Saturday, September 15, 2012

Snapshots of Old Fish Phylogenies, Part I


Phylogenetics became a science with a consistent and objective methodology after the introduction of phylogenetic systematics, or cladistics, by Willi Hennig in the 1950s and 1960s (1, 2). As a life-long student of ichthyology and a scientist who specializes in phylogenetic methods, I have been interested in hypotheses and graphical depictions of phylogenetic relationships of ray-finned fishes that were published prior to the introduction of cladistics.

There is no longer much attention paid to these early views of fish phylogeny, which I think is unfortunate. There is an opinion that with the advent of cladistics, there is no need to study and understand these pre-cladistic hypotheses of fish relationships. However, it is important to note that most biologists in the 19th Century immediately accepted Darwin’s fundamental thesis that all life on Earth shares common ancestry (3). Notable examples of ichthyologists that never accepted evolution include Louis Agassiz, a professor at Harvard University, and Albert K. L. G. Günther. The late 19th and early 20th Century ichthyologists that were thinking about how lineages of fishes were related to one another were explicitly attempting to create taxonomies that reflect hypothesized genealogical relationships. The problem is that prior to Hennig there was no standard method to infer these relationships, which meant that even when using the same type of information scientists could arrive at dramatically different conclusions about phylogeny.

Phylogeny of teleost fishes from E.D. Cope's book, Primary Factors of
Organic Evolution, 1896.
After starting to offer an ichthyology course at the University of Tennessee, and now at Yale University, I started to become interested in the history of the scientific study of fish phylogeny to augment and accentuate my lectures. My foray into pre-cladistic fish phylogenies was greatly helped by Colin Patterson’s masterly review that successfully demonstrates the influence fossil lineages had on the study of teleost relationships (4), with Patterson’s thesis that the most direct path to the inference of phylogeny is the study of living lineages (5).

It is not entirely clear to me what we can specifically learn by studying pre-cladistic efforts at fish phylogeny. Will we discover a hypothesis that is now again finding support in explicit post-Hennig phylogenetic analyses, or will we see reflections of both method and theory that will allow a more nuanced view of how we approach phylogeny inference in the 21st Century? Even if there are no obvious undiscovered gems in these old phylogenetic trees, an understanding of this history will minimally allow us to appreciate the set of objective approaches shared by most comparative biologists interested in phylogeny, regardless of the group of organisms investigated. What I think we do see in these old trees is that the approach used by different scientists to infer relationships was idiosyncratic and often limited by the patterns of biological diversity exhibited in the specific organismal lineage.

Phylogeny of fishes from Gill's 1871 work,
Arrangement of the Families of Fishes, or
Classes Pisces, Marsipobranchii, and
Leptocardii
Among the earliest diagrammatic fish phylogenies are from 1866 (6) by Ernst Haeckel (1834-1919), who is credited with the introduction of the term “phylogeny.” One of the first comprehensive post-Darwin classifications of fishes was introduced by Edward D. Cope (7-9). Cope emphasized osteology as evidence for his conclusions on relationships of fishes (8, p. 446). Cope’s publications on ray-finned fish classification did not include any diagrammatic representation of phylogeny, but his work is noteworthy for the description of Actinopteri and the delimitation of Nematognathi that includes catfishes and sturgeons, and the decision to not recognize Müller’s Teleostei. Twenty-five years later Cope published a branching diagram that represented his views on relationships of what would encompass the teleosts in his book “Primary Factors of Organic Evolution (10).”

The earliest fish phylogeny shown here is from Theodore Gill’s very influential and informed classification of fishes that includes Cope’s Nematognathi and Müller’s Teleostei (11, p. xliii), which as mentioned above, was not recognized by Cope.

Phylogeny of ray-finned fishes from Dean's book
Fishes, Living and Fossil, 1895.
The next fish phylogeny shown here is from Bashford Dean’s (1867-1928) book “Fishes, living and fossil” published in 1895 (12). Dean does not discuss any specifics of this tree, but it appears to reflect Cope's classification because it shows a close relationship of catfish and sturgeons (Nematognathi). Dean was impressed with teleosts stating, “Teleosts have diverged most widely of all fishes from what seem to have been their primitive structural conditions.” Later, Dean notes that convergent evolution is pervasive among teleosts and this makes inferences regarding relationships within the group difficult, “Environment, like a mould, has impressed itself upon forms genetically remote, and in the end has place them side by side, apparently closely akin, similar in form and structure (12, p. 167).”

Part II will begin with George A. Boulenger.

References

1.  Hennig, W. 1950. Grundzüge einer Theorie der phylogenetischen Systematik. Berlin: Deutscher Zentralverlag.
2.  Hennig, W. 1966. Phylogenetic systematics. Urbana: University of Illinois Press.
3.  Darwin, C. 1859. On the origin of species. London: John Murray.
4.  Patterson, C. 1977. The contribution of paleontology to teleostean phylogeny, in Major patterns in vertebrate evolution, P.C. Hecht, P.C. Goody, and B.M. Hecht, Editors. Plenum Press: New York. p. 579-643.
5.  Patterson, C. 1981. Significance of fossils in determining evolutionary relationships. Annual Review of Ecology and Systematics. 12:195-223.
6.  Haeckel, E. 1866. Generalle morphologie der organismen. Berlin: G. Reimer.
7.  Cope, E.D. 1871. Observations on the systematic relations of the fishes. American Naturalist. 5:579-593.
8.  Cope, E.D. 1871. Contribution to the ichthyology of the Lesser Antilles. Transactions of the American Philosophical Society. N.S., 14:445-483.
9.  Cope, E.D. 1872. Observations on the systematic relations of the fishes. Proceedings of the American Society for the Advancement of Science. 20:317-343.
10.  Cope, E.D. 1896. Primary factors of organic evolution. Chicago: The Open Court Publishing Company.
11.  Gill, T.N. 1872. Arrangement of the families of fishes, or classes Pisces, Marsipobranchii, and Leptocardii. Smithsonian Miscellaneous Collections. 11:i-xlvi, 1-49.
12.  Dean, B. 1895. Fishes, living and fossil. New York: Columbia University Press.

7 comments:

  1. Good stuff Tom. Especially like Cope's tree!

    M

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    1. Thanks Mark. At Yale we are supposed to like O.C. Marsh, but I am definitely more of a fan of Cope.

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  2. It seems like your section beginning with, "It is not entirely clear to me what we can specifically learn by studying pre-cladistic efforts at fish phylogeny," makes the point that the emphasis on trees/analysis prevents useful long-term discussion of fish evolution. This seems like the same point highlighted by some folks on your Facebook repost? Isn't the answer to this issue of learning for prior works to focus on characters? In other words, isn't the answer to focus on the underlying data not the results?

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    1. Liam, thank you for your comment. I am not sure what you are referring by the focus on trees versus characters. Any post-Hennig phylogenetic tree will be based on an optimal distribution of character state changes. These old trees are not based on character optimization, and you are right it is often not clear what they are based on. I think the focus on trees, based on character optimization, is how we will understand the relationships and evolution of fishes. One can study the underlying data of any phylogeny published in the early 21st Century, but that was not the case prior to the introduction of phylogenetic systematics.

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    2. Sorry that I was not clear. I guess what I meant was that something like Agassiz's scale characters are still mostly (3/4 to 4/4) relevant for vertebrate relationships. So, those characters and countless others could still be included in a modern analysis. In other words, it is the characters themselves that are the comparative points, not the trees. A character does not have to be discovered in a post-hennig world for it to now be a synapomorphy (or at least included in an analysis). Many characters, like the scales, can be added to modern studies and be useful. It seems clear to me that this is exactly how we can learn from studying pre-cladistic efforts.

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