Roberto F. Nespolo

Daily and seasonal limits of time and temperature to activity of degus

Presentamos un analisis de la flexibilidad conductual en la actividad diaria del degu (Octodon degus), un roedor caviomorfo, en respuesta a la heterogeneidad del ambiente temporal (diario y estacional), espacial y termico. Junto con las condiciones termicas, cuantificamos la conducta de actividad y forrajeo en una poblacion que vive en un habitat abierto en el matorral arido y estacional de Chile central. La actividad de verano fue bimodal, con 2,5 h de actividad de forrajeo intenso durante la manana y con 2 h durante la tarde. No hubo actividad por mas de 8 h entre ambos eventos. Mas de la mitad de las 4,5 h diarias de actividad de la manana y de la tarde ocurrieron en la sombra, cuando el sol se encuentra bajo la linea local del cielo. La actividad durante el otono y la primavera tambien fue bimodal pero con una mayor proporcion de actividad bajo radiacion solar directa y con un periodo de inactividad menor entre los dos eventos principales. La actividad de invierno fue unimodal y bajo radiacion solar directa. En verano, otono y primavera la actividad estuvo sesgada cuando nuestro indice de temperatura operativa, Te, supero los 40 °C. Usamos una medida de Te (registrada en un maniqui termico que representa las propiedades de forma, tamano y superficie de un degu) como un indice de los efectos interactivos de la radiacion solar y la conveccion sobre la temperatura corporal. Durante el solsticio de invierno (junio), cuando los degus permanecieron todo el dia totalmente expuestos al sol, Te generalmente permanecio bajo 30 °C. La flexibilidad en el tiempo de la actividad superficial le permitio a los degus mantener su homeostasis termica y balance de energia anual. Los degus cambiaron sus periodos de inicio y termino asi como el numero de eventos de actividad (unimodal o bimodal) durante el ano. Estos roedores permanecieron activos en la superficie bajo un rango mucho mas estrecho de condiciones termicas que las que ocurren durante el largo del dia y ano

When Nonshivering Thermogenesis Equals Maximum Metabolic Rate: Thermal Acclimation and Phenotypic Plasticity of Fossorial Spalacopus cyanus (Rodentia)

Many small mammals inhabiting fluctuating and cold environments display enhanced capacity for seasonal changes in nonshivering thermogenesis (NST) and thermoregulatory maximum metabolic rate (MMR). However, it is not known how this plasticity remains in a mammal that rarely experiences extreme thermal fluctuations. In order to answer this question, we determined body mass (mb), basal metabolic rate (BMR), NST, MMR, and minimum thermal conductance (C) on a Chilean fossorial caviomorph (Spalacopus cyanus) from a coastal population, acclimated to cold (15°C) and warm (30°C) conditions. NST was measured as the maximum response of metabolic rate (NSTmax) after injection of norepinephrine (NE) in thermoneutrality minus BMR. Maximum metabolic rate was assessed in animals exposed to enhanced heat‐loss atmosphere (He‐O2) connected with an open‐flow respirometer. Body mass and metabolic variables increased significantly after cold acclimation with respect to warm acclimation but to a low extent (BMR, 26%; NST, 10%; and MMR, 12%). However, aerobic scope (MMR/BMR), calculated shivering thermogenesis (ST), and C did not change with acclimation regime. Our data suggest that physiological plasticity of S. cyanus is relatively low, which is in accordance with a fossorial mode of life. Although little is known about MMR and NST in fossorial mammals, S. cyanus has remarkably high NST; low MMR; and surprisingly, a nil capacity of ST when compared with other rodents.

THE QUANTITATIVE GENETICS OF SUSTAINED ENERGY BUDGET IN A WILD MOUSE

Abstract We explored how morphological and physiological traits associated with energy expenditure over long periods of cold exposure would be integrated in a potential response to natural selection in a wild mammal, Phyllotis darwini. In particular, we studied sustained energy expenditure (SusMR), the rate of expenditure fueled by concurrent energy intake, basal metabolic rate (BMR), and sustained metabolic scope (SusMS = SusMR/BMR), a measure of the reserve for sustained work. We included the masses of different central processing organs as an underlying factor that could have a mechanistic link with whole animal traits. Only the liver had heritability statistically different from zero (0.73). Physiological and morphological traits had high levels of specific environmental variance (average 70%) and postnatal common environmental variance (average 30%) which could explain the low heritabilities estimates. Our results, (1) are in accordance with previous studies in mammals that report low heritabilities for metabolic traits (SusMR, BMR, SusMS), (2) but not completely with previous ones that report high heritabilities for morphological traits (masses of central organs), and (3) provide important evidence of the relevance of postnatal common environmental variance to sustained energy expenditure.

Thermal acclimation, maximum metabolic rate, and nonshivering thermogenesis of Phyllotis xanthopygus (Rodentia) in the Andes Mountains

We determined non-shivering thermogensis (NST) and maximum metabolic rate (MMR) as functions of thermal acclimation in a small mammal species in a seasonal environment. We studied the rodent Phyllotis xanthopygus (Muridae) living in the cool to cold climate of the high Andean Plateau of northern Chile. As expected, NST and MMR were constantly higher in cool-acclimated individuals. Nevertheless, the observed differences in shivering thermogenesis (ST) as a result of temperature acclimation (>200%) exceeded our expectations. The large contributions of ST was due to a 94% increase in MMR while a 49% of increased in NST. Thus, changes in ST in P. xanthopygus account for most of the metabolic plasticity and thermogenic capability that enables this species to cope with thermal variations in the Andean environment.

Arousal from torpor in the chilean mouse-opposum (Thylamys elegans): does non-shivering thermogenesis play a role?

We examined the effect of norepinephrine injections on non-shivering thermogenesis (NST), rewarming rate, and metabolic cost during torpor arousal in warm- and cool-acclimated Chilean mouse-opposums, Thylamys elegans. Warm- and cool-acclimated animals did not display NST in response to NE injections. Values of VO2 (resting, after saline and NE injections) were not significantly different within treatments. Rewarming rates of warm-acclimated animals did not differ significantly from those in cool-acclimated animals. In contrast, the metabolic cost of torpor arousal was significantly affected by acclimation temperature. Warm-acclimated animals required more energy for arousal than cool-acclimated animals. Our study suggests that the main thermoregulatory mechanism during torpor arousal in this Chilean marsupial is shivering thermogenesis, and that its amount can be changed by thermal acclimation.

The influence of heat increment of feeding on basal metabolic rate in Phyllotis darwini (Muridae)

One of the most important prerequisites for obtaining a reliable measure of basal metabolic rate (BMR) in endotherms is that the animal must be in a post-absorptive condition. However, because of the diversity of nutrition and digestion modes in vertebrates, it is not simple to generalize a standard procedure for BMR measurement. Thus, information in this regard must be experimentally obtained by measuring the heat increment of feeding (HIF). We used a repeated-measures design to test for the effects of HIF on BMR in Phyllotis darwini, a granivorous rodent. Our results suggest that, in this species, feeding induces an elevation in O(2) consumption that can persist up to 4 h after the last meal. In addition, and irrespective of the fasting period, measures made with less than 2 h of fasting yield BMR values that are significantly higher than measurements after longer fasting periods (i.e. 3 and 4 h).

A time-energy analysis of daytime surface activity in degus, Octodon degus

Presentamos un analisis de la asignacion de tiempo y energia en un roedor caviomorfo diurno el degu, Octodon degus, en Chile central. Cuantificamos los componentes de actividad superficial en el campo sobre una base diaria durante el solsticio de verano en condiciones de calor y aridez extrema, para contestar la siguiente pregunta: ?el tiempo absoluto disponible para la actividad superficial limita el rendimiento? ?la asignacion de tiempo y energia a locomocion juega un limitacion funcional significativa en el presupuesto de energia total y en el rendimiento? Los degus permanecen forrajeando cerca de 2/3 de su tiempo fuera de las cuevas; estan estacionarios cerca de 88 % del tiempo, caminan cerca del 10 %, y corren rapidamente de un punto a otro solamente un 2 % del tiempo. Los costos netos de locomocion (caminando y corriendo) fueron calculados en 2,2 % del gasto energetico total. Esta baja asignacion neta de tiempo y energia a locomocion, junto a la abundante distribucion de alimento en un ambito de hogar pequeno, sugieren que el rendimiento diario de los degus no esta limitado por el tiempo absoluto disponible bajo condiciones normales en el solsticio de verano (extremo estacional de largo del dia, calor y aridez). Las demandas de energia totales se lograrian con 4,5 h de actividad superficial por dia. Las observaciones empiricas, junto a un modelo simple de gasto de energia y tiempo entregan una validacion simple de la actividad del balance de energia total en roedores de vida libre. El bajo impacto de la locomocion sobre el presupuesto de energia total representa una economia en la conducta de estos animales, los rapidos modos de locomocion minimizarian el riego de predacion. Postulamos que estos analisis cuantitativos de gasto de energia asociados con la conducta de campo contribuirian a la modelacion teorica del uso de tiempo y energia

Water economy of three Cinclodes (Furnariidae) species inhabiting marine and freshwater ecosystems

Las aves que habitan ambientes deserticos han sido modelos de estudio preferidos para el estudio de adaptaciones fisiologicas a la escasez de agua. Las aves paseriformes que habitan habitat costeros enfrentan problemas similares, aunque las posibles adaptaciones fisiologicas para la conservacion de agua en dichas especies han sido pobremente documentadas. En este estudio se determino la perdida total de agua por evaporacion (TEWL) y la tasa de consumo de oxigeno (VO2) en tres especies de aves paseriformes que habitan ambientes marinos y de agua dulce. La perdida total de agua por evaporacion masa-especifica fue significativamente menor en la especie marina, Cinclodes nigrofumosus, que en especies que habitan areas cercanas a fuentes de agua dulce. Se encontro una relacion positiva y significativa entre TEWL y VO2. La razon entre TEWL y el VO2 (perdida relativa de agua por evaporacion, RTEWL) presento una variacion significativa entre las especies de Cinclodes, siendo mayor para las especies de agua dulce C. oustaleti y C. fuscus. La variacion en TEWL encontrada en Cinclodes es probablemente una consecuencia de la explotacion diferencial de presas marinas con una alta carga osmotica, lo que a su vez, puede imponer la necesidad de conservacion de agua

A phylogenetic analysis of macroevolutionary patterns in fermentative yeasts

Abstract When novel sources of ecological opportunity are available, physiological innovations can trigger adaptive radiations. This could be the case of yeasts (Saccharomycotina), in which an evolutionary novelty is represented by the capacity to exploit simple sugars from fruits (fermentation). During adaptive radiations, diversification and morphological evolution are predicted to slow‐down after early bursts of diversification. Here, we performed the first comparative phylogenetic analysis in yeasts, testing the “early burst” prediction on species diversification and also on traits of putative ecological relevance (cell‐size and fermentation versatility). We found that speciation rates are constant during the time‐range we considered (ca., 150 millions of years). Phylogenetic signal of both traits was significant (but lower for cell‐size), suggesting that lineages resemble each other in trait‐values. Disparity analysis suggested accelerated evolution (diversification in trait values above Brownian Motion expectations) in cell‐size. We also found a significant phylogenetic regression between cell‐size and fermentation versatility (R 2 = 0.10), which suggests correlated evolution between both traits. Overall, our results do not support the early burst prediction both in species and traits, but suggest a number of interesting evolutionary patterns, that warrant further exploration. For instance, we show that the Whole Genomic Duplication that affected a whole clade of yeasts, does not seems to have a statistically detectable phenotypic effect at our level of analysis. In this regard, further studies of fermentation under common‐garden conditions combined with comparative analyses are warranted.

Aerobic power and flight capacity in birds: a phylogenetic test of the heart-size hypothesis

ABSTRACT Flight capacity is one of the most important innovations in animal evolution; it only evolved in insects, birds, mammals and the extinct pterodactyls. Given that powered flight represents a demanding aerobic activity, an efficient cardiovascular system is essential for the continuous delivery of oxygen to the pectoral muscles during flight. It is well known that the limiting step in the circulation is stroke volume (the volume of blood pumped from the ventricle to the body during each beat), which is determined by the size of the ventricle. Thus, the fresh mass of the heart represents a simple and repeatable anatomical measure of the aerobic power of an animal. Although several authors have compared heart masses across bird species, a phylogenetic comparative analysis is still lacking. By compiling heart sizes for 915 species and applying several statistical procedures controlling for body size and/or testing for adaptive trends in the dataset (e.g. model selection approaches, phylogenetic generalized linear models), we found that (residuals of) heart size is consistently associated with four categories of flight capacity. In general, our results indicate that species exhibiting continuous hovering flight (i.e. hummingbirds) have substantially larger hearts than other groups, species that use flapping flight and gliding show intermediate values, and that species categorized as poor flyers show the smallest values. Our study reveals that on a broad scale, routine flight modes seem to have shaped the energetic requirements of birds sufficiently to be anatomically detected at the comparative level. Summary: Routine flight modes seem to have shaped the energetic requirements of birds sufficiently to be anatomically detected at the comparative level.