Fig. 1: Alternative hypotheses explaining potential variability among consensus processes across regenerative organisms.

a Two example species that exhibit epimorphic regeneration: Acomys cahirinus (spiny mouse) and Schmidtea mediterranea (freshwater planarian). Complex tissue regeneration of the ear pinna (spiny mouse) and head (planarian) is depicted as occurring from an initial tissue injury through complete regeneration. Individual processes as presented in Table 1 are contained within three general phases of regeneration: wound healing, blastema formation, and morphogenesis. Because the timescale over which these processes occur in individual species is highly variable, regeneration in a is depicted independent of time. b–d Three alternative hypotheses describing variability between comparable processes across regenerative species as a function of time. b Variability between component processes during the time course of regeneration is either low (i.e., genetic, molecular, and cellular mechanisms are highly conserved across species, bottom arrow) or high (mechanisms are not well conserved, upper arrow). c The initial injury response between species is very similar, but variability increases for mechanisms associated with cell activation, cell cycle progression, blastema formation, and morphogenesis, and then becomes more similar again during the differentiation and scaling phases of regeneration. The hypothesis represented in d asserts that variation between species is relatively large for processes that occur during wound healing, but low in the processes involved in blastema formation; after blastema formation, process variability may remain low (conserved) or increase (divergent).