Hydrocoryne iemanja (Cnidaria) - Instituto de Biociências - USP

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74 andre c.morandiniet al. Table 1. Compilation of hydrozoan species where fission is already known, and taxonomic arrangements including these species. Species Transversal fission Longitudinal fission Classification (Petersen, 1990) (only for Capitata) Classification (Bouillon, 1994) Hydrocoryne iemanja – this work Sphaearocorynida Hydrocorynoidea Hydrocorynidae Corynoidea Hydrocorynidae Polypodium hydriforme Bouillon (1985) Bouillon (1985) Not included in the Capitata Narcomedusae Polypodiidae Hydractinia pruvoti Bavestrello et al. (2000a) Not included in the Capitata Filifera Hydractiniidae Unindentified Bavestrello et al. (2000b) Not included in the Capitata Filifera Bougainvilloidea Staurocladia spp. Hirano et al. (2000) Corynoidea Cladonematidae Tubulariida Cladonematidae Hydra spp. Hyman (1928) Parke (1900) Moerisiida Moerisioidea Hydridae Moerisioidea Hydridae Moerisia lyonsi Ritchie (1915) – Moerisiida Moerisioidea Moerisiidae Moerisioidea Moerisiidae Acauloides ilonae Brinckmann-Voss (1967) Brinckmann-Voss (1967) Tubulariida Corymorphoidea Acaulidae Acauloidea Acaulidae Boreohydra simplex Leloup (1952) – Tubulariida Corymorphoidea Acaulidae Tubularioidea Boreohydridae Ectopleura larynx Tardent (1963) – Tubulariida Tubularioidea Tubulariidae Tubularioidea Tubulariidae Euphysa sp. Brinckmann-Voss (1967) – Tubulariida Corymorphoidea Corymorphidae Tubularioidea Euphysidae Protohydra leuckarti Leloup (1952) – Not included in the study Moerisioidea Protohydridae Psammohydra nana Schulz (1950) – Not included in the study Tubularioidea Boreohydridae Zelounies estrambordi Gravier-Bonnet (1992) – Not included in the study Not included in the study production of the hard plate on the column may exist in other species of Hydrocoryne. From laboratory cultures, Kubota (1988: 4) found a polyp of Hydrocoryne miurensis ‘bifurcated at the lowest portion of hydrocaulus’, but he neither recorded a new hard plate nor that the bifurcation apparently had given rise to a new, independent polyp. The asexual reproduction observed for Hydrocoryne iemanja sp. nov. suggests that its hydroid generation may disperse and successfully colonize new and favourable habitats. However, once the hard plate of the new free-living polyp generated by asexual reproduction is negative buoyant, it tends to sink fast and, therefore, its dispersal is probably limited to the surroundings of the mother colony. The chances of survival of the new colony are probably high, because the propagules derived by longitudinal fission are large and provided with nematocysts, which probably makes them less vulnerable to predation than the sexually produced ones (planulae). Also, the new large polyp is capable to feed just after settlement, enhancing the chance to establish a new colony. Furthermore, keeping settlement near the parental colony increases the chance of the new hydroid to stay within the ecological tolerance limits of the species. Besides the possible occurrence of longitudinal fission in other species of Hydrocoryne, the universality of this reproductive type is restricted in other cnidarians. In general, some kind of longitudinal fission occurs in polyps of a few species of Scyphozoa (e.g. Aurelia aurita and Catostylus mosaicus; Pérez, 1920; Pitt, 2000), in which the fission begins at base and runs to the oral disc. This kind of reproduction also represents a common mode of vegetative proliferation among certain Anthozoa (Actiniaria, Scleractinia, Corallimorpharia and Zoanthidae) (Cairns, 1988; Ryland, 1997; Fautin, 2002; Geller et al., 2005), in which the fission also proceeds from the base towards the oral disc (Geller et al., 2005). A detailed analysis on these processes, however, indicates that they are not homologous, even in less inclusive groups (cf. Daly et al., 2003). The uniqueness of the process among the hydrozoans highlights the importance of the new finding. The Hydrozoa has a vast repertoire of asexual processes, which usually includes budding (almost universal and plesiomorphic for the species of the group), and the formation of different types of propagules (podocysts, frustules), more restricted to some specific groups. Fission seems to be rare in Hydrozoa, being only reported in a few species (Table 1). Fissiparity (either longitudinal or transversal) is an interesting character to be investigated concerning its phylogenetic significance. Presently, a simple optimization of fissiparity on hydrozoan phylogenies is impossible, because of the lack of consistent and broad phylogenetic frameworks for the hydrozoansasawhole.However,someinteresting taxonomic significance inthegroupmaybedepicted.Longitudinal fission is taxonomically scattered among Hydrozoa and, most probably, arose several independent times in its evolutionary history, while transverse fission is characteristic of somewhat taxonomically (though still considering classical taxonomy) related groups (Table 1). The existence of transverse fission seems to be restricted to the Capitata, although this is probably not a monophyletic group (cf. Collins et al., 2005, 2006). Many groups presenting transverse fission belong to the Aplanulata (a group supported by mitochondrial 16S and 28S rDNA analyses, and consisting of a putative
hydrocoryne iemanja sp. nov., a new hydroid with longitudinal fission 75 clade uniting Hydridae with Candelabridae, Corymorphidae, and Tubulariidae; Collins et al., 2005, 2006). However, as noticed by Collins et al. (2006: 111), to confirm the monophyly of Aplanulata and understand the relationship among their families, many taxa have yet to be sampled, for instance Acaulidae, Margelopsidae, Paracorynidae and Tricyclusidae. Compilatory literature studies overlooked the process of longitudinal fission (e.g. Boero et al., 2002), although it has already been described. In Hydrozoa, the most similar phenomenon occurs in the model organism genus Hydra (Parke, 1900; Hyman, 1928). However, longitudinal fission is not an ordinary type of asexual reproduction in Hydra, and apparently occurs in damaged, regenerating, or abnormal specimens (Hyman, 1928; Shostak, 1993). The sequence of the process is the same as we found in Hydrocoryne iemanja sp. nov., beginning at the hypostome, and requiring several days to reach the basal disc. Polypodium hydriforme Ussow, 1887 is a specialized parasitic species of sturgeon ova (Raikova, 1994) and, besides its odd morphology and life cycle, has been considered by some authors as a Hydrozoa (e.g. Smothers et al., 1994), though some others have proposed a new class to accommodate the species (Raikova, 1988). The free-living, creeping, non-sexual stage of this species multiplies by longitudinal fission, but this fission begins at the aboral pole and progresses towards mouth (Raikova, 2002). Cnidarians are a key early diverging lineage among metazoans and, therefore, phenomena observed in the group may be precursors to derived key characteristics in evolution of animals, including traits of reproduction and body plans (e.g. Galliot & Schmid, 2002). The data shown above indicates that the longitudinal fission in Hydrocoryne iemanja sp. nov. is a process distinct from the longitudinal fission exhibited by other cnidarians. Therefore, the importance in the understanding of this asexual process may be in the investigation of regulatory genes in lower metazoans and their significance in the production of clonal organisms and evolutionary trends. The asexual reproduction is also a divergent point to understand the evolution of polarity processes within Cnidaria (for more detailed accounts see Geller et al., 2005; Collins et al., 2006). The hypothesis of a new method of reproduction, the longitudinal fission in the Hydrocoryne iemanja sp. nov., may shed light on the understanding of the evolutionary pathways in Cnidaria and animals. ACKNOWLEDGEMENTS We thank F.L. da Silveira (IBUSP) for providing laboratory facilities and commenting on the manuscript; Ricardo Miyazaki and Augusto A. Tinfre (Água e Estilo) for providing aquarium facilities; and H.M. Pacca for the line-art drawings. A.C. Morandini was supported by a FAPESP (2003/02433-0) postdoctoral scholarship, CEPG/UFRJ–FUJB (ALV 0 2006 13126-1), CNPq (481399/2007-0) and FAPERJ (E-26/ 171.150/2006); S.N.S. was supported by CAPES MSc scholarship from ‘Programa de Pós-Graduação em Ciências Biológicas, Área Zoologia, IBUSP’; A.E.M. is supported by CNPq (300194/1994-3) and FAPESP (2006/05821-9); A.C. Marquer has financial support from CNPq (55.7333/ 2005-9, 490348/2006-8, 305735/2006-3), FAPESP (2003/ 02432-3; 2004/09961-4) and NSF (AToL-EF-0531779). The experiments herein performed (cultivation) comply with the current laws of Brazil. REFERENCES Bavestrello G., Puce S., Cerrano C. and Castellano L. (2000a) Water movement activating fragmentation: a new dispersal strategy for hydractiniid hydroids. Journal of the Marine Biological Association of the United Kingdom 80, 361–362. 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