Mauricio Canals

Energetics and geometry of huddling in small mammals.

Huddling in small mammals appears as an efficient response to low ambient temperatures with important consequences in thermoregulatory energy savings. These energy savings have been ascribed to a decrease in the exposed area in relation to the animals volume. It has been proposed that during huddling reductions in the exposed area and in the metabolic rate are equal functions of the number of grouped individuals with a common exponent of -1/3. However, reported data shows a great variability of this exponent. In this paper we present a geometrical and energetic analysis on several huddling efficiencies in small mammals and in geometric bodies. Our theoretical analysis shows a variability in the efficiency of huddling, depending on the morphological characteristics of the geometric bodies. At the same time original and literature information show an analogous interspecific variability in small mammals. Finally, a general mathematical expression is proposed which represents and explains the energetic and geometric specific variations of huddling in small mammals.

Blood Host Sources of Mepraia spinolai (Heteroptera: Reduviidae), Wild Vector of Chagas Disease in Chile

Abstract There are two vectors of the Chagas’ disease in Chile: Triatoma infestans Klug the domestic vector and Mepraia spinolai Porter the sylvatic vector. The alimentary profile of M. spinolai has been poorly studied. In this work we study the participation of humans, goats, dogs, cats, rodents, rabbits, birds (hens), and reptiles in the diet of M. spinolai by analyzing the intestinal content through immunoradiometric assay. To put our results in a general context, we also compared the diet with that described for T. infestans. In decreasing order, we detected blood of rabbits, dogs, goats, rodents, humans, and birds (hens). There were 12.3% of insects infected with T. cruzi, but this fact was not significant for diet variance. In warm weather there was a larger diversity of alimentary sources than in a cold one. The niche breadth increased from 0.029 in cold weather to 0.464 in warm weather. The niche overlap of T. infestans and M. spinolai was 0.23.

Comparison of some behavioral and physiological feeding parameters of Triatoma infestans klug, 1834 and Mepraia spinolai porter, 1934, vectors of chagas disease in Chile

There are two vectors of Chagas disease in Chile: Triatoma infestans and Mepraia spinolai. We studied the feeding behavior of these species, looking for differences which could possibly explain the low impact of the latter species on Chagas disease. Both species used thermal cues to locate their feeding source and consumed a similar volume of blood which was inversely related to the body weight before the meal and directly related to the time between meals. The average time between bites were 6.24 and 10.74 days. The average bite of M. spinolai lasted 9.68 min, significantly shorter than the 19.46 min for T. infestans. Furthermore, while T. infestans always defecated on the host, this behavior was observed in M. spinolai in only one case of 27 (3.7%). The delay between the bites and defecation was very long in M. spinolai and short in T. infestans. These differences may affect the reduced efficiency of transmission of Chagas infection by M. spinolai.

Ontogenetic changes in the fractal geometry of the bronchial tree in Rattus norvegicus

Respiration and metabolism change dramatically over the course of the development of vertebrates. In mammals these changes may be ascribed to organogenesis and differentiation of structures involved in gas exchange and transport and the increase in size. Since young as well as mature individuals must be well-designed if the species is to survive, the physiological changes during the development should be matched with geometrical or structural adjustments of the respiratory system. The aim of this study was to evaluate changes in the fractal geometry of the bronchial tree during the postnatal development of the rat. The average fractal dimension of the bronchial tree of the rats was 1.587, but that of juveniles was larger than that of the adults. We found a significant negative correlation between age and fractal dimension. This correlation could be considered be misleading because of the difficulty of separating age/body size effects. Nevertheless, because fractal dimensions of the bronchial tree of rabbits and humans are known to be similar, 1.58 and 1.57 respectively, the body size effect may be nil. To our knowledge, this is the first report of ontogenetic changes in the fractal dimension of the bronchial tree in mammals.

Huddling behavior as critical phase transition triggered by low temperatures

Huddling is a grouping behavior where animals maintain close bodily contact and save energy. We tested the hypothesis that this thermoregulatory behavior behaves as a system with continuous (second-order phase) transition called critical when the environmental temperature (driving parameter) is near a critical value. To do so, we followed theoretical and experimental approaches, examining data from geometrical models, metabolic rate during huddling in small mammals, and also conducting an experiment on thermoregulatory huddling behavior with white mice. Our results support all predictions for systems under continuous-phase transition triggered by low temperatures, a phenomenon reported for first time in a biological system. We suggest that huddling behavior in social animals, a recognized adaptive behavior, may be considered a self-organized system coupled with an external driving parameter.

Abundance of Mepraia spinolai in a Periurban zone of Chile.

Mepraia spinolai is a silvatic species of Triatominae which prefers microhabitats near to or in rock piles. It is also able to maintain similar or higher size populations near houses. The density of bugs in quarries near Santiago, Chile, differed within microhabitats and varied significantly within sites according to season. M. spinolai was not found in sites characterized by human perturbation of quarries. Our results confirm M. spinolai as a silvatic triatomine whose importance as a vector of Chagas disease will depend on contact with humans. This could occur if the habitats where populations of this species are found become exploited for the building of urban areas.

Field tests of carbon dioxide and conspecifics as baits for Mepraiaspinolai, wild vector of Chagas disease

In spite of extensive evidence showing an association between host stimuli and insect finding behaviour, the importance of carbon dioxide in attracting Triatominae is not entirely understood. We assessed the potential of conspecific individuals and CO2 in attracting free-ranging individuals of Mepraia spinolai in a Chilean semiarid locality. While the presence of conspecific individuals had no effect on the triatomine behaviour, solid CO2-baited traps were more effective in attracting M. spinolai than control (empty) traps. We conclude that CO2 trapping is an effective field technique for M. spinolai detection and potential control.

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.

Respiratory Refinements In The Mygalomorph Spider Grammostola rosea Walckenaer 1837 (Araneae, Theraphosidae)

Abstract In this study we hypothesized that Grammostola rosea Walckenaer 1837, an active predator of large size that depends on its two paired book lungs for respiration, would have a refined low energy strategy based on its thin air-hemolymph barrier. The morphology of book lungs and the oxygen consumption at 20° and 30° C under normal and starvation conditions were studied. The oxygen consumption was low compared to that expected for spiders from the allometric relationship, 0.027 ± 0.01 ml O2 g−1 h−1 (average ± standard deviation), and it was depressed at 30° C under starvation. The harmonic mean thickness of the air-hemolymph barrier was 0.14 ± 0.03 µm, the respiratory surface density was 122.99 ± 35.84 mm−1, and the book lung volume ranged from 12.2 to 37.5 mm3. With these parameters a high oxygen diffusion capacity was estimated. The combination of low resting oxygen consumption and high pulmonary oxygen conductance results in very low gradients of partial oxygen pressures across the air-hemolymph barrier (0.12–0.16 kPa) required to satisfy the resting oxygen demands.

Biomechanic consequences of differences in wing morphology between Tadarida brasiliensis and Myotis chiloensis

The wing morphology of bats is very diverse, and may correlate with energetic, behavioural, and ecological demands. If these demands conflict, wing shape may reflect compromise solutions. In this study, we compared the wing morphology of two bats,Tadarida brasiliensis (Geoffroy, 1824) andMyotis chiloensis (Waterhouse, 1828), that differ in body size, habitat, and foraging behaviour. We analyzed features of biomechanical and energetic relevance, and sought evidence of compromise solutions to energetic, ecological, and behavioural demands. We found that wing span of both species conformed to expectations based on allometric relationships, but that although the wing area ofM. chiloensis did not differ from predictions, the wing area ofT. brasiliensis was lower.M. chiloensis possessed an unusually low second moment of area of the humerus. Wing form ofM. chiloensis is consistent with highly maneuverable flight needed to live between shrubs and wooded habitats, and its low aspect ratio and low wing loading indicate a high energetic cost and a low flight speed, respectively. The low humeral second moment of area may be related to a reduction of wing mass and may result in decreased inertial power. In contrast,T. brasiliensis showed high aspect ratio and wing loading, characteristic of high speed, energetically economic flight.