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

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4-5-20 Chapter 4-5: Invertebrates: Rotifersattached, the pegs adhere, using lectin/carbohydratebonding, and the fungus penetrates the rotifer, ultimatelyparasitizing it.Figure 77. Lecophagus longispora infecting four rotifers.Photo by George Barron.Figure 74. Lecophagus longispora, fungus that trapstardigrades and rotifers and may be a threat in mosses. Lowerimage is hypha of fungus with cluster of conidia and adhesivepegs. Inset shows adhesive pegs. Photos by George Barron.Figure 78. Lecophagus longispora infecting a rotifer; hyphawith adhering pegs. Such infections are also known fortardigrades. Photo by George Barron.Figure 75. Lecophagus longispora infecting rotifers andshowing an elongate branch with terminal conidiogenous cellbearing a cluster of developing conidia. (X450). Photo by GeorgeBarron.Figure 76. Lecophagus muscicola that has captured tworotifers and two adhesive pegs. Photo by George Barron.Figure 79. Rotifer with hyphae of Lecophagus muscicolainside. Photo by George Barron.
Chapter 4-5: Invertebrates: Rotifers 4-5-21Figure 80. Conidia (X600) of Lecophagus muscicola.Photo by George Barron.Another fungus dangerous to some bryophyte-dwellingspecies is Zoophagus insidians (Figure 81). Aquaticrotifers attempt to feed on its branch tips, but the adhesivetips bond (possibly lectin/carbohydrate bonding) to therotifer mouth and inside the oral cavity (Barron 2012). Thetip grows there and assimilative hyphae penetrate the bodycavity of the rotifer, releasing digestive enzymes thatultimately digest the rotifer from the inside. This attack onthe rotifer mouth permits this fungal species to selectloricate rotifers (Prowse 1954).Whisler and Travland (1974) refer to the fungus as"wily" because of its sneak attack on the rotifers. When theadhesive peg of the fungus contacts the rotifer (Figure 82),it is stimulated to release a glue from its trap. The traps arebranches that are packed with vesicles containing anelectron-dense glue, and upon contact the two layers of thefungal wall separate and the vesicles fuse with the cellmembrane. The cilia of the rotifer are stuck by this glue tothe fungal trap. The fungal haustorium growth proceedsrapidly, digesting the rotifer within a few hours.Figure 81. Philodina roseola, sometimes a bryophytedweller, caught by the fungus Zoophagus insidians. Photo byWim van Egmond.Zoophagus apparently does not produce zoospores,with those few such spores reported apparently belongingto contaminants (Dick 1990; Powell et al. 1990). Instead itreproduces by fusiform conidiospores (asexual fungalspore), which are asexual, and it has been placed in theZygomycetes (Powell et al. 1990) due to its reproductivedifferences. These conidiospores are sometimes referred toas gemmae.Figure 82. Rotifer caught by the fungus Zoophagusinsidians. Photo by Wim van Egmond.Ozone Hole Dangers?Although there seemed to be no differences in growthof Sphagnum magellanicum under the ambient UV-Bradiation in the ozone hole and reduced UV-B under filtersin Tierra del Fuego, southern Argentina, the rotifer fauna ofthis moss seems to prefer the greater UV-B under ambientconditions (Searles et al. 1999). The rotifers were actuallymore numerous under the ambient conditions of UV-B inthe ozone hole than the reduced UV-B under the filters.Extraction TechniquesWhen comparing numbers of nematodes, tardigrades,mites, and annelids to rotifers among bryophytes,Merrifield and Ingham (1998) found low numbers ofrotifers, with no seasonal variation. They suggested thatthe low numbers of rotifers in moss samples may be due tothe use of the Baermann funnel for sampling. Thistechnique is not suitable for immobile organisms likerotifers, as indicated by comparison with subsequentsqueezings and agitation of the moss.To further complicate finding rotifers even under thedissecting microscope, rotifers respond to disturbance byretracting their corona and toes, appearing like a ball. Inthis condition, they are difficult to locate, even with adissecting microscope. You can place a branch ofbryophyte in a Petri dish or watch glass and cover it withwater (Fox 2001). Then let it sit quietly, preferably on thestage of a dissecting microscope, for 15-30 minutes untilthe rotifers become active again. They can then beremoved with microforceps by removing several leaves onwhich you have observed rotifers. If they are placed on aglass slide or hanging drop slide, you can observe thesewith the compound microscope at 40X.But some rotifers are too small for this technique andare likely to be missed. Peters et al. (1993) suggest adifferent method that appears to be a somewhat reliablequantitative technique. They tested it on 74 samples ofmixed Brachythecium rutabulum and Ceratodonpurpureus. Their criteria for establishing a method werethat it should not kill the organisms because some must bealive to be identified, it must be equally effective for all
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