Behaviour Physiology
Brian
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A recently developed integrative framework proposes that the vulnerability of a species to environmental change depends on the species' exposure and sensitivity to environmental change, its resilience to perturbations and its potential to adapt to change. These vulnerability criteria require behavioural, physiological and genetic data. With this information in hand, biologists can predict organisms most at risk from environmental change. Biologists and managers can then target organisms and habitats most at risk. Unfortunately, the required data (e.g. optimal physiological temperatures) are rarely available. Here, we evaluate the reliability of potential proxies (e.g. critical temperatures) that are often available for some groups. Several proxies for ectotherms are promising, but analogous ones for endotherms are lacking. We also develop a simple graphical model of how behavioural thermoregulation, acclimation and adaptation may interact to influence vulnerability over time. After considering this model together with the proxies available for physiological sensitivity to climate change, we conclude that ectotherms sharing vulnerability traits seem concentrated in lowland tropical forests. Their vulnerability may be exacerbated by negative biotic interactions. Whether tropical forest (or other) species can adapt to warming environments is unclear, as genetic and selective data are scant. Nevertheless, the prospects for tropical forest ectotherms appear grim.
Research in multisensory processes has exploded over the last decade. Tremendous advances have been made in a variety of fields from single-unit neural recordings and functional brain imaging through to behaviour, perception and cognition. These diverse approaches have highlighted how the senses work together to produce a coherent multimodal representation of the external world that enables us to function better by exploiting the redundancies and complementarities provided by multiple sensory modalities. With large numbers of new students and researchers being attracted to multisensory research, and the multi-disciplinary nature of the work, our aim in this review is to provide an overview of multisensory processing that includes all fields in a single review. Our intention is to provide a comprehensive source for those interested in learning about multisensory processes, covering a variety of sensory combinations and methodologies, and tracing the path from single-unit neurophysiology through to perception and cognitive functions such as attention and speech.
In juvenile leatherbacks, heat gain is controlled behaviourally by increasing activity while heat flux is regulated physiologically, presumably by regulation of blood flow distribution. Hence, harnessing physiology and behaviour allows leatherbacks to keep warm while foraging in cold sub-polar waters and to prevent overheating in a tropical environment.
This is an open-access article distributed under the terms of the Creative Commons Public Domain declaration which stipulates that, once placed in the public domain, this work may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose.
Funding: This work was supported by a NSERC Discovery Grant to David R. Jones ( -crsng.gc.ca/). The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.
While different components of leatherback thermal biology have been measured and/or modelled in several studies, an holistic approach to quantifying the collective leatherback thermoregulatory response is lacking. In this study, we report the first empirical observations of the physiological and behavioral responses of leatherbacks to controlled variations in thermal environment. We apply our results to thermoregulation of leatherbacks, from juveniles to adults, in their natural environment, from tropical to polar seas.
In tank water 22C and higher the 37 kg leatherback was nearly inactive swimming at a flipper stroke frequency ranging between 2 and 8 strokes per minute, SPM (Table 1). The 16 kg leatherback on the other hand became nearly inactive in water that was any warmer 22C (Table 2). Stroke frequency greatly increased in both leatherbacks after a drop in temperature from 22C. After each reduction in TW the animals stroke rate increased and the rate was maintained over the entire time the turtle was in that TW. In the coldest water (16C) the 37 and 16 kg leatherbacks maintained their highest average activity rates at 29 and 36 SPM, respectively.
In the coldest water (16C) both turtles lost about 7% of qT through their flippers with the remaining 93% being lost through the body (ie. plastron and carapace, Table 1 and 2). The proportion of heat lost from the flippers increased as TW rose in both turtles. In 28 and 31C TW around 30% of qT was lost from the flippers compared with 70% from the plastron and carapace.
There has been considerable speculation that leatherbacks are endothermic and able to thermoregulate based upon the fact that their global range spans from cold northern foraging grounds to tropical nesting beaches. In the coldest water we tested (16C) the 16 and 37 kg leatherback maintained a thermal gradient of 2.0 and 2.3C, respectively, while in the warmest water (31C) the thermal gradient was reduced to 0.5 and 0.8C (Table 1 and 2). Therefore, we have shown for the first time, using juveniles in a controlled temperature environment, that leatherbacks possess the ability to hold and regulate their thermal gradient. Furthermore, since the heat energy to hold these thermal gradients is metabolically derived the animals are, by definition, endothermic.
A 3D image showing how activity (heat production) and thermal admittance (heat loss) affect the thermal gradient (TB-TW) held by juvenile leatherbacks. In cold water heat loss was minimized and activity was proportional to the thermal gradient held. In warm water activity was very low and thermal gradient was due to varying heat loss.
As the leatherbacks were in steady state at each TW and held a stable TB, the total rate of heat production must equal the total rate of heat loss. Therefore the sum of the heat lost from the plastron, carapace and flippers (ie. qT) will allow prediction of total heat produced (Table 1 and 2). A caveat is that heat loss is modelled to occur evenly over the entire surface. Total heat production was greatest when the animals were most active and therefore in the coldest water. Despite activity falling as water was warmed from 19 to 25C, heat loss was constant in both animals and this was probably due to the Q10 effect on basal metabolic processes as TB was increasing. In 28 and 31C TW the 37 kg leatherbacks heat production rate further increased despite having a very low activity rate, again due to temperature effects on metabolism. In adult leatherbacks that maintain stable TB's the heat production rate would be expected to more closely reflect rate of activity because basal metabolic rate should be constant.
where a is the proportionality coefficient. The body shape of juvenile leatherbacks is similar to those of sub-adults and adults so A scales with MB to the 2/3 power and L will scale with MB to the 1/3 power since MB has dimensions of L3. Therefore if k is constant then the thermal gradient scales with MB to the 0.5 power as:(2)
Due to scaling effects, the achievable thermal gradient is predicted to scale with MB, at a given metabolic cost, to the 0.5 power (Eq. 2). Therefore if leatherbacks maintain their TB above a minimum value only larger animals should be found foraging in colder waters. Eckert (2002) noted that animals
These animals were held for research purposes and all animal care/research standards of the Canadian Council for Animal Care (CCAC) and the UBC Animal Care Committee (UBC Animal Care Protocol: A04-0323) were met.
Leatherbacks have an oceanic-pelagic lifestyle and do not recognize barriers. Consequently, the animals were tethered to the centre of their housing tank by a short length of monofilament fishing line attached to a custom made harness (Figure 4A). The animals could swim or dive without touching the walls or bottom of the tank. The animals were exposed to a 12 hour light/dark cycle. Water quality was maintained by a biological filter, UV sterilization and a protein skimmer. A reservoir tank of equal volume was plumbed into the holding tank. Water temperature of the reservoir was varied and mixing the water in the two tanks allowed TW to be changed rapidly. TW was maintained within 0.25C in the holding tank by a thermostat that controlled hot or cold water flow through a stainless steel heat exchanger. The animal was instrumented and put in the tank at the beginning of the experiment and disturbed only to repair instruments or for feeding which was attempted twice a day.
Surface area of both leatherbacks was measured post-mortem. When the large and small animals died of natural causes their masses were 42.0 and 22.3 kg, respectively. Half the carapace, half the plastron, the ventral side of the left front and rear flipper of each animal was covered in paper. The paper was then removed, laid flat and the area was determined by creating geometric shapes with an easily measured area. Total body area (AB) was twice the measured area of plastron and carapace and total flipper area (AF) was four times the measured area of both front and rear flippers. These areas were scaled allometrically with MB in order to predict the surface area of the turtles during experimentation.
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