Reverse development in Cnidaria

Abstract

Cnidarians have long been considered simple animals in spite of the variety of their complex life cycles and developmental patterns. Several cases of developmental conversion are known, leading to the formation of resting stages or to offspring proliferation. Besides their high regenerative and asexual-reproduction potential, a number of cnidarians can undergo ontogeny reversal, or reverse development: one or more stages in the life cycle can reactivate genetic programs specific to earlier stages, leading to back-transformation and morph rejuvenation. The switch is achieved by a variable combination of cellular processes, such as transdifferentiation, programmed cell death, and proliferation of interstitial cells. The potential for ontogeny reversal has limited ecological meaning and is probably just an extreme example of a more general strategy for withstanding unfavourable periods and allowing temporal persistence of species in the environment.Résumé : Depuis longtemps, on considère les cnidaires comme des animaux simples, malgré la variété de leurs cycles biologiques et de leurs patterns de développement complexes. Il existe plusieurs cas de conversions au cours du déve-loppement qui mènent à la formation de stades de repos ou à la prolifération de rejetons. En plus de leur fort potentiel de régénération et de reproduction asexuée, plusieurs cnidaires peuvent subir un renversement de leur ontogenèse ou un développement inversé : un ou plusieurs stades dans le cycle biologique peuvent réactiver des programmes génétiques spécifiques de stades antérieurs, ce qui donne une rétro-transformation et un rajeunissement des morphes. Le revirement est provoqué par une combinaison variable de processus cellulaires, tels que la transdifférentiation, la mort cellulaire programmée et la prolifération de cellules interstitielles. Le potentiel de renversement ontogénique a une signification écologique limitée; il s'agit probablement d'un état extrême d'une stratégie plus générale pour survivre aux périodes défavorables et permettre à l'espèce de se maintenir dans le temps dans son milieu.[Traduit par la Rédaction] Piraino et al. 1754

ITAG: an eco-sensor for fine-scale behavioral measurements of soft-bodied marine invertebrates

“…Vertical movements and respiratory patterns of the Humboldt (jumbo) squid Dosidicus gigas appear tied to both dissolved oxygen and local environmental temperatures [18][19][20]. Some medusae may undergo reverse development when environmental conditions are reproductively unfavorable, enabling "temporal persistence" and longer foraging periods [21]. Understanding these changes is vital to properly manage soft-bodied invertebrates fisheries (i.e., ecosystemically), as well as other fisheries and systems where these species play a key ecological role [22,23].…”

Induction of reverse development in two marine Hydrozoans

“…Many variations to this scheme are possible (Boero et al, 2002 for a review). Among them, reverse development (RD) was first discovered in scyphozoans nearly a century ago (Hadzi, 1909) and it represents an unparalleled feature of cnidarians within the animal kingdom (Piraino et al, 2004) (Fig. 1).…”

“…1). In several representatives of both Anthozoa and Medusozoa, one stage in the life cycle can transform back -by morphological reorganization -to the preceding stage: e.g., a medusa or medusa bud reverting back into stolons and polyps, an ephyra back into a scyphistoma, a primary polyp back into a planktonic larva (see Piraino et al, 2004 for review of RD cases). This phenomenon can be interpreted as an adaptive response to unfavourable changes in the environmental quality or to physiological feedbacks: in the hydrozoan Turritopsis dohrnii (not T. nutricula; see Schuchert, 2004) RD (medusae to polyps) is activated either by epigenetic, sub-lethal stress (e.g.…”

“…This phenomenon can be interpreted as an adaptive response to unfavourable changes in the environmental quality or to physiological feedbacks: in the hydrozoan Turritopsis dohrnii (not T. nutricula; see Schuchert, 2004) RD (medusae to polyps) is activated either by epigenetic, sub-lethal stress (e.g. starvation, temperature or salinity changes) or by an endogenous, genetically programmed induction when sexual maturity, marking the beginning of senescence, is attained (Bavestrello et al, 1992;Piraino et al, 1996, Piraino et al, 2004. Formerly considered as an extraordinary feature limited to a few species, the RD potential has been recently discovered in other cnidarian taxa (e.g., De Vito et al, 2006), suggesting that it might be a more general property than previously thought.…”

“…Several hydrozoan species show the potency to revert their ontogenetic programs (see Piraino et al, 2004 for a list) but most of them have some restrictions. For instance, the potential for RD of medusa bud to the polyp stage is known in H. carnea up to early isolated stages and is lost in older medusa stages (Müller, 1913, Frey, 1968, Schmid, 1972 (Fig.…”