Females first? Past, present and future variability in offspring sex ratio at a temperate sea turtle breeding area

Abstract

The long-term survival of species with temperature-dependant sex determination requires a sufficient range of incubation temperatures to ensure that both males and females are produced. The primary sex ratio of sea turtles is determined by the temperature experienced by eggs during the middle third of incubation. Here, we investigated the variability in the production of male and female offspring by loggerhead sea turtles Caretta caretta at six nesting beaches in the temperate breeding area of Zakynthos, Greece. Hatchling sex ratios were estimated using incubation durations and sand temperatures for 2007-2009, while the empirical relationship between air and sand temperature was used to infer historical (1875-2010) and future (2011-2100) hatchling sex ratios. First, all six beaches produced males; 55% of production was across five beaches, while 45% was focused on one beach (primarily in July). Second, male production varied across the season in different years; there was an initial peak in June, with production (rising, declining or plateauing) later in the season being regulated by August air temperatures. Interestingly, the annual male production rate estimated from the 3-year dataset (23%) was half that estimated from the 135-year reconstruction (50%), with the latter showing broad interannual variation. Finally, modelled predictions of future sex ratios ranged from a conservative 7.6% decline in male production by 2100 versus no production by 2038. This study provides a baseline from which predicted trends in hatchling sex ratio, in parallel to regular field assessments, could be used to provide guidelines for the selection of appropriate nest protection management protocols, to maintain required sex ratios that safeguard the future of this population. bs_bs_banner Animal Conservation. Print ISSN 1367-9430 508 Animal Conservation 15 (2012) 508-518

Forecasting the viability of sea turtle eggs in a warming world

“…This has led to speculation that nesting females could compensate for the effects of climate change by continuing to locate microhabitats that maximize fitness (Mitchell et al ., ; Telemeco et al ., , ). The sandy, sun‐exposed beaches upon which sea turtles nest can experience high temperatures (Tapilatu & Tiwari, ; Katselidis et al ., ), but we do not yet understand whether maternal nest‐site selection could compensate for temperature increases under climate change. Data from other, smaller reptile species that dig shallower nests suggest that morphological constraints on the ability to dig deeper nests could limit potential adaptive responses to climate change, and lead to skewed sex ratios and increased embryonic mortality (Mitchell et al ., ; Katselidis et al ., ; Telemeco et al ., ).…”

Hatching and emergence success in green turtle Chelonia mydas nests in the Galápagos Islands

“…Katselidis et al (2012), studying long-term variation of hatchling sex ratios from loggerhead turtle nests at Zakynthos, Greece, showed that males and females were produced at different times within a season and that some beaches were responsible for male production, while females were produced on other beaches. Understanding the range of male versus female offspring production within a rookery may be critical for specific management actions at each nesting beach.…”

Phenology shifts in leatherback turtles (Dermochelys coriacea) due to changes in sea surface temperature

“…Some authors suggest that turtles start their migration due to a temperature cue and then nest soon after arriving at their nesting grounds (Mazaris et al, 2009), while others suggest that turtles arrive early at the nesting beaches (Eckert and Eckert, 1988;Pike, 2009) in order to mate with males and complete the development of their first clutch of eggs (Schofield et al, 2013). The cues would then be at the nesting grounds, where they would wait to nest when the environmental conditions are optimal (Eckert and Eckert, 1988;Katselidis et al, 2012;Pike, 2009). This is confounded further due to findings that some leatherback populations engage in foraging excursions during their internesting interval (Byrne et al, 2009;Georges et al, 2007), potentially encountering temperature or resource cues not considered before.…”

“…Phenological shifts might also mean that developing nests now face a potentially different set of conditions such as temperature and rainfall, which will determine their sex ratios (Ackerman, 1997;Hays et al, 2010;Katselidis et al, 2012) and hatching success (Miller, 1997;Saba et al, 2012). In addition, since hatchlings disperse after emergence mostly due to passive drift on oceanic currents, which change at different times of the year, phenological shifts may alter their spatial fate and possible survival (Blanco, 2010;Gaspar et al, 2012;Shillinger et al, 2012).…”