Reproductive Cycles of Males and Females
147
completed 9–10 days after ovulation (Owens, 1980; Owens and Morris, 1985; Miller,
1985; Solomon and Baird, 1979). Development of the embryo advances to middle
gastrulation, when it is arrested until shortly after oviposition (Miller, 1985).
5.5.6 OVIPOSITION
Although for some species frequent daytime nesting has been observed (e.g., L.
kempii, E. imbricata, and N. depressus), for most sea turtle populations nesting
usually occurs nocturnally (see Ehrhart, 1982; Miller, 1997). Although hormones
such as prostaglandin, arginine vasotocin (AVT), and neurophysin have all been
related to particular stages of oviposition (Figler et al., 1989; Guillette et al., 1991),
little is known about the concert of physiological and mechanical events that occur
to initiate a nesting emergence.
5.5.7 REPRODUCTIVE OUTPUT
Female C. mydas from the southern GBR genetic stock have a mean life expectancy
of around 55–60 years, including a reproductive period of around 19 years (Chaloupka and Limpus, in press). Tag recapture data of nesting females from this
population indicated that the average remigration interval is greater than 5 years (5.8
and 5.9 years; Limpus et al., 1994c and Hamann, 2002, respectively), and females
on average lay five clutches of 115 eggs (Bustard, 1972; Limpus et al., 1984b;
Hamann, 2002). To summarize, they have an estimated lifetime reproductive output
of approximately 2000 eggs. Even though these turtles have a high annual survivorship (Chaloupka and Limpus, in press), because they take decades to reach maturity,
there will be a low probability of an individual’s surviving to adulthood. Similarly,
given the long interval between breeding seasons for adult females, a large proportion
of individuals will not survive to breed a second season because of natural attrition
of the breeding cohorts. Therefore, maximizing seasonal reproductive output (in
terms of eggs laid) is an extremely important facet of sea turtle life history.
5.5.7.1 Ecological Variation in Reproductive Output
Differences in reproductive output may be dependent on numerous endogenous
(e.g., genetics, age, body size, health and condition, and reproductive history) and
exogenous (e.g., migratory distance, latitude of the foraging area, and foraging area
quality) factors. Female turtles migrate to rookeries from foraging areas some tens
to thousands of kilometers distant, and the foraging areas supporting a nesting
population may cover a broad geographical range (Carr, 1965; Meylan, 1982; 1999;
Mortimer and Carr, 1987; Limpus et al., 1992; Bowen and Karl, 1997; Miller et al.,
1998; Mortimer and Balazs, 2000; Horricks et al., 2001). Furthermore, proximal
cues (such as temperature and photoperiod) will undoubtedly differ in strength,
intensity, and/or timing between foraging areas (especially along a latitudinal gradient). Consequently, some interesting questions arise. Are females from various
locations responding to the same cues? Is there some plasticity in the way females
respond to proximal cues? Are females that reside in optimal (both quantity and
quality) foraging areas breeding more frequently and/or having higher reproductive
1123 book.book Page 147 Thursday, November 14, 2002 11:50 AM
147
completed 9–10 days after ovulation (Owens, 1980; Owens and Morris, 1985; Miller,
1985; Solomon and Baird, 1979). Development of the embryo advances to middle
gastrulation, when it is arrested until shortly after oviposition (Miller, 1985).
5.5.6 OVIPOSITION
Although for some species frequent daytime nesting has been observed (e.g., L.
kempii, E. imbricata, and N. depressus), for most sea turtle populations nesting
usually occurs nocturnally (see Ehrhart, 1982; Miller, 1997). Although hormones
such as prostaglandin, arginine vasotocin (AVT), and neurophysin have all been
related to particular stages of oviposition (Figler et al., 1989; Guillette et al., 1991),
little is known about the concert of physiological and mechanical events that occur
to initiate a nesting emergence.
5.5.7 REPRODUCTIVE OUTPUT
Female C. mydas from the southern GBR genetic stock have a mean life expectancy
of around 55–60 years, including a reproductive period of around 19 years (Chaloupka and Limpus, in press). Tag recapture data of nesting females from this
population indicated that the average remigration interval is greater than 5 years (5.8
and 5.9 years; Limpus et al., 1994c and Hamann, 2002, respectively), and females
on average lay five clutches of 115 eggs (Bustard, 1972; Limpus et al., 1984b;
Hamann, 2002). To summarize, they have an estimated lifetime reproductive output
of approximately 2000 eggs. Even though these turtles have a high annual survivorship (Chaloupka and Limpus, in press), because they take decades to reach maturity,
there will be a low probability of an individual’s surviving to adulthood. Similarly,
given the long interval between breeding seasons for adult females, a large proportion
of individuals will not survive to breed a second season because of natural attrition
of the breeding cohorts. Therefore, maximizing seasonal reproductive output (in
terms of eggs laid) is an extremely important facet of sea turtle life history.
5.5.7.1 Ecological Variation in Reproductive Output
Differences in reproductive output may be dependent on numerous endogenous
(e.g., genetics, age, body size, health and condition, and reproductive history) and
exogenous (e.g., migratory distance, latitude of the foraging area, and foraging area
quality) factors. Female turtles migrate to rookeries from foraging areas some tens
to thousands of kilometers distant, and the foraging areas supporting a nesting
population may cover a broad geographical range (Carr, 1965; Meylan, 1982; 1999;
Mortimer and Carr, 1987; Limpus et al., 1992; Bowen and Karl, 1997; Miller et al.,
1998; Mortimer and Balazs, 2000; Horricks et al., 2001). Furthermore, proximal
cues (such as temperature and photoperiod) will undoubtedly differ in strength,
intensity, and/or timing between foraging areas (especially along a latitudinal gradient). Consequently, some interesting questions arise. Are females from various
locations responding to the same cues? Is there some plasticity in the way females
respond to proximal cues? Are females that reside in optimal (both quantity and
quality) foraging areas breeding more frequently and/or having higher reproductive
1123 book.book Page 147 Thursday, November 14, 2002 11:50 AM