Critical Approaches to Sex Determination in Sea Turtles
111
synchronizing the development of the eggs. Depending on the type of incubators,
the eggs may need to be placed on a moist substrate (e.g., moistened vermiculite)
and kept in covered containers to prevent desiccation. 34 Some of the homemade
incubators maintain a very high humidity (because of a water-filled heat sink in the
bottom of the incubator), so moist substrate is not necessary. Eggs from different
clutches should be randomly assigned a position in the incubator to prevent the effect
of location within the incubator being misinterpreted as clutch effects. The location
of eggs should be rotated periodically (e.g., daily) within the incubator to minimize
any position effects in the incubators. Temperature data loggers and/or temperature
probes should be placed adjacent to eggs within the incubators, and temperatures
should be recorded a minimum of several times per hour throughout the incubation.
Upon hatching, the sex of each hatchling must be verified (see Section 4.3.7).
Although most studies have used constant temperatures to analyze pivotal temperature and TRT, studies using fluctuating (e.g., natural) temperature regimes are
of distinct interest. Such studies are of particular relevance for sea turtle conservation
programs that incubate eggs in natural or translocated nests on natural nesting
beaches. Some studies have reported sex ratios relative to natural nest incubation
temperatures. 11,46,47 This subject has been addressed experimentally by Georges et
al., 36 and their findings indicate that daily temperature fluctuations can have a
profound effect on sex determination, but the effect is dependent upon the magnitude
of the fluctuation. The depth of sea turtle nests limits the daily temperature fluctuations (e.g., maximum of 0.3–1.4∞C in studies of loggerhead turtles). 48,49 On the
basis of the model by Georges et al., 36 fluctuations of this magnitude would alter
the effect of temperature by a maximum of only a few tenths of a degree Celsius in
comparison with constant temperatures. This suggests that data from constanttemperature studies are generally applicable to studies examining natural sea turtle
nests with fluctuating temperatures. However, this concept is based on a single study
that examined temperatures fluctuating around a single mean temperature. 36 Thus,
it would be useful to have future studies addressing this subject in sea turtles.
Once sex ratio data are obtained from pivotal temperature and TRT studies, they
must be analyzed. Analysis in previous studies has varied from simple estimates to
elaborate statistical analyses. A rigorous and standardized statistical method of
describing pivotal temperature and TRT has been reported. 50 In addition to describing
TSD in a particular population, these statistics allow for comparison of TRT and
pivotal temperatures among sea turtle populations. 32,50
4.3 SEX RATIOS IN SEA TURTLE POPULATIONS
Evolutionary theory suggests that the primary sex ratio (i.e., the sex ratio of the
hatchlings) should be 1:1 if parental investment in both sexes (among other factors)
is equal. 51,52 However, TSD has the potential of producing a wide variety of sex
ratios, and numerous questions arise regarding sex ratio produced from TSD. For
example, do naturally occurring sex ratios conform to a 1:1 sex ratio, as suggested
by evolutionary theory? 51,52 What range of sea turtle sex ratios occurs in nature? Do
sex ratios vary over time and within a population (e.g., seasonal, yearly, by size
class, etc.)? What effects does sex ratio have on reproductive success in a population?
1123 book.book Page 111 Monday, November 11, 2002 11:11 AM
111
synchronizing the development of the eggs. Depending on the type of incubators,
the eggs may need to be placed on a moist substrate (e.g., moistened vermiculite)
and kept in covered containers to prevent desiccation. 34 Some of the homemade
incubators maintain a very high humidity (because of a water-filled heat sink in the
bottom of the incubator), so moist substrate is not necessary. Eggs from different
clutches should be randomly assigned a position in the incubator to prevent the effect
of location within the incubator being misinterpreted as clutch effects. The location
of eggs should be rotated periodically (e.g., daily) within the incubator to minimize
any position effects in the incubators. Temperature data loggers and/or temperature
probes should be placed adjacent to eggs within the incubators, and temperatures
should be recorded a minimum of several times per hour throughout the incubation.
Upon hatching, the sex of each hatchling must be verified (see Section 4.3.7).
Although most studies have used constant temperatures to analyze pivotal temperature and TRT, studies using fluctuating (e.g., natural) temperature regimes are
of distinct interest. Such studies are of particular relevance for sea turtle conservation
programs that incubate eggs in natural or translocated nests on natural nesting
beaches. Some studies have reported sex ratios relative to natural nest incubation
temperatures. 11,46,47 This subject has been addressed experimentally by Georges et
al., 36 and their findings indicate that daily temperature fluctuations can have a
profound effect on sex determination, but the effect is dependent upon the magnitude
of the fluctuation. The depth of sea turtle nests limits the daily temperature fluctuations (e.g., maximum of 0.3–1.4∞C in studies of loggerhead turtles). 48,49 On the
basis of the model by Georges et al., 36 fluctuations of this magnitude would alter
the effect of temperature by a maximum of only a few tenths of a degree Celsius in
comparison with constant temperatures. This suggests that data from constanttemperature studies are generally applicable to studies examining natural sea turtle
nests with fluctuating temperatures. However, this concept is based on a single study
that examined temperatures fluctuating around a single mean temperature. 36 Thus,
it would be useful to have future studies addressing this subject in sea turtles.
Once sex ratio data are obtained from pivotal temperature and TRT studies, they
must be analyzed. Analysis in previous studies has varied from simple estimates to
elaborate statistical analyses. A rigorous and standardized statistical method of
describing pivotal temperature and TRT has been reported. 50 In addition to describing
TSD in a particular population, these statistics allow for comparison of TRT and
pivotal temperatures among sea turtle populations. 32,50
4.3 SEX RATIOS IN SEA TURTLE POPULATIONS
Evolutionary theory suggests that the primary sex ratio (i.e., the sex ratio of the
hatchlings) should be 1:1 if parental investment in both sexes (among other factors)
is equal. 51,52 However, TSD has the potential of producing a wide variety of sex
ratios, and numerous questions arise regarding sex ratio produced from TSD. For
example, do naturally occurring sex ratios conform to a 1:1 sex ratio, as suggested
by evolutionary theory? 51,52 What range of sea turtle sex ratios occurs in nature? Do
sex ratios vary over time and within a population (e.g., seasonal, yearly, by size
class, etc.)? What effects does sex ratio have on reproductive success in a population?
1123 book.book Page 111 Monday, November 11, 2002 11:11 AM