Sex Determination and Sex Ratios in Sea Turtles: From the Lab to the Field
MRRI Auditorium at Fort Johnson
Fort Johnson Marine Science Series Seminar:
Alejandra Garcia, Ph.D.
Centre for Research on Nutrition and
Sex determination and sex ratios in sea turtles: from the lab to the field. Many species of reptiles lack sex chromosomes and display temperature-dependent sex determination (TSD). Generally in sea turtles, lower incubation temperatures (25-28-C) produce males while higher temperatures (30-32-C) produce females, outside of this temperature range embryos may not survive. Temperature affects sex determination during the second third of the incubation period, known as thermo-sensitive period (TSP), which has been defined as the time in which any change in the incubation temperature affects sex ratio in embryos, or the time required to establish an irreversible molecular process which promotes sex differentiation. In the olive ridley (Lepidochelys olivacea), male-promoting temperature (MPT) under controlled conditions occurs at 26-C whereas female-promoting temperature (FPT)
occurs at 33-C. In the field, MPT and FPT have been estimated at 27.03 and 32.86-C respectively. The pivotal temperature (temperature producing equal proportions of males and females) has been calculated for Mexican populations in the field at 29.95-C; however it may vary from one population
to another, or even within the same population.
We are interested in understanding the molecular mechanisms underlying TSD in sea turtles; we work with the olive ridley because is the most abundant species nesting in the Mexican Pacific coast. We have been studying the expression of sex-related genes at MPT and FPT during and after the TSP, also we have developed an RNAi-based method to silence a sex-specific gene (Sox9) in a gonad culture system, representing a novel approach to investigate the roles of this and other important genes involved in sex determination or differentiation in species with TSD. Since sex determination is temperature-dependent, we have also been working in the field calculating sex ratios of embryos and hatchlings during different nesting seasons in order to know the tendency in a time series, taking into account environmental temperature records and climatic events.