Reproductive Cycles of Males and Females
149
However, this is not supported by preliminary results of gonad examination of firsttime breeding females: these data indicate that females with reduced clutch production ovulate approximately all available follicles similar to females that are more
productive. Third, turtles living at different distances from the rookery can be
expected to arrive for commencement of nesting at different times; in particular,
turtles from very distant feeding grounds may arrive later in the season. First-time
migrants may swim slower and navigate less precisely, thus consuming more energy
on migration. However, the first-time breeding C. caretta tracked by satellite telemetry from her home foraging area in Moreton Bay did not display any evidence of
slow swimming or less precise navigation (Limpus and Limpus, 2001). It is also
possible that some first-time breeders may simply leave their home foraging area at
a later date than the more experienced nesters, especially if hormone concentrations
required to initiate migration are a function of the number of mature follicles in the
ovary. Unfortunately, most studies addressing variability in egg production have
focused on the turtles once they have arrived at the nesting beach. There has also
been a deficiency in studies at the foraging areas to address the factors that might
impact the number and size of mature follicles that a female develops in her ovaries
prior to commencement of her breeding migration.
5.5.7.2 A Role for Hormones in Maximizing Reproductive
Effort
Valverde et al. (1999), Jessop et al. (1999b; 2000), and Jessop (2001) recently investigated hormonal mechanisms that may act to facilitate maximal reproductive output.
It now appears that at least four species of sea turtles (L. olivacea, C. caretta, C.
mydas, and E. imbricata) have a physiological ability to downregulate or desensitize
their corticosterone stress response (adrenocortical modulation) (Gregory et al.,
1996; Valverde et al., 1999; Jessop et al., 1999b; 2000; Jessop, 2001). Moreover,
this reduced stress response occurred in females prior to migration and persisted
through the nesting season, regardless of the level of reproductive investment that
remained (Jessop, 2001). Thus, the effects that ecological stressors (such as disturbance by conspecifics or competition for nesting space) may otherwise have on a
female’s ability to successfully oviposit are negated or temporarily set aside as
physiological safeguards are set in place to maximize current reproductive output.
5.5.8 REGULATION OF A NESTING SEASON
Marine turtles show significant weight gains during the internesting period while
preparing clutches for laying (C. caretta: Limpus, 1973; D. coreacea: Eckert et al.,
1989; E. imbricata: Limpus et al., 1983). Limpus (1973) incorrectly attributed
these weight gains to the female’s feeding during the internesting period, whereas
he ignored the possibility that water uptake could account for the weight changes.
There was negligible food contained in the gastrointestinal (GI) tract of the
internesting females examined in this latter study compared to the abundance of
food in the GI tract of nonbreeding C. caretta that live within the same internesting
habitat (Limpus et al., 2001b).
1123 book.book Page 149 Thursday, November 14, 2002 11:50 AM
149
However, this is not supported by preliminary results of gonad examination of firsttime breeding females: these data indicate that females with reduced clutch production ovulate approximately all available follicles similar to females that are more
productive. Third, turtles living at different distances from the rookery can be
expected to arrive for commencement of nesting at different times; in particular,
turtles from very distant feeding grounds may arrive later in the season. First-time
migrants may swim slower and navigate less precisely, thus consuming more energy
on migration. However, the first-time breeding C. caretta tracked by satellite telemetry from her home foraging area in Moreton Bay did not display any evidence of
slow swimming or less precise navigation (Limpus and Limpus, 2001). It is also
possible that some first-time breeders may simply leave their home foraging area at
a later date than the more experienced nesters, especially if hormone concentrations
required to initiate migration are a function of the number of mature follicles in the
ovary. Unfortunately, most studies addressing variability in egg production have
focused on the turtles once they have arrived at the nesting beach. There has also
been a deficiency in studies at the foraging areas to address the factors that might
impact the number and size of mature follicles that a female develops in her ovaries
prior to commencement of her breeding migration.
5.5.7.2 A Role for Hormones in Maximizing Reproductive
Effort
Valverde et al. (1999), Jessop et al. (1999b; 2000), and Jessop (2001) recently investigated hormonal mechanisms that may act to facilitate maximal reproductive output.
It now appears that at least four species of sea turtles (L. olivacea, C. caretta, C.
mydas, and E. imbricata) have a physiological ability to downregulate or desensitize
their corticosterone stress response (adrenocortical modulation) (Gregory et al.,
1996; Valverde et al., 1999; Jessop et al., 1999b; 2000; Jessop, 2001). Moreover,
this reduced stress response occurred in females prior to migration and persisted
through the nesting season, regardless of the level of reproductive investment that
remained (Jessop, 2001). Thus, the effects that ecological stressors (such as disturbance by conspecifics or competition for nesting space) may otherwise have on a
female’s ability to successfully oviposit are negated or temporarily set aside as
physiological safeguards are set in place to maximize current reproductive output.
5.5.8 REGULATION OF A NESTING SEASON
Marine turtles show significant weight gains during the internesting period while
preparing clutches for laying (C. caretta: Limpus, 1973; D. coreacea: Eckert et al.,
1989; E. imbricata: Limpus et al., 1983). Limpus (1973) incorrectly attributed
these weight gains to the female’s feeding during the internesting period, whereas
he ignored the possibility that water uptake could account for the weight changes.
There was negligible food contained in the gastrointestinal (GI) tract of the
internesting females examined in this latter study compared to the abundance of
food in the GI tract of nonbreeding C. caretta that live within the same internesting
habitat (Limpus et al., 2001b).
1123 book.book Page 149 Thursday, November 14, 2002 11:50 AM