Email updates

Keep up to date with the latest news and content from EvoDevo and BioMed Central.

Open Access Highly Accessed Research

Crocodylians evolved scattered multi-sensory micro-organs

Nicolas Di-Poï and Michel C Milinkovitch*

Author Affiliations

Department of Genetics & Evolution, Laboratory of Artificial & Natural Evolution (LANE), University of Geneva, 1211, Geneva 4, Switzerland

For all author emails, please log on.

EvoDevo 2013, 4:19  doi:10.1186/2041-9139-4-19

Published: 2 July 2013

Abstract

Background

During their evolution towards a complete life cycle on land, stem reptiles developed both an impermeable multi-layered keratinized epidermis and skin appendages (scales) providing mechanical, thermal, and chemical protection. Previous studies have demonstrated that, despite the presence of a particularly armored skin, crocodylians have exquisite mechanosensory abilities thanks to the presence of small integumentary sensory organs (ISOs) distributed on postcranial and/or cranial scales.

Results

Here, we analyze and compare the structure, innervation, embryonic morphogenesis and sensory functions of postcranial, cranial, and lingual sensory organs of the Nile crocodile (Crocodylus niloticus) and the spectacled caiman (Caiman crocodilus). Our molecular analyses indicate that sensory neurons of crocodylian ISOs express a large repertoire of transduction channels involved in mechano-, thermo-, and chemosensory functions, and our electrophysiological analyses confirm that each ISO exhibits a combined sensitivity to mechanical, thermal and pH stimuli (but not hyper-osmotic salinity), making them remarkable multi-sensorial micro-organs with no equivalent in the sensory systems of other vertebrate lineages. We also show that ISOs all exhibit similar morphologies and modes of development, despite forming at different stages of scale morphogenesis across the body.

Conclusions

The ancestral vertebrate diffused sensory system of the skin was transformed in the crocodylian lineages into an array of discrete multi-sensory micro-organs innervated by multiple pools of sensory neurons. This discretization of skin sensory expression sites is unique among vertebrates and allowed crocodylians to develop a highly-armored, but very sensitive, skin.

Keywords:
Crocodylians; Integument; Scale; Sensory organ; ISO; DPR