Thermal Adaptation - Cutaneous Water Transport

Internal body temperature is affected by the availability of water to the cells. Osmoregulation is the process of water transfer between cells, and as a direct impactor of body temperature, is closely linked to the thermoregulation of animals. Desert inhabitants are threatened by dehydration, and will perish without adaptations allowing them to access water found in plants, ground surface or underground. The thorny devil is a lizard inhabiting large areas of arid Australian land, where rainfall is irregular and surface water largely unavailable (Sherbrooke 1993). The adaptations that allow the thorny devil to access water, thus regulate internal temperature will be discussed in this post.

(Fig.1 - Thorny Devil (Moloch horridus) in walking stance)
(Clemente et al 2004)

The thorny devil has hygroscopic skin, allowing for accumulation of water to ‘stick’ to the skin surface. Spines and thorns on the skin increase surface area, aiding condensation of water. However, the thick scales it possesses for predatory protection are non-permeable, so an adaptation must have developed to allow transportation of water to the mouth. The thorny devil achieves transportation of water through interscalar channels on its back, in some cases ‘drawing’ water from its legs and stomach to the jaw. The channel is formed by the scale hinge joint that is interconnected with all scale hinges on the body, and composed of a very thin layer of keratin. Capillary forces fill the channels with water and physical pumping mechanisms of the jaw and upper body depress local water pressure, pulling water up through the channels toward the mouth (Sherbrooke 2005). The thorny devil can also access water by walking through wet spinifex and lying on wet substrates such as undersides of rocks. However wet vegetation and rocks are rare occurrences in the desert, so it depends predominantly on accumulation of water on the skin, and subsequent transport to the mouth through capillary channels.

(Fig.2 - Thorny Devil (Moloch horridus) in drinkning stance (A) and in process of jaw movement (B))
(Sherbrooke 1993)

The thorny devil is specifically adapted to living in extremely arid and dry conditions. Its ability to transport water along its capillary inter-scalar channels is gravity defying and fascinating. Extreme environmental conditions are correlated with complex adaptations, and the thorny devil is a perfect example of this. The evolution of species can be achieved in seemingly uninhabitable conditions, as long as genetic variation and enough time is available. 

References:

Sherbrooke, W.C 1993, Rain-drinking Behaviors of the Australian Thorny Devil (Sauria: Agamidae), Journal of Herpetology, Vol. 27, No. 3, pp. 270-275

Sherbrooke, W.C 2005, Functional morphology of scale hinges used to transport water: convergent drinking adaptations in desert lizards (Moloch horridus and Phrynosoma cornutum), Zoomorphology (2007) Vol. 126, pp. 89–102

Figures:

Fig.1: Clemente, C.J, Thompson, G.G, Withers, P.C, Lloyd, D. 2004, 'Kinematics, maximal metabolic rate, sprint and endurance for a slow-moving lizard, the thorny devil (Moloch horridus), Australian Journal of Zoology, Vol. 52, page 488

Fig. 2: Sherbrooke, W.C 1993, Rain-drinking Behaviors of the Australian Thorny Devil (Sauria: Agamidae), Journal of Herpetology, Vol. 27, No. 3, page 272

Thermal Adaptation - Coral Symbiosis

The Great Barrier Reef (GBR) is an important environmental and economic asset to North Queensland. As a result of warming ocean temperatures, six coral bleaching events have occurred in the GBR since 1980 (Berkelmans 2001). Progression of coral bleaching in this ecosystem will affect countless marine species with negative economic impacts to tourism (Strasser et al 1999). This blog post will discuss the potential of thermally-resilient symbiotic algae in order to reduce coral bleaching in the GBR.

Coral is the foundation of the GBR, providing shelter, feeding and breeding grounds for many marine organisms. However due to increasing ocean temperatures, coral bleaching is occurring (Fig.1). A 2001 JCU study found that upper thermal limits of coral in the GBR were only 2-4°C higher than average summer temperature, and within 1°C of daily average temperatures during summer periods (Berkelmans 2001). The white colour is caused by the death of zooxanthellae (Symbiodinium), occurrent within the gastrodermic cells of the coral as a symbiotic relationship (Ban & Graham 2012). The physiology of bleaching is not fully understood but involves the production of oxygen radicals, which are highly corrosive and damage chloroplasts (Berkelmans 2001).

(Fig. 1 - Coral Bleaching events between 1994 and 1998 - dark spots represent reports of bleached coral, light spots represent reports of healthy coral)
(Berkelmans 2001)

Thermal adaptation of coral could be achieved by transplanting heat-resilient zooxanthellae. A 2004 study found that in Guam, corals of the genus Pocillopora associate with both Symbiodinium C and thermally resilient species ‘D’ (Rowan 2004). In a 2006 research project, coral nubbins containing Symbiodinium D were transplanted to Magnetic Island, North Keppel Island and Davies Reef. Magnetic and North Keppel islands experienced significant increases in zooxanthellae density and reductions in bleaching/death of coral. Corals exposed to 32°C in the Keppel control had no zooxanthellae, with more than 60% of corals bleached and the rest dead. After treatment, over 50% of corals in this area at 32°C were surviving with reduced bleaching and significant reduction in mortality (Fig. 2) (Berkelmans & Van Oppen 2006).

(Fig. 2 - Zooxanthellae density in corals before and after transplanting at North Keppel Island sites (bar graph), pie graphs represent coral status; (grey) healthy, (white), bleached and (black) dead) (Berkelmans & Van Oppen 2006)

Coral bleaching is a significant problem for the GBR. In 1998, 87% of 2900 reef systems were affected by at least moderate bleaching (Berkelmans 2001). Coral transplanting has increased zooxanthellae density, and reduced coral bleaching/mortality but only in 30 - 32°C conditions. The increased tolerance of Keppel corals with Symbiodinium D is only about 1 - 1.5°C (Berkelmans & Van Oppen 2006). Transplanting of corals with Symbiodinium D has resulted in increased thermal tolerance of corals, however application of this research as a thermal adaptation would only be effective temporarily as temperatures continue to rise. 

References:

Ban, S.S. Graham, N.A.J. 2012, ‘Relationships between temperature, bleaching and white syndrome on the Great Barrier Reef’, Coral Reefs, Vol. 32, pages 1–12

Berkelmans, R. 2001, ‘Bleaching, upper thermal limits and temperature adaptation in reef corals’, PhD thesis, James Cook University

Berkelmans, R. Van Oppen, M.J.H. 2006, ‘The role of zooxanthellae in the thermal tolerance of corals: a ‘nugget of hope’ for coral reefs in an era of climate change’, Proceedings of The Royal Society of Biology, Volume 273, pages 2305-2312. 

Rowan, R. 2004, ‘Thermal adaptation in reef coral symbionts’, Nature, Vol. 430, page 742

Strasser, R.J. Tsimilli-Michael, M. Pecheux, M. 1999, ‘Perpetual adaptation in a perpetually changing environment as a survival strategy of plants: a case study in foraminifers concerning coral reef bleaching’, Photosynthetica, Vol. 37, pages 71-85

Figures:

Figure 1: Berkelmans, R. 2001, ‘Bleaching, upper thermal limits and temperature adaptation in reef corals’, "Records of bleaching on the reef from 1994 to 1998", PhD thesis, James Cook University

Figure 2: Berkelmans, R. Van Oppen, M.J.H. 2006, ‘The role of zooxanthellae in the thermal tolerance of corals: a ‘nugget of hope’ for coral reefs in an era of climate change’, "Zooxanthella densityGs.e. (bars) and coral condition (pies) of coral nubbins", Proceedings of The Royal Society of Biology, Volume 273, page 2311