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.

The Gerenuk

Height is a characteristic that is commonly asked about as we grow up. However, not everyone grows to be the height that they originally want to be. I am one of those people. Even though I’m short the only time it really bothers me is when I need to reach for something in a grocery store or something in the top cupboard. In order to get the item I want I have learned that I will need to either climb onto something or find a spatula so I can extend my reach. In north-eastern Africa the gerenuk (Litocranius walleri) will stand on its hind legs in order to reach food.

Gerenuk Standing up
 (Miller, 2005)

The gerenuk has long, slender limbs and an elongated neck which separates it from other gazelles. There are many other herbivores living in the same arid conditions resulting in more competition for food in these areas. To reach higher food sources the gerenuk will stand on its hind legs to reach food that other herbivores are unable to reach. This adaptation also helps them in the arid conditions of Africa (Leuthold, 1978a). By standing on their hind legs they are able to reach food sources that contain more water. Their diet has been found to consist mostly of leaves and the tips of shoots. No herbs or grasses were found in their diet suggesting that they rely more on food sources that are higher up (Leuthold, 1978b).

Even though this adaptation helps the gerenuk reach higher food sources and gives it an advantage over species that can’t reach as high, its legs are fragile. If the gerenuk feels threatened and has to run across uneven ground it is more likely to injure its leg. This can be considered a trade-off between its ability to escape and its ability to continuously get food which affects the cost of survival and costs for future reproduction (Steams, 1989). The costs of not getting enough food most likely outweigh the costs of having fragile legs in gerenuks.

Here’s a video of a gerenuk giving birth and the calf taking its first steps:

References:

Leuthold, W 1978a, ‘On social organization and behavior of the gerenuk Litocranius walleri (Brooke 1878)’, Ethology, vol. 47, no. 2, pp. 194-216, doi:10.1111/j.1439-0310.1978.tb01831.x.

Leuthold, W 1978b, ‘On the ecology of the gerenuk Litocranius walleri’, Journal of Animal Ecology, vol. 47, no. 2, pp. 561-580, doi:10.2307/3801.

Miller, R 2005, Gerenuk standing up, Photo, PBase, <http://www.pbase.com/millerr/image/53997572>

Stearns, SC 1989, ‘Trade-offs in life-history evolution’, Functional Ecology, vol. 3, no. 3, pp. 259-268, doi:10.2307/2389364.

Lyrebird Song

Do you enjoy singing? I think it’s really fun to sing even if I’m not the most talented singer. However, I prefer to sing when nobody is around or when you can’t distinguish my voice in a crowd of people. My attitude towards singing is a lot different from bird species, such as the lyrebird (Menura novaehollandiae), that sing to attract mates.

Lyrebirds have amazing mimicry abilities. They are able to mimic the songs of different birds they have heard and incorporate it into their own song. However, they aren’t limited to songs of other birds. Male lyrebirds will incorporate other sounds they have heard in the forest into their song in order to have a unique song that will attract females. When mimicking songs they will maintain the complex structure of songs but will not repeat elements of the songs as originally heard. There is a trade-off between the accuracy of mimicry and versatility. It has been found that there is strong selection on males that imitate accurately (Dalziell & Magrath, 2012).

When a male is trying to attract a mate it will perform a spectacular display on carefully tended mounds. They will choose positions that give them a good acoustical advantage and in cooler areas, covered in dense ground cover that is cleared for the display (Robinson & Frith, 1981). Even though the song of the lyrebird is considered to be part of its mating ritual that isn’t the case for all birds. The songs of birds can have other purposes such as being territorial. However, Murie (1962) proposed that birds, and other animals, may sing because it is aesthetically pleasing. He argued that as humans we enjoy the beats and melodies of music, not just the lyrics. With this being the case we can assume that this enjoyment can have evolutionary roots and therefore that animals may sing because it is pleasing to the ear. What do you think? Do you think that the enjoyment of music is limited to humans or do animals sing their songs because they enjoy it?

Here is a video of the lyrebird’s song:

References:

Dalziell, AH & Magrath, RD 2012, ‘Fooling the experts: accurate vocal mimicry in the song of the superb lyrebird, Menura novaehollandiae’, Animal Behavior, vol. 83, no. 6, pp. 1401-1410, doi:10.1016/j.anbehav.2012.03.009.

Murie,OJ 1962, ‘Why do birds sing?’, The Wilson Bulletin, vol. 74, no. 2, pp. 177-182, <http://www.jstor.org/stable/4159044>.

Robinson, FN & Frith, HJ 1981, ‘The superb lyrebird Menura novaehollandiae at Tidbinbilla, ACT’, Emu, vol. 81, no. 3, pp. 145-157, doi:10.1071/MU9810145.