Another Case of Species Versus Subspecies

Abstract

Herpetological and systematic literature has recently been augmented by the appearance of a very admirable revision and summary of Long-Nosed Snakes of the Genus Rhinocheilus (Trans. San Diego Soc. Nat. Hist., vol. 9, No. 29, 1941, pp. 289-332, pis. 12-13, map) from the prolific pen of Laurence M. Klauber. The work mentioned was completed with no less painstakingly accurate care than usual in Klauber's studies; in fact only because of this thoroughness was the study brought to a satisfactory conclusion. More than one other author in recent years has given up a study of this genus with its seemingly meaningless complexity of variation of many types. The genus includes certain forms occurring in Mexico, the herpetological fauna of which has been a subject of my interest for some time, and accordingly I have had more than casual reason for examining Klauber's arrangement of species and subspecies. Only through a different manner of interpretation of his data can I suggest a certain change in the arrangement he proposes. The map reproduced herewith from Klauber's paper shows the distribution of the four forms of the genus, all of which he concludes represent subspecies of a single species. Two of the subspecies (antonii and tessellatus) are geographically distinct, while two others (clarus and lecontei) overlap so extensively both geographically and ecologically (at least no ecological segregation is yet apparent) that the relation between them cannot be visualized as the usual territorial one. As Klauber states (p. 320) : It may be suggested that these two forms were once separated until they had become distinct, but have not recontacted and are spreading through each other's territories, without completely merging into an intermediate pattern. This is a very plausible?? in fact almost inevitable?conclusion if the geographic or territorially theory is assumed to account for the evolution of these two races. This theory is, of course, almost universally accepted as an explanation of most speciation in animals. On the contrary, however, clarus and lecontei may have become differentiated in at least one other fashion?by some type of DeVriesian mutation. In the latter case, admittedly of very little potential occurrence, the newly-formed species may, and presumably usually does, spread through part or all of the range of the parent species, but on the other hand it may, of course, occupy a distinct area, providing conditions (both intrinsic and extrinsic) permit. Accordingly, either Klauber's explanation or the DeVriesian mutation theory may account for the curious association of clarus and lecontei.