Breeding periodicity for male sea turtles, operational sex ratios, and implications in the face of climate change

Hays, Graeme C., Fossette, Sabrina, Katselidis, Kostas A., Schofield, Gail and Gravenor, Mike B. 2010, Breeding periodicity for male sea turtles, operational sex ratios, and implications in the face of climate change, Conservation biology, vol. 24, no. 6, pp. 1636-1643, doi: 10.1111/j.1523-1739.2010.01531.x.

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Title Breeding periodicity for male sea turtles, operational sex ratios, and implications in the face of climate change
Author(s) Hays, Graeme C.ORCID iD for Hays, Graeme C.
Fossette, Sabrina
Katselidis, Kostas A.
Schofield, Gail
Gravenor, Mike B.
Journal name Conservation biology
Volume number 24
Issue number 6
Start page 1636
End page 1643
Total pages 8
Publisher Wiley
Place of publication London, England
Publication date 2010-12
ISSN 0888-8892
Keyword(s) Caretta
climate change
GPS tracking
operational sex ratio
population dynamics
Summary Species that have temperature-dependent sex determination (TSD) often produce highly skewed offspring sex ratios contrary to long-standing theoretical predictions. This ecological enigma has provoked concern that climate change may induce the production of single-sex generations and hence lead to population extirpation. All species of sea turtles exhibit TSD, many are already endangered, and most already produce sex ratios skewed to the sex produced at warmer temperatures (females). We tracked male loggerhead turtles (Caretta caretta) from Zakynthos, Greece, throughout the entire interval between successive breeding seasons and identified individuals on their breeding grounds, using photoidentification, to determine breeding periodicity and operational sex ratios. Males returned to breed at least twice as frequently as females. We estimated that the hatchling sex ratio of 70:30 female to male for this rookery will translate into an overall operational sex ratio (OSR) (i.e., ratio of total number of males vs females breeding each year) of close to 50:50 female to male. We followed three male turtles for between 10 and 12 months during which time they all traveled back to the breeding grounds. Flipper tagging revealed the proportion of females returning to nest after intervals of 1, 2, 3, and 4 years were 0.21, 0.38, 0.29, and 0.12, respectively (mean interval 2.3 years). A further nine male turtles were tracked for short periods to determine their departure date from the breeding grounds. These departure dates were combined with a photoidentification data set of 165 individuals identified on in-water transect surveys at the start of the breeding season to develop a statistical model of the population dynamics. This model produced a maximum likelihood estimate that males visit the breeding site 2.6 times more often than females (95%CI 2.1, 3.1), which was consistent with the data from satellite tracking and flipper tagging. Increased frequency of male breeding will help ameliorate female-biased hatchling sex ratios. Combined with the ability of males to fertilize the eggs of many females and for females to store sperm to fertilize many clutches, our results imply that effects of climate change on the viability of sea turtle populations are likely to be less acute than previously suspected.
Language eng
DOI 10.1111/j.1523-1739.2010.01531.x
Field of Research 069999 Biological Sciences not elsewhere classified
Socio Economic Objective 970106 Expanding Knowledge in the Biological Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2010, Wiley
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