Part 9

FIG. 10. Reactions of unformolized antigens of Richmondena, Zonotrichia, and Molothrus with anti-Richmondena serum. FIG. 11. Reactions of formolized antigens of Richmondena, Zonotrichia, and Molothrus with anti-Richmondena serum. FIG. 12. Reactions of anti-Richmondena serum prepared against native antigen with antigens of Richmondena, Zonotrichia, Carpodacus, and Spinus. FIG. 13. Reactions of anti-Richmondena serum prepared against formolized antigen with antigens of Richmondena, Zonotrichia, Poephila, Spinus, and Myiarchus.]

FIG. 14. Serological relationships of Richmondena, Spiza, and Molothrus. FIG. 15. Serological relationships of Richmondena, Spiza, and Molothrus. FIG. 16. Serological relationships of Carpodacus with the richmondenine-emberizine-thraupid assemblage. FIG. 17. Serological relationships of Carpodacus and Spinus with Richmondena and Junco.]

FIG. 18. Serological relationships of Spinus and Poephila with the richmondenines. FIG. 19. Serological relationships of Carpodacus and Spinus with Richmondena and Piranga. FIG. 20. Serological relationships of Poephila and Richmondena with the carduelines. FIG. 21. Serological relationships of Richmondena and Spinus with the estrildines.]

Genera Pi . . . . Piranga C . . . . Carpodacus Po . . . . Poephila E . . . . Estrilda R . . . . Richmondena J . . . . Junco Sn . . . . Spinus M . . . . Molothrus Sz . . . . Spiza Pa . . . . Passer Z . . . . Zonotrichia]

Genera Pi . . . . Piranga C . . . . Carpodacus Po . . . . Poephila E . . . . Estrilda R . . . . Richmondena J . . . . Junco Sn . . . . Spinus M . . . . Molothrus Sz . . . . Spiza Pa . . . . Passer Z . . . . Zonotrichia]

Within the richmondenine-emberizine-thraupid assemblage, Junco and Zonotrichia constitute a sub-group apart from the others. Piranga and Richmondena show close serological correspondence. The present taxonomic position of Spiza in the Richmondeninae, which has been questioned by Beecher (1951a:431; 1953:309), is corroborated at least insofar as the serological evidence is concerned. Certainly, serological correspondence of Spiza with the richmondenine-emberizine-thraupid assemblage is greater than with any other group of birds tested.

It is obvious that the serological affinities of the carduelines do not lie with the richmondenines, emberizines, or thraupids. The carduelines show greater serological correspondence with the estrildines than they do with any of the other groups tested. Further serological investigation involving other species, however, is necessary before the nearest relatives of the carduelines can be determined with certainty.

The two estrildines tested (Estrilda and Poephila) show close serological relationship. Their nearest relatives, serologically, seem to be the carduelines. The classification (Wetmore, 1951) that places Passer in the same family with the estrildines is not upheld by the serological data available. Passer is not, serologically, closely related to any of the birds tested. It is of interest that Beecher (1953:303-305), on the basis of jaw musculature, places Passer and the estrildines in separate families (Ploceidae and Estrildidae, respectively).

Molothrus shows greater serological correspondence to the richmondenine-emberizine-thraupid assemblage than to any of the other birds tested. It is definitely set apart from this group, however, and its position, serologically, is compatible with that based on evidence from other sources.

There seems to be but little argument among ornithologists that icterids, fringillids, and ploceids constitute families which are distinct from one another. If, then, the serological differences between Molothrus (Icteridae) and Richmondena (Fringillidae), between Molothrus and Zonotrichia (Fringillidae), and between Richmondena and Poephila (Ploceidae) are indicative of family differences, there are four families represented by the birds involved. Molothrus represents one family; Piranga, Richmondena, Spiza, Junco, and Zonotrichia, a second; Estrilda, Poephila, Carpodacus, and Spinus, a third; and Passer, a fourth.

CONCLUSIONS

The heterogeneity of the Family Fringillidae has been emphasized by many authors. The relationships of the species now included in this Family have been the subject of much discussion and constitute an important problem in avian systematics.

Sushkin's studies (1924, 1925) of features of the horny and bony palates have served as a basis for the present division of the Family into subfamilies. Recently, Beecher (1951a, 1951b, 1953) and Tordoff (1954) have used these features and others which they thought to be of value in an attempt to clarify the relationships of the species involved.

Beecher's work (1951a, 1951b, 1953) on jaw-musculature is a valuable contribution to our knowledge of the anatomy of passerine birds. His myological studies were so thorough and his presentation so detailed that students who disagree with his interpretations can draw their own conclusions. Beecher (1951b:276) points out that there are two basic types of skeletal muscle--those with parallel fibers and those with pinnately arranged fibers. The muscles with pinnate fibers seem to be more efficient, each muscle having a greater functional cross section for its bulk than does one with parallel fibers. He assumes that muscles with parallel fibers are more primitive, phylogenetically, than are those with fibers arranged pinnately. Since his study of the jaw muscles of the Icteridae (1951a) revealed that patterns of jaw-musculature within this Family remain constant regardless of the methods used in procuring food, he assumes that such patterns may be used as indicators of relationship throughout the entire oscinine group. These two assumptions, then, serve as the basis for his hypothesis concerning relationship and phylogeny within this assemblage. Beecher (1951b:278-280; 1953:310-312) maintains that within the Family Thraupidae there are two main lines which lead with almost no disjunction to the Carduelinae and Richmondeninae. The thraupid-richmondenine line involves a shift in the nature of the m. adductor mandibulae externus superficialis, which becomes more pinnate in the richmondenines. This results in greater crushing power. The thraupid-cardueline line involves a shift in emphasis from the the m. adductor mandibulae externus medialis to the m. pseudotemporalis superficialis and the forward advance of the insertion of the latter. This, also, promotes greater crushing ability. He states that features of the horny palate and of the plumage provide further evidence of close relationship of these groups. He includes, therefore, the Thraupinae, the Carduelinae, and the Pyrrhuloxiinae (=Richmondeninae) in the Family Thraupidae. Beecher (1953:307) indicates that the patterns of jaw-musculature of the Parulinae (wood warblers) and Emberizinae (buntings) are similar and suggests that the buntings had their origin from the wood warblers. He includes these subfamilies, therefore, in the Family Parulidae.

Beecher's reasoning may be criticized on several points. It may be, as he suggests, that muscles with parallel fibers evolved earlier, phylogenetically, than did muscles with pinnate fibers, but he does not give adequate consideration, it seems to me, to the possibility that parallel fibers may also have evolved secondarily from pinnate fibers. Since Beecher (1951a) found that patterns of jaw-musculature within the Family Icteridae were conservative, he is reluctant to admit the possibility of convergence among any of the other families. Differences in patterns of jaw-musculature are, however, functional adaptations and like the bill, which is also associated with food-getting may be subject to rapid evolutionary change. Finally, in attempting to classify the oscines, he has relied almost entirely on a single character--the pattern of jaw-musculature.

Tordoff's attempts (1954) to clarify the relationships of the fringillids and related species are based chiefly on features of the bony palate. He assumes that since palato-maxillaries seem to be absent in the majority of passerine birds, their occurrence in certain nine-primaried oscine groups indicates relationship among these groups. He points out that these bones, when present, are important areas of origin of the m. pterygoideus which functions in depression of the upper jaw and in elevation of the lower jaw. He assumes, therefore, that palato-maxillaries were evolved to provide for a more effective action of the m. pterygoideus. The need for such action could be associated with a seed-eating habit. All richmondenines and emberizines possess palato-maxillary bones either free or fused to the prepalatine bar, but there is no trace of these bones in the carduelines. Carduelines, furthermore, possess prepalatine bars that are characteristically flared anteriorly. This condition does not exist in the richmondenines or in the emberizines.

Tordoff points out, also, that the irregular, erratic migrations of the New World Carduelinae are unlike the more regular migrations of the richmondenines and emberizines. The carduelines, furthermore, are more arboreal in their habits than are these other groups and exhibit a decided lack of nest sanitation during the later stages of nesting, a situation which contrasts with that found in the Richmondeninae and Emberizinae. He suggests, therefore, that the carduelines are not so closely related to the richmondenines and the emberizines as previously has been thought.

Since there are only two cardueline genera, Loximitris and Hesperiphona, endemic to the New World and at least 10 genera with many species endemic to the Old World, Tordoff (1954:15) suggests an Old World origin for the carduelines. He strengthens his argument for this hypothesis by pointing out that in features of the bony palate and in habits the carduelines resemble the estrildines of the Family Ploceidae.

Tordoff (1954:29-30) states that the tanagers not only merge with the richmondenines but also grade imperceptibly into the emberizines. He includes, therefore, the Richmondeninae, Emberizinae, and Thraupinae in the Family Fringillidae. He suggests that the carduelines are ploceids, closely related to the Subfamily Estrildinae, on the basis of structure of the bony palate, geographic distribution, social behavior, and habits such as nest-fouling and nest-building.

Tordoff, like Beecher, has based his interpretations chiefly on one feature--structure of the bony palate. Since this feature also is associated with food-getting, the possibilities of convergence of distantly related species with similar habits and divergence of closely related species with different habits may not be excluded.

The hazard of unrecognized adaptive convergence cannot, of course, be excluded from most fields of taxonomic research, but some features of morphology and biochemistry are notably more conservative than others and undergo slower evolutionary change. Such features are often of utmost importance in distinguishing the higher taxonomic categories.

Most ornithologists are aware that, within the Order Passeriformes, patterns of musculature in the leg have evolved at a slow rate and exhibit little variation within the Order. Differences which do occur, therefore, probably are significant, especially those that are consistent between groups of species. As I have pointed out earlier (p. 184), there are no significant differences in leg-musculature between the Richmondeninae, Emberizinae, and Thraupidae. Indeed, it is difficult to define these groups on the basis of leg-musculature. If these groups are of common origin, the lack of distinct boundaries between them is not surprising. A muscular band which extends from the pars interna of the m. gastrocnemius around the front of the knee is present in every emberizine species that I studied and in the Genus Piranga. With the exception of Spiza none of the richmondenines possesses this band.

The significant differences in leg-musculature which have been discussed above (pp. 183-184) distinguish the carduelines from the New World finches and tanagers. Even the cardueline Leucosticte and the emberizine Calcarius, which resemble one another in general adaptations and in several myological features of the leg (p. 183), agree in significant features of the musculature with the respective groups to which they belong. The carduelines agree in the major features of leg-musculature with the ploceids which I studied.

The use of serological techniques in taxonomic work has two main advantages. The biochemical systems involved in such investigations seem to be relatively slow to change in response to external environmental influences, and the quantitative nature of the results obtained makes possible objective measurement of resemblances among species.

I have pointed out (p. 200) that the carduelines are excluded, serologically, from the distinct assemblage formed by the richmondenines, emberizines, and tanagers. Actually, the carduelines show less serological resemblance to this assemblage than do the estrildines, and most ornithologists agree that the Estrildinae are not at all closely related to the Richmondeninae, Emberizinae, and Thraupidae. Molothrus, representing a family (Icteridae) recognized as distinct from the Family Fringillidae, also more closely resembles the fringillid assemblage, serologically, than do the carduelines. Although the Carduelinae constitute a distinct group serologically, they show greater serological resemblance to the estrildines of the Family Ploceidae than to any of the other species tested. At least the carduelines and the estrildines form a group as compact as the subfamilies of the Fringillidae. Thus, the serological data correlate well with those obtained from the study of the leg-musculature.

Present systems of classification include the subfamilies Passerinae and Estrildinae in the Family Ploceidae. Passer, however, is less closely related to the estrildines serologically than are the carduelines, and is less closely related to the estrildines than Molothrus, an icterid, is to the fringillids. This raises a question as to the homogeneity of the Family Ploceidae as presently recognized by most ornithologists. If the Passerinae and the Estrildinae are placed in a single family, the serological divergence among members of this group is certainly greater than it is in the Family Fringillidae. Additionally, Beecher (1953:303-304) found that the estrildines possess a pattern of jaw-musculature different from those in other ploceids.

The combined evidence from jaw-musculature and serology has caused me to conclude that the estrildines should be excluded from the Family Ploceidae (see below).

In an attempt to clarify the relationships of the Fringillidae and allied groups, I here review briefly the evidence which has been presented. From his studies of jaw-musculature (1951a, 1951b, 1953) Beecher concludes that the Pyrrhuloxinae (=Richmondeninae), the Carduelinae, and the Thraupinae are closely related. He places these groups in the Family Thraupidae. He excludes the Emberizinae from this group and places them with the wood warblers in the Family Parulidae. He suggests that the estrildines constitute a family (Estrildidae) separate from the Family Ploceidae.