Characterization of Ochetosoma aniarum (Leidy, 1891) (Digenea: Ochetosomatidae) as a biological species using intraspecific variation

Abstract

Inasmuch of prior zoogeographic surveys in Texas did not produce evidence for retaining the separate identity of six closely related digenetic trematode [i.e., Ochetosoma anairum (Leidy, 1891), O. acetabularis (Crow, 1913), O. matricis (MacCallum, 1921), O. texanus (Harwood, 1932), O. orula (Talbot, 1934), and O. wardi (Byrd, 1936)], the four most important sources of populational variation were examined in an attempt to explain the phenic differences between them. These sources of variation included techniques of preservation (artificially induced variation), fluke crowding, fluke age, and the hose (considering both species and size). Statistically significant effects of the sources on the morphological characteristics (mensural and meristic) of the parasite were determined through an examination of an experimental population consisting of laboratory reared offspring from the eggs of a single typical specimen of O. aniarum. The parasite life-cycle established in the laboratory included cultures of the aquatic snail Physa heterostropha and tadpoles of Rana catesbeiana (the first and second intermediate hosts, respectively), and nine species of colubrid snakes (the definitive host). A total of 255 gravid flukes were retrieved from the experimental infection, and compared morphologically to the O. aniarum complex. Results follow: 1) The range of expression of gross morphological features in the experimental population, found to be primarily intrinsic, was greater than that of the complex. 2) It was shown that the linear dimensions and two-dimensional size estimates of the characteristic structures are predictable in their response to particular extrinsic factors, e.g., sizes of the muscular structures (oral sucker; acetabulum, and pharynx) were not significantly affected by fluke age. 3) An evaluation of the extrinsic effects on the morphometric criteria showed that linear dimensions were the least stable and the most liberal in the range of variation, two-dimensional size estimates [(length + width)/2] were more stable and more conservative, and certain ratios derived from linear dimensions and sizes were very stable and the most conservative. 4)...