Jacques Larochelle

Behavioural responses of moose to thermal conditions in the boreal forest

Abstract: Among ungulate species living in boreal regions, moose (Alces alces) are most likely to suffer from heat stress since they have a relatively low upper critical temperature (14 °C in summer and -5 °C in winter). We tested the hypothesis that moose adopt behaviours to reduce thermoregulatory costs. We predicted that moose exposed to high intensities of solar radiation or high air temperatures would 1) seek a type of vegetation association that provides thermal shelter and 2) reduce activity. We also predicted that these behaviours would be most evident in summer. Thermal-shelter use and activity of 30 free-ranging moose were measured over 3 y in a 940-km2 study area of boreal forest using GPS telemetry collars. The effect of solar radiation and air temperature on thermal-shelter use and activity were assessed using logistic and multiple regression analyses. Habitat use and activity rates of moose were related to air temperature but not solar radiation. The probability of finding moose in thermal shelters increased with air temperature in summer and fall. Moose activity did not decrease as air temperature increased, but it increased at night during hot periods. As expected, moose response to thermal conditions was most noted in summer. Our results suggest that moose reduce exposure to thermal stress by using thermal shelters during the day and by increasing nocturnal activity. These behavioural adaptations allow moose to cope with thermal stress on a small temporal scale. Negative effects of heat stress could be important in areas where air temperatures are very high for extended periods of time or where thermal cover is scarce.

AN ALTERNATE GROWTH PATTERN FOR LAMINARIA LONGICRURIS1,2

A population of Laminaria longicruris de la Pylaie was followed for a year at Bic Island, Quebec, Canada where nutrient levels in the seawater were elevated throughout the year. Tagged kelp were measured each month for growth and analyzed for alginic acid, laminaran, mannitol, carbon, nitrogen, and nitrate. Maximum growth (3.5 cm · d−1) was observed in June, and minimal growth (0.18 cm · d−1) from December to February, when ice cover limited light levels. No reserves of carbon or nitrate were formed. Laminaran levels remained below 2.7% dry weight while tissue nitrate did not exceed 0.75 μmol · g−1 dry weight. Total carbon produced per plant was 40 g C · yr−1. Nutrient availability enables the kelp to take advantage of summer light and temperature conditions to grow rapidly.

Polyamines in Acanthamoeba castellanii: Presence of an unusually high, osmotically sensitive pool of 1,3-diaminopropane

High (15-25 mM) concentrations of 1,3-diaminopropane, a normally minor derivative of polyamine metabolism, have been observed in vegetative cells of Acanthamoeba castellanii. Trace amounts of a putative polyamine, which chromatographically behaved like norspermidine, were also found. The size of the intracellular pool of 1,3-diaminopropane was inversely related to the ambient osmolality and to the free amino acid levels during osmotic shock experiments. Due to its high concentration in A. castellanii, this diamine may be operative in ionic regulation during environmental stress. 1,3-diaminopropane may substitute for putrescine, a common diamine which was undetectable in A. castellanii.

On the importance of radiative heat exchange during nocturnal flight in birds

SUMMARY Many migratory flights take place during cloudless nights, thus under conditions where the sky temperature can commonly be 20°C below local air temperature. The sky then acts as a radiative sink, leading objects exposed to it to have a lower surface temperature than unexposed ones because less infrared energy is received from the sky than from the surfaces that are isothermic to air. To investigate the significance of this effect for heat dissipation during nocturnal flight in birds, we built a wind tunnel with the facility to control wall temperature (TASK) and air temperature (TAIR) independently at air speeds (UWIN) comparable to flying speeds. We used it to measure the influence of TASK, TAIR and UWIN on plumage and skin temperatures in pigeons having to dissipate a thermal load while constrained at rest in a flight posture. Our results show that the temperature of the flight and insulation plumages exposed to a radiative sink can be accurately described by multiple regression models (r2>0.96) based only on TAIR, TASK and UWIN. Predictions based on these models indicate that while convection dominates heat loss for a plumage exposed to air moving at flight speed in a thermally uniform environment, radiation may dominate in the presence of a radiative sink comparable to a clear sky. Our data also indicate that reducing TASK to a temperature 20°C below TAIR can increase the temperature difference across the exposed plumage by at least 13% and thus facilitate heat flow through the main thermal resistance to the loss of internally produced heat in birds. While extrapolation from our experimentally constrained conditions to free flight in the atmosphere is difficult, our results suggest that the sky temperature has been a neglected factor in determining the range of TAIR over which prolonged flight is possible.

Intermittent hypoxia and plasticity of respiratory chemoreflexes in metamorphic bullfrog tadpoles.

We tested the hypothesis that intermittent hypoxia elicits plasticity in respiratory chemoreflexes in bullfrog tadpoles. Metamorphic tadpoles (Taylor-Kollros stages XVI-XX) were subjected to intermittent hypoxia (PW(O(2))=45 Torr; 12 h/day) or constant normoxia (PW(O(2))=156 Torr) for 2 weeks before ventilatory responses to hypoxia and hypercarbia were measured. Buccal pressure changes were used to quantify the frequency and amplitude of movements associated with gill and lung ventilation. Morphometric assessment showed that intermittent hypoxia delayed development in comparison with controls. Oxygen consumption was enhanced in tadpoles subjected to intermittent hypoxia; however, this increase was not sufficient to affect basal ventilatory activity or the hypoxic ventilatory response. During acute hypercarbic exposure, tadpoles subjected to intermittent hypoxia showed (1) a greater decrease in gill ventilation frequency and (2) a greater increase in lung ventilation frequency than tadpoles maintained under control conditions. We conclude that intermittent hypoxia augments the responsiveness to hypercarbia, thereby promoting lung ventilation when animals face this stimulus. This manifestation of respiratory plasticity may reflect uncoupling between physiological and morphological development in the bi-modally breathing bullfrog tadpole.

Does hyperthermia constrain flight duration in a short-distance migrant?

While some migratory birds perform non-stop flights of over 11 000 km, many species only spend around 15% of the day in flight during migration, posing a question as to why flight times for many species are so short. Here, we test the idea that hyperthermia might constrain flight duration (FD) in a short-distance migrant using remote biologging technology to measure heart rate, hydrostatic pressure and body temperature in 19 migrating eider ducks (Somateria mollissima), a short-distance migrant. Our results reveal a stop-and-go migration strategy where migratory flights were frequent (14 flights day−1) and short (15.7 min), together with the fact that body temperature increases by 1°C, on average, during such flights, which equates to a rate of heat storage index (HSI) of 4°C h−1. Furthermore, we could not find any evidence that short flights were limited by heart rate, together with the fact that the numerous stops could not be explained by the need to feed, as the frequency of dives and the time spent feeding were comparatively small during the migratory period. We thus conclude that hyperthermia appears to be the predominant determinant of the observed migration strategy, and suggest that such a physiological limitation to FD may also occur in other species. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.

Cryoprotective mechanisms in subtidally cultivated and intertidal blue mussels (mytilus edulis) from the Magdalen Islands, Québec

Abstract Centrifuged extracts from subtidally cultivated and intertidal blue mussels have higher supercooling points (up to -5.5°C) in winter than in summer (up to -12.5°C). The concentration of nucleators (as estimated by the dilution factor) is greater in winter than in summer in both groups. The nucleator concentration in the extracts of winter mussels is one to two orders of magnitude higher than that in the haemolymph of Norwegian mussels. Although these extracts show spilule-like growth of ice crystals, they caused no thermal hystersis. The seasonal variation of these cryoprotective mechanisms is similar for intertidal and cultivated mussels. However, in the spring, cultivated mussels have a lower supercooling point and a lower concentration of nucleators than their intertidal counterparts. This suggests that cultivated mussels decrease their cryoprotective capacity earlier than intertidal mussels.