Thursday, 1 November 2012

Ground Pangolins and Convergent Evolution

On a recent safari I was fortunate to get my first ever sighting of a Ground Pangolin. This animal is quite fascinating.
1.     What is it?

Kakakuona (Swahili) is a mammal that belongs to its own Order called Pholidota. It is a monophyletic order which means there is only one family Manidae.

2.     What is it doing?

Well, the pangolin we found wasn’t doing much because in fact some Hadza had found it and were keeping it to show their children this special animal and probably eventually eat it. Kindly they let it out so that I could take some photos and get a little video. Of course it was tightly curled in a ball leaving only the very hard scales on the outside. This is a very effective defense mechanism and I have friends who have seen pangolins in Selous Game Reserve rolled up the whole day with young lions trying to figure out how to unroll them until the lions eventually get bored and leave.

When the pangolin eventually relaxed and unrolled, it looked around and then started to shuffle on its back legs, holding its front feet off the ground. It’s really quite an interesting sight. Most of the mammals I come across are quadruped. Now these types of things fascinate me, because they make me think about the whole evolutionary process. But I’ll come back to that later.

3.     What is its role in the environment?

This question is sometimes a little tricky because when we think of animals with roles in the environment we often think of keystone species or ecosystem engineers, with an obvious example being elephants. Pangolins eat mostly ants and termites (one website says 70 million a year), but there are so many ants and termites and we see so few Ground pangolins that I wonder whether they have any effect on the population at all. The defense mechanism of pangolins is also so effective that they aren’t a significant prey species for any of the carnivores I know.

But, Ground pangolins aren’t the only species of pangolin in the World. In fact, there are 8 species in the world and some of them must be quite abundant (or were at one time) because every once in a while you hear shocking news about containers full of pangolins being seized on their way to Phillipines or China. So, if pangolins are more abundant in other parts of Africa than here, they will play an important role in controlling ant and termite populations.

Now, one of my approaches in guide training is to try to think not necessarily of the role of an animal in the environment, but why does it have certain features or display certain behavior in other words, what is the role of the environment in shaping an animals behavior and physiology. Every living thing is trying to survive first but with the ultimate goal of reproducing. This leads to competition within species (intraspecific competition), competition between species (interspecific competition), and a whole lot of other interactions like symbiosis or predator-prey interactions.

So, when I look at a pangolin and I see its scales, I immediately think- this is an adaptation that allows the pangolin to escape predation- simply survival. Being a myrmecophagous (ant eating) animal it has to have tools adapted to finding food (survival), which is why it has very strong limbs and big sharp claws for digging into ant nests and termite mounds. Pangolins have long thin sticky tongues that can extend up to 50 cm to lap up ants.

What’s more interesting to me though is that there are a number of species of animals throughout the world that have evolved to be very similar but are in fact not closely related. This is called convergent evolution.

Ants and termites are obviously an extremely abundant and quick reproducing prey species and packed with protein. We know that the pressures for survival are so intense that anytime there is a resource in the environment, animals are going to take advantage of it. And, in taking advantage of it, have better chances of survival, the individuals with features that make them better at exploiting the resource.

So in different areas of the world animals evolve from different lineages to to exploit similar resources, and the similarities are amazing. So Pangolins (Pholidota), Aardvarks (Tubulidentata), South-American Anteaters (Xenartha) have very similar adaptations to eating ants.

Adaptations to a lifestyle of eating ants:
·      Long sticky tongue for lapping up ants and termites
·      Sharp claws and strong limbs for digging into termite mounds and ant nests
·      Reduced or no teeth
·      Big strong tail

The following images are from a book: Evolution in Action: Natural History Through Spectacular Skeletons. Photos by Patrick Gries. 



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