Sex ratio estimations of loggerhead marine turtle hatchlings by incubation duration and nest temperature at Sirte beaches (Libya)

Abstract

SUMMARY: Hatchling sex ratios in loggerhead marine turtles (Caretta caretta) were estimated on the beaches near Sirte (Libya), using two methods: incubation duration and nest mean temperature during the middle third of the incubation period. Electronic temperature/humidity loggers were deployed at a total of 13 selected nests at Al-Ghbeba, Al-Thalateen, west of Al-Thalateen, Shash and Al-Arbaeen. The incubation period ranged from 47 to 58 days and average temperature ranged from 29°C to 31.8°C. The maximum temperature during this period increased to between 0.6°C and 3.5°C, while the mean temperature also increased during the middle third of the incubation period compared with the first third and continued to increase during the last third. As expected, this study showed that the temperature in the nest decreased with increasing depth of the nest. The results showed a female-dominated sex ratio at 85.4% on the basis of incubation duration and 70.4% on the basis of mean temperature. These findings support the reported highly female-skewed sex ratios in the Mediterranean and elsewhere.Keywords: loggerhead turtle, hatchlings, sex ratio, incubation duration, nest temperature, Libya. RESUMEN: Estimación de la proporción de sexos de crías de tortugas marinas caguama, mediante la duración de incubación y temperatura de los nidos en las playas de Sirte (Libia). -Se ha efectuado una estimación de proporción de sexos en las crías de tortugas marinas caguama (Caretta caretta) en las playas cerca de Sirte (Libia) utilizando dos métodos: la duración de la incubación y la temperatura media del nido durante el segundo tercio del período de incubación. Se registraron electrónicamente los valores de temperatura/humedad en un total de 13 nidos seleccionados en Al-Ghbeba, Al-Thalateen, zona oeste de Al-Thalateen, Shash y Al-Arbaeen. El período de incubación varió desde 47 hasta 58 días y la temperatura media osciló desde 29 hasta 31.8°C. La temperatura máxima durante este período aumentó entre 0,6 y 3.5°C, mientras que la temperatura media también aumentó durante el segundo tercio del período de incubación en comparación con el primer tercio y siguió aumentando durante el último tercio. Como era de esperar, este estudio mostró que la temperatura en el nido disminuyó con el aumento de la profundidad de la jerarquía. Los resultados basados en la duración de la incubación mostraron una sex-ratio en favor de las hembras del 85.4%, mientras que este valor fue del 70.4% si los resultados se basaban en la temperatura media. Estos datos concuerdan con los estudios efectuados en el Mediterráneo y en otras zonas, en los que se aprecia una sex-ratio altamente sesgada en favor de las hembras.Palabras clave: tortuga boba, crías, proporción de sexos, duración de la incubación, temperatura del nido, Libia. Scientia Marina 77(4)

Loggerhead sea turtle hatchling sex ratio differences between two nesting beaches in Turkey

“…In several studies, it was reported that majority of the hatchlings were female due to high nest temperatures. Sex ratios skewed as much as 90% towards females have been found or inferred for loggerhead turtle hatchlings in the USA (Mrosovsky & Provancha 1992;Hanson et al 1998), in Brazil (Marcovaldi et al 1997;Mrosovsky et al 1999) and in the Mediterranean (Kaska et al 1998;Godley et al 2001;Mrosovsky et al 2002;€ Oz et al 2004;Kaska et al 2006;Uçar et al 2012;Jribi et al 2013). Although the majority of the nesting beaches in the world produce highly female-dominated hatchling sex ratios, there are some key sites having conditions that are biased toward producing male hatchlings ) and some small beaches having nearly 1:1 hatchling sex ratios (Mrosovsky et al 1984;Marcovaldi et al 1997;Foley et al 2000;Hawkes et al 2007).…”

Incubation temperatures, sex ratio and hatching success of leatherback turtles (Dermochelys coriacea) in two protected hatcheries on the central Mexican coast of the Eastern Tropical Pacific Ocean

“…This study showed that mean temperature in the nest chamber increases 3.2 ºC with respect to the reference sites, and heating was observed in all monitored nests. Yntema and Mrosovsky (1980) stated that a change of 1-2 ºC can make a considerable difference in the sex ratios of hatchlings, and some studies have documented sufficient metabolic heating in nests during TSP to significantly alter the hatchling sex ratios (Broderick et al, 2001;Kaska et al, 2006;Jribi et al, 2013;Tapilatu and Ballamu, 2015;Özdilek et al, 2016). This is because sexual differentiation in sea turtles is strongly influenced by ambient incubation temperature (Standora and Spotila, 1985;Mrosovsky, 1994); more specifically, the embryo is exposed to a continuous temperature during the middle trimester of incubation, which determines the eventual gonadal differentiation and sex of the hatchling (Wibbels, 2003).…”

Sex Ratio Estimations of Loggerhead Sea Turtle Hatchlings at Kuriat Islands, Tunisia: Can Minor Nesting Sites Contribute to Compensate Globally Female-Biased Sex Ratio?

“…Therefore, it is less accurate, as it is indirect and based not only on the middle third of the incubation duration when sex is thought to be determined. The other thirds may confound results in case of within clutch heterogeneous temperature regimes [ 19 ].…”

“…The sex ratio curve (% of females) as a function of incubation duration [ 29 ] was also adapted to the field by adding 4 days, which corresponds to the interval between hatching and the emergence of hatchlings at the sand surface [ 36 ]. The equations of the two curves used (after corrections) calculated by Jribi et al [ 19 ] were used and the exact values of sex ratios were derived.…”

“…Studies of hatchlings sex-ratio in the Mediterranean concerned mainly major nesting sites such as Zakynthos [ 3 ] and Kyparissia Bay [ 29 , 30 ] in Greece, Alagadi in Cyprus [ 16 ], Fethiye [ 31 ], Patara beaches [ 17 ] in Turkey, Sirte in Libya [ 19 ] but few studies have been conducted for minor nesting sites such as Sicily in Italy [ 32 ]. The protection and the study of these minor nesting sites are informative because they can give an appreciable contribution to sea turtle biology, both in number and in genetic diversity [ 24 ].…”