Abstract
The molecular understanding of crustacean metamorphosis is hindered by small sized individuals and inability to accurately define molt stages. We used the spiny lobster Sagmariasus verreauxi where the large, transparent larvae enable accurate tracing of the transition from a leaf-shaped phyllosoma to an intermediate larval-juvenile phase (puerulus). Transcriptomic analysis of larvae at well-defined stages prior to, during, and following this transition show that the phyllosoma-puerulus metamorphic transition is accompanied by vast transcriptomic changes exceeding 25% of the transcriptome. Notably, genes previously identified as regulating metamorphosis in other crustaceans do not fluctuate during this transition but in the later, morphologically-subtle puerulus-juvenile transition, indicating that the dramatic phyllosoma-puerulus morphological shift relies on a different, yet to be identified metamorphic mechanism. We examined the change in expression of domains and gene families, with focus on several key genes. Our research implies that the separation in molecular triggering systems between the phyllosoma-puerulus and puerulus-juvenile transitions might have enabled the extension of the oceanic phase in spiny lobsters. Study of similar transitions, where metamorphosis is uncoupled from the transition into the benthic juvenile form, in other commercially important crustacean groups might show common features to point on the evolutionary advantage of this two staged regulation.
Highlights
The molecular understanding of crustacean metamorphosis is hindered by small sized individuals and inability to accurately define molt stages
From a total of more than 450 million reads generated for ten samples, a total of 107,333 transcripts were assembled using Trinity
In light of the recent finding in the giant freshwater prawn M. rosenbergii, where CYP15A1 was absent in larvae and present in post larvae, with the opposite trend of FAMeT33, these results indicate that a different mechanism regulates the transition from phyllosoma to puerulus in S. verreauxi, while perhaps a similar mechanism applies for the metamorphosis of the final puerulus H phase to the juvenile stage (Fig. 1)
Summary
The molecular understanding of crustacean metamorphosis is hindered by small sized individuals and inability to accurately define molt stages. We used the spiny lobster Sagmariasus verreauxi where the large, transparent larvae enable accurate tracing of the transition from a leaf-shaped phyllosoma to an intermediate larval-juvenile phase (puerulus). Spiny lobsters transform from a leaf-shaped larva (phyllosoma) into an intermediary free-swimming (nektonic) phase called a puerulus (resembling the adult body plan) which transports the animal from a pelagic, oceanic stage to the benthic, juvenile development[3]. During metamorphosis in spiny lobsters, the transparent phyllosoma undergo gut atrophy where the digestive glands retract from the edges of the cephalic shield towards the center[5] (Fig. 1) Unlike other crustaceans, this gradual retraction occurs over many hours to days, depending on species, before transition to puerulus, and due to the larval transparency it enables an accurate tracking of the exact advancement towards the transitory molt. Recent advances in hatchery technologies have enabled closing the life cycle of this species in captivity, overcoming several hurdles including stocking densities[13,14], temperature and photoperiod requirements[15,16] and perhaps most challenging, the phyllosoma-puerulus transition[3]
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