146
The Biology of Sea Turtles, Vol. II
that leptin could be involved with the control of energy thresholds and important
decision-making stages in reptiles. Expression of a similar “obesity gene” in sea
turtles could be one signal that initiates or regulates vitellogenesis or metabolic
homeostasis during the nesting (aphagia) season.
5.5.4 FOLLICULAR ATRESIA
The degeneration of ovarian follicles (atresia) is common in most vertebrates and
can occur in follicles at various stages of development (Guraya, 1989). In this
chapter, we will limit our discussion to atresia of mature preovulatory follicles.
Atresia of these follicles has been reported in all species of sea turtle (Owens, 1980;
Limpus, 1985; Rostal et al., 1996; 1997; Hamann et al., 2002b; Limpus, unpublished
data). Our understanding of the mechanisms and functional role(s) of atresia is
limited. However, the perceived benefit for the female of selecting a follicle for
atresia is that the lipid can be resorbed, mobilized, and used for other metabolic
needs (Kuchling and Bradshaw, 1993). It would be interesting to investigate whether
females have the ability to compensate for decreased somatic energy by selecting
follicles for atresia, or whether some females, especially those that migrate longer
than average distances, have higher rates of follicular atresia to compensate for
increased migratory costs.
5.5.5 COURTSHIP AND CLUTCH PREPARATION
Observations of courtship activity suggest that courtship generally occurs in the
vicinity of the nesting beach (Booth and Peters, 1972; Owens and Morris, 1985;
Limpus, 1993). Females may mate with several males, and average cumulative
mating times are on the order of 25 h (Wood and Wood, 1980; Limpus, 1993;
FitzSimmons, 1997). It is not yet possible from behavioral observations to distinguish successful from unsuccessful mating, or to determine whether insemination
occurred (Wood and Wood, 1980; Limpus, 1993; FitzSimmons, 1997). Although
spermatozoa have been found adjacent to the vagina and the junction between the
magnum and aglandular zone, specialized sperm storage areas have not been identified in sea turtles (Solomon and Baird, 1979).
Although the courtship period appears to be well constrained temporally for the
individual, arrival of turtles at the nesting beach is scattered over several months
(Limpus, 1985; Dobbs et al., 1999; Godley et al., 2001; Limpus et al., 2001a). In
captive C. mydas the average period from mating to nesting is 34.7 days (Wood and
Wood, 1980). This period comprises two phases: the first period from insemination
to ovulation, the second period from ovulation to oviposition. The latter has been
extensively studied (Miller, 1997), but the former has never been investigated.
The control of ovulation and egg development has been linked to various endocrine pathways (see Owens 1980; 1997; Owens and Morris, 1985). Briefly, ovulation
occurs approximately 36 h postoviposition and coincides with peaks in gonadotropins (luteinizing hormone and follicle-stimulating hormone) and a decrease in
plasma testosterone (Licht et al., 1982; Wibbels et al., 1990). Albumin production
and deposition coincide with a peak in progesterone, and shell formation is generally
1123 book.book Page 146 Thursday, November 14, 2002 11:50 AM
The Biology of Sea Turtles, Vol. II
that leptin could be involved with the control of energy thresholds and important
decision-making stages in reptiles. Expression of a similar “obesity gene” in sea
turtles could be one signal that initiates or regulates vitellogenesis or metabolic
homeostasis during the nesting (aphagia) season.
5.5.4 FOLLICULAR ATRESIA
The degeneration of ovarian follicles (atresia) is common in most vertebrates and
can occur in follicles at various stages of development (Guraya, 1989). In this
chapter, we will limit our discussion to atresia of mature preovulatory follicles.
Atresia of these follicles has been reported in all species of sea turtle (Owens, 1980;
Limpus, 1985; Rostal et al., 1996; 1997; Hamann et al., 2002b; Limpus, unpublished
data). Our understanding of the mechanisms and functional role(s) of atresia is
limited. However, the perceived benefit for the female of selecting a follicle for
atresia is that the lipid can be resorbed, mobilized, and used for other metabolic
needs (Kuchling and Bradshaw, 1993). It would be interesting to investigate whether
females have the ability to compensate for decreased somatic energy by selecting
follicles for atresia, or whether some females, especially those that migrate longer
than average distances, have higher rates of follicular atresia to compensate for
increased migratory costs.
5.5.5 COURTSHIP AND CLUTCH PREPARATION
Observations of courtship activity suggest that courtship generally occurs in the
vicinity of the nesting beach (Booth and Peters, 1972; Owens and Morris, 1985;
Limpus, 1993). Females may mate with several males, and average cumulative
mating times are on the order of 25 h (Wood and Wood, 1980; Limpus, 1993;
FitzSimmons, 1997). It is not yet possible from behavioral observations to distinguish successful from unsuccessful mating, or to determine whether insemination
occurred (Wood and Wood, 1980; Limpus, 1993; FitzSimmons, 1997). Although
spermatozoa have been found adjacent to the vagina and the junction between the
magnum and aglandular zone, specialized sperm storage areas have not been identified in sea turtles (Solomon and Baird, 1979).
Although the courtship period appears to be well constrained temporally for the
individual, arrival of turtles at the nesting beach is scattered over several months
(Limpus, 1985; Dobbs et al., 1999; Godley et al., 2001; Limpus et al., 2001a). In
captive C. mydas the average period from mating to nesting is 34.7 days (Wood and
Wood, 1980). This period comprises two phases: the first period from insemination
to ovulation, the second period from ovulation to oviposition. The latter has been
extensively studied (Miller, 1997), but the former has never been investigated.
The control of ovulation and egg development has been linked to various endocrine pathways (see Owens 1980; 1997; Owens and Morris, 1985). Briefly, ovulation
occurs approximately 36 h postoviposition and coincides with peaks in gonadotropins (luteinizing hormone and follicle-stimulating hormone) and a decrease in
plasma testosterone (Licht et al., 1982; Wibbels et al., 1990). Albumin production
and deposition coincide with a peak in progesterone, and shell formation is generally
1123 book.book Page 146 Thursday, November 14, 2002 11:50 AM