Morphological Variation in the Gullet Nematode, Gongylonema pulchrum Molin, 1857, from Eight Species of Definitive Hosts with a Consideration of Gongylonema from Macaca spp.

Abstract

The morphology of Gongylonema pulchrum was studied in specimens from both natural and experimental infections. These included natural infections in man, whitetail deer, domestic sheep, cattle, and pigs; and experimental infections derived from naturally infected sheep, in domestic pigs, white Norway rats, guinea pigs, and European rabbits. In addition, specimens of Gongylonema from natural infections of Macaca spp. were studied. Nematodes from various hosts differed greatly in sizes and proportions of various characters commonly used in nematode systematics. Regression analysis was employed to describe the morphometric variation and evaluate the various characters. Characters showing relatively little variation from regression, low coefficients of variation, and high degrees of correlation with other characters include left spicule length/total body length, right spicule length/left spicule length, glandular esophagus length/total body length, and distance of excretory pore from anterior end of nematode/total body length. These are considered to be the most useful morphometric characters for comparing this species with others of the genus. Specimens from Macaca spp. differed markedly in the ratios of left spicule length/total body length from the corresponding ratios observed for G. pulchrum from all other hosts. They were assigned to G. microgubernaculum Gebauer, 1933 (type host: Macaca mulatta). Transfaunation experiments may be useful in determining the validity of the latter species. Previously neglected details of the oral region of Gongylonema are described. Studies of the range of variation within characters used in the classification of nematodes is basic to their proper classification. However, such information is generally lacking (Chitwood, 1957; Lancaster, 1968). Without such knowledge, recognition of similar species, subspecies, strains, races, populations from different hosts, or even individuals from a single population cannot be made with confidence. The present report describes variation in various characters of Gongylonema pulchrum Molin, 1857, from eight host species and weighs the characters for their systematic value. Gongylonema pulchrum can infect a large variety of definitive hosts, and mature adults from different hosts differ greatly in size (Baylis, 1925; Baylis et al., 1926; Lucker, 1932; Goldberg, 1954; Groschaft, 1962). However, the size differences have been reported only as ranges and means of measurements and have not been described in enough detail for their systematic value to be determined. Systematists generally regard size differences as having little value, but differences in body proportion are usually considered important. Received for publication 29 June 1970. In t e present study, the relationships of pairs of characters are described by regression analysis, thereby providing: (1) quantitative characters of the organism for systematic use; (2) a means of evaluating differences in proportion; and (3) a measure of variation of a character after variation that was due to another has been