of environmental conditions. We examined phenotypic flexibility in digestive responses of the leaf-eared mouse Phyllotis darwini to increments in total energy demands ( via sequential exposure to 26, 12 and 0 degreesC). Additionally, we evaluated the effect of a moderate energy demand ( 12 degreesC) over three different time periods ( 7, 17 and 27 days) on digestive traits. Moderate increases in energy demand were associated with changes in the distribution of digesta in the gut, whereas higher increases in energy demand involved increases in the tissue mass of digestive organs. Time-course analysis showed that at 12 degreesC practically all digestive variables reached stable values within 7 days, which is in agreement with empirical data and theoretical deductions from cellular turnover rates. We conclude that although the input of energy and nutrients into the digestive tract is typically periodic, many aspects of digestive physiology are likely to be flexible in response to environmental variability over both short-term ( daily) and long-term ( seasonal) time scales.
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    Pinniped diets inferred from scats: analysis of biases in prey occurrence
    (2003) Arim, M; Naya, DE
    The diets of pinnipeds have often been used to study their ecology and resource dynamics and in ecosystem monitoring. Scat analysis is now the most widely used method of inferring the diets of pinnipeds. Using a mathematical model the present study explores the expected biases in prey occurrence that are related to prey mass, proportion of loss of remains, predator assimilation efficiency, size of the scats collected, and meal size. With the exception of meal size, variation in parameters implied variation in the probability of biases in prey occurrence. Biases were asymmetric among prey sizes, but in contrast with previous ideas, the results indicate that small prey have smaller biases than large ones do. Furthermore, the number of scats required to detect a large prey was notably larger than that needed to detect a small prey with the same occurrence. The present study is not limited to a particular pinniped or prey species, so it has the potential to represent a general framework for interpreting the results of scat analysis in pinnipeds. The model complements empirical studies, advancing our comprehension of biases associated with prey occurrence in dietary studies of pinnipeds.
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    Seasonal activity and the body size-fecundity relationship in a population of Physalaemus gracilis (Boulenger, 1883) (Anura, Leptodactylidae) from Uruguay
    (2005) Camargo, A; Naya, DE; Canavero, A; da Rosa, I; Maneyro, R
    Two key life history attributes are temporal reproductive patterns and inter- and intraspecific variation in clutch size. In this work, we collected individuals of Physalaemus gracilis in Espinas stream (Maldonado, Uruguay) to analyze the correlation of activity with environmental variables and to evaluate the influence of reproductive investment on the body size-fecundity (BSF) relationship. In contrast to previous reports, the reproductive activity peaked in spring and was not correlated with temperature or rainfall in either sex. Regression analysis showed that the BSF relationship varied with size, and that larger females had a steeper slope than smaller females. Reproductive investment data indicate that smaller females invested less energy in their offspring than larger females, which is probably due to the imposed cost of continued growth.