Question

Some species of animals, like some water fleas (Daphnia pulex), are able to alternate parthenogenesis with sexual reproduction. In natural populations, parthenogenesis is the common mode of reproduction, and parthenogenetic offspring are all female. However, in response to certain environmental conditions, male offspring are also produced parthenogenetically, and sexual reproduction occurs. Speculate on what types of conditions might trigger this form of reproduction, and why this might be “the best of both worlds”.

Answer 1

The parthenogenesis is defined as the phenomena in which the embryo is directly developed from the egg without the process of fertlilsation. That's why in this case, mother produces egg by the process of mitosis. That's why there is found same genotype of offspring as found in the female. It will respond to the same way as mother respond to the environment because of same genotype.

Now some water fleas are able to do sexual reproduction. Hence there is found male also. Now the male produces male gametes where as female produces female gametes. The fusion of these gametes leads to produce new offspring. In this case there is fusion of two kinds of gametes occurs. That's why there is found chances of variation in the offspring. These variation helps the water flea to accommodate in the changing environment.

The parthenogenesis is suitable for only the constant environment whereas sexual reproduction allows the organism to better fit in the changing environment.