Reproductive Cycles of Males and Females
153
zones (Houghton et al., 1996), climatic conditions that may lead to the onset of
vitellogenesis or migration may not lead to an adequate arrival date at the nesting
beach (or both), or the optimum time to arrive at the nesting beach may vary over
time (Both and Visser, 2001). At nesting beaches, increased temperatures may affect
embryo development, and could lead to a significant shift toward female-producing
temperatures (Davenport, 1997). Increased sea levels could substantially alter available nesting environments (Daniels et al., 1993) and factors controlling incubation,
such as moisture, salinity, and gas exchange (see Ackerman, 1997).
It is probable that increased contaminant levels at both nesting beaches and
foraging areas could affect physiological systems. For example, altered sex ratios
and decreased fertility have been reported for some alligator populations that are
exposed to a variety of xenobiotics (see Crain and Guillette, 1998). Although no
direct cause has been identified, the reported incidence of fibropapilloma virus
among sea turtles is highest in habitats in close proximity to large human population
centers (see Davidson, 2001). Data from southern Queensland suggest that outbreaks
of the toxic cyanobacteria Lyngbya majuscula are increasing in frequency and
severity, and have the potential to alter sea grass quality and quantity, and thus
potentially affect sea turtle distribution, growth, and breeding rates (Dennison et al.,
1999; Osborne et al., 2001).
The metaphor of the environmental canary has been used when describing the
decline of nesting D. coriacea populations in the eastern Pacific (Reina et al., 2000),
and can be expanded to include what this decline insinuates about the quality or
rate of change to conditions in foraging, migratory areas, and nesting beaches. Other
early warning systems of population change may well be manifest in alterations to
sex ratios of young recruits, growth rates, breeding rates, or a changing demographic
within foraging areas. Thus, continued collection of baseline and experimental data
across species and populations dealing with reproductive cycles, physiological control systems, and pertinent ecological parameters is of paramount importance. Otherwise, in times of rapidly changing environments, we will not have the necessary
information to assess possible and probable impacts on sea turtle populations and
apply early and appropriate management practices.
ACKNOWLEDGMENTS
The authors would like to thank Chloe Schäuble, Karen Arthur, and Tim Jessop for
helpful comments on the manuscript.
REFERENCES
Ackerman, R.A., The nest environment and the embryonic development of sea turtles, in The
Biology of Sea Turtles, Lutz, P.L. and Musick, J.A., Eds., CRC Publishing, Boca
Raton, FL, 83–107, 1997.
Ahima, R.S. and Flier, J.S., Adipose tissue as an endocrine organ, Trends Endocrinol. Metab.,
11, 327, 2000.
1123 book.book Page 153 Thursday, November 14, 2002 11:50 AM
153
zones (Houghton et al., 1996), climatic conditions that may lead to the onset of
vitellogenesis or migration may not lead to an adequate arrival date at the nesting
beach (or both), or the optimum time to arrive at the nesting beach may vary over
time (Both and Visser, 2001). At nesting beaches, increased temperatures may affect
embryo development, and could lead to a significant shift toward female-producing
temperatures (Davenport, 1997). Increased sea levels could substantially alter available nesting environments (Daniels et al., 1993) and factors controlling incubation,
such as moisture, salinity, and gas exchange (see Ackerman, 1997).
It is probable that increased contaminant levels at both nesting beaches and
foraging areas could affect physiological systems. For example, altered sex ratios
and decreased fertility have been reported for some alligator populations that are
exposed to a variety of xenobiotics (see Crain and Guillette, 1998). Although no
direct cause has been identified, the reported incidence of fibropapilloma virus
among sea turtles is highest in habitats in close proximity to large human population
centers (see Davidson, 2001). Data from southern Queensland suggest that outbreaks
of the toxic cyanobacteria Lyngbya majuscula are increasing in frequency and
severity, and have the potential to alter sea grass quality and quantity, and thus
potentially affect sea turtle distribution, growth, and breeding rates (Dennison et al.,
1999; Osborne et al., 2001).
The metaphor of the environmental canary has been used when describing the
decline of nesting D. coriacea populations in the eastern Pacific (Reina et al., 2000),
and can be expanded to include what this decline insinuates about the quality or
rate of change to conditions in foraging, migratory areas, and nesting beaches. Other
early warning systems of population change may well be manifest in alterations to
sex ratios of young recruits, growth rates, breeding rates, or a changing demographic
within foraging areas. Thus, continued collection of baseline and experimental data
across species and populations dealing with reproductive cycles, physiological control systems, and pertinent ecological parameters is of paramount importance. Otherwise, in times of rapidly changing environments, we will not have the necessary
information to assess possible and probable impacts on sea turtle populations and
apply early and appropriate management practices.
ACKNOWLEDGMENTS
The authors would like to thank Chloe Schäuble, Karen Arthur, and Tim Jessop for
helpful comments on the manuscript.
REFERENCES
Ackerman, R.A., The nest environment and the embryonic development of sea turtles, in The
Biology of Sea Turtles, Lutz, P.L. and Musick, J.A., Eds., CRC Publishing, Boca
Raton, FL, 83–107, 1997.
Ahima, R.S. and Flier, J.S., Adipose tissue as an endocrine organ, Trends Endocrinol. Metab.,
11, 327, 2000.
1123 book.book Page 153 Thursday, November 14, 2002 11:50 AM