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

Astrid Deryckere,Erica A G Vidal,Eve Seuntjens,Ruth Styfhals,Eduardo Almansa

doi:10.1186/s12861-020-00212-6

Abstract

BackgroundOctopus 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.ResultsHere, 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.ConclusionBesides 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.

Highlights

Octopus vulgaris has been an iconic cephalopod species for neurobiology research as well as for cephalopod aquaculture
We introduced a low-cost standalone system that runs on artificial seawater for incubating small-egged Octopus species without maternal care
Whereas embryonic development progress is more difficult to assess before Stage VII.2, after the first reversion, a number of hallmarks can be used to assess vitality of the embryos, such as yolk contractions, and later on heart beating, these might be irregular at early embryonic stages

Summary

Introduction

Octopus vulgaris has been an iconic cephalopod species for neurobiology research as well as for cephalopod aquaculture. O. vulgaris females spawn thousands of small eggs and remain with their clutch during their entire development, cleaning, venting and protecting the eggs. 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. While the common cuttlefish lays individual medium-sized encapsulated eggs covered by an ink stained multilayer gelatinous envelope, the common octopus produces small eggs with a single transparent chorionic coat, devoid of a protective gelatinous capsule, which significantly increases their ease of use in laboratory experimental studies. In O. vulgaris eggs, this swelling process affects egg width and wet weight whereas length is nearly unaffected [8]

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