A metadata approach to documenting sex in phylum Rotifera: diapausing embryos, males, and hatchlings from sediments

We present a survey of the literature documenting sexuality in monogonont rotifers, including reports of diapausing embryos (DEs), males, and/or hatchlings from dry sediments. Of 30 families, 27 possess species with documented occurrences of sex. Information on DEs is lacking in 41 genera. Of ~300 species with evidence of sexuality (~20% of ~1500 monogononts), only 172 had direct observations of DEs; in the others, DE production was inferred from observations of males and/or hatchlings. DEs are sufficiently widespread to affirm that their presence is plesiomorphic, however few DE characteristics show a phylogenetic signature. They differ widely in volume (~0.11–100 × 105 µm3) and have a varied surface morphology (smooth to highly structured and ornamented). Some species retain DEs within their bodies; others carry them, deposit them on or attach them to surfaces, or release them free into the water. To better understand the evolutionary forces that influence monogonont sexuality and DE biology, a more comprehensive and uniform reporting scheme is needed. To enhance information dissemination, we propose that new and existing data on sex in monogonont rotifers (DEs, males, and hatchlings from dry sediments) be placed in an Internet-based repository.