Lungfish axial muscle function and the vertebrate water to land transition.

Angela M Horner,Bruce C Jayne,David Carrier

doi:10.1371/journal.pone.0096516

Abstract

The role of axial form and function during the vertebrate water to land transition is poorly understood, in part because patterns of axial movement lack morphological correlates. The few studies available from elongate, semi-aquatic vertebrates suggest that moving on land may be powered simply from modifications of generalized swimming axial motor patterns and kinematics. Lungfish are an ideal group to study the role of axial function in terrestrial locomotion as they are the sister taxon to tetrapods and regularly move on land. Here we use electromyography and high-speed video to test whether lungfish moving on land use axial muscles similar to undulatory swimming or demonstrate novelty. We compared terrestrial lungfish data to data from lungfish swimming in different viscosities as well as to salamander locomotion. The terrestrial locomotion of lungfish involved substantial activity in the trunk muscles but almost no tail activity. Unlike other elongate vertebrates, lungfish moved on land with a standing wave pattern of axial muscle activity that closely resembled the pattern observed in terrestrially locomoting salamanders. The similarity in axial motor pattern in salamanders and lungfish suggests that some aspects of neuromuscular control for the axial movements involved in terrestrial locomotion were present before derived appendicular structures.

Highlights

The transition from water to land was a pivotal event in the evolution of vertebrates, and many of the associated morphological innovations, especially those of the appendicular structures, are well documented from a rich fossil record [1]
The segmental axial muscles and skeleton and the sizeable post-anal tail in early tetrapods are all ancient features of chordates and vertebrates that were retained with little apparent modification
EMGs from the most anterior and most posterior locations in the trunk region overlapped an average of 85.0611.9% (Fig. 5)

Summary

Introduction

The transition from water to land was a pivotal event in the evolution of vertebrates, and many of the associated morphological innovations, especially those of the appendicular structures, are well documented from a rich fossil record [1]. The segmental axial muscles and skeleton and the sizeable post-anal tail in early tetrapods are all ancient features of chordates and vertebrates that were retained with little apparent modification. Studies of extant taxa can provide insights into ancient forms of locomotion in several ways. Extant groups with ecological niches similar to those of extinct forms may be placed into putatively ancestral or derived environments to determine how locomotor strategies may vary with changes in habitat

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Conclusion