Discuss the implications of this type of sex determination in the C-fern’s natur

Question

Discuss the implications of this type of sex determination in the C-fern’s natural habitat. What
sort of environmental condition(s) is this system suited to?

            a)what happens to C.ferns in large and small density population, how this advantages in sex ratio? (1 mark)

           b) what do environmental, general nutrient availability push toward, male or hermaphrodites? (1mark)

           c) Draw conclusion for the relationship of population density vs sex (male, hermaphrodites)? (1mark)

Explanation / Answer

Environmental sex determination (ESD) is a mechanism by which sex is decided after conception, depending on the environment, rather than being genetically fixed.

During ESD, selection favours ESD when three conditions are met:

(i) the environment strongly influences lifetime fitness,

(ii) the environment is patchy with females performing better than males in some patches and vice versa, and

(iii) individuals have little control on the patch they land on.

Among the relevant aspects of environment contributing to patchiness are local mate competition, resource availability and sex-specific mortality .

a) Under good growth conditions (low density or high nutrient), gametophytes matured sexually at a relatively large size and turned into females and subsequently into bisexuals.   

Stress (limited nutrient supply, crowding/ high density) affected sexual expression in W. radicans gametophytes in a way compatible with ESD. Under harsh growth conditions, gametophytes matured sexually at a smaller size and turned into males.

gametophyte sexual expression remains consistent with the size-advantage model, because the number of archegonia increased with gametophyte size, but not the number of antheridia.

Stress-induced male expression in gametophytes in a way compatible with ESD.

b) hermaphrodites

size-related patterns of sexual expression were consistent with the size-advantage model because female function benefited more from a larger size than did male function.

c) high density - harsh growth --- >male

low density - high growth --- > hermaphrodites

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