Onset of feeding in juvenile sea urchins and its relation to nutrient signalling

ABSTRACT

The purple sea urchin, Strongylocentrotus purpuratus, has been the focus of extensive ecological and developmental research over the years. Strongylocentrotus purpuratus larvae transition into the juvenile stage after an extensive planktonic period. The metamorphic transition is characterized by dramatic changes in morphology and physiology of the juvenile compared to the larval form and mechanisms underlying this process, especially the early days post-settlement, remain poorly understood. We used SEM and phalloidin stain analysis as well as whole mount in situ hybridization to gain a detailed understanding of juvenile development in relation to nutrient signalling [insulin-like growth factor (IIS), FoxO (forkhead box, sub-group ‘O’) and TOR (target of rampamycin), also known as IIS/TOR/FoxO signalling]. Our results show that the majority of juvenile feeding features are fully developed only after 8-days of juvenile development, leaving an extensive period of nutritional stress. We found that FoxO gene expression increases during that time period and is localized in juvenile tube feet, potentially associated with sensory structures involved in nutrient signalling. Our data complement existing work on sea urchin juvenile development and shed new light on the perimetamorphic period of Strongylocentrotus purpuratus, with respect to nutrient signalling and the potential stressful pre-feeding period of juvenile sea urchins.

KEYWORDS:

• Sea urchin
• metamorphosis
• Aristotle’s lantern
• tube feet
• musculature
• FoxO

Disclosure statement

No potential conflict of interest was reported by the authors.

Impact statement

• We provide a detailed description of settlement and feeding structures in juvenile sea urchins.

• Our analysis revealed that a complete juvenile mouth and well-developed Aristotle’s lantern were formed by day eight post-settlement.

• We have established that muscle fibres that play a significant role in both of movement of spines and in the mouth area, are one of the early structures that develop in the juvenile sea urchin after settlement.

• We provided supporting evidence for the hypothesis that FoxO signalling is involved in the nutrient stress response of pre-feeding juvenile sea urchins.

Additional information

Funding

The authors acknowledge financial supports from Egypt Ministry of Higher education and NSERC Discovery Grant (400230 to AH).