Experimental assessment of moisture effects on loggerhead sea turtle sex ratios

Nest sand temperature strongly influences development of sea turtle embryos and sex differentiation;
however in nature eggs experience temperature along with other environmental factors. We tested the
hypothesis that moisture effects sea turtle hatchling sex ratios. We studied the relationships among
moisture, temperature, and loggerhead Caretta caretta sex ratios in an experimental study. Eggs were incubated in sterile nest sand in the laboratory under different moisture regimes to test the role of
humidity at a constant incubation temperature. Incubator temperature was set at 29.4 degrees C, a
temperature that is slightly above the temperature that should yield a 1:1 sex ratio. Nest moisture was
maintained by daily DI water treatments and high relative humidity was maintained with the aid of a mist
humidifier throughout incubation. All hatchlings were collected, raised for several months and sexed
laparoscopically to establish sex ratios for each treatment. The experimental treatments tested the
effects of i very high moisture, ii moisture with potential for evaporative cooling, and iii moisture added
at average rain temperatures plus the potential for evaporative cooling. The nests were expected to
produce a moderate female bias if moisture played no role. We found 87-96 males across all
experimental treatments. Our results support our hypothesis. High moisture conditions can produce
shifts in developmental response from that
expected based on temperature alone.