What’s in a Name?

Part Two: How’s Your Latin?

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The awesomely named Obamadon gracilis.  Image: Reuters

What do Barack Obama, Marco Polo, and the band Green Day have in common? They all have at least one organism named after them. Obama has several, including a bird called Nystalus obamai and an extinct reptile named Obamadon gracilis. Green Day’s honorary organism is the plant Macrocarpaea dies-viridis, “dies-viridis” being Latin for “green day.” Many scientists also have species named after them, usually as recognition for their contributions to a field. My own PhD advisor, Dr. Anne Bruneau, has a genus of legumes, Annea, named after her for her work in legume systematics.

Nashi_pear
“Pear-leaved Pear”   Photo via Wikimedia Commons

Scientific names, which are colloquially called Latin names, but which often draw from Greek as well, consist of two parts: the genus, and the specific epithet. The two parts together are called the species. Though many well-known scientists, celebrities, and other note-worthies do have species named after them, most specific epithets are descriptive of some element of the organism or its life cycle. Many of these are useful descriptions, such as the (not so bald) bald eagle, whose scientific name is the more accurate Haliaeetus leucocephalus, which translates to “white-headed sea eagle.” (See here for some more interesting examples.) A few are just botanists being hilariously lazy with names, as in the case of Pyrus pyrifolia, the Asian pear, whose name translates as “pear-leaved pear.” So we know that this pear tree has leaves like those of pear trees. Great.

In contrast to common names, discussed in our last post, Latin names are much less changeable over time, and do not have local variants. Soybeans are known to scientists as Glycine max all over the world, and this provides a common understanding for researchers who do not speak the same language. Latin is a good base language for scientific description because it’s a dead language, and so its usage and meanings don’t shift over time the way living languages do. Until recently, all new plant species had to be officially described in Latin in order to be recognized. Increasingly now, though, descriptions in only English are being accepted. Whether this is a good idea remains to be seen, since English usage may shift enough over the years to make today’s descriptions inaccurate in a few centuries’ time.

This isn’t to say that scientific names don’t change at all. Because scientific names are based in organisms’ evolutionary relationships to one another (with very closely related species sharing a genus, for example), if our understanding of those relationships changes, the name must change, too. Sometimes, this causes controversy. The most contentious such case in the botanical world has been the recent splitting of the genus Acacia.

acacia
The tree formerly known as Acacia. Via: Swahili Modern

Acacia is/was a large genus of legumes found primarily in Africa and Australia (discussed previously on this blog for their cool symbiosis with ants). In Africa, where the genus was first created and described, the tree is iconic. The image of the short, flat-topped tree against a savanna sunset, perhaps accompanied by the silhouette of a giraffe or elephant, is a visual shorthand for southern Africa in the popular imagination, and has been used in many tourism campaigns. The vast majority of species in the genus, however, are found in Australia, where they are known as wattles. When it became apparent that these sub-groups needed to be split into two different genera, one or the other was going to have to give up the name. A motion was put forth at the International Botanical Congress (IBC) in Vienna in 2005 to have the Australian species retain the name Acacia, because fewer total species would have to be renamed that way. Many African botanists and those with a stake in the acacias of Africa objected. After all, African acacias were the original acacias. The motion was passed, however, then challenged and upheld again at the next IBC in Melbourne in 2011. (As a PhD student in legume biology at the time, I recall people having firm and passionate opinions on this subject, which was a regular topic of debate at conferences.) It is possible it will come up again at this year’s IBC in China. Failing a major turnaround, though, the 80 or so African acacias are now known as Vachellia, while the over one thousand species of Australian acacias continue to be known as Acacia.

The point of this story is, though Latin names may seem unchanging and of little importance other than a means of cataloguing species, they are sometimes both a topic of lively debate and an adaptable reflection of our scientific understanding of the world.

Do you have a favourite weird or interesting Latin species name? Make a comment and let me know!

EVOLUTION TAG TEAM, Part 1: Acacia Domatia

The first in an ongoing series of biology’s greatest duos. (Here’s Part 2 and Part 3)

Home, Sweet Home.
(via: Flickr)

Common Name (Plants): Bullhorn Acacias, Whistling Thorns

  • A.K.A.: Acacia cornigera, Acacia drepanolobium, and several other Acacia species

Common Name (Ants): Acacia Ants

  • A.K.A.: Pseudomyrmex and Crematogaster species

Found: Central America (Bullhorn Acacias) and East Africa (Whistling Thorns)

It Does What?!

Life as a tree is tough, particularly when you live in a part of the world that’s home to the biggest herbivores on Earth and happen to have delicate, delicious leaves. Such is the case for the African acacias. Without sufficient defences, they’d be gobbled up in no time by elephants, rhinos, and giraffes. The trees are known for having huge, sharp thorns, but even that’s sometimes not enough; the lips and tongues of giraffes are so tough and dexterous, they can often strip the leaves right out from between the thorns. So what’s a stressed acacia to do? Recruit a freaking army, that’s what.

Pseudomyrmex ferruginea: the giraffe’s worst enemy.
(Photo by April Nobile)

A few species of acacia in both Africa and Central America (where the herbivores are smaller, but no less voracious) have developed a symbiosis wherein they enjoy the services of ant colonies numbering up to 30,000 individuals, tirelessly patrolling their branches 24 hours a day. Should a hungry elephant or goat wander up and take a bite, nearby patrol ants will call in reinforcements and soon the interloper will be utterly overrun with angry, biting ants. What’s more, the protection extends beyond just animal threats. The ants will go so far as to kill other insects, remove fungal pathogens from the surface of the tree and even uproot nearby seedlings because, you know, they might eventually steal some sunlight from the beloved acacia.

“Trespassers Will Be Drawn and Quartered”
(via Wikimedia Commons)

So what do the troops get out of this? Quite a bit, actually. In ant-protected acacias (‘myrmecophytes’, they’re called), the thorns that normally grow at the base of a leaf swell up. In the Central American species, they grow into something that looks like a bull’s horn (hence their common name), while the African ones become more bulbous. These specialized structures, called domatia, are hollow inside and serve as very convenient housing for the ants. What’s more, the trees produce not one, but two different kinds of nourishment for the colony- regular, and baby food. The adult ants will feed from a sweet liquid exuded by nectaries on the branches. Meanwhile, on the tips of the tree’s leaflets, small white structures called Beltian bodies are formed which are high in the protein every growing child ant-larva needs. These are collected by workers and inserted right into the larval pouches, to be eaten before the ants are even fully formed.

The Bullhorn Acacia, now with more Beltian bodies!
(via Flickr)

Sounds like the perfect partnership, right? Usually, yes, but in nature, a symbiosis is only a symbiosis until one side figures out how to take advantage of the other. From the ants’ side, for example, any energy spent by the tree on reproduction is energy not spent on new homes and sweet, sweet nectar for them. Therefore, the ants will sometimes systematically nip all the flowers off the tree as it attempts to bloom. They’ll also prune the acacia’s outward growth if those new shoots may come into contact with a neighbouring tree, allowing invasion by another ant colony. Conversely, if herbivores become scarce and the acacia no longer requires such a strong protection force, it will begin to produce fewer domatia and less nectar in a move to starve some of the ants out. This has been shown to actually be a bad strategy for the acacia, since the soldiers, not to be outsmarted by a tree, turn to farming and begin raising sap-sucking insects on the bark, thereby getting their sugar fix anyway. And so it goes, oscillating between advantageous partnership and opportunistic parasitism… like so many things in life.

The roomier, more spacious African domatium.
(Image by Martin Sharman)

[Side note: While I’ve never personally encountered ant-acacias, I have disturbed an ant-protected tree of another family in the rainforests of Guyana, and can attest to the fact that the retaliation was both swift and intense. I was in a small boat at the edge of a river collecting botanical specimens, and I nearly jumped in the river to escape the onslaught. Don’t mess with ants.]

Says Who?

  • Clement et al. (2008) Behav. Ecol. Sociobiol. 62: 953-962.
  • Frederickson (2009) American Naturalist 173(5): 675-681.
  • Huntzinger et al. (2004) Ecology 85(3): 609-614.
  • Janzen (1966) Evolution 20(3): 249-275.
  • Nicklen & Wagner (2006) Oecologia 148: 81-87.
  • Stapley (1998) Oecologia 115: 401-405.