Similarity of morphological composition and developmental patterning in paired fins of the elephant shark

Cyrena Riley,Richard Cloutier,Eileen D Grogan

doi:10.1038/s41598-017-10538-0

Cyrena Riley, Richard Cloutier + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-10538-0

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Abstract

Jawed vertebrates, or gnathostomes, have two sets of paired appendages, pectoral and pelvic fins in fishes and fore- and hindlimbs in tetrapods. As for paired limbs, paired fins are purported serial homologues, and the advent of pelvic fins has been hypothesized to have resulted from a duplication of the developmental mechanisms present in the pectoral fins, but re-iterated at a posterior location. Developmental similarity of gene expression between pectoral and pelvic fins has been documented in chondrichthyans, but a detailed morphological description of the progression of paired fin development for this group is still lacking. We studied paired fin development in an ontogenetic series of a phylogenetically basal chondrichthyan, the elephant shark Callorhinchus milii. A strong similarity in the morphology and progression of chondrification between the pectoral and pelvic fins was found, which could be interpretated as further evidence of serial homology in paired fins, that could have arisen by duplication. Furthermore, this high degree of morphological and developmental similarity suggests the presence of morphological and developmental modules within paired fins, as observed in paired limbs. This is the first time morphological and developmental modules are described for the paired fins of chimaeras.

Highlights

Amongst the evolutionary novelties associated to the origin of jawed vertebrates figure the simultaneous presence of paired appendages[1]
The morphology of paired fins in chondrichthyans (Elasmobranchii and Holocephali), which are living gnathostomes occupying a basal phylogenetic position[17], is generally accepted as reflecting a comparatively less derived condition compared to osteichthyans[14, 18], since pectoral and pelvic fins in some osteichthyans have different morphologies and developmental patterns[5, 19]
Chimaeras (Holocephali) occupy a basal phylogenetic position[20], possess the slowest evolving genome of vertebrates currently sequenced[21], and retain a greater number of less derived genes compared to osteichthyans[22]

Summary

Introduction

Amongst the evolutionary novelties associated to the origin of jawed vertebrates (including “placoderms†,” “acanthodians†,” chondrichthyans, and osteichthyans) figure the simultaneous presence of paired appendages (pectoral and pelvic fins or limbs)[1]. The morphology and development of paired fins are not as well characterized, especially in groups occupying a basal phylogenetic position. The morphology of paired fins in chondrichthyans (Elasmobranchii and Holocephali), which are living gnathostomes occupying a basal phylogenetic position[17], is generally accepted as reflecting a comparatively less derived condition compared to osteichthyans (including Actinopterygii and Sarcopterygii)[14, 18], since pectoral and pelvic fins in some osteichthyans have different morphologies and developmental patterns[5, 19]. Chimaeras (Holocephali) occupy a basal phylogenetic position[20], possess the slowest evolving genome of vertebrates currently sequenced[21], and retain a greater number of less derived genes compared to osteichthyans[22]. The main goals of this study are 1) to provide a description of the morphology and chondrification pattern of the pectoral and pelvic fins of C. milii and 2) to verify whether pectoral and pelvic fins have similar morphology and similar chondrification patterns

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