Daniela Figueroa

Functional and structural optimization of the respiratory system of the bat Tadarida brasiliensis (Chiroptera, Molossidae): does airway geometry matter?

SUMMARY We studied structure and function of the respiratory system in the bat Tadarida brasiliensis and compared it with those of two species of rodents, Abrothrix andinus and A. olivaceus. Tadarida brasiliensis had lower resting oxygen consumption, but higher maximum oxygen consumption and aerobic scope, than the rodents. The blood–gas barrier of the bat was thinner and its relative lung size was larger; however, alveolar surface density was similar among the three species. In consequence, T. brasiliensis has an oxygen diffusion capacity two or three times higher than that of the rodents. In Tadarida brasiliensis the characteristics of the lung were accompanied by geometrical changes in the proximal airway, such as high physical optimization as a consequence of small variations in the symmetry and the scaling ratio of the bronchial diameters. These may constitute an efficient way to save energy in respiratory mechanics and are the first report of airway adjustments to decrease entropy generation in bats.

Participation of book lungs in evaporative water loss in Paraphysa parvula, a migalomorph spider from Chilean Andes

Small animals need efficient water conservation mechanisms for survival and reproduction, which is relevant for the spiders that have large book lungs with large respiratory surface. If lung evaporation is relevant to limit water loss, adjustments of the spiracle opening to metabolic demands should be expected. In this study, we measured the metabolic rate and total evaporative water loss mediated by the opening of the spiracles in the migalomorph spider Paraphysa parvula, a resident of fluctuating Mediterranean environments of the mountains of central Chile. We found that the metabolism of P. parvula was similar to other Theraphosidae and low compared to other arthropods. Carbon dioxide production and evaporative water loss increased with temperature, particularly at 40 degrees C. The total evaporative water loss at 40 degrees C increased dramatically to about 10 times that found with the lower temperatures. Thus, 40 degrees C will be the limit temperature for this species after which evaporative water loss starts to become damaging, so it has to avoid it. The exposition to hypercapnic environments had as a consequence an increase in evaporative water loss and the involvement of the book lungs in this loss was about 60%. The possibility of losing water could condition this species to seek temperate and oxygenated shelters under rocks.

Interplay between the morphometry of the lungs and the mode of locomotion in birds and mammals.

We studied the lung diffusion parameters of two species of birds and two species of mammals to explore how structural and functional features may be paralleled by differences in life style or phylogenetic origin. We used two fast-flying species (one mammal and one bird), one running mammal and one bird species that flies only occasionally as models. The harmonic mean thickness of the air-blood barrier was very thin in the species we studied. An exception was the Chilean tinamou Notoprocta perdicaria, which only flies occasionally. It showed an air-blood barrier as thick as that of flightless Galliformes. We found that the respiratory surface density was significantly greater in flying species compared to running species. The estimated values for the oxygen diffusion capacity, DtO2 follow the same pattern: the highest values were obtained in the flying species, the bat and the eared dove. The lowest value was in N. perdicaria. Our findings suggest that the studied species show refinements in their morphometric lung parameters commensurate to their energetic requirements as dictated by their mode of locomotion, rather than their phylogenetic origin. The air-blood barrier appears to be thin in most birds and small mammals, except those with low energetic requirements such as the Chilean tinamou. In the species we studied, the respiratory surface density appears to be the factor most responsive to the energetic requirements of flight.

Effects of diet and water supply on energy intake and water loss in a mygalomorph spider in a fluctuating environment of the central Andes

The metabolic and water evaporation strategies in spiders may be part of a set of physiological adaptations to tolerate low or unpredictable food availability, buffering spiders against environmental fluctuations such as those of the high mountains of the central Andes. The aim of this study is to analyze experimentally the variations in metabolic rate and the rate of evaporative water with food and/or water restriction in a high mountain mygalomorph spider population (Paraphysa sp.). We found that the low metabolism of this spider was not affected by water restriction, but its metabolism was depressed after 3 weeks of food deprivation. The spider did not show seasonal metabolic changes but it presented seasonal changes in the rate of evaporative water loss at high temperatures. Females with egg sacs reduced their metabolic rate and evaporative water at high temperatures. These findings constitute a set of possible adaptations to a highly fluctuating Mediterranean environment, which is completely covered with snow for many months and then progresses rapidly to a very dry climate with high temperatures.

Effects of environmental temperature on oxygen diffusion capacity during post-natal development in the altricial rodent, Phyllotis darwini

Estudiamos la plasticidad fenotipica del desarrollo de las estructuras respiratorias responsables del intercambio de oxigeno en el roedor altricial Phyllotis darwini. Investigamos los parametros morfologicos del pulmon en animales aclimatados a alta temperatura (bajo requerimiento energetico de termorregulacion: 30 °C) y a baja temperatura (alto requerimiento: 15 °C) en diferentes etapas del desarrollo. Encontramos que la temperatura ambiental no afecto el volumen pulmonar, el grosor de la barrera alveolo-capilar ni la densidad de superficie alveolar. Y en consecuencia, tampoco la capacidad de difusion de oxigeno. Aun cuando Phyllotis darwini mostro los cambios respiratorios esperados de acuerdo a su desarrollo ontogenico, las estructuras evaluadas no fueron afectadas por la aclimatacion termica durante el desarrollo postnatal.

Effect of thermal acclimation on preferred temperatures in two mygalomorph spiders inhabiting contrasting habitats

Variations in the preferred temperatures during the rest periods of Grammostola rosea Walckenaer and Paraphysa parvula Pocock, two mygalomorph spiders occupying different habitats in central Chile, are analyzed. The former inhabits arid and semi‐arid lowland near plant communities, composed of shrubs (evergreens with small leathery leaves) and small trees; the latter is found in the central mountains of the Chilean Andes, above 2000 m.a.s.l. The preferred temperatures of these spiders at different times of day and exposure to cold (15 °C) and warm (25 °C) acclimation temperatures are compared. Body mass does not affect the preferred temperature of the larger spider G. rosea, although P. parvula, a spider with half of the body mass of G. rosea, shows a decrease in preferred temperature with body mass. This can be explained by a higher plasticity and thermal sensitivity of the smaller species as result of increased surface : volume ratio. The preferred temperature increases with the hour of the day under both acclimation conditions in P. parvula and in cold‐acclimated G. rosea, which is likely associated with crepuscular and nocturnal behaviour in both species. Grammostola rosea shows temperature preferences lower than those of P. parvula under both acclimation conditions. The increase of the acclimation temperature from 15 to 25 °C results in an increment of 2–3 °C in the preferred temperature of P. parvula but only 0.2 °C in that of G. rosea. Two contrasting lifestyle strategies are found: a small mygalomorph spider with phenotypic plasticity and adaptation to the fluctuating environment of high altitude, and a large mygalomorph spider with higher thermal inertia adapted to the more stable environment of lowlands.

Dinámica epidemiológica del dengue en Isla de Pascua

Dengue is considered an emerging disease with an increasing prevalence especially in South America. In 2002, an epidemic of classic Dengue (DENV-1) occurred unexpectedly on Easter Island, where it had never been detected before. It reappeared in 2006-2007 and 2008, 2009 and 2011. The aim of this study was to estimate the most relevant parameters of the epidemiological dynamics of transmission of Dengue on Easter Island and to model the dynamics since 2002, comparing the predictions with the actual situation observed. Of the total cases, 52.27% were females and 47.73% men. The average age of infection was 31.38 ± 18.37 years, similar in men and women. We estimated the reproductive number R0 = 3.005 with an IC0,95 = [1.92, 4.61]. The inter-epidemic period reached an estimated T = 5.20 to 6.8 years. The case simulation showed recurrent epidemics with decreasing magnitude (damped oscillations), which is a known phenomenon in models of dengue and malaria. There was good qualitative fit to the epidemiological dynamics from 2002 onwards. It accurately predicted the rise in cases between 2006 and 2011. The predicted number of cases during the 2002 epidemic is greater than the confirmed cases and the predicted epidemic was faster than notified cases. Interepidemic period in the simulation was 6.72 years between 2002 and 2008 and 4.68 years between 2008 and 2013. From the theoretical perspective, the first epidemic had affected 94% of the population (approximately 3500 cases), but 639 were reported suggesting underreporting and a lot of sub-clinical cases occurred. Future epidemic of decreasing size are expected, although the main danger are epidemics of hemorrhagic dengue fever resulting from the introduction of different dengue virus serotypes.

Symmorphosis in the proximal pathway for oxygen in the leaf-eared mouse Phyllotis darwini

In this report, we explore the matching of structures to functional needs by comparing previously reported data of maximal oxygen consumption and the development of the lung in the leaf-eared mouse Phyllotis darwini in warm and cold environments. We discuss whether the state of structural design is commensurate with functional needs from regulated morphogenesis as predicted by the hypothesis of symmorphosis. We found a close match between respiratory structures and functional needs during postnatal development, expressed as safety factors close to unity. However, in the adult stage the safety factors were greater than two, which suggests that adult animals acquired a structure greater than that required considering their maximum capacities. A high safety factor in the respiratory system of adult mice may be a consequence of the symmorphosis that operates during ontogeny and does not necessarily support a rejection of this hypothesis.

Adjustments of the oxygen diffusing capacity to energetic demands during the development of the quail (Coturnix coturnix japonica).

One of the hypotheses that attempt to explain physiological limitations of energy budgets is the symmorphosis hypothesis, which proposes that if matching structures to functional needs were combined with the strict economy of energy and materials, the result would be an optimal organ design for the specific function it serves. Evidence in favor of symmorphosis in adults is as abundant as evidence against it, but the plasticity of some morphological traits may be dependent on the ontogenetic stage at which acclimation acts. Thus, here we studied the adjustment of structure and function in lungs at different stages of development in the quail Coturnix coturnix japonica under two thermal regimes. Our main results show that i) resting metabolic rate, maximum thermogenic oxygen consumption and oxygen diffusion capacity did not exhibit developmental plasticity for two thermal environments; and ii) oxygen diffusion capacity fully adjusted to resting metabolic rate and maximum oxygen consumption during development. C. coturnix has a low safety factor close to 1 which is consistent with the symmorphosis hypothesis.