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Crocodylian multi-sensory micro-organs (free pdf)

From: Ben Creisler

A new paper in open-access:

Nicolas Di-Poï and Michel C. Milinkovitch (2013)
Crocodylians evolved scattered multi-sensory micro-organs.
EvoDevo 2013, 4:19

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.

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.

The ancestral vertebrate diffused sensory system of the skin was
transformed in the crocodylian lineages into an array of scattered
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.


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