Types
Within the mechanism, two distinct patterns have been discovered and named Pattern I and Pattern II, with Pattern I further divided into IA and IB. Pattern IA has a single transition zone, where eggs predominantly hatch males if incubated below this temperature zone, and predominantly hatch females if incubated above it. Pattern IB also has a single transition zone, but females are produced below it and males above it. Pattern II has two transition zones, with males dominating at intermediate temperatures and females dominating at both extremes. Very near or at the pivotal temperature of sex determination, mixed sex ratios and, more rarely, intersex individuals are produced.
In turtles with TSD, males are generally produced at lower incubation temperatures than females (TSD IA), with this change occurring over a range of temperatures as little as 1-2 °C. At cooler temperatures ranging between 22.5 and 27 degrees Celsius mostly male turtles arise, and at warmer temperatures around 30 degrees Celsius only female turtles arise. In lizards and crocodilians, this pattern is reversed (TSD IB).
It has been proposed that essentially all modes of TSD are actually type II and those that deviate from the expected female-male-female pattern are simply never exposed to extreme temperature ranges on either end.
Read more about this topic: Temperature-dependent Sex Determination
Famous quotes containing the word types:
“Our major universities are now stuck with an army of pedestrian, toadying careerists, Fifties types who wave around Sixties banners to conceal their record of ruthless, beaverlike tunneling to the top.”
—Camille Paglia (b. 1947)
“The rank and file have let their servants become their masters and dictators.... Provision should be made in all union constitutions for the recall of leaders. Big salaries should not be paid. Career hunters should be driven out, as well as leaders who use labor for political ends. These types are menaces to the advancement of labor.”
—Mother Jones (1830–1930)
“The American man is a very simple and cheap mechanism. The American woman I find a complicated and expensive one. Contrasts of feminine types are possible. I am not absolutely sure that there is more than one American man.”
—Henry Brooks Adams (1838–1918)