Monogonont rotifers are reproducing by facultative parthenogenesis, i.e.most of the times they reproduce asexually, but under certain conditions they reproduce sexually. In consequence there are different types of eggs. The eggs that are produced while reproducing parthenogenetically are diploid (red: 2n) and are either carried by the female, for example Anuraeopsis, Brachionus, deposited near the sheath (for example: Collotheca; Ptygura) or they develop inside the mother until the daughter is born (eg. Asplanchna; Rhinoglena). These eggs are called amictic eggs, because they develop without mixis (fertilization by a haploid sperm cell). Parthenogenetic reproduction enables the population to increase rapidly because there is no need for finding a sexual partner, which is always an advantage if the distance between specimen is large, eg in lakes or ponds. As a consequence the rotifer population can more effectively exploit food resources, for example planktonic algae which start growing with increasing day length / light in spring. |
