Effect of Environmental Factors
some lower organisms, though the genetic determiners of the sexes are present, the ambient environment plays a decisive role in the development of a particular sex type. And it .appears that sex determination is non-genetic. The males and females have similar genotype, but stimuli from environmental factors initiate development towards one sex.or the other. In Equisetum (horse tail) plant, for example, female characteristics develop when the plant is raised under favourable growth conditions, while in pooer or unfavourable conditions males are formed.
Another salient example is of the marine worm Bonellia. These worms are very small. The males remain in a highly reduced form in the reproductive tract of female. The female is many times larger than the male (compare their size). Any young worm reared from a single isolated egg becomes a female. If the newly hatched worms are released into water containing mature females, some young worms are attracted to females and become attached to the female proboscis. These are then transformed into males and these migrate to the female reproductive tract, where they become parasitic. Experimental studies have shown that even the extracts made from the female proboscis influence young worms towards maleness.
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. High temperatures during incubation have opposite effects on Sex determination in. different species. In the lizard Agama agaxna, some crocodiles and alligators, incubation at high temperature resuIts in all male offspring while at low temperature it results in females. On the other hand, in the turtle, Chrysema picta, high egg incubation temperatures result in the production of mostly female progeny.
An interesting example is of the slipper shell Crepidula, where individuals tend to live stacked up on one another. Young Crepidula are always male. However, as an individual ages, the male reproductive system degenerates. The reproductive system can then re-form as a male or become female, depending on the sexes of the othcr organisms in the cluster. If thc organism is attached to a female, the reproductive system will redevelop as male. Isolation or the presence of a large number of males wilI induce a male to become a female. Once a female, the individual will no longer change.
These examples clearly illustrate the diversity of sex determintion mechanisms that exist in nature. Although the segregation on specific sex-determining genes and chromosomosis responsible for sex phenokype, but in most species such as Bonellia, Chrysema picta and Agama agama, some specific factor in the environment triggers the expression of either the genes producing a male pheliotype or the genes producing a female phenotype. This knowledge has a great potential use in agriculture and conservation method.