A practical staging atlas to study embryonic development of Octopus vulgaris under controlled laboratory conditions

Abstract

Background: Octopus vulgaris has been an iconic cephalopod species for neurobiology research as well as for cephalopod aquaculture. It is one of the most intelligent and well-studied invertebrates, possessing both long-and short-term memory and the striking ability to perform complex cognitive tasks. Nevertheless, how the common octopus developed these uncommon features remains enigmatic. O. vulgaris females spawn thousands of small eggs and remain with their clutch during their entire development, cleaning, venting and protecting the eggs. In fact, eggs incubated without females usually do not develop normally, mainly due to biological contamination (fungi, bacteria, etc.). This high level of parental care might have hampered laboratory research on the embryonic development of this intriguing cephalopod. Results: Here, we present a completely parameter-controlled artificial seawater standalone egg incubation system that replaces maternal care and allows successful embryonic development of a small-egged octopus species until hatching in a laboratory environment. We also provide a practical and detailed staging atlas based on bright-field and light sheet fluorescence microscopy imaging for precise monitoring of embryonic development. The atlas has a comparative section to benchmark stages to the different scales published by Naef (1928), Arnold (1965) and Boletzky (2016). Finally, we provide methods to monitor health and wellbeing of embryos during organogenesis. Conclusion: Besides introducing the study of O. vulgaris embryonic development to a wider community, this work can be a high-quality reference for comparative evolutionary developmental biology.

Identification of neural progenitor cells and their progeny reveals long distance migration in the developing octopus brain

“…The rapidly growing octopus brain suggests massive embryonic neurogenesis O. vulgaris displays a direct embryonic development, giving rise to actively feeding paralarvae. Their embryonic development takes approximately 40 days at 19 °C and has been classified in 20 major stages I-XX, with some stages subdivided in an early and late part (Deryckere et al, 2020;Naef, 1928).…”

Effects of temperature on the rate of embryonic development of cephalopods in the light of thermal time applied to aquaculture

“…According to Deryckere et al . (2020), the boundary between epiboly and the onset of organogenesis lies in the middle of the stage VII (the authors defined two new sub‐stages, VII.1 and VII.2, but because the distinction between stage VII.1 and VII.2 is so recent, stage VII was taken as the boundary between pre‐organogenesis and organogenesis phases) of the scale of Naef (1928) (comprising stages I–XX and defined for several species), and organogenesis is finished by the stage XVII. Therefore, the boundaries set for pre‐organogenesis, organogenesis and growth in Naef scale were I–VII.1, VII.2–XVII and XVIII–XX, respectively.…”

“…More recently, Deryckere et al . (2020) changed the boundary to Naef stage XVII after revising the development of O. vulgaris , since the internalization of the mouth is attained during stages XV–XVI. Deryckere et al .…”

“…Deryckere et al . (2020) also established the connection between the scale of Naef (1928) and the scale of Arnold (1965), the latter one comprises stages 1–30 and was defined for Loligo pealii . Since Naef stages VII and XVII approximately correspond to Arnold stages 18 and 27, the boundaries of pre‐organogenesis, organogenesis and growth phases of developing embryos of Loligo vulgaris were approximately 1–18, 19–27 and 28–30 (Arnold scale), respectively.…”

“…In addition, since embryonic development in cephalopods can be subdivided into two or three consecutive periods (perhaps with some overlapping), being pre‐organogenesis (segmentation, gastrulation and epiboly), organogenesis (development of external and internal organs) and growth (mainly growth and pigmentation; Boletzky 1989; Deryckere et al . 2020), it remains to be tested if the LMD can also be applied for all these species and to each of those embryonic periods.…”