LECTURE NOTES ON Reproduction,development and life cycle in rotifers

Rotifers reproduce by both parthenogenesis and sexual reproduction. In the former.

ova develop without fertilization, where as in the latter ova develop only after fertilization.

Thus, in parthenogenesis, only the female parent is involved, but in sexual reproduction,

male and female parents are involved. Fertilization is intemal . Development is direct and external. Early cleavage is determinate and spiral.  Male rotifers hatch out as sexually mature adults. Hence they remain small-sized through out life. On the other hand, females grow to sexual maturity only after hatching. Life cycle of rotifers is highly interesting in that there is a cyclic occurrence of syngamic and parthenogenetic generations in tune with the cyclic seasonal changes. Generally, there are two kinds of females among rotifers, namely amiotic females and mictic females. Amictic females produce larger eggs which develop only parthenogeneti cally into amictic or mictic females: they cannot develop through fertilization. On the other hand, the eggs of mictic females can develop either by parthenogenesis or by fertilization. If these eggs are not fertilized, they parthenogenetically develop to males. if they are fertilized, they develop to amictic females.

Examples: Brachionus, Polyarthra, Asplanchna,Keratella. Cellotheca.