However, contemporary rates of environmental change raise a number of pressing questions linked to survivorship. The diverse circumstances of this long evolutionary period have required cnidarians to tolerate and adapt to ever-changing oceanic conditions. Here, we describe a novel, “indirect development” reproductive strategy that may contribute to the success of scyphozoans across time and habitats within the frame of a reproductive plasticity which increases the fitness of this group to diverse environmental conditions. However, while this finding clarifies the phylogeny of the phylum, the key(s) to such adaptive success have not been identified. The analysis of the genome within and across the classes of cnidarians indicates that Anthozoa have a circular DNA, while Medusozoa possess a linear genome, which suggests that the Anthozoa preceded the Medusozoa 6.
Four classes (Anthozoa, Hydrozoa, Scyphozoa, Cubozoa) have been identified within the Ediacaran fauna 1, although interpretation of Ediacaran fossils as medusae 2, 3, 4 remains contentious 5. Cnidarians branched off early within metazoan evolution and differentiated as key predators during the Middle Cambrian. Cnidarian colonisations started near the initial stages of animal evolution on Earth. suggest that this reproductive mode may be crucial for the survival of some scyphozoan populations within the frame of a bet-hedging strategy and contribute to their long evolutionary success throughout the varied conditions of past and future oceans.Ĭnidaria-Anthozoa (stony and soft corals and sea anemones) and Medusozoa (Hydrozoa, Scyphozoa and Cubozoa)-display a high degree of adaptive radiation and have colonised almost all marine as well as some brackish and freshwater habitats. Our observations of this pattern in co-occurrence with mono- and polydisk strobilation in Aurelia spp. We provide a fully detailed description of this variant that increases reproductive plasticity within scyphozoan life cycles and is different than either true direct development or the monodisk strobilation.
In distinction to monodisk strobilation, the basal polyp of indirect development was merely a non-tentaculate stalk that dissolved shortly after detachment of the ephyra.
2017 and Cotylorhiza tuberculata (Macri 1778) settled and formed fully-grown polyps which transformed into ephyrae within several days. Planulae of Aurelia relicta Scorrano et al. In addition to these reproductive modes, here we provide evidence of a third ephyral production which has been rarely observed and often confused with direct development from planula into ephyra. Their ability to generate young medusae (ephyrae) via two distinct reproductive strategies, strobilation or direct development from planula into ephyra without a polyp stage, has been a potential explanation. Ecologists and evolutionary biologists have been looking for the key(s) to the success of scyphomedusae through their long evolutionary history in multiple habitats.
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