Hierarchical analysis of ontogenetic time to describe heterochrony and taxonomy of developmental stages

Guillaume Lecointre,Nalani K Schnell,Fabrice Teletchea

doi:10.1038/s41598-020-76270-4

Abstract

Even though an accurate description of early life stages is available for some teleostean species in form of embryonic and post-embryonic developmental tables, there is poor overlap between species-specific staging vocabularies beyond the taxonomic family level. What is called “embryonic period”, “larval period”, “metamorphosis”, or “juvenile” is anatomically different across teleostean families. This problem, already pointed out 50 years ago, challenges the consistency of developmental biology, embryology, systematics, and hampers an efficient aquaculture diversification. We propose a general solution by producing a proof-of-concept hierarchical analysis of ontogenetic time using a set of four freshwater species displaying strongly divergent reproductive traits. With a parsimony analysis of a matrix where “operational taxonomic units” are species at a given ontogenetic time segment and characters are organs or structures which are coded present or absent at this time, we show that the hierarchies obtained have both very high consistency and retention index, indicating that the ontogenetic time is correctly grasped through a hierarchical graph. This allows to formally detect developmental heterochronies and might provide a baseline to name early life stages for any set of species. The present method performs a phylogenetic segmentation of ontogenetic time, which can be correctly seen as depicting ontophylogenesis.

Highlights

Even though an accurate description of early life stages is available for some teleostean species in form of embryonic and post-embryonic developmental tables, there is poor overlap between speciesspecific staging vocabularies beyond the taxonomic family level
Even though an accurate description of early life stages is available for a few teleostean species in form of embryonic or post-embryonic developmental tables, there is poor overlap between species-specific staging vocabulary beyond the taxonomic level of family[3]
Note that at 25% and 50% of their developmental time, Hucho hucho was late compared to Thymallus thymallus; grayling is late compared to Tinca tinca; tench is late compared to Barbus barbus

Summary

Introduction

Even though an accurate description of early life stages is available for some teleostean species in form of embryonic and post-embryonic developmental tables, there is poor overlap between speciesspecific staging vocabularies beyond the taxonomic family level. With a parsimony analysis of a matrix where “operational taxonomic units” are species at a given ontogenetic time segment and characters are organs or structures which are coded present or absent at this time, we show that the hierarchies obtained have both very high consistency and retention index, indicating that the ontogenetic time is correctly grasped through a hierarchical graph This allows to formally detect developmental heterochronies and might provide a baseline to name early life stages for any set of species. One terminology example is the ontogenetic index[27], another example is based on the degree of flexion of the terminal section of the notochord during caudal fin development, separating pre-flexion, flexion and post-flexion s tages[8,28,29], especially useful for identification of marine teleostean larvae

Objectives

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Conclusion