Life cycle traits of Philodina roseola Ehrenberg, 1830 (Rotifera, Bdelloidea), a model organism for bioassays

This paper describes experimental results on the life cycle of the rotifer Philodina roseola cultured in the laboratory. Detailed information on life-cycle parameters of a certain species provides a deep understanding and contributes to a better knowledge of the role of the species in the community, besides providing data that are basic to other ecological investigations such as secondary production estimates and knowledge for applications such as its utilization as test-organism in ecotoxicological studies. The average duration of embryonic development of P. roseola was 23.88 h, the age at maturity of primipara was 3.5 days and the maximum lifespan was 23 days. The average size of the rotifer neonate was 198.77 µm, the mean size of primipara was 395.56 µm and for adults 429.96 µm. The average fecundity was 1.22 eggs per female per day and the mean number of eggs produced per female during the entire life was 22.33. The deceleration of somatic growth from the start of the reproductive stage represents a trade-off between growth and reproduction that is often seen in micrometazoans. The life history of P. roseola follows the strategy of other bdelloid species characterized by a rapid pre-reproductive development and canalization of most assimilated energy to reproduction after reaching maturity. The differences observed in total fecundity and longevity between our P. roseola cultures and those from previous studies were probably due to differences of intrinsic adaptation of this species ecotypes to the conditions of their natural environments.

Mutualistic association of rotifer Philodina roseola with the branchiuran fish ectoparasite Argulus bengalensis at its embryonic stage

Several rotifers including Philodina spp. are well known to make commensal and parasitic associations with different animals. The present investigation was carried out to decipher the relationship of Philodina roseola with a piscine ectoparasite Argulus bengalensis in its embryonic stage. Mechanical removal of the symbiont P. roseola from the argulid egg strips resulted in the complete (100%) failure in hatching. Several P. roseola individuals were found to feed on the solidified jelly coat of the eggs enabling the larvae to emerge under both laboratory and field conditions. Under the laboratory condition, the experimental removal of P. roseola did not affect the embryonic development, but it rendered the jelly coat intact; therefore, the larvae were unable to make hatching furrow and subsequently died. The results of our experiments thus prove this service–resource relationship to be a mutualism. Although the association is facultative for P. roseola , it is obligatory for Argulus spp. An act of intervention in this relationship thus offers a promising control of argulosis.