Memory and obesity affect the population dynamics of asexual freshwater planarians

Dunkel, Jörn; Talbot, Jared A.; Schötz, Eva-Maria

doi:10.1088/1478-3975/8/2/026003

Cited by 21 publications

(39 citation statements)

References 56 publications

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“…Fission is the sole mode of reproduction of the asexual planarians studied here, which poses the question of how this species creates population diversity. Where a planarian divides affects the fitness and reproductive behaviors of its offspring (7,(11)(12)(13). Therefore, understanding how fission location is regulated is an important evolutionary question to be answered.…”

Section: Discussionmentioning

confidence: 99%

“…One must limit oneself to giving the general trends and looks of this phenomenon without trying to explain all the observed exceptions" [author translation] (10). Because where along the body axis a planarian divides affects the fitness and reproductive behaviors of its offspring (7,(11)(12)(13), understanding how fission location is regulated is an important question to be answered. Regarding the division process, Vandel described fission as a mechanical process, whereby the anterior and posterior parts act independently, with the anterior part rhythmically pulsing and the posterior part largely adhering to the substrate.…”

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confidence: 99%

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Mechanics dictate where and how freshwater planarians fission

Malinowski

Cochet‐Escartin

Kaj

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Asexual freshwater planarians reproduce by tearing themselves into two pieces by a process called binary fission. The resulting head and tail pieces regenerate within about a week forming two new worms. Understanding this process of ripping oneself into two parts poses a challenging biomechanical problem. Since planarians stop "doing it" at the slightest disturbance, this remained a centuries-old puzzle. We focus on Dugesia japonica fission and show that it proceeds in three stages: a local constriction ("waist formation"), pulsationwhich increases waist longitudinal stresses -and transverse rupture. We developed a linear mechanical model with a planarian represented by a thin shell. The model fully captures the pulsation dynamics leading to rupture and reproduces empirical time scales and stresses. It asserts that fission execution is a mechanical process. Furthermore, we show that the location of waist formation, and thus fission, is determined by physical constraints. Together, our results demonstrate that where and how a planarian rips itself apart during asexual reproduction can be fully explained through biomechanics.Keywords: planarians, biomechanics, fission, rupture, traction forces Significance Statement: How planarians reproduce by ripping themselves into a head and a tail piece, which subsequently regenerate into two new worms, is a centuries-old biomechanics problem. Michael Faraday contemplated how this feat can be achieved in the 1800s, but it remained unanswered because it is experimentally difficult to observe planarians "doing it". We recorded Dugesia japonica planarians in the act and developed a physical model which captures pivotal steps of their reproduction dynamics. The model reproduces experimental time scales and rupture stresses without fit parameters. The key to rupture is a local reduction of the animal's cross-sectional area, which greatly amplifies the stresses exerted by the planarian's musculature and enables rupture at substrate stresses in the Pa range. \body Already Michael Faraday and his contemporaries were intrigued by the observation that asexual freshwater planarians, squishy worms a few mm in length, reproduced by tearing themselves into a head and tail offspring, in a process called binary fission (1). How was it possible for these animals to generate the forces necessary to rip themselves using only their

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Mechanics dictate where and how freshwater planarians fission

Malinowski

Cochet‐Escartin

Kaj

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Most turbellarians have neoblasts (Newmark and Alvarado, 2000) which allow them to be good models for this type of research. Neoblasts also allow these multicellular organisms to reproduce asexually, primarily by transverse fission, which complicates the study of their demographic characteristics, whereby these studies are scarce and the data are highly variable (Egger et al, 2007;Mouton et al, 2009;Dunkel et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Demography and feeding behavior of Stenostomum leucops (Dugés, 1828)

Núñez-Ortiz

Sarma

2016

J Limnol

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“…Use of an inverted microscope greatly enhances stability because the weight of the chip is on top of the specimen, and all images reported in this paper were taken using an inverted microscope. The PIC enables the manipulation of planarians of various sizes (a few millimeters up to 1–2 centimeters), an important advantage because planarians can vary substantially in size depending on the species as well as environmental factors such as feeding frequency and temperature36. The agarose-coated PDMS membrane and plastic film are not permanently bonded at any point, and peeling apart the two layers releases the worm uninjured within seconds (see Methods).…”

Section: Resultsmentioning

confidence: 99%

“…Immobilization of freshwater planarians, however, presents several unique challenges: Planarians are about an order of magnitude larger than C. elegans , have a squishy, readily deformed body, vary in size depending on the species, feeding state, last asexual reproduction event, and other factors36, and are significantly more photophobic than C. elegans or D. melanogaster larvae. These characteristics make it infeasible to apply existing microfluidic immobilization techniques directly to planarians, which prompted us to develop an alternative method.…”

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On-chip immobilization of planarians for in vivo imaging

Dexter

Tamme

Lind

et al. 2014

Sci Rep

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Planarians are an important model organism for regeneration and stem cell research. A complete understanding of stem cell and regeneration dynamics in these animals requires time-lapse imaging in vivo, which has been difficult to achieve due to a lack of tissue-specific markers and the strong negative phototaxis of planarians. We have developed the Planarian Immobilization Chip (PIC) for rapid, stable immobilization of planarians for in vivo imaging without injury or biochemical alteration. The chip is easy and inexpensive to fabricate, and worms can be mounted for and removed after imaging within minutes. We show that the PIC enables significantly higher-stability immobilization than can be achieved with standard techniques, allowing for imaging of planarians at sub-cellular resolution in vivo using brightfield and fluorescence microscopy. We validate the performance of the PIC by performing time-lapse imaging of planarian wound closure and sequential imaging over days of head regeneration. We further show that the device can be used to immobilize Hydra, another photophobic regenerative model organism. The simple fabrication, low cost, ease of use, and enhanced specimen stability of the PIC should enable its broad application to in vivo studies of stem cell and regeneration dynamics in planarians and Hydra.

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Memory and obesity affect the population dynamics of asexual freshwater planarians

Cited by 21 publications

References 56 publications

Mechanics dictate where and how freshwater planarians fission

Mechanics dictate where and how freshwater planarians fission

Demography and feeding behavior of Stenostomum leucops (Dugés, 1828)

On-chip immobilization of planarians for in vivo imaging

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