Hydrobiologia 305 : 261, 1995 .

G .R .G . Cannon (ed .), Biology gf Turbellaria and some Related Flatworms .

©1995 Kluwer Academic Publishers . Printed in Belgium .

Regenerative and reproductive capacities of the fissiparous planarianDugesia tahitiensis

Roland PeterDepartment of Genetics and General Biology, University of Salzburg, Hellbrunnerstr 34, A-5020 Salzburg,Austria

Key words : architomy, asexual reproduction, Dugesia tahitiensis, fission, head frequency, photoperiod, planarians,regeneration, Tricladida, Turbellaria

Abstract

A pilot study was performed to assess the regenerative capacities of Dugesia tahitiensis Gourbault, 1977, anexclusively fissiparous planarian species. Animals measuring 9 .5-12.5 mm in length were used . Head regenerationrate determined by the appearance of eye spots (Brondsted, 1969 : 29-46) was extremely high : at 23 °C, it took43-59 h to regenerate clearly discernible eye spots in 28 specimens . For comparison, 3.8 days were reported forthe regeneration of eye spots in 11 .9-12.7 mm long D. tigrina (Girard) at 24 °C (Mead, 1985) . As all posteriorfragments regenerated a head, irrespective of the cutting level, D. tahitiensis seems to match the Phagocata velata(Stinger) type with a head frequency of 100% at every level (Teshirogi et al., 1977; cf. also Brtndsted, 1969 :30) .

Fissioning (architomy) occurs postpharyngeally . It cutsoff the hindmost fifth to third of the body . A constric-tion of variable width precedes fission, the processitself being executed by mechanical tearing, appar-ently due to reduced coordination between head andtail: see Morita & Best (1984) for D. dorotocephala(Woodworth) . Fission rate depends on population den-sity and/or group size . A maximal population growth,by a factor of 7 within 22 days, was achieved whenanimals were kept singly (1 specimen per 44.2 cm2 ofsurface area, 10 ml of culture water) with a photope-riod of 12 h per day (700-1,400 lx) . They were fedTubifex every fourth day. Fission rate declined by 22%for 30 specimens kept together (1 animal per 6 .8 cm 2 ) .Fission occurred even in groups of 60 animals, with1 planarian per 1 .3 cm2 . D. dorotocephala exhibits amuch more pronounced dependence of fission on pop-ulation density (Best et al., 1974 ; see there for furtherreferences and cf. Davison, 1973, for D. tigrina) .

References

Best, J . B ., W. Howell, V. Riegel & M. Abelein, 1974 . Cephalicmechanism for social control of fissioning in planarians . I. Feed-back cue and switching characteristics . J. Neurobiol. 5 : 421-442 .

Brgndsted, H . V., 1969 . Planarian Regeneration . Pergamon Press,Oxford .

Davison, J ., 1973 . Population growth in planaria Dugesia tigrina(Guard) - Regulation by the absolute number in the population .J . Gen . Physiol . 61 : 767-785 .

Mead, R. W., 1985 . Proportioning and regeneration in fissioned andunfissioned individuals of the planarian Dugesia tigrina . J . exp .Zool . 235 : 45-54 .

Morita, M. & J . B . Best, 1984 . Effects of photoperiods and melatoninon planarian asexual reproduction . J. exp . Zool . 231 : 273-282.

Teshirogi, W., S . Ishida & H . Yamazaki, 1977. Regenerative ca-pacities of transverse pieces in the two species of freshwaterplanarian, Dendrocoelopsis lactea and Polycelis sapporo . Sci .Rep . Hirosaki Univ . 24 : 55-72 .

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