Describe various environmental factors that help in sex-determination.

Explanation

The different environmental factors responsible for sex-determination are :
(i) Chemotactic Sex - Determination
It is seen in males of the marine worm Bonellia. These are small, degnerate and live within the reproductive tract of the larger femal. All organs of male worm.s boby are degenerate except those of the reproductive system
Bonellia, the larvae of male and female are genetically and cytologically similar, i.e. it is hermaphrodite. A newly hatched worm if reared from a single cell kept in isolation, it develops into a female. If the larvae are reared with mature females in water, they adhere to the proboscis
Later they transform into males who eventually migrate into the female reproductive tract, where they become parasitic
It has been found that a chemotactic substance secreted by the proboscis of a mature female Bonellia induces the differentiation of larva into males.
(ii) Temperature Dependent Sex-Determination
In some reptiles, the temperature at which the fertilised eggs are incubated prior to hatching plays a major role in determining the sex of the offspring. Surprisingly high temperature during incubation have opposite effect on sex-determination in different species.
In turtles, high incubation temperature (above `30^(@)C` ) of eggs results in the production of female progeny whereas in the lizard and crocodiles, high incubation temperature results in the production of male offspring. At the lower temperature range between `22.5-27^(@)C` , male turtles are produced. This pattern is reversed in lizards and crocodiles .