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A New and Easily Cultured Model Organism for Experimental Studies on Bdelloid Rotifers

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A New and Easily Cultured Model Organism for Experimental Studies on Bdelloid Rotifers Hydrobiologia (2005) 546:141–145 Ó Springer 2005 A. Herzig, R.D. Gulati, C.D. Jersabek & L. May (eds.) Rotifera X: Rotifer Research: Trends, New Tools and Recent Advances DOI 10.1007/s10750-005-4111-8 Tale of a sleeping beauty: a new and easily cultured model organism for experimental studies on bdelloid rotifers Hendrik Segers1,* & Russell J. Shiel2 1Royal Belgian Institute for Natural Sciences, Freshwater Laboratory, Vautierstaat 29, B-1000, Brussels, Belgium 2Department of Environmental Biology, University of Adelaide, 5005, Adelaide, S.A, Australia (*Author for correspondence: E-mail: [email protected]) Key words: Rotifera, Bdelloidea, new species, Australia, anhydrobiosis Abstract We present the description of a new species of bdelloid rotifer, Adineta ricciae n. sp., which emerged from dry mud of RyanÕs billabong, Victoria, Australia. Its conspicuous frontal eyes easily diagnose the species; it differs from A. oculata (Milne) by the position of the eyes and its general habitus. The animal came to our attention because it is exceptionally easy to culture, so that the species already is being used in diverse experimental studies utilising bdelloid rotifers as model organisms. Introduction hatching from the mud. Knowing that many bdelloid rotifers are rather difficult or even Bdelloid rotifers have several features that make impossible to culture (e.g., see Ricci, 1984), it was them outstandingly interesting model organisms. a surprise to find that a large population of the These include their ability to sustain prolonged animal had developed after a few weeks. As it dormancy periods as individual organisms (anhy- appeared impossible to match the specimens with drobiosis: see Ricci, 2001a), and their exclusive any described species and as abundant material parthenogenetic reproduction (Mark Welch & was available, a number of specimens were sent to Meselson, 2000), two key features explaining the Professor C. RicciÕs laboratory in Milan, Italy. She ecological and evolutionary success of the group confirmed our initial suspicion that the species was (Ricci, 1987). The study of bdelloid biology, new to science, and even found it back personally however, is hampered by our poor understanding and recorded it as Adineta cf. oculata, also from of the systematics of the group (Ricci, 2001b), and RyanÕs III billabong (Ricci et a1., 2003). by the labour-intensive techniques required to Because the new species turned out to be culture the animals. extraordinarily easy to culture, it was used as model During a study on the hatchability of endemic organism in several studies by C. Ricci and students, Australian rotifers from resting eggs, we noted, in and by D.B. Mark Welch, to whom specimens were 1998, a rather peculiar bdelloid emerging from sent subsequently. Several studies involving the new rehydrated mud samples. One specimen of the species were presented at the Xth rotifer sympo- species (independent evolutionary lineage, in these sium, including one in which the ‘sleeping beautyÕ asexual organisms) was placed in an embryo dish strategy in responding to anhydrobiosis of the new in some water extracted from the experimental species is demonstrated (Ricci & Covino, 2005, vials, and stored in a wet chamber under room present volume). In view of these studies, we deci- conditions. As bdelloid rotifers were not the main ded not to postpone the description of the species focus of the study, the embryo dish was left while any longer. Therefore, we herewith present an attention was paid to the monogonont rotifers account of the species, which we dedicate, with 142 pleasure, to our friend and colleague Professor eyes in A. ricciae n. sp. are sometimes represented Claudia Ricci in recognition of her contributions to in illustrations of A. grandis (Murray, 1910) and the knowledge of bdelloid biology. A. vaga (Davis, 1873) (see Fig. 200a and c in Donner, 1965). In contrast to A. vaga minor, the pseudosegmentation of the body and foot is rela- tively obvious in A. ricciae n. sp. Whereas the Adineta ricciae new species trophi of A. oculata is unknown, that of A. vaga (see Melone et al., 1998) appears to have a few (Figures 1 a–e and 2 a–d) more minor teeth than A. ricciae n. sp. Holotype and paratype: in the collection of the Description: Body elongate, pseudosegmented. royal Belgian Institute of Natural Sciences, Brus- Head short, about 10% of total body length; neck sels, Belgium (IG 30060 RIR 147–148). Specimens slightly longer, about 20% of body length; trunk isolated from rehydrated dry mud of RyanÕs bil- and foot each about 35% of body length. Head labong, collected by R.S. and L.W. Tan on June slightly longer than wide, strongly flattened dorso- 26, 1998. Material consists of animals anaesthe- ventrally. Rotatory organ a ciliated ventral field, Ò tised using Marcaine , in permanent slides (Note: terminated by a pair of rakes (Melone & Ricci, the colour of the eyes has faded in the type spec- 1995) consisting of four anterior-pointed teeth. imens). Vestibulum and mouth aperture immediately Type locality: RyanÕs III billabong, Bonegilla, posterior to the rakes. Two pigmented frontal Victoria, Australia. GPS 36° 06¢ 32.1¢¢ S/146° eyes. Rostrum short, broad, with short lateral 58¢ 37.5¢¢ E. lamellas. Dorsal antenna two-pseudosegmented. Material: Abundant specimens of the species Neck slightly narrower than the head anteriorly, were present in the original culture. Populations of widening to distally. Oesophagus relatively long, A. ricciae n. sp. are at present held at the straight. Mastax small. Trunk filled with stomach Department of Biology, State University of Milan, and short intestine, paired vitellaria with 8 nuclei. Milano, Italy, and at the Josephine Bay Paul Foot with cloaca, numerous foot glands and Center for Comparative Molecular Biology and pseudosegments, these difficult to discern. Spurs Evolution, Marine Biological Laboratory, Woods short, triangular, with off-set tips; three toes. Hole, USA. Material can be obtained on request Trophi (Figures 1d–e) ramate, with two pairs from C. Ricci (Milano) or D.B. Mark Welch of major unci teeth. Nine pairs of minor unci teeth (Woods Hole). in the proximal, 12/13 pairs in the distal group (see Differential diagnosis: A. ricciae n. sp. is one of Melone et al., 1998). only two species in the genus Adineta Hudson & Additional information on the morphology of Gosse, 1886: that have distinct eyes. It can be A. ricciae n. sp. is provided by Santo (in press), distinguished from A. oculata (Milne, 1886) by the who studied the musculature of the species using position of these eyes (frontal in A. ricciae n. sp., confocal microscopy. Mark Welch & Meselson on the rostrum in A. oculata: Milne, 1886), and (2003) report on its genome size, Mark Welch shape of foot (relatively longer in A. ricciae n. sp.) (2005, present volume) uses a copy of its 82 kD and spurs (generally triangular with set-off tips in heat-shock protein gene in a phylogenetic study of A. ricciae n. sp., crescent-shaped in A. oculata). Rotifera, and Mark Welch & Mark Welch (2005, Also, A. ricciae n. sp. is much smaller than A. present volume) report on the use of DNA of oculata (about 200 lminA. ricciae n. sp., 500 lm A. ricciae n. sp. in microarrays. in A. oculata. Sla´ decˇ ek (1969) records A. oculata of Measurements: Total length 220 lm, head width 350 lm long, and provides a report on trophi 31 lm, length 43 lm, greatest trunk width 54 lm, morphology, however, the taxonomic identity of spurs 10 lm (of creeping specimen). Trophi: length his specimens is uncertain. 13 lm, width (closed) 15 lm. Ramus: length Morphologically, the new species appears close 11 lm, major unci teeth length 4.8–5.4 lm. to A. vaga minor (Bryce, 1893), but this taxon lacks Distribution and ecology: The new species is eyes, although it should be noted that colorless only known from its type locality. However, it may globules at more or less the same position of the have been overlooked in the past: all Adineta g ( ) p ( ) g; ( ) g py p g p ( y , , y) 143 Figure 1. (a–e) Adineta ricciae n. sp. a: habitus, ventral view; (b) dorsal antenna, lateral; (c) foot and spurs, lateral; (d–e) trophi, SEM photographs; (d) frontal; (e) caudal. Scale bars: (a) 50 lm, (b–c) 10 lm, (d–e) 1 lm. specimens with eyes have to date been identified as temporary pond in north-eastern Victoria, Aus- A. oculata, and there are strong indications that tralia. This billabong is notable in that it has the several different species are lumped under this greatest rotifer biodiversity yet known from a name (e.g., A. oculata sensu Sla´ decˇ ek, 1969). The single site for the continent (>200 spp., cf. Brock et ease with which the species can be cultured indi- al., 2003; Shiel & Green, unpublished data). About cates that it is probably eurytopic. A. ricciae n. sp. >106 spp. of rotifers were recorded in a single net is recorded from RyanÕs III billabong, a weedy tow during a wetted phase (Shiel et al., 1998). New 144 Figure 2. (a–d) Adineta ricciae n. sp. (a) habitus drawing; (b–d) light microscopy photographs (courtesy of G. Melone, Milano, Italy). records for Australia, including new species, con- encouraging us to describe the animal. Lor Wai tinue to be recorded there, even after >20 years Tan assisted in the collection of sediment samples relatively intensive sampling (Langley et al., 2001). from the RyanÕs Billabong series. David Mark The long evolutionary history of the River Murray Welch and Christian Jersabek are thanked for floodplain is a likely major driver of high micro- reviewing the manuscript. faunal diversity in both ephemeral and permanent waters in the region – the basin was in its present References location >100 MY BP in Gondwana, in its present channel for >2 MY.
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