Browsing by Author "Cortés, A"

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    Energetics thermoreoulation and torpor in the Chilean mouse-opossum Thylamys elegans (Didelphidae)
    (2005) Bozinovic, F; Ruiz, G; Cortés, A; Rosenmann, M
    In this paper we Studied the energetics and thermoregulation of the Chilean mouse-opossum Thylamys elegans (Dielphidae) a nocturnal small marsupial, endemic Of Southern South America. We Studied their standard energetic and determined whether they exhibit shallow daily torpor or deep prolonged torpor as a function of ambient temperature and food availability. Thylamys elegans partially supports the hypothesis that Neotropical marsupials have somewhat a higher basal metabolic rate (BMR) and thermal conductance (C-m) than Australian Ones. In fact, BMR was higher but C-m was lower than expected for their body mass, The higher mass-independent BMR of the Chilean mouse-opossum may be explained by its insectivorous food habits and its low C-m by its temperate habitats. Euthermic Chilean mouse-opossum showed daily fluctuations in body temperature being significantly hi-her during night time. In addition T. elegans entered in daily torpor and aroused spontaneously only was food was absent. That is, this species display a facultative type of daily torpor because propensity to enter in torpor was dependent of the combination of food absence and low ambient temperature. No torpor was observed when food was available. During torpor ambient temperature was slightly above ambient temperature between 0.3 to 0.5 degrees C. Torpor in this species as well as in marsupials in general. appears to be a flexible and an opportunistic response to unpredictable environmental conditions.
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    Seasonal acclimatization in water flux rate, urine osmolality and kidney water channels in free-living degus
    (2003) Bozinovic, F; Gallardo, PA; Visser, GH; Cortés, A
    The environmental modification of an organism's physiology in the field is often hypothesized to be responsible for allowing an organism to adjust to changing biotic and abiotic environmental conditions through increases in biological performance. Here, we examine the phenotypic flexibility of water flux rate, urine osmolality and the expression of kidney aquaporins (AQP; or water channels) in free-ranging Octodon degus, a South American desert-dwelling rodent, through an integrative study at cellular, systemic and organismal levels. Water flux rates varied seasonally and were significantly lower in austral summer than in winter, while urine osmolality was higher in summer than during winter. The observed water influx rate during summer was 10.3+/-2.3 ml day(-1) and during winter was 40.4+/-9.1 ml day(-1). Mean urine osmolality was 3137 +/- 472 mosmol kg(-1) during summer and 1123 +/- 472 mosmol kg(-1) during winter. AQP-2 medullary immunolabeling was more abundant in the kidneys of degus captured during summer than those captured during winter. This immunoreactivity was higher in apical cell membranes of medullary collecting ducts of degus in summer. AQP-1 immunostaining did not differ between seasons. Consistently, AQP-2 protein levels were increased in medulla from the summer individuals, as judged by the size of the 29 kDa band in the immunoblot. Here, we reveal how the integration of flexible mechanisms acting at cellular, systemic and organismal levels allows a small desert-dwelling mammal to cope with seasonal water scarcity in its semi-arid habitat.