African Bullfrog

I really enjoy winter time. It’s not my favourite season but I usually prefer winter over summer. The main reason for this is because I feel like I can do more do keep myself warm than I can do keep myself warm. When it’s really cold I can add more and more layers and curl up under blankets to stay warm. However, when it’s hot I try to wear as little clothing as possible. Unlike my method, the African bullfrog (Pyxicephalus adspersus) has a different approach to staying cool that involves forming a cocoon with many layers.

The African Bullfrog lives in desert areas and will form a cocoon to hibernate in to reduce water loss. The cocoon is made from the epidermal cell layers that the frog will shed. In six weeks 26 cocoon layers can accumulate around the frog. When the frog emerges it consume the cocoon (Withers, 1995). Before initiating the formation of the cocoon the African bullfrog will remain dormant for 20-30 days. The cocoon has been proven to beneficial early in its development. The rate of water lost by the frog inside the cocoon quickly declines and each cocoon layer increases resistance to evaporation (McClanahan et al., 1983).

The formation of this cocoon is a response caused by dehydration stress. By forming these cocoons the frog is able to survive long periods of seasonal desiccation while they are buried underground (Loveridge & Withers, 1981). Many other desert-dwelling frogs have similar formations of cocoons to survive harsh conditions (Lee & Mercer, 1967). Because a similar adaptation can be found in other species it is likely that convergent evolution occurred because of similar environmental conditions.

 Here's a video of the African Bullfrog helping its tadpoles survive during dry periods:

References:

Lee, AK & Mercer, EH 1967, ‘Cocoon surrounding desert-dwelling frogs’, Science, vol. 157, no. 3784, pp. 87-88, doi:10.1126/science.157.3784.87.

Loveridge, JP & Withers, PC 1981, ‘Metabolism and water balance of active and cocooned African bullfrogs Pyxicepalus adspersus’, Physiological Zoology, vol. 54, no. 2, pp. 203-214, <http://www.jstor.org/stable/30155821>.

McClanahan, LL, Ruibal, R & Shoemaker, VH 1983, ‘Rate of cocoon formation and its physiological correlates in a Ceratophryd frog’, Physiological Zoology, vol. 56, no. 3, pp. 430-435, <http://www.jstor.org/stable/30152608>.

Withers, PC 1995, ‘Cocoon formation and structure in the estivating Australian desert frogs, Neobatrachus and Cyclorana’, Australian Journal of Zoology, vol. 43, no. 5, pp. 429-441, doi:10.1071/ZO9950429.