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, 10 (12), e0145314
eCollection

Life Cycle Reversal in Aurelia sp.1 (Cnidaria, Scyphozoa)

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Life Cycle Reversal in Aurelia sp.1 (Cnidaria, Scyphozoa)

Jinru He et al. PLoS One.

Abstract

The genus Aurelia is one of the major contributors to jellyfish blooms in coastal waters, possibly due in part to hydroclimatic and anthropogenic causes, as well as their highly adaptive reproductive traits. Despite the wide plasticity of cnidarian life cycles, especially those recognized in certain Hydroza species, the known modifications of Aurelia life history were mostly restricted to its polyp stage. In this study, we document the formation of polyps directly from the ectoderm of degenerating juvenile medusae, cell masses from medusa tissue fragments, and subumbrella of living medusae. This is the first evidence for back-transformation of sexually mature medusae into polyps in Aurelia sp.1. The resulting reconstruction of the schematic life cycle of Aurelia reveals the underestimated potential of life cycle reversal in scyphozoan medusae, with possible implications for biological and ecological studies.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Species information of Aurelia sp.1 in Xiamen Bay, East China Sea.
A: sampling location for Aurelia sp.1 from Xiamen Bay, which was indicated as the red dot in the map. B and C: Neighbor-Joining cladogram of Aurelia based on mitochondrial COI (B) and nuclear ITS (C) sequences, bootstrap values higher than 70 were shown close to each branch node, number of sequences belonging to the same species were indicated in the bracket following the species name, and sequences of Aurelia sp.1 obtained in this study were highlighted.
Fig 2
Fig 2. Direct polyp formation from degenerating juvenile Aurelia sp.1 medusae.
A-D: normal development from ephyrae to juvenile medusae, showing individuals of newly released (A), 5-day (B), 10-day (C) and 20-day (D) old, respectively. E, F: aboral (E) and oral (F) view of a 25-day old medusa after 5 days post settlement. G-L: juvenile medusae during reverse transformation. Scale bars = 0.2 mm (A, B); 0.5 mm (C-L). Arrows showed degeneration of medusa tentacles (E), occurrence of polyp stolon (G), development of polyp tentacles (H), and remains of medusa rhopalia (I and J).
Fig 3
Fig 3. Direct polyp formation from Aurelia sp.1 medusae tissue fragments.
A: a 25-day old medusa. B: juvenile medusae 5 days after settlement. C: oral arms 1 month after settlement. D-G: tissue fragments from juvenile medusae. H-K: polyps arose from juvenile medusae fragments. L: a 1-year old male medusa (collected from the field). M: settled broken or fragmented adult medusae. N: oral arms 3 months after settlement. O-R: tissue fragments from adult medusae. S-V: polyps arose from adult medusae fragments. Scale bars = 1 mm (A, B, C); 0.2 mm (D-G); 0.1 mm (H-K, O-V); 1 cm (L-N). Arrows showed newly developed polyps.
Fig 4
Fig 4. Direct polyp formation from living Aurelia sp.1 medusae.
A, D: 3-month old medusae. B, C: the same individual as (A) after 75 days, showing the thickened layers and projecting pointed ends at different scales. E-G: the same individual as (D) after 75 days, showing the derived colonies (E and F) and thickened layers (G) at different scales. H-L: proportions of living medusae at different stages of direct polyp formation. Scale bars = 1 cm (A, B, D, E); 5 mm (C, F, G-L). Arrows showed transformation process at different stages.
Fig 5
Fig 5. Schematic life cycle of Aurelia.
Normal development traits and stages were presented with black illustrates and arrows, whereas modifications of the typical life cycle were drawn with colored objects (Red: process described in this study; others: process published with references herein). I: direct development of planula; II: production of elongated stolons, podocysts, and free-swimming propagules from scyphistoma; III: reverse development of ephyra; IV: direct polyp formation from degenerating juvenile medusa and medusa tissue fragments; V: direct polyp formation from living medusa; VI: polyp colony release from medusa-polyp complex.

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Grant support

This work was supported by the National Natural Science Foundation of China under contract No. 41006078 (LZ), No. J1210050 (LZ) and No. J1310037 (LZ); the Public Science and Technology Research Funds Projects of Ocean under contract No. 201505034 (LZ). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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