Planarian Asexual Reproduction via Mechanical Tearing - One Problem, Multiple Solutions

Asexual freshwater planarians reproduce by tearing themselves into a head and tail piece (“fission”) using only their musculature and substrate traction. What sets the division plane and how they divide has been a longstanding open question. We have previously explained where and how Dugesia japonica planarians divide using a linear elastic model [1]. Surprisingly, we found that other planarian species - Schmidtea mediterranea and Girardia tigrina, found different solutions to the same problem. Since the 3 species have distinct reproductive strategies, optimizing different parameters (resource allocation to offspring, reproductive waiting time, number of offspring)[2], we hypothesized a link between the fission mechanism on the organismal level and the population level strategy. We quantified the fission dynamics and offspring sizes for all 3 species and found that substrate traction and differences in body shape changes during fission constrain the location of the division plane and thus determine relative resource allocation to offspring.

[1] Malinowski, Paul T., et al. "Mechanics dictate where and how freshwater planarians fission. PNAS(2017)
[2] Carter, Jason A., et al. "To each his own." Journal of Statistical Physics(2015)