To Each His Own
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Planarians are among the most complex animals with the ability to regenerate complete organisms from small tissue pieces. This ability allows them to reproduce by splitting themselves into a head and a tail piece, making them a rare example of asexual reproduction via transverse fission in multi-cellular organisms. Due to the stochastic nature of long reproductive cycles, which range from days to months, few and primarily qualitative studies have been conducted to understand the reproductive behaviors of asexual planarians. We have executed the largest long-term study on planarian asexual reproduction to date, tracking more than 23,000 reproductive events of three common planarian species found in Europe, North America, and Asia, respectively: Schmidtea mediterranea, Dugesia tigrina, and Dugesia japonica. This unique data collection allowed us to perform a detailed statistical analysis of their reproductive strategies. Since the three species share a similar anatomy and mode of reproduction by transverse division, we were surprised to find that each species had acquired its own distinct strategy for optimizing its reproductive success. We statistically examined each strategy, associated trade-offs, and the potential regulatory mechanisms on the population level. Interestingly, models for cell cycle length regulation in unicellular organisms could be directly applied to describe reproductive cycle lengths of planarians, despite the difference in underlying biological mechanisms. Finally, we examined the ecological implications of each strategy through intra- and inter-species competition experiments and found that D. japonica outcompeted the other two species due to its relatively equal distribution of resources on head and tail pieces, its cannibalistic behaviors and ability to thrive in crowded environments. These results show that this species would pose a serious threat to endogenous planarian populations if accidentally introduced in their habitats.
KeywordsPlanarians Asexual reproductive strategies Fission Fragmentation Size control
The authors thank Olivier Cochet-Escartin for Supplemental Movie 1 and helpful comments on the manuscript, Danielle Hagstrom for manuscript suggestions, and My Du Dang for help with worm maintenance and imaging. This research was funded by the Burroughs Wellcome Fund CASI Award, and the Alfred P. Sloan Fellowship (to E.-M.S.C.). J.A.C was partially supported by the Ledell Family Scholarship.
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- 1.Abril, J.F., Cebria, F., Rodriguez-Esteban, G., Horn, T., Fraguas, S., Calvo, B., Bartscherer, K., Salo, E.: Smed454 dataset: unraveling the transcriptome of Schmidtea mediterranea. BMC Genom. 11(731), 1–19 (2010)Google Scholar
- 2.Armstrong, J.T.: The population dynamics of the planarian Dugesia tigrina. ESA 45, 361–365 (1964)Google Scholar
- 3.Baguna, J., Carranza, S., Pala, M., Ribera, C., Giribet, G., Arnedo, M.A., Ribas, M., Riutort, M.: From morphology and karyology to molecules. New methods for taxonomical identification of asexual populations of freshwater planarians. A tribute to Professor Mario Benazzi. Ital. J. Zool. 66, 207–214 (1999)CrossRefGoogle Scholar
- 13.Fantes, P.A.: Control of cell size and cycle time in Schizosaccharomyces pombe. J. Cell Sci. 24, 51–67 (1977)Google Scholar
- 19.Kawakatsu, M.: An experimental study of the life-history of Japanese freshwater planaria, p. vivida (ijima et kaburaki), with special reference to the fragmentation. Bull Kyoto Gakugei Univ. Ser. B 14, 35–39 (1959)Google Scholar
- 24.Pringle, J., Hartwell, L.: The Saccharomyces cerevisiae cell cycle. In: The Molecular Biology of the Yeast Saccharomyces: Life Cycle and Inheritance. Cold Spring Harbor Monograph 11 (1981)Google Scholar
- 32.Stearns, S.: The Evolution of Life Histories. Oxford University Press, London (1992)Google Scholar
- 34.Sveiczer, A., Novak, B., Mitchison, J.: The size control of fission yeast revisited. J. Cell Sci. 109, 2947–2957 (1996)Google Scholar