A comparative analysis of the ontogeny of syngnathids (pipefishes & seahorses) reveals how heterochrony contributed to their diversification

Abstract

Background Syngnathids are a highly derived and diverse fish clade comprising the pipefishes, pipe-horses and seahorses. They are characterized by a plethora of iconic traits that increasingly capture the attention of biologists, including geneticists, ecologists and developmental biologists. The current understanding of the origins of their derived body plan is, however, hampered by incomplete and limited descriptions of the early syngnathid ontogeny. Results We provide a comprehensive description of the development of Nerophis ophidion, Syngnathus typhle, Hippocampus erectus from early cleavage stages to release from the male brooding organ and beyond, including juvenile development. We comparatively describe skeletogenesis with a particular focus on dermal bony plates, the snout-like jaw morphology, and appendages. Conclusions This most comprehensive and detailed account of syngnathid development to date suggests that convergent phenotypes (e.g. reduction and loss of the caudal fins), likely arose by distinct ontogenetic means in pipefish and seahorses. Comparison of the ontogenetic trajectories of S. typhle and H. erectus provides indications that characteristic features of the seahorse body plan result from developmental truncation. Altogether this work provides a valuable resource and framework for future research to understand the evolution of the outlandish syngnathid morphology from a developmental perspective.

Parent-specific transgenerational immune priming enhances offspring defense – unless heat-stress negates it all

“…Over the season, Vibrio bacteria may alter from mutualistic members of the microbiome to virulent disease agents through rapid changes in abiotic factors (e.g., temperature and salinity), reinforced by the increasing frequency of heatwaves in recent years (69)(70)(71). The pipefishes' unique male pregnancy makes them prime model systems for the investigation of trans-generational effects (23,37,38,51,72,73). While mothers may transfer their experience directly through the eggs, fathers prime their offspring through their intimate contact during their male pregnancy that evolved with a placenta-like structure in Syngnathus and Hippocampus, among others (74).…”