Title: Behavioral and metabolic contributions to thermoregulation in freely swimming leatherback turtles at high latitudes
By: James P. Casey, Michael C. James, Amanda S. Williard
Published: The journal of experimental biology
Volume-217 issue-13
Published in 2014
Background/ introduction
- Leather back sea turtles and seen in waters from the tropical equator to islands off of Canada (Nova scotia)
- They travel to the northern Atlantic in the late summer/ autumn to eat gelatinous zooplankton
- Proposed that by maintaining a thermal gradient between core body temperature and ambient water temperature
- With average water surface temps of 16.2 °C they maintained a thermal gradient of 5.1- 10.8 °C
- Usually weigh from 250-600 g’s with a small surface area to volume ratio and numerous and robust fat deposits makes them predetermined to hold in heat
- Vascular heat exchangers at the base of the flippers and blood flow adjustments permit tight control of heat loss at the extremities, and a vascular plexus lining the trachea minimizes respiratory heat loss. They utilize counter current heat exchange
- Metabolic heat production is the primary source of heat gain for the leatherback
- Its seen that juveniles with increase their activity when swimming in cold water. The metabolic heat from the moving muscles is used to generate heat for the body and maintain a thermal gradient.
- In adults its proposed that they utilize the metabolic heat gained from internal organs and foraging
- Some behavioral adaptations for leatherbacks are seen in the tropics where they will dive very deep in order to prevent overheating. This may be a strategy used in cold water except instead of diving very deep they may just remain closer to the surface to bask.
- Our primary goal was to investigate the behavioral and metabolic factors that contribute to the maintenance of elevated Tb under natural conditions.
Methods
- We deployed a combination of stomach temperature pills (STPs) and satellite-linked data recorders on leatherback turtles offshore Eastern Canada.
- The instrumentation provided data on dive patterns, Tb within the gastrointestinal tract, Ta, and location via the Argos Satellite System. Linear mixed models were used to explore the effects of dive behavior, diel status and residency status on Tb and the maximum change in Tb (ΔTb). We used our calculated values for mean Tg, a range of values for insulation thickness of the shell (L), and data and equations from the published literature to estimate rates
- We evaluate the contribution of SDA to heat production in foraging leatherbacks, and consider the energetic cost associated with thermoregulation.
- Resident= foraging, post resident = migratory
Results
- Only used data collected north of 42°N
- Turtles with 56 to 131 days of collection were used
- All turtles maintained a constant diving patter with dives being on average 20+- 6 m
- All turtles showed roughly the same mean time for basking from 41% +- 8% to 36%+- 13%
AVG Tb |
AVG Ta |
AVG Tg |
AVG mass |
27.3+-0.3, 25.4+-1.4 |
13.6+-6.4, 15.9+-2.0 |
10.7+-2.4, 12.1+-1.7 |
467+-76 kg |
- They found no significant correlation between mass and Tb
- Surface and diel status were the best determinants for Tb
- Tb increased with increased time at the surface in addition Tb was higher at night than it was in the day
- Cooling occurred during the day warming occurred at night
- Heat loss decreased as the turtles got thicker
Discussion
- Found that leatherbacks keep a Tg >10°C in Canadian waters through behavioral, and physiological means
- Individual leatherbacks spent 16–54% of time at the surface while north of 42°N. These results align with previous research at our study site, which documented surface times up to 41% for leatherbacks
- leatherbacks passively floating at the surface, flippers extended, during daylight hours at northern foraging grounds provide evidence that turtles may also bask to absorb solar radiation
- Modification of dive patterns to exploit warmer water at the surface and reduce rates of heat loss may be an important component of the leatherback's thermoregulatory strategy at high latitudes.
- It is important to note that we measured Tb from within the gastrointestinal tract; consequently, variation in Tb reflects cooling due to prey ingestion and warming due to SDA and transfer of heat via blood flow.
- heat gain for leatherbacks derives from metabolic processes
- so alterations in dive behavior are unlikely to contribute to the night-time warming trend
- We conclude that endogenous heat production warms gastrointestinal tract contents and accounts for the positive ΔTb observed during the night.
- Issues in the study – Some of the core temperatures taken could’ve been from parts in the turtle that are hotter than the periphery and organs next to them. On example is that the cloaca is 2.1°C warmer than the gastrointestinal tract.
- The metabolic processes to generate heat relied heavily on the rate of c consumption of prey, and the amount of thickness in the turtles insulating layer. Needed a thickness of 3.5 cm.
- These estimates illustrate that visceral metabolic heat production plays an important role in maintaining stable Tb for leatherbacks foraging in cold water.\
- The study also found that leatherbacks continue to forage in the beginning of their migration back south
Comments
Lots of information so it was
Lots of information so it was hard to follow but discussion part made lots of sense.