Genetical studies of Arthur Wilson Stelfox

By L. M. Cook

Extracted from Journal of Conchology, Volume 27, pp.526–527

A. W. Stelfox ranks with Oldham and Diver as a major investigator of the genetics of helicid snails. All of them carried out breeding experiments in the time left over from other activities, but in this way discovered or confirmed a very large body of comparative information on C. nemoralis, C. hortensis, H. aspersa and A. arbustorum. Although they published little their work has been influential as a result of discussion, correspondence and exhibition at scientific meetings.

Stelfox began to breed snails at the beginning of the century, starting when he decided to raise to adulthood for his collection some rare varieties of Cepaea taken as juveniles. His principal work on Mendelian genetics was carried out between 1910 and 1930. Later he kept numerous stocks, but did not pursue the avenues he had opened, such as the investigation of linkage and the detailed study of the wide range of colours found in Irish C. nemoralis. Instead, he turned his attention to the inheritance of size and shape, a much more difficult field of study when working with a slow-growing species. He never thought of himself as a geneticist, being more concerned with the ecology and distribution of land mollusca; indeed, his comments on genetical work of his contemporaries were sometimes quite tart. This makes his varied contributions to the genetics of the group the more impressive. The following notes, which trace the course of his genetical activities, are taken from a review by L. M. Cook published in 1970 in the Irish Naturalists’ Journal (Vol. 16, 249—52).

The genetics of Cepaea were first investigated at the beginning of this century by Arnold Lang. Among other things, Lang established the dominance relations of many of the major genes. Stelfox’s early papers on snail genetics, which were published in 1915 and 1918, do the same for the exalbida form of Helix aspersa, controlled by an allelomorph recessive to the typical dark form, and add to the data on C. nemoralis. He showed that hyalozonate banding is recessive to full banding, while punctate, or interrupted banding, is a dominant trait; and that yellow colour is recessive to pink. In addition, the papers contain observations on the biology of the species and on features such as variation in band formula between individuals in a brood, the genetic basis of which has never been fully analysed. He also noticed something that was not understood until the work of Cain and Sheppard many years later, namely that completely unbanded individuals may arise among the progeny of extreme punctate parents.

There followed a period of intensive breeding of C. nemoralis and C. hortensis in which Stelfox investigated the genetic control of banding variants and of the unusual colour forms of nemoralis that occur in Ireland. Some of the results were displayed by Diver at the Sixth International Congress of Genetics in 1932, and must have influenced many workers on genetics and evolution at the time. Most of the breeding was concerned with the effects of allelomorphs at single loci, but Stelfox also contributed to knowledge of the linkage relationships of the genes, his results being quoted in 1934 in a paper on linkage by Sir Ronald Fisher and Diver, and referred to in the 1932 Congress report.

While investigating segregating factors, Stelfox also took an interest in the non-segregating trait shell size in Cepaea nemoralis. The mean dimensions in populations of this species have long interested naturalists in Ireland, owing to the curious distribution of large forms about the country. The species is wide-spread, being present in all counties, and the shells are usually similar in size to British ones. In some areas, however, there are populations of large-shelled individuals, often with a high frequency of the recessive character white lip. Stelfox did much to establish the distribution of the species and of the variant forms. He bred some from two localities, showing that the large size persisted through several generations in the environment of the breeding boxes, where they remained quite distinct from lineages of small-shelled individuals. One of his last papers on molluscs, published in 1968, describes the results of an attempt to modify the expression of another non-segregating trait, scalarifomiity. Stelfox found a “nice scalariform specimen” of C. nemoralis at Strandhill while on the Irish Field Club excursion in 1904. Another appeared unheralded in one of his breeding experiments, all the relatives being completely normal in shape. In helicids these aberrant individuals are always rare in the wild and apparently of low viability. Stelfox began selective breeding of H. aspersa to investigate the condition by crossing two individuals with comparatively high spires that he had found in his garden. In each generation the progeny with the most conical shape were selected, and in his hands the experiment continued over more than a dozen generations. During this period extreme scalariform individuals were produced, showing conclusively that control of shell shape has a genetic component which is responsive to selective breeding. These lines are now being maintained by others. The bulk of his bred material was presented by him to the Manchester Museum, where it forms a very valuable reference collection.