140
The Biology of Sea Turtles, Vol. II
Histological analysis of sperm samples collected via testes biopsy suggests that
the spermatogenic process lasts approximately 9 months in C. caretta (Wibbels et al.,
1990), with primary and secondary spermatocytes present for 6 months and spermatids becoming abundant 2–3 months prior to maximal spermiogenesis (Wibbels
et al ., 1990; Rostal et al. , 1998). Visual differentiation between the epididymis of
spermatogenic and nonspermatogenic adult males is possible from late spermatogenic stage 2 (Wibbels et al ., 1990) through early stage 8 (Figure 5.2; Limpus, unpublished data). The relative mass of gonads (gonadal somatic index [GSI]) collected
from male C. mydas indicates that during active spermatogenesis the GSI increases
from 1.33 to 3.08 g/kg (Licht et al. , 1985). Among temperate zone reptiles the
spermatogenic cycle can occur either pre- or postnuptial. Although detailed descriptions exist only for C. caretta (Wibbels et al ., 1990) and L. kempii (Rostal et al .,
1998), there is a general consensus that spermatogenesis in sea turtles occurs prenuptially, and is completed prior to the courtship period (Licht et al., 1985; Wibbels
et al., 1990; Engstrom, 1994; Rostal et al. , 1998). Because the testes become flaccid
during this quiescent period, it is most likely that sperm in the epididymis is viable
for only a few months. In annual breeding males it is therefore likely that only a
short (2–3 month) quiescent period exists between maximal spermiogenesis during
the courtship period and the beginning of the next spermatogenic cycle.
Recent correlative evidence suggests that breeding rates of male C. mydas in
southern Queensland fluctuate synchronously with the numbers of females breeding annually (Limpus and Nicholls, 1988; 2000). Moreover, they appear to
respond to ENSO on a similar time scale to that of females (Limpus and Nicholls,
2000). Males require lower levels of fat deposition for breeding than females
(Kwan, 1994), and it appears that a high proportion of males in a particular
foraging area prepare to breed each year. Indeed, annual baseline breeding rates
of males from Shoalwater Bay in southern Queensland is approximately 15–20%
(FitzSimmons, 1997). Furthermore, Licht et al. (1985) report that most “if not
all” males in their captive C. mydas population showed annual signs of spermatogenesis and elevated testosterone. Although some males migrate considerable
distances to courtship areas, a large proportion of males in the southern Great
Barrier Reef (GBR) population appear to be resident in the vicinity of the
courtship area year round (Limpus, 1993; FitzSimmons, 1997). Some males from
this population have been followed for more than 10 years, and among them are
several males that have been recorded in multiple breeding seasons, including
some annual breeders (FitzSimmons, 1997). It is, however, unknown whether the
resident group of males is breeding more frequently than males migrating into
the area, or whether they have significantly lengthened breeding periods. Furthermore, data pertaining to breeding rates in other C. mydas populations and
other species are lacking and present one of the challenges for future research.
It would be interesting to know whether breeding rates differ among males from
different foraging areas for the same genetic stock and between stocks within the
same species. Similarly, the issue can be investigated from the perspective of
whether smaller species (e.g., Lepidochelys spp.) breed more frequently than
larger species (e.g., C. mydas or Dermochelys coriacea ) or whether carnivores
recover into the next breeding season sooner than herbivores.
1123 book.book Page 140 Thursday, November 14, 2002 11:50 AM
The Biology of Sea Turtles, Vol. II
Histological analysis of sperm samples collected via testes biopsy suggests that
the spermatogenic process lasts approximately 9 months in C. caretta (Wibbels et al.,
1990), with primary and secondary spermatocytes present for 6 months and spermatids becoming abundant 2–3 months prior to maximal spermiogenesis (Wibbels
et al ., 1990; Rostal et al. , 1998). Visual differentiation between the epididymis of
spermatogenic and nonspermatogenic adult males is possible from late spermatogenic stage 2 (Wibbels et al ., 1990) through early stage 8 (Figure 5.2; Limpus, unpublished data). The relative mass of gonads (gonadal somatic index [GSI]) collected
from male C. mydas indicates that during active spermatogenesis the GSI increases
from 1.33 to 3.08 g/kg (Licht et al. , 1985). Among temperate zone reptiles the
spermatogenic cycle can occur either pre- or postnuptial. Although detailed descriptions exist only for C. caretta (Wibbels et al ., 1990) and L. kempii (Rostal et al .,
1998), there is a general consensus that spermatogenesis in sea turtles occurs prenuptially, and is completed prior to the courtship period (Licht et al., 1985; Wibbels
et al., 1990; Engstrom, 1994; Rostal et al. , 1998). Because the testes become flaccid
during this quiescent period, it is most likely that sperm in the epididymis is viable
for only a few months. In annual breeding males it is therefore likely that only a
short (2–3 month) quiescent period exists between maximal spermiogenesis during
the courtship period and the beginning of the next spermatogenic cycle.
Recent correlative evidence suggests that breeding rates of male C. mydas in
southern Queensland fluctuate synchronously with the numbers of females breeding annually (Limpus and Nicholls, 1988; 2000). Moreover, they appear to
respond to ENSO on a similar time scale to that of females (Limpus and Nicholls,
2000). Males require lower levels of fat deposition for breeding than females
(Kwan, 1994), and it appears that a high proportion of males in a particular
foraging area prepare to breed each year. Indeed, annual baseline breeding rates
of males from Shoalwater Bay in southern Queensland is approximately 15–20%
(FitzSimmons, 1997). Furthermore, Licht et al. (1985) report that most “if not
all” males in their captive C. mydas population showed annual signs of spermatogenesis and elevated testosterone. Although some males migrate considerable
distances to courtship areas, a large proportion of males in the southern Great
Barrier Reef (GBR) population appear to be resident in the vicinity of the
courtship area year round (Limpus, 1993; FitzSimmons, 1997). Some males from
this population have been followed for more than 10 years, and among them are
several males that have been recorded in multiple breeding seasons, including
some annual breeders (FitzSimmons, 1997). It is, however, unknown whether the
resident group of males is breeding more frequently than males migrating into
the area, or whether they have significantly lengthened breeding periods. Furthermore, data pertaining to breeding rates in other C. mydas populations and
other species are lacking and present one of the challenges for future research.
It would be interesting to know whether breeding rates differ among males from
different foraging areas for the same genetic stock and between stocks within the
same species. Similarly, the issue can be investigated from the perspective of
whether smaller species (e.g., Lepidochelys spp.) breed more frequently than
larger species (e.g., C. mydas or Dermochelys coriacea ) or whether carnivores
recover into the next breeding season sooner than herbivores.
1123 book.book Page 140 Thursday, November 14, 2002 11:50 AM