Moloch horridus,
commonly known as the Thorny Devil, is a small ant-eating lizard of the family
Agamidae. It inhabits much of arid Australia living in sandy areas vegetated by
spinifex grasses and shrubs (Shark Bay World Heritage Area 2009). Measuring
lengths of less than 20cm, the Thorny Devil has one of the more peculiar scale
constructions of most lizards, where its scales form an array of spines
effectively deterring many predators (Withers 1993). Although these scales
perform various different roles in the life strategy of the Thorny Devil, they
have developed the spectacular ability to transport water over the surface of
their skin.
You may be asking, what is the
purpose of such an adaptation? In order to answer this we must look at the
environment in which the Thorny Devil inhabits. These dry sandy areas are a
hotspot for the Thorny Devils main food source, ants, however it is generally
lacking in large supplies of water, which of course is essential for the Devils
survival. In order to cope with the general lack of long term water sources
available, the Thorny Devil has developed two co-evolved adaptations for the
capture, transport and drinking of water from sporadic rainfall (Sherbrooke et al 2007).
Occurrence records map of the Thorny Devil <http://bie.ala.org.au/species/Moloch+horridus>
The first of these adaptations is
the structure and arrangement of the Thorny Devils scales, where the Devil is
able to transport water using capillary forces generated by scale ‘hinges’, or
channels, located between the scales. This system of water transport has been
observed to be so effective that the devil is able to remove water from damp
sand by rubbing their ventral scales into the sand (Sherbrooke 1993; Wither
1993)
The second of these co-evolved
adaptations is the pumping forces created by the jaw during drinking. In their
study, Sherbrooke et al (2007)
described that once the water holding areas of the scale hinges are saturated
(filled to capacity), capillary forces no longer facilitate the movement of
water toward the mouth. In order to promote water flow through the scale hinges
after saturation, a negative pressure is generated at the jaw and in the mouth
by the movement of the jaw and the tongue, drawing water through the scales and
into the mouth of the Thorny Devil.
References
Atlas of Living Australia, 2013,
Australian Government, viewed 26 May 2014
<http://bie.ala.org.au/species/Moloch+horridus>
Arkive, 2013, Wildscreen, viewed
26 May 2014 < http://www.arkive.org/thorny-
devil/moloch-horridus/video-10.html>
Shark Bay World Heritage Area,
2009, Department of Parks and Wildlife, viewed 25
May 2014 <http://www.sharkbay.org/Thornydevilfactsheet.aspx>
Sherbrooke, W., 1993,
Rain-drinking behaviors of the Australian Thorny Devil (Sauria:
Agamidae), Journal of
Herpetology, vol. 27, no. 3, pp. 270 – 275
Sherbrooke, W et al, 2007, Functional morphology of
scale hinges used to transport
water: convergent drinking adaptations in desert lizards (Moloch horridus and Phrynosoma cornutum), Zoomorphology,
vol. 126, pp. 89 – 102
Withers, P., 1993, Cutaneous
water acquisition by the Thorny Devil (Moloch
horridus: agamidae), Journal
of Herpetology, vol. 27, no. 3, pp. 265 – 270
Zenith Images, 2006, Thorny Devil, Flickr, viewed 26 May 2014
<https://www.flickr.com/search/?q=Thorny+devil>
This is a great adaptation! There are some other examples of arid adapted reptiles (e.g. Namibian dwarf adders) using capillary action to move water across the skin. If it is such a successful strategy for harvesting water, why don’t more arid-adapted reptiles show this adaptation? How long does it take for water to be moved from the substrate surface to the mouth? Very interesting!
ReplyDeleteI'm glad you wrote this blog - I have been meaning to read about how this system worked. Cool little lizard.
ReplyDeleteIt's amazing what adaptations creatures can develop to cope with harsh conditions. Very well written
ReplyDelete