Abstracts (first author)
Revisting Gavin de Beer’s classic example of heterochrony: the developmental basis of jaw growth in halfbeaks and needlefish
Author(s): Meyer A, Gunter H, Fan S
Heterochronic shifts in growth can generate novel, adaptive phenotypes that facilitate access to previously unoccupied niches. As they can arise from simple developmental switches, encoded by few mutations, novelties that arise through heterochronic shifts, are ideal systems for investigating the molecular basis of evolutionary change. Fishes from the suborder Belonioidei achieved a vast array of craniofacial morphologies that appear to have arisen through a series of heterochronic shifts. In some species (needlefishes) both the upper and lower jaws are highly elongated in others only the lower jaw (half-beaks). We examined the molecular basis of accelerated heterochronic growth in the lower jaw, relative to the upper jaw in the half beak Dermogenys pusilla, and compared it to a their sister group of the suborder the medaka, where this trait is ancestral, i.e., both jaws are equally long. Previous investigations have identified Calmodulin as a likely molecular determinant of accelerated jaw growth in D. pusilla, as its developmental expression reflects the relative growth of the jaws, while expression remains equal between the upper and lower jaws in medaka. Here we describe new transcriptome-wide analyses identify further candidates for accelerated jaw growth in the halfbeak, which also shed light on the structural composition of the tissues that comprise this morphological novelty. Furthermore, comparative gene expression analyses in medaka provide insights into the ancestral condition, enabling further assessments of mutational changes that may underlie a major heterochronic shift that is shared amongst the Belonoidei. As this shift appears to have been critical enabling the Belonoidei to occupy a greater number of trophic niches than the medaka, we postulate that this heterochronic shift explain the considerably greater evolutionary success of the Belonoidei compared to the medaka lineage.