Browsing by Author "Maldonado, K"

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    Coping with salt without salt glands
    (2004) Sabat, P; Maldonado, K; Rivera-Hutinel, A; Farfan, G
    We investigated the phenotypic plasticity of renal function in three South American coastal passerine Cinclodes (ovenbirds) differing in the proportion of marine prey they consume. Individuals were acclimated to two regimes of salinity for 15 days, and then the maximal urine-concentrating ability (U-max), hematological parameters and kidney morphology of each species were determined. The proportion of kidney mass occupied by medullary tissue, the number of medullary cones in the kidneys, plasma osmolality and U-max differed among the three species, supporting the hypothesis of an adaptation for excretion of the high salt load in the strictly marine C. nigrofumosus. Our results indicate that species of Cinclodes are able to modify the proportion of medullary tissue and the U-max. In addition, we found interspecific differences in the magnitude to which these osmoregulatory parameters can be modified. The greater ability to modify the osmoregulatory features in the migrant species C. oustaleti may enable it to cope with seasonal changes in salt load imposed by the winter consumption of hypertonic prey.
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    Physiological and biochemical responses to dietary protein in the omnivore passerine Zonotrichia capensis (Emberizidae)
    (2004) Sabat, P; Sepúlveda-Kattan, E; Maldonado, K
    We studied the physiological, biochemical and morphological responses of the omnivore sparrow Zonotrichia capensis, a small opportunistic passerine from Central Chile acclimated to high- and low-protein diets. After 4 weeks of acclimation to 30% (high-protein group) or 7% (low-protein group) dietary casein, we collected urine and plasma for nitrogen waste production and osmometry analysis, and measured gross renal morphology. Plasma osmolality and hematocrit were not significantly affected by dietary treatment, but urine osmolality was higher in the high-protein group than in the low-protein group. Kidney and heart masses were higher in animals acclimated to the high-protein diet. Mean total nitrogen waste was significantly higher in the high-protein group, but the proportions of nitrogen excreted as uric acid, urea and ammonia were unaffected by diet. Our data suggest that the response of Z. capensis to an increase in dietary protein content is through greater amounts of total nitrogen excretion and hypertrophy of kidney structures, without any modification of the proportion of excretory compounds. (C) 2003 Elsevier Inc. All rights reserved.