생물의 명명에 대한 좋은 글

생물의 명명에 대한 좋은 글

  9월 30, 2008    oulim78

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생물이름과 어원, 명명에 대해 오랫동안 관심을 가져왔는데 외국사이트에서 좋은 글이 있어 인용해봅니다.
해석해보세요. 아주 깔끔하고 잘 정리된 내용이라 읽고 감탄했습니다.
소제목이 붙어있으니 관심있는 주제부터 읽어보는 것도 좋겠습니다.
간단히 소개하면
taxonomy와 systematics의 개념차이, 이름의 필요성, 왜 latin명을 쓰는가?, 종이란, 종을 기술하기, 삼명법을 왜 쓰는가?, 왜 이름(학명)은 변하는가?등에 대한 내용입니다. 관심있는 분들은 재미있게 읽을 수 있을 겁니다.

참고사이트 : http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=108
글쓴이 : Mary Bailey
Mary Bailey is the UK's best-known cichlid writer and has been a PFK regular for decades. Mary has also written and contributed to a number of books, and made several trips to Lake Malawi to cichlids in the wild.
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What's in a name?
Do scientific names leave your mouth feeling dry and head spinning? Does the sight of Latin make you go weak at the knees? Mary Bailey comes to the rescue with her one stop guide to taxonomy.



Copyright © Practical Fishkeeping

A lot of aquarists don't like scientific names. They are perceived as difficult to pronounce, even though we apparently have no such problems with Japanese names such as Kawasaki and Mitsubishi...... And it appears that scientists cannot make up their minds, so the names are always changing. In fact that's an exaggeration, but I concede that it does sometimes feel that bad!

However, there are very good reasons not only for the use of scientific names, but also for those annoying changes. In this article I will try to explain this, as understanding is often a great aid to acceptance!

Taxonomy and Systematics
These two terms are often used interchangeably to refer to our human system of cataloguing animals and plants, but in fact they are two separate aspects of the process that work together hand in hand.

Taxonomy deals with the formation and validity of scientific names. A taxon (plural taxa) is a name, and by extension the group of animals or plants to which it applies. The term taxonomy is used to refer not only to the overall "science" of scientific nomenclature (= names), but also to the nomenclatural status and history of any individual taxon. This will - I hope! - become clearer later.

Systematics is the study of the ancestry and relationships of animals and plants, and their position in the relevant kingdom. If systematics decides that a species is new to science, or occupies a different place in the structure to that previously believed (it may, for example, be the same as another species, or have been placed in the wrong group) then taxonomy steps in and deals with the naming side of things.

The need for names
So why does taxonomy use Latin names? To explain that we must first consider why we need to catalogue all of Nature's creations at all.

Firstly, leaving aside the human compulsion to pigeonhole everything, communication is greatly assisted by the use of names. You might, for example, refer to me as the middle-aged lady with glasses who writes about cichlids for PFK, but it's a lot easier to say Mary Bailey! Also, my neighbours here at Cichlid Towers would be more likely to refer to me as the lady down the lane with the horse, cats, and lots of fish in a shed out back. So, what happens if you meet one of my neighbours? You could both be talking about me without realising you were discussing the same person. Or you might find it slow going constantly describing me in your personal terms of reference. Giving me a name makes it all much easier.

By the same token, it is much easier to refer to Cryptoheros nigrofasciatus (the convict cichlid) by its name than as a small, thuggish cichlid from Nicaragua with black vertical bars. Especially as the typical morph of Amphilophus citrinellus (the Midas cichlid) also comes from Nicaragua, has black vertical bars, is decidedly thuggish, and is small in comparison to many fishes. The description could thus refer to either species. Giving each its own, unique, name resolves this difficulty. And this is, of course, another reason why we use names in general.

But, you might argue, why use a Latin scientific name, why not use the nice easy common name, convict cichlid? Simple, because that is its English common name. In Germany, for example, the common name of the same fish is zebra cichlid. But in English the zebra cichlid is a Lake Malawi species, Metriaclima zebra. So you could find yourself talking to a German hobbyist about zebra cichlids, and you would be talking about completely different species! Very few species have a common name that is used universally all over the world. Even the angelfish that graces most communities is the Segelflosser (sail-fin) in Germany, while to us, of course, a sailfin is a type of molly.

The point is, common names may not be unique (refer to more than one species), and a species may have more than one common name. I tend to tear hair if someone writes to me for information about butterfly cichlids, as this could mean Microgeophagus ramirezi or Anomalochromis thomasi. I did tear hair after paying to have a new mbuna, Pseudotropheus "newsi" railed to me from the north of England some years ago, only to find it was a species I had been keeping and breeding for some time, known to me as Ps. "ornatus".

So why Latin?
Back in the 18th century, recognising the potential for confusion without a strict system of scientific nomenclature, a Swedish scientist named Carl Linn頭 better known to us by his Latin name, Linnaeus - came up with a system for giving each animal and plant its own scientific name, unique to that taxon. The idea had been mooted previously, but Linnaeus was the first to formulate a workable system that soon became universally accepted and is still, essentially, in use today. Effectively, modern taxonomy dates from the publication of Linnaeus's work in 1758.

Latin was chosen as the language of taxonomy because in Linnaeus's day Latin was the normal language of science. And the reason for that was universality. Latin is - and was even then - a "dead" language, not used for normal day-to-day communication for centuries, but one that until recently formed a normal part of education (if you received any education at all). Thus anyone who became an expert in any field was likely to have a knowledge of Latin.

In addition, if a "live" language had been chosen, this would undoubtedly have created conflict and ill-feeling, eg if the language of taxonomy were English, the French, Germans, Italians, etc wouldn't have liked it at all. And vice versa.

Today, of course, Latin isn't in general use any more, even among educated people, but it still has the great advantage of lacking any political connotations. Moreover, because it is different to any of the "live" languages used for writings in which scientific names appear, these names stand out clearly as such. Even so, to make it absolutely clear where a scientific name begins and ends, at genus and species level (see below) we also print them in italics (or underline them in handwritten or typed documents).

Systematics for beginners
But before we give any species a scientific name, systematics must decide where in the animal or plant kingdom it belongs, its systematic placement.

One way of looking at systematics is to imagine something that looks like a sort of huge family tree. However, instead of individuals and marriages in this tree producing the next generation, the elements in our tree are groups, and the tree involves no element of time or ancestry. Except at the very bottom of the tree, each group contains a number (sometimes just one) of other groups, which is itself subdivided to form the next level down.

Thus, at the head of the tree that covers animals we have the kingdom Animales (Latin for animals) which is split into a number of phyla (singular phylum), each of which is in turn split into a number of classes. This system continues through a number of additional descending levels to the bottom of the tree, which is the area that mainly concerns us aquarists. Here, to take an example from my own speciality, we find the order Perciformes, the perch-like fishes, which is split into a number of families, including the family Cichlidae, the cichlids. The Cichlidae are split into a number of genera, each of which contains one or more species. Sometimes the species may be further subdivided into subspecies.

Although this is not a family tree as such, ancestry is a very important factor in its make-up, because at each level in any branch of the tree, all the elements are thought to be more closely related to each other than to the elements in any other branch, and to probably share a single ancestor back in the mists of time. Thus, to take the Cichlidae again: the Perciformes also contains the families Anabantidae (anabantids) and Channidae (snakeheads), and these and all the other families in the Perciformes are what we may think of as "sister" families. Meanwhile all the families that make up the Siluriformes (catfishes) are also "sisters" to each other, but the perciform and siluriform families are only "cousins".

Likewise the genera that make up the Cichlidae are "sisters" but only cousins to the two snakehead genera, Channa and Parachanna. And again at species level - the species within a genus are "sisters"(and if they are very closely related indeed then they are actually called sibling species) but only "cousins" to the species in all the other cichlid genera.

Each group at each level - eg all the phyla, orders, families, genera, species - is made up of all the individual elements from the next level down that exist today or ever existed. Thus, at the top, the Animales comprises every single phylum, order, family, genus, species, and individual that exists or existed in the past, and will expand to include any new ones that come into existence in the future. Systematics and taxonomy also cover extinct species like the dodo and a number of fishes known only from the fossil record!

Meanwhile, at the bottom of the tree, a species comprises all its individuals, living or dead.

Each of these groups, whether it be a phylum, order, family, genus, or species, is termed a taxon, and has a unique name, also a taxon. Guess what, we are back to taxonomy!

What is a species?
But before a species can be given a name, it must be discovered (obviously), studied, and a number of questions asked. What genus does it belong to? Is it really a new species? Or maybe just a subspecies?

And this is where the trouble starts! Our complex system of systematics is something we have evolved to deal with our need to categorise and name Mother Nature's creations.

Unfortunately, however, Mother Nature didn't just wave a magic wand and create all the plants and animals we see today, she has been inexorably at work for billions of years - and still is!

And evolution of new taxa is not a magic wand affair, it does not happen overnight. Effectively, there is probably no single point in time - at least that we can identify - at which we can say, this animal has just become a new species. For example, two populations of a species may be created by a geological upheaval, and start to evolve as they now have separate gene pools and are subject to different environmental pressures and may mutate in response.

For a long time they may remain similar, but eventually they may become so different that they are unmistakeably separate species. However, in between there is a grey area where they have started to diverge, but, if another cataclysm threw them back together, they would merge into a single species again.

An example of this is the forms of Pelvicachromis taeniatus in Cameroon. Each of these inhabits a different river and has evolved individual colour characteristics. However, they can still interbreed, and it is thought that, every decade or so, exceptionally high floods bring populations back into contact, gene pools merge, and the whole process of new forms starts again when the waters subside and new separate populations are created. So they are all a single species.

The question of what constitutes a species is often hotly disputed, with some systematicists (known as "splitters") tending to "create" new species on the basis of small differences and geographical separation, while others ("lumpers") put put them all together as a single species. In all probability both are wrong!

It was thought that DNA study would help resolve the question of whether or not a population had become a species or not, but although many useful clues to generic placement have been found through this research, the dividing line between distinct form and distinct species remains elusive.

Describing a species
Let us assume, however, that our systematicist is lucky and has an indisputably new species, under his microscope. He will have established this by checking that its morphometric characters - scale and fin-ray counts and various measurements and morphological structures (including dentition - the teeth) are different to those of all the other known members of the genus. He will include these counts and measurements in a published description.

He will also describe the coloration of the new fish. Nowadays he may have live specimens or colour photos to work from, instead of describing coloration on the basis of preserved material (invariably quite different in colour to live fishes). Until a decade or so ago almost all descriptions were based on dead, preserved, coloration only.

Nowadays he will also usually have a whole set of specimens, which he gives reference numbers and stores in the archives of one of more institutions as reference material for use by future researchers. The set of specimens is called the type series and their reference numbers are listed in his description.

From them he selects one that he regards as typical, and this is the type specimen or holotype. If he has only one specimen - often the case in the past - then that too is the holotype.

The other specimens in the type series are called paratypes. The holotype will be the primary reference material for the species forever (unless it is lost or destroyed).

And now, having described his new species, our systematist must become a taxonomist and give his new fish a name, using

The trinomial system
The original Linnaean system of scientific nomenclature was binomial, ie consisted of two names - the generic (genus) and the specific (species) - for each species.

However, with the realisation that some species consisted of two or more subspecies, it was necessary for the trinomial system to be introduced, with a third name, the subspecific.

If a species has no subspecies then the subspecific name is not normally cited.

The first subspecies to be discovered and described is termed the nominate subspecies (or nominate form) and its subspecific name is always the same as the specific, eg Oreochromis pangani pangani, while the other subspecies have their own special names, eg Oreochromis pangani girigan.

Genus names are always nouns, and - as Latin names have a gender - masculine, feminine, or neuter. Specific and subspecific names are often adjectives and in such cases their gender (shown by the ending of the name) must agree with the current genus name.

Thus when the Mozambique mouthbrooder - formerly Tilapia mossambica (feminine) - was re-assigned to the masculine genus Oreochromis, the specific name also took the masculine ending mossambicus. If the specific name is a genitive (of someone or somewhere, eg Steatocranus irvinei - "of Irvine") or another noun in apposition (placed next) to the genus name (eg Apistogramma viejita - "little old lady") then it remains unchanged.

You will often find a name and date after the italicised name of a species. This a "quick reference" to the original description: the name is the surname of the author of the species (the person who first described and named it) and the date is the publication date of his work. If the author/date appear in round brackets () this denotes that the species was originally assigned to a different genus. Thus Symphysodon discus Heckel, 1840 was described by Heckel in 1840 and placed in Symphysodon where it has remained, but Metriaclima zebra (Boulenger, 1899) was originally described by Boulenger in another genus (actually as Tilapia zebra).

Why names change
As mentioned earlier, the object of the taxonomic exercise is that every taxon should have its own unique name so that anyone, anywhere in the world, can look at that name and know to precisely which species it refers. However, as we are all aware, in practice it isn't quite that simple, because scientists often change the scientific name. So why is this?

The answer is that science isn't static. Maybe one day we will know everything there is to know and everything will be correct and in its place. But, as knowledge increases and new investigative techniques are developed, scientists realise that errors have been made in the past.

This has been going on for a long time. For example, back in Linnaeus's day scientists thought that the relationship between cichlids and marine damselfishes was much closer than it is, and they were all placed in a single group. This is why today we have a marine genus Chromis and the suffix - chromis crops up in many cichlid genus names. Some cichlids were originally described as Chromis. The first species of Chromis to be described (the type species, the generic equivalent of the type specimen for a species, ie the one on which the description and the name are based) was a marine species, so all the cichlids had to be relocated.

A genus should contain only species that are descended from a common ancestor, and even now some cichlid genera are known to be polyphyletic, which means they contain species from two different ancestries - "cousin species" in other words. Cichlasoma and Haplochromis are two important cichlid genera that have quite recently been revised so they are now monophyletic - ie are descended from a single ancestor. And that is why so many species formerly in those two genera have had to be given new genus names.

There are many other reasons for name changes. For example, two people may have described the same taxon and given it different names. In such cases the earlier name takes precedence and the later one becomes invalid, a junior synonym. An example is Pterophyllum dumerilii, a junior synonym of Pt. scalare, the common angelfish.

Sometimes a name is found to be pre-occupied, which means that somebody else used it earlier and the author of the later taxon didn't realise. This doesn't usually happen within a small area of systematics such as cichlids, or even fishes, where the researcher will know all the names, but does occur if the name has been used in another part of the animal kingdom.

The Lake Barombi mbo cichlid Pungu maclareni was described as Barombia maclareni, but later Barombia was found to already belong to a genus of insects and a new name had to be devised. The former cichlid genus Acara also had to be replaced because pre-occupied.

Doing our bit
None of these changes cause scientists much grief, as they are experts in their field and will thus know the detailed taxonomy (past and present) of each species (or where to find the information), and they will be rapidly aware of any new changes, as part of their job is to keep up to date by reading newly published work on their speciality.

It isn't, of course, as easy for aquarists, but there is no point in us burying our heads in the sand and pretending it isn't happening! If someone we know gets married and changes their name, we don't just keep on using their old name, do we? And it is equally pointless to ignore changes in fish taxonomy. Otherwise we may as well revert to the "cichlid from Nicaragua with black bars" scenario, ie confusion with no chance of clear communication.

Serious hobbyists and dealers, like scientists, try to keep up to date, and can be expected to use the correct (as currently understood) name. If you go back to the hobby literature of the 1940s you will find the guppy referred to as Lebistes reticulatus, but it is, of course, now Poecilia reticulata, and has been for several decades. Doubtless aquarists would still be using the old name if the professionals in the hobby hadn't taken a professional attitude and introduced the new one in books, magazines, shops, etc.

Perhaps the most helpful way for the professionals to help is to use the common name plus the latest scientific name, but mention the earlier one too - eg "the jaguar cichlid, Parachromis managuensis (formerly Cichlasoma managuense)". Thus the new names can gradually become general knowledge in the hobby.

And of course, the true expert will know the old and new names and will know what you are talking about when you ask for advice even if you use an out-of-date name. But please don't be upset or offended if you are gently corrected on the nomenclature!

Even when a new name enters general usage, inevitably books and magazines that predate a name change will use only the old name, so if you want to be well informed on the fishes you keep you may have to put in a little effort and detective work in the matter of names. As with most problems, awareness and acceptance that the problem exists is half the battle!

Pronunciation of Latin names
Latin has not been used in everyday speech since Roman times, and no-one is really sure quite how the Romans themselves pronounced it. So no pronunciation can be judged "right" or "wrong".

Taxonomic Latin is intended primarily for written communication, where, of course, pronunciation doesn't matter at all.

The best course is to pronounce Latin names as closely as possible to how they look, and even this will result in different pronunciations in different countries, as different modern languages pronounce some combinations of letters different ways.

The important point is simply to use these names, and if anyone is ignorant enough to criticise your pronunciation, just ignore them!

Tip
Some names contain Latinised Greek words, and use strange combinations of consonants that represent special Greek letters not in the Roman (or our) alphabet. BUT, we actually use some of these same combinations in English, again where a word is Greek in origin. Thus if you know how to pronounce pterodactyl, Pterophyllum presents no problems! Likewise pseudonym/ Pseudotropheus. In all cases the second letter is the important one, thus a name beginning with Ct (for which I can think of no everyday English word) should be thought of as starting with T. Thus Ctenochromis is pronounced Tee-no-crow-mis

ICZN
The International Commission for Zoological Nomenclature (ICZN)
The ICZN is the governing body for matters pertaining to zoological nomenclature, and publishes a rulebook - the International Code for Zoological Nomenclature (usually known as "The Code" for short) - which is amended and updated as problems are recognised and addressed. The ICZN also adjudicates in the case of (not uncommon) disputes about the validity or otherwise of names and "taxonomic acts".

Botanists have their own, totally separate (but not dissimilar) set of rules and ruling body.
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