snell@utzoo.UUCP (Richard Snell) (03/23/87)
Keywords: evolution speciation clines In article <14184@cca.CCA.COM> g-rh@cca.UUCP writes > You are talking about clines (a chain of sub species). a specific >example is the herring gull cline consisting of > >(1) The British lesser black-backed gull, Larus fuscus graellsii, >(2) Scandanavian lesser black=backed gull, Larus fuscus fuscu, >(3) Siberian vega gull, Larus argentatus vegae, >(4) American herring gull, Larus argentatus smithsonianus, >(5) British herring gull, Larus argentatus argentatus > >1 can interbreed with 2, 2 with 3, and so on, but 5 and 1 cannot >interbreed. The difference is one of size -- the British herring >gull is twice as big as the lesser black-backed gull. ^^^^^^^^^^^^ What are your sources for the statements that 2 can breed with 3, and 3 with 4. What evidence do you have that 4 ever _actually_ breeds with 5? A few references would be nice. In fact, 1 and 5 certainly _can_ interbreed, as was shown by the experimental inducement of hybrization by M.P. Harris (Ibis 112:488, 1970). Harris includes a partial review of the instances of non-experimentally induced (i.e., natural) hybridization between these two types of gull. As well, the difference between these "species" is _not_ size. It is primarily colour, particularly the colour of the back. Here are some data on the `size' of the males of these birds (data from _Birds of the Western Palearctic, Vol. 3_, by Cramp and Simmons, 1983). Herring Gull Lesser Black-backed Gull (L. argentatus) (L. fuscus) average winglength 425 mm 430 mm average tail length 170 mm 163 mm range of weights 750-1150 g 770-1000 g The systematics of these large gulls is most complex. It is also poorly understood. The supposed subspecies mentioned above may, or may not, represent biologically meaningful units. Of course, the issue of whether _any_ subspecies are taxonomically meaningful is quite separate from any discussion of clines and their significance. A brief summary of the current taxonomy of these two "species" Herring Gulls (Larus argentatus) and Lesser Black-backed Gulls (Larus fuscus) is in Cramp and Simmons. __ Name: Richard Snell Mail: Dept. Zoology, Univ. Toronto Toronto, Ontario, Canada M5S 1A1 UUCP: {allegra,decvax,ihnp4,linus,pyramid,yetti}!utzoo!snell
g-rh@cca.UUCP (03/28/87)
Richard Snell writes an excellent article on the gull cline. It is always a pleasure to read material from people who have the facts and the current data at hand. He asks for sources for the article I wrote, particularly with reference to interbreeding of intermediates in the claimed cline and the stated size difference between the British lesser black-backed gull and the British herring gull. Fair enough. First of all, the purported size difference was a misreading on my part, for which my apologies. Mea culpa, and all that. The source was "After Man, a Zoology of the Future", by Dougal Dixon St. Martins press, 1981. The dust jacket description of the author reads: "Dougal Dixon studied geology and paleontology at the University of St. Andrews, where he continued as a research student to revise the standard work on the paleontology of the British Isles. In recent years he has worked in publishing and has contributed numerous articles about earth science and evolution to encyclopedias and popular science books. Model making and the creation of animated films occupy much of his spare time..." The book is a fun book -- it is a speculation about the course of evolution in the next fifty million years with the fundamental assumption that homo sapiens goes extinct in the near future. The book definitely is not a scholarly work, but it is a great pleasure to read, and I can recommend it. Although the book is not a scholarly work, it does draw upon and explains a multitude of concepts in Zoology, Ecology, and Evolutionary theory. The prolog contains a summary of major concepts in these fields. Among them is a description of what a cline is, and the example I gave, with no more detail than I gave. It is disappointing to learn that the example is not solid. At least that is what Richard is saying and it seems clear that he has detailed professional knowledge at hand, so I expect that he is right. My guess is that the cited example was a standard example of a cline a number of years ago, and that the author simply used a textbook example, which, in the light of detailed examination turned out to be much less clear cut than was assumed. The book does give a bibliography and a list of sources of reference but there are no specific citations. [In checking the bibliography I note the presence of the notorious Hoyle "Lifecloud" article and Dawkin's "The Selfish Gene", which does not give me warm fuzzy feelings of confidence in the reliability of his sources.] There is a moral here: when you give information, include your sources. There is a tendency on my part, and I suppose on many people's part, to read something and remember the assertion without remembering where it came from. The result is that one ends up "knowing" a lot of things as isolated "facts" without knowing where they came from or how good they are. -- Richard Harter, SMDS Inc. [Disclaimers not permitted by company policy.]