Tembo na pimbi

A common request I get during guide training is to explain the relationship between hyrax and elephants. It seems to be one of the go-to facts when guides see a hyrax- to say “that’s the elephant’s closest living relative” or something along those lines.

In the past scientists studied animal relationships by comparing physical features. There are some features that can change very quickly, and there are features that take a long time to change, but it can be difficult to tell the difference. Scientists have to be very careful to identify features that changed more slowly over evolutionary time to determine relationships than features that change quickly over evolutionary time.

For example, both genets and cats have retractable claws, but genets are not cats. They are in the same family as civets (the Viveridae). Cats are in the cat family (the Felidae). Likewise, cheetah’s claws are different from the other cats which leads a lot of people to think that they’re not true cats, but of course they are. This is an example of a feature that can change fairly quickly- claw shape or function. This is also an example of what we call convergent evolution, where unrelated groups of animals develop a similar looking solution to an environmental challenge. (Read about the cheetah here).

If we want to understand animal relationships, we need to look at things that are deeper. Leg and foot bone structure is a fairly good one. We put zebra and horses together with the rhinos because they’re standing on the same fused toes. The horse family has just taken it to an extreme of standing on just one. There’s also fossil evidence of a three-toed horse so it makes sense that they’re closely related, and there are other features like their digestive systems that reinforce these relationships. Another good feature is to look at reproductive organs and in mammals, features like the structure of the placenta. No one doubts that the marsupials in Australia are more closely related to each other than they are to mammals outside of Australia.

Africa has a set of animals whose evolutionary history is deeply rooted called the Afrotherians. Between about 105 million years ago and less than 40 million years ago, Africa was isolated from the other continents. A “mother group” of mammals evolved on the isolated island and filled a lot of different niches from tiny insect eating elephant shrews and golden mole, to the termite eating Aardvark. One branch of that tree evolved into the elephants and hyrax and it might surprise you that sea cows or dugongs also come from this branch. Because they share an ancestry, they share some deep-rooted physical features- like placenta shape. There are some features that elephants and hyrax share. People also like to point out their jaw and skull shape, foot bone structure, and a few things like that, but the truth is that those features don’t actually make us sure. If you compare the digestive system of a hyrax with a zebra, they look and function much more alike than a hyrax stomach and an elephant stomach. The challenge is to figure out their ancestry or in other words evolutionary history. This is where advances in science really help.

We know that our DNA comes from our parents and that by comparing DNA between species and families we can get a more accurate picture of how things are related than by comparing physical features that could give us a false picture. Techniques for comparing DNA have improved and become a lot cheaper and currently the information that we’re getting from DNA studies is revealing some surprises. These techniques have also confirmed the hyrax and elephant relationship, but it is one that is very old. 

If you want to get technical, when you’re looking at a bush hyrax (the most common hyrax) it’s actual closest relative is the tree hyrax. Their next closest relative will be a rock hyrax. The elephant we see in East Africa’s closest living relative is of course the Forest elephant of the Congo basin, and their closest relative- the Indian elephant. Some studies show that the elephants are actually also more closely related to the dugongs than they are to hyrax. Both lineages also have a lot of other closely related species that went extinct. The wooly mammoth, the fossilized elephant species found in Olduvai are all more closely related to the elephant than hyrax. Likewise, there are a lot of species of hyrax that went extinct when the hares, ruminant and rodent lineages invaded Africa.

(Swahili version)

Hua ninapokea swali mara kwa mara nikiwa ninafanya mafunzo ya ‘guide’ kuelezea uhusiano kati ya pimbi na tembo. Ni jambo la kawaida ya ‘guides’ kuona pimbi halafu kuelezea kwamba “huyo ni ndugu wa karibu wa tembo kuliko mnama mwingine wowote” au kitu kama hicho.

Zamani watafiti walichunguza uhusiano kati ya wanyama kwa kufananisha sini. Kuna sini zingine zinabadilika haraka, na kuna sini zinazochukua muda mrefu kubadilika, lakini inaweza kuwa ngumu kutofautisha. Wanasayansi wanahitaji kuwa makini kutambua sini zinazochukua muda mrefu zaidi kubadilika ili kugungdua uhusuiano kuliko sini zinazobadilika haraka.

Kwa mfano, ngawa (’genet’) na paka wote wana kucha zinazorudi ndani, lakini ngawa sio paka. Ngawa wapo kwenye familia mmoja na fungo. Hiyo familia inaitwa ‘Viveridae’. Paka wako kwenye familia ya paka (‘Felidae’). Vilevile, duma ana kucha tofauti na paka wengine, jambo linachowapelekesha watu kuhisi kwamba duma sio paka, lakini hakika ni paka. Huu ni mfano wa alama inayoweza kubadilika haraka – mchoro wa kucha au kazi yake. Pia ni mfano wa mabadiliko yanayoelekea mamoja ya spishi tofauti – ‘convergent evolution’, ambapo aina tofauti za wanyama wanabadilika kwa njia na sura zinazofanana ili kupambana na mazingira. (Soma zaidi huhusu duma na paka kwenye kiungo hichi).

Ukitaka kuelewa uhusiano kati ya wanyama, tunahitaji kuangalia sifa za ndani zaidi. Mpangilio wa mifupa kwenye miguu ni sehemu nzuri kuangalia. Tunawaweka punda milia na farasi pamoja na kifaru kwa sababu wanasimama  juu ya mifupa ya vidole vilivyo ungana. Farasi amechukua hatua zaidi ya kusimama katika kidole kimoja badala ya vitatu, lakini kwenye historia ya wanyama waliogeukia kuwa mawe ‘kisukusuku’ kuna farasi mwenye vidole vitatu, na vinginevyo hata ufananishaji wa sifa zingine kama mfumo wa tumbo huwa unaongeza uhakika wa uhusiano huo. Sini nyingine ya kufananisha ni mfumo wa uzazi, kwa mfano sini ya placenta. Hakuna mtu anakataa uhusiano wa karibu kati wa wanyama wenye vifuko-tumbo ya kubeba watoto wanaopatikana Australia kuliko wanyama wanyonyeshao watoto wao ‘mamalia’ wanaopatikana bara zingine.

Afrika ina kundi la wanyama wenye historia ya mageuzi ndefu wanaoitwa ‘Afrotherian’. Kati ya miaka milioni 105 na si zaidi  ya miaka milioni 40, Afrika ilikua imetenganishwa na bara zingine. Kundi la ‘mammalia’ ilibadilika kwenye kisiwa hicho kilichotenganishwa na kujaza nafasi za maisha tofauti tofauti kuanzia walawadudu wadogo kama sengi na ‘golden mole’, hadi walamchwa kama mhanga. Tawi moja ya ukoo huo ulibadilika kuwa tembo na pimbi, na labda itakushangaza kujua kwamba nguva (dugong) na ng’ombe wa baharini (sea cows). Kwa sababu ya ukoo wao, wanyama hawa wanasifa za ndani zinazofanana, kwa mfano mfumo wa placenta. Kuna sini zingine zinazofanana kati ya tembo na pimbi. Huwa watu wanapenda kuwafananisha kwa fuvu na taya ya tembo na pimbi, na mfumo wa mifupa kwenye miguu, lakini sini hizo hazileti uhakika. Ukifananisha mfumo wa tumbo ya pimbi na punda milia utakuta zinafanana zaidi kuliko mfuma wa tumbo ya pimbi na tumbo ya tembo. Changamoto ni kugundua ukoo na kwa maneno tofauti –  historia ya mabadiliko. Hapa ndipo tunaposaidiwa na maendeleo ya kisayansi.

Tunafahamu kwamba DNA yetu inatoka kwa wazazi wetu na tukifananisha DNA ya spishi na familia tofauti tunaweza kupata picha halisi zaidi ya historia ya mabadiliko kuliko kutofautisha sifa au alama zinazoweza kutupa picha isio kweli. Siku hizi, mbinu za kufananisha kwa DNA zimeendelea sana na kupunguza gharama na habari tunazo zipata kwa kufananisha DNA zinatushangaza kwa vitu vingine. Mbinu hizi zimethibitisha kwamba kuna uhusiano kati ya tembo na pimbi, lakini ni wa siku nyingi sana.

Ukipenda kuingia kiutalamu, unapomtazama pimbi wa vichaka (bush hyrax ambaye ni wa kwaida), ndugu yake wa karibu ni pimbi wa miti (tree hyrax). Ndugu wao wa karibu atakua pimbi wa mawe (rock hyrax). Ndugu wa karibu wa tembo tunayemwona Afrika Mashariki ni tembo wa msituni (Forest elephant) anayepatikana kwenye bonde la Congo, na ndugu yao wa karibu ni tembo wa kihindi. Ukoo hizo nazo zina ndugu wengi waliopotea zamani. ‘Wooly mammoth’, na visukusuku vya tembo waliopatikana Olduvai wana uhusiano wa karibu na tembo wa kwetu kuliko pimbi. Vilevile kuna jamii ya pimbi nyingi zilizopotea wakati sungura, ruminantia, na ukoo wa panya walivyohamia Afrika.

Sources:

Kingdon, J et al., 2013. Mammals of Africa, Volume 1, Introductory Chapters & Afrotheria. Bloomsbury.

Maswanganye, A. Cunningham, M, et al. 2017. Life on the rocks: Multilocus phylogeography of rock hyrax (Procavia capensis) from southern Africa. Molecular Phylogenetics & Evolution, Elsevier.

Asher, R, Bennett, N, & Lehmann, T. 2009. The New Framework for Understanding Placental Mammal Evolution. Bioessays, Wiley.

Kuntner, M. May-Collado, L. Agnarsson, I. 2009. Phylogeny and Conservation Priorities of Afrotherian Mammals (Afrotheria, Mammalia). Zoologica Scripta.