Chapter 4-5 Invertebrates Rotifers - Bryophyte Ecology - Michigan ...

4-5-2 Chapter 4-5: Invertebrates: RotifersCHAPTER 4-5INVERTEBRATES: ROTIFERSFigure 1. Two bdelloid rotifers like those that commonly inhabit bryophytes. Photo by Paul Davison.Rotifera – RotifersRotifers, also known as wheel animals, are naturalpartners for organisms like bryophytes that oftenexperience extended periods of drought. Anthony vonLeeuwenhoek discovered in 1702 that rotifers couldtolerate months in a state of desiccation, hence marking theearliest studies on cryptobiosis, or life in a dormant statewithout water (Alpert 2000). In this dry state, they areeasily dispersed along with fragments of the mosses theyinhabit.Not much bigger than some protozoa (up to 2 mm),they form a phylum of their own, the Rotifera, with at least2000 species (Howey 1999). They are multicellular andeven possess a primitive brain, at least in females (Hingley1993).ReproductionRotifers (depending on the taxon) have three types ofindividuals: mictic (mixing) females, amictic females (notreproducing sexually), and males. Bdelloid rotifers (classBdelloidea; Figure 2), known as moss rotifers, are themost common rotifers in mosses (Sayre & Brunson 1971;Ricci et al. 2003b; Gilbert & Mitchell 2006), andapparently all of these taxa are parthenogenetic, i.e., theyhave only females that reproduce asexually, giving rise tomore females (Hingley 1993). However, Danchin et al.(2011) analyzed the genome of one of these, Adineta vaga(Figure 3), and found four genotype modifications thatsuggested rare events of sexual reproduction may haveoccurred.The Monogononta are the second major class ofrotifers, and by far the largest (ca 1500 species) (Wikipedia2012a). Among these are members that have both sexualand asexual reproduction. The short-lived, uncommonmales, however, serve only for reproduction and thus aremuch smaller than females. Some males are so reducedthat they have little more than a bladder and a penis! An