Environmental Determination of Sex

In Bonellia, a marine worm, the swimming larva has no sex if it settles down alone, it develops into a large ( $2.5\, cm$ ) female. If it lands on or near an existing female, a chemical from female causes the larva to develop into a tiny ( $1.3\, cm$ ) male.

In turtles, alligators, a temperature below $28^{\circ} C$ produces more males, above $33^{\circ} C$ produces more females and between $28^{\circ} C -33^{\circ} C$ produces males and females in equal proportion