JAIPUR: A recent study of the gender ratio of sea turtle hatchlings from Australia's Northern Great Barrier Reeffound that 99 percent of hatchlings are female, clearly depicting that male sea turtlesare disappearing. Earlier, scientists found that hatchlings in Palm Beach County of Florida too were nearly all female.
A report of the study on the website 'Science Daily' explained that sex in sea turtle hatchlings is determined by warmth and moisture in the nest's environment. Unlike humans, turtles have no sex chromosomes, and hatchlings emerge from the eggs - male or female depending on the environment. The study was published in journal Zoology by researchers at Florida Atlantic University, US.
"It is not just temperature that affects embryogenesis and the phenotype of the resulting hatchlings. Moisture changes the microclimate experienced by the eggs inside the nest and can significantly affect their development. Wetter substrates tend to produce more males and drier substrates tend to produce more females," Science Daily reported.
This study is the first to show how moisture affects the sex ratios of turtle embryos. Researchers used a male-specific, transcriptional molecular marker Sox9, a marker of testis development in turtles. "The researchers found that the coolest and the wettest substrates produce 100 percent males compared to 42 percent males from the warmest and driest treatment. They also found that embryonic growth appears to be more sensitive to temperature at earlier stages of development and to moisture at later stages," the website report said.
Jeanette Wyneken, professor of biological studies at FAU and author of the report, explained that turtle embryos grow inside the nest during incubation, developing from a few cells to a fully formed, independent organism. "For proper development, embryos require an appropriate range of temperature, moisture, salinity, and respiratory gases."
Researchers found that embryos developed slowly in cooler and wetter sand substrates, while water uptake by eggs was significantly greater on wetter substrates.
Science Daily explained that researchers incubated eggs from the Trachemys scripta elegans, a semi-aquatic turtle, under different temperature and moisture regimes to study the effect of the temperature and moisture on developmental rate, egg mass, embryo mass and length, and sex ratio.
"They monitored embryonic development until stage 22 when their sex is determined. Turtle embryonic development is divided into 27 stages. The pivotal temperature is the constant temperature (29 degrees Celsius or 84.2 degrees Fahrenheit) at which 50:50 sex ratio is expected. Sex ratio was based on expression levels of Sox9 and all data were tested for normality and for homogeneity before statistical analysis," the website explained.
