Bed and Breakfast: the parasitic life of Proales werneckii (Ploimida: Proalidae) within the alga Vaucheria (Xanthophyceae: Vaucheriales)

Abstract

The unusual parasitic association between Proales werneckii (Ehrenberg, 1834) (Ploimida: Proalidae) and the psychrophilic, coenocytic, filamentous alga, Vaucheria De Candolle, 1801 (Xanthophyceae: Vaucheriales), is documented using light and electron microscopy. A young female rotifer colonizes a Vaucheria filament (ca. 80 µm × 10 cm) by gaining entrance to the cell at a growing region where the wall has not yet matured. After achieving access to the cell, it disrupts development of either a gametophore or an apical tip by inducing cell hypertrophy and formation of an excrescent gall (ca. 80–120 × 140–1500 µm). Remaining within the vacuole of the gall for the rest of her life, the female deposits her eggs after feeding on the rich food supply furnished by the alga’s organelles which continue to translocate within the cytoplasm. This abundant nourishment provides the adult rotifer with energy sufficient to permit an enormous reproductive potential (e.g. galls with >80 subitaneous eggs have been seen). Upon hatching, some offspring emigrate to other immature gametophores or growing tips within the same filament, while others may leave to colonize new filaments. Here, we present the life history of this parasitic relationship, highlighting previously unknown aspects of the association as well as noting differences among the accounts of previous authors. To our knowledge, this is the first description of this parasitic relationship to include electron photomicrographs.