110
The Biology of Sea Turtles, Vol. II
computer to program the unit and to download data. When purchasing data loggers,
one should consider factors such as resolution and accuracy of temperature recordings, amount of memory, size of data logger, battery life, and cost. In general, the
resolution of many typical data loggers ranges from approximately 0.2 to 0.4∞C. All
data loggers and temperature probes should be calibrated before and after use.
Calibration requires comparison to a thermometer that is traceable to National
Institute of Standards and Technology (NIST) or its equivalent in other countries.
Temperature recordings from each data logger and/or temperature probe should be
taken simultaneously with the NIST-traceable thermometer in an incubator with a
stable temperature in the typical range of sea turtle nest temperatures (e.g., approximately 26 to 35∞C). If the values are not consistent, a correction factor should be
determined for each data logger and temperature probe.
The majority of previous studies of pivotal temperatures and TRT in sea turtles
have involved the incubation of eggs at constant temperatures in laboratory incubators. This represents an efficient means of examining the effects of constant temperatures on sex determination because a wide variety of specific temperatures can be
examined. In such studies, the thermal characteristics of the incubator should be
evaluated prior to the experiments because they can have a profound effect on the
results. Factors such as the thermal stability of the incubator and thermal gradients
within the incubator should be examined. For example, incubators often develop
“thermal inertia” when the heating or cooling system is activated and will often
overshoot the preset temperature. Incubators with the smallest amount of thermal
inertia are preferred. An incubator that can maintain a preset temperature to plus or
minus a few tenths of a degree should be adequate. The cost of the incubator does
not necessarily reflect its effectiveness for this sort of study. It is possible to build
incubators using polystyrene (Styrofoam) boxes and aquarium heaters for a relatively
modest price that may outperform some of the commercial models. 43 Furthermore,
the home-built incubators may be the only option if the experiments are performed
in the field, where it is not practical to have large commercial incubators. 17
Incubation temperatures for these studies should be chosen in an attempt to
resolutely determine the lower and upper limits of the TRT and the pivotal temperature. Multiple temperatures (and thus incubators) will be needed to identify each
parameter. Data from previous studies of other populations of the same species
should provide insight on appropriate temperatures to examine. Ideally, eggs should
be placed into incubators as soon as possible after they are laid. However, this is
not a necessity, because previous studies indicate that the temperature-sensitive
period of sex determination is approximately the middle third of the incubation
period 44 (reviewed by Ref. 45). Given the increased sensitivity of sea turtle eggs to
movement after the first day of incubation, however, it is advisable to place the eggs
in the incubators as soon as possible after they are laid.
Because variation in pivotal temperatures has been detected between clutches
of eggs, it is important to use multiple clutches of eggs for estimating pivotal
temperatures. For example, it is far superior to use 20 eggs from each of five clutches
than to use 100 eggs from a single clutch. Ideally, large samples from multiple
clutches can be used to evaluate average pivotal temperature and interclutch variation. It is also better to use clutches that have all been laid on the same day, thus
1123 book.book Page 110 Monday, November 11, 2002 11:11 AM
The Biology of Sea Turtles, Vol. II
computer to program the unit and to download data. When purchasing data loggers,
one should consider factors such as resolution and accuracy of temperature recordings, amount of memory, size of data logger, battery life, and cost. In general, the
resolution of many typical data loggers ranges from approximately 0.2 to 0.4∞C. All
data loggers and temperature probes should be calibrated before and after use.
Calibration requires comparison to a thermometer that is traceable to National
Institute of Standards and Technology (NIST) or its equivalent in other countries.
Temperature recordings from each data logger and/or temperature probe should be
taken simultaneously with the NIST-traceable thermometer in an incubator with a
stable temperature in the typical range of sea turtle nest temperatures (e.g., approximately 26 to 35∞C). If the values are not consistent, a correction factor should be
determined for each data logger and temperature probe.
The majority of previous studies of pivotal temperatures and TRT in sea turtles
have involved the incubation of eggs at constant temperatures in laboratory incubators. This represents an efficient means of examining the effects of constant temperatures on sex determination because a wide variety of specific temperatures can be
examined. In such studies, the thermal characteristics of the incubator should be
evaluated prior to the experiments because they can have a profound effect on the
results. Factors such as the thermal stability of the incubator and thermal gradients
within the incubator should be examined. For example, incubators often develop
“thermal inertia” when the heating or cooling system is activated and will often
overshoot the preset temperature. Incubators with the smallest amount of thermal
inertia are preferred. An incubator that can maintain a preset temperature to plus or
minus a few tenths of a degree should be adequate. The cost of the incubator does
not necessarily reflect its effectiveness for this sort of study. It is possible to build
incubators using polystyrene (Styrofoam) boxes and aquarium heaters for a relatively
modest price that may outperform some of the commercial models. 43 Furthermore,
the home-built incubators may be the only option if the experiments are performed
in the field, where it is not practical to have large commercial incubators. 17
Incubation temperatures for these studies should be chosen in an attempt to
resolutely determine the lower and upper limits of the TRT and the pivotal temperature. Multiple temperatures (and thus incubators) will be needed to identify each
parameter. Data from previous studies of other populations of the same species
should provide insight on appropriate temperatures to examine. Ideally, eggs should
be placed into incubators as soon as possible after they are laid. However, this is
not a necessity, because previous studies indicate that the temperature-sensitive
period of sex determination is approximately the middle third of the incubation
period 44 (reviewed by Ref. 45). Given the increased sensitivity of sea turtle eggs to
movement after the first day of incubation, however, it is advisable to place the eggs
in the incubators as soon as possible after they are laid.
Because variation in pivotal temperatures has been detected between clutches
of eggs, it is important to use multiple clutches of eggs for estimating pivotal
temperatures. For example, it is far superior to use 20 eggs from each of five clutches
than to use 100 eggs from a single clutch. Ideally, large samples from multiple
clutches can be used to evaluate average pivotal temperature and interclutch variation. It is also better to use clutches that have all been laid on the same day, thus
1123 book.book Page 110 Monday, November 11, 2002 11:11 AM