It’s that time of year again, when female Snapping Turtles are leaving ponds, digging holes in sandy soil and depositing up to 80 eggs (20-30 is typical) before covering them up and returning to their ponds. While the sex of most snakes and lizards is determined by sex chromosomes at the time of fertilization, the sex of most turtles is determined by the environment after fertilization. In these reptiles, the temperature of the eggs during a certain period of development is the deciding factor in determining sex, and small changes in temperature can cause dramatic changes in the sex ratio.
Often, eggs incubated at low temperatures (72°F – 80°F) produce one sex, whereas eggs incubated at higher temperatures (86°F and above) produce the other. There is only a small range of temperatures that permits both males and females to hatch from the same brood of eggs. The eggs of the Snapping Turtle become female at either cool (72°F or lower) or hot (82°F or above) temperatures. Between these extremes, males predominate. (Developmental Biology by S. Gilbert)
If the cool temperatures we’ve experienced thus far this spring continue, there could be a lot of female Snapping Turtles climbing up out of the earth come September. (Thanks to Clyde Jenne and Jeffrey Hamelman for photo opportunity)
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