Evolution and development of scyphozoan jellyfish

Abstract

Scyphozoan jellyfish, or scyphomedusae, are conspicuous members of many ocean ecosystems, and have large impacts on human health and industry. Most scyphomedusae are the final stage in a complex life cycle that also includes two intermediate stages: the larval planula and benthic polyp. In species with all three life-cycle stages, the metamorphosis of a polyp into a juvenile scyphomedusa (ephyra) is termed strobilation, and polyps can produce one ephyra (termed monodisc strobilation) or many ephyrae (termed polydisc strobilation). In contrast to species with planula, polyp and medusa stages, a handful of scyphozoan species possess modified life cycles with reduced or absent stages. The evolutionary patterns associated with strobilation and life-cycle type have not been thoroughly investigated, and many studies of ephyra development and strobilation induction are not yet synthesized. Herein, I place the development of scyphomedusae in an evolutionary context. I first review the current evolutionary hypotheses for Scyphozoa. Next, I review what is known about scyphomedusa development across a broad diversity of species, including the first signs of strobilation, the formation of strobila segments, and the morphogenesis of ephyrae. I then review cases where the canonical scyphozoan life cycle has been modified, and take advantage of phylogenetic hypotheses to place these observations in an evolutionary context. I show that the evolution of monodisc strobilation occurred at least twice, and that the loss of intermediate life-cycle stages occurred several times independently; by contrast, the reduction of the medusa stage appears to have occurred within a single clade. I then briefly review the major natural cues of strobilation induction. Finally, I summarize what is currently known about the molecular mechanisms of strobilation induction and ephyra development. I conclude with suggestions for future directions in the field.

Jellyfish genomes reveal distinct homeobox gene clusters and conservation of small RNA processing

“…Many cnidarians undergo dramatic metamorphosis or developmental transitions, including budding in hydrozoans and strobilation in jellyfish. To date, very little is known about factors that regulate cnidarian life cycles 46 . In a recent study, genes encoding the neuropeptides eclosion hormone and bursicon, both formerly thought specific to insects, with eclosion hormone involved in ecdysone-regulated timing of moulting and bursicon involved in insect wing expansion during adult emergence, were found in cnidarian genomes 47 .…”

Box, stalked, and upside-down? Draft genomes from diverse jellyfish (Cnidaria, Acraspeda) lineages: Alatina alata (Cubozoa), Calvadosia cruxmelitensis (Staurozoa), and Cassiopea xamachana (Scyphozoa)

“…Cubozoan polyps undergo partial or complete metamorphosis and develop into the adult medusoid form capable of sexual reproduction, although in some cases a polyp rudiment remains [23]. Scyphozoan polyps (scyphistomae) undergo a transition known as strobilation, in which the upper calyx proceeds through metamorphosis and transverse fission to produce a medusa [24]. Unlike other medusozoans, staurozoans lack a free-swimming medusa stage but exhibit medusa-associated characters that are present in other medusozoans [25].…”

First description of the life cycle of the jellyfish Rhizostoma luteum (Scyphozoa: Rhizostomeae)

“…On the other hand, all Kolpophorae species with known life cycles are brooding species and their strobilation type is monodisc. Within Scyphozoa evolution, polydisc strobilation appears to be an ancestral character [ 36 ] with monodisc strobilation having arisen in Kolpophorae, Sanderia malayensis (reviewed in [ 37 ]) and in R . luteum (present study).…”