Why is Common Gull (canus canus) named Mew Gull (canus brachyrhynchus)?

Gestart door batsvensson, januari 03, 2014, 11:50:20 AM

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batsvensson

I noticed the Common Gull (Larus canus canus) is labeled as Mew Gull (Larus canus brachyrhynchus) at waarnemingen.nl.



From what I understand the Mew Gull has a pale iris while the Common Gull has a dark iris. The bird I have a picture of has a brown iris, i.e. dark, hence it is a L. canus canus.

Waarneming.nl says that the Common gull (Larus canus canus) is a subspecies of the Mew Gull (Larus canus) according to Linnaeus, 1758 (?). But if Common Gull scientific name is L. canus canus and Mew Gull scientific name is L. canus brachyrhynchus then doesn't that mean they share a common ancestor (L. canus)? I understand their scientific names as they can be regarded as belonging to the same genus. Therefore I wonder how the Common Gull possible can be called Mew Gull if none of them are subspecies of each other? Is it because their common ancestor (Larus canus) also is called Mew Gull or what is it that I miss or do not understand correctly in this?

Klaas van Dijk

hi Anders,

There is no agreement between various groups of people & various societies & the literature (etc.) if these group of gulls belong to one species (named Larus canus) or to two species (Larus canus and Larus brachyrhynchus).

There is, however, agreement between all groups that birds belonging to the taxon brachyrhynchus only breed in a region in the Northwestern part of North America (and as well do not occur in Europe).

Besides that, European people are familiar with the vernacular name 'Common Gull', whereas American people are familiar with the vernacular name 'Mew Gull'. This means that there is also no good agreement between all groups of people (etc.) if you should call them 'Common Gull' or 'Mew Gull' when you think its all one species.

Americans talk about 'fall', whereas European people talk about 'autumn'. Americans talk about 'shorebirds', European people talk about 'waders'. That's how it is.

Best wishes,
Klaas

batsvensson

#2
Thanks for the clarification Klaas.

I guess since 'mew' is old English for 'gull', using the name Mew Gull, i.e. "Gull Gull", as a collective name for Larus canus makes more sense than using the name Common Gull.

Btw, I am curious, do brachyrhynchus and canus still interbreed to some extent or are they f.a.p.p. reproductive isolated, or what else would cause an disagreement on the issue weather they are one or two species ?

gull-research.org  states : Brachyrhynchus can be readily told from nominate canus, and therefore sometimes considered a full species: Mew Gull. The differences can be found in the bill (in some birds obviously small), but most in plumage.

I raised an eyebrow when I read this, it seam to me like a very subjective and arbitrary way to judge on if two populations should be considered a sub-species or separate species. I mean, can this be quantified in some general way for any organism how much differences that are required? For instance are black and white people subspecies of Homo sapiens sapiens or two different species, or can a division even be made as Homo sapiens, or has the Tamaskan Dog re-evolved to become a wolf (Canis lupus) or is it still a subspecies of wolf (Canis lupus familiaris) according to the "method" used by gull-research.org ? In other words, what are, if any, the quantification factors?


Klaas van Dijk

hi Anders,

Among biologists there is no worldwide agreement about the definition of a species, but this disagreement does not mean that the concept of species is invalid.

Currently, quite a few ornithological groups follow guidelines in a paper published in 2002 in Ibis, the journal of the British Ornithological Union (see ftp://swfscftp.ucsd.edu/users/bhhanser/Subspecies%20general%20literature/HelbigEtal2002IbisV144n3pp518-525.pdf for a PDF). Several times I have started with reading this paper in order to understand what the authors are trying to tell me. Invariably I failed to understand this, and I got stuck around halfway in this paper.

It seems to me that there is no proof if brachyrhynchus and canus are indeed totally reproductive isolated, or not. So I cannot give you an answer to this question.

"Gulls of Europe, Asia and North America" (Olsen & Larsson reprint of 2004) considers brachyrhynchus and canus as two different species. These authors state: "Mew Gull is the Nearctic counterpart to Common Gull, from which it differs in structure, plumages and mitochondrial DNA (Zink et al. 1995)." Zink et al. (1995) is a paper about mitochondrial DNA, published in the journal Condor (97: 639-649), see https://sora.unm.edu/node/194 (when you would like to read this paper).

You do have a point that it is indeed subjective and arbitrary in such kind of cases (also with the group of Large White-headed Gulls) to judge if two populations are a sub-species or a species. On the other hand, that's how evolution is working and that also means that there are various cases in which you simply cannot decide that any individual either belongs to group A or to group B. So there will always be a grey area, at least in some cases.

Such a grey area is also not a problem for population biologists who are doing research on populations which are clearly separated from each other (eg the population of Brent Geese breeding on Svalbard and the population of Brent Geese breeding in the Russian Arctic).

You might have a point that it should be good that gull-research.org clearly states which kind of species concept they are using (including with a detailed account why they have choosen for that particular species concept).

Best wishes, Klaas

batsvensson

#4
The problem with classification of species is not as much, for known reason, biological but linguistic as well historical in our concept of ideas. If it wasn't for the the fact that most variation of (larger) organisms has died out and erased the smooth transition between organisms we would had treated the classification of organisms (in our language) more like colors than discrete entities and not like kinds as we do now. In principle I do not see any difference between any eukaryote and have no problem as treating them as 'all the same' - some eukaryotes just happens to do some tricks that other don't or can't.

But this does, and should, not prevent use from inventing some arbitrary quantitative system to quantify organisms as different 'species', just as we have done with colors.

Why do I push this point? Well, simply for the reason if ecologist claims a certain species is threaten and advice to allocate resources to preserve, for whatever reasons,  that species to go extinct then we need at least some kind of (arbitrary) objective way to tell what a specie is - and perhaps that definition needs something more than mere a biological foundation but also an ethical part. So it may not only be up to biologist only to decide what and what not should be considered a species but a political as well - because in essence species classification is not a biological but a human problem...

Citaat van: Klaas van Dijk op januari 05, 2014, 10:37:59 AMYou might have a point that it should be good that gull-research.org clearly states which kind of species concept they are using (including with a detailed account why they have choosen for that particular species concept).

Compare their stemente to this:

Caucasians can be readily told from nominate negroid, and therefore sometimes considered a full species: Caucasian. The differences can be found in the nose (in some people obviously small), but most in skin color.

Which obvious shows how arbitrary the statement is (and why it needs to be ethical considered as well)....


Anyway, thanks for the suggested reading... will take a look at them. :-)

batsvensson

Citaat van: Klaas van Dijk op januari 05, 2014, 10:37:59 AM
Among biologists there is no worldwide agreement about the definition of a species, but this disagreement does not mean that the concept of species is invalid.

In my understanding of the species problem, there exists no single unified way to classify an organism as a species but I also understand it as there exist agreement of a precis definition of species for a sufficient small and restricted taxon - which still does not prevent biologist, for whatever reasons, to quarrel more about the chosen method than the actual accuracy of the species definitions itself.

batsvensson

#6
Citaat van: batsvensson op januari 05, 2014, 11:57:18 AM
In my understanding of the species problem, there exists no single unified way to classify an organism as a species but I also understand it as there exist agreement of a precis definition of species for a sufficient small and restricted taxon - which still does not prevent biologist, for whatever reasons, to quarrel more about the chosen method than the actual accuracy of the species definitions itself.

If I trust this expert statement on the words, then it appears as I stand corrected:

It would be a mistake to believe that the adoption of any particular species concept will eliminate subjectivity in reaching decisions.
-- Guidelines for assigning species rank, Hebling et al.

In the next sentence they write:

Adopting a different species concept merely moves the boundaries, and changes the individual taxonomic decisions that are controversial.

Yes, we know, it is arbitrary but it is unclear to me how this prevent it from being objective?


Klaas van Dijk

hi Anders,

There are many reasons why this problems will never got solved.

(1): you cannot look back in history (= carry out detailed studies on any common ancestor of any particular group of birds you are interested in).
(2): all current DNA studies are based on alot of assumptions (eg. about a particular chance of a mutation, and a particular rate of the amount of mutations).
(3): you cannot carry out any experiment you would like to carry out (eg, mating experiments with populations of birds living on islands and populations living on the mainland, and/or with populations living on different islands, etc.).

Good to see you also came across such unclear sentences in the paper of Helbig et al. Please also be aware that it is not a 'peer-reviewed' paper (in contrast to other papers in Ibis), but an 'opinion' of the "BOU's Taxonomic Subcommittee".

Best wishes, Klaas

batsvensson

#8
Citaat van: Klaas van Dijk op januari 05, 2014, 13:00:42 PM
There are many reasons why this problems will never got solved.

(1): you cannot look back in history (= carry out detailed studies on any common ancestor of any particular group of birds you are interested in).

I understand the need of classification with a proper scientific name but the question of being a subspecies or not is a historical question of relations and it is unclear to me why the fact that, to exaggerate strongly, L. c. canus is less related to a carrot than to L. c. brachyrhynchus in any way affects the ability to objectively decide weather and L. c. canus and L. c. brachyrhynchus should be defined as separate species or not?

Citaat van: Klaas
(2): all current DNA studies are based on alot of assumptions (eg. about a particular chance of a mutation, and a particular rate of the amount of mutations).
Why are these assumptions significant for the concept of classifying two population into a different species or not?

Sound more like the presence of genetic variations vindicates differences and just add to the justification to the classification as different species. As I see it the question why genetic variation exists is a historical question about the relation among species not a question weather they are different or not, because genetic variation is obvious a difference - should not the the question for deciding on species based on genetics be based on if a particular variation do or do not exists in different population? Be it that the mutation is there for whatever reasons. Let say a variation exists in two separate, but closely related, population due to coevolution, then that particular species has evolved twice. Again, as I see it, it is a historical question of why (and where) a species exists.


Citaat van: Klaas
(3): you cannot carry out any experiment you would like to carry out (eg, mating experiments with populations of birds living on islands and populations living on the mainland, and/or with populations living on different islands, etc.).
It is unclear to me how this makes the classification of species subjective?

Citaat van: Klaas
Good to see you also came across such unclear sentences in the paper of Helbig et al. Please also be aware that it is not a 'peer-reviewed' paper (in contrast to other papers in Ibis), but an 'opinion' of the "BOU's Taxonomic Subcommittee".

Skimmed through it now and one question that arose in my mind was weather or not a population in a hybridization zone could be regarded, by some obstinate biologists, as a separate species as well... ?

Klaas van Dijk

hi Anders,

Thanks for your extensive answer with alot of new questions and please excuse me for some delay in giving you this reply. I was wondering if you are aware of conflicting ideas of botanists about the amount of species in Taraxacum (a plant, common in The Netherlands). From Wikipedia ( http://en.wikipedia.org/wiki/Taraxacum ):

CiteerThe genus Taraxacum is taxonomically complex, with some botanists dividing the group into about 34 macrospecies, and about 2000 microspecies; approximately 235 apomictic and polyploid microspecies have been recorded in Great Britain and Ireland.[11] Some botanists take a much narrower view and only accept a total of about 60 species.

You wrote: "Why are these assumptions significant for the concept of classifying two population into a different species or not?" It is, eg, assumed that there is a fixed rate of the amount of mutations taking place during a given amount of generations. So you can use this fixed rate to go back in time and to make reconstructions when the DNA of two species (subspecies / populations) was similar to each other, and see if this moment in time can be linked to, eg, climatic events (eg, ice ages).

You wrote: "Skimmed through it now and one question that arose in my mind was weather or not a population in a hybridization zone could be regarded, by some obstinate biologists, as a separate species as well... ?" I don't exclude that biologists might argue that such a population indeeds can be defined as a separate species. This items is as well one of the critics of biologists on the definition in the paper of Helbig et al.

Best wishes, Klaas