Developmental Heterochronies and Dioxygen Constraints in Teleostean Fishes

It has been hypothesized that a lack of dioxygen could be the trigger of hatching. Here we address the question of whether developmental heterochronies could be an indirect way to study adaptation to lack of dioxygen. To answer this question, we aim to explore the potential of an original method which compares the relative rate of anatomical development across an extended set of 19 species using a hierarchical analysis of ontogenetic time. Then we compare heterochronic rates with the relative time at hatching and information about dioxygen availability. Pairwise independence between dioxygen richness, rate of development and relative time at hatching are all rejected at the 5% threshold. This suggests a link between these three variables, and provides consilient evidence for the hypothesis that lack of dioxygen is a trigger of hatching. A possible scenario is the following: hatching early relatively to developmental time (because of a lack of dioxygen) exposes larvae to predation, and concomitant accelerated early anatomical development could be the result of a selective constraint which consists of being able to escape predators. We conjecture that accelerated embryonic development might be linked to adaptation against predation in dioxygen-poor waters.