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Many animals are equipped with specialized defensive systems that function in a
coordinated manner involving morphological structure, physiological processes and
behaviour. Nucho-dorsal glands, unusual organs known in a few Asian natricine
snakes, are believed to function in avoidance of predation, based on the defensive
function of similar organs in a related Japanese species that sequesters prey toxins
and stores them in the glands. We examined the arrangement of the nucho-dorsal
glands of Rhabdophis nuchalis, R. pentasupralabialis and Macropisthodon plumbicolor and tested behavioural responses to tapping stimulation to investigate the spatial distribution of glands on the body and related defensive displays respectively.
We confirmed the presence of glands that extend from the neck along the length
of the body in all three species. The spatial arrangement of the glands was similar
between the two Rhabdophis species, but it differed substantially in M. plumbicolor. In M. plumbicolor, there were two uninterrupted rows of glands throughout
the full length of the body, whereas in the two Rhabdophis species, the position
and size of the glands differed between the neck and trunk regions, with the two
series separated by a spatial gap. In spite of these structural differences, M. plumbicolor and R. pentasupralabialis exhibited a similar defensive display, which we
refer to as body lift, in response to a tapping stimulus on the body. Our study
shows detailed morphological features of the nucho-dorsal glands and a novel display that are consistent with the presumed predator deterrent function of the glands,
which have evolved as a unique defensive system in this lineage of snakes.
