Strict Host Research Articles

Observations on Tripartiella bursiformis, Trichodina nigra and a Pathogenic Trichodinid, Trichodina fultoni

A series of epizootics caused by Trichodina fultoni is reported. Fish kept in running water at 12°c showed severe signs of trichodiniasis. At 12 °C T. fultoni lacked strict host specificity, but demonstrated some preference.

Host Specificity and Long Persistence of Pox Infection in the Flicker (Colaptes auratus)

The persistence of cutaneous lesions of avian pox virus infection in a yellow-shafted flicker (Colaptes auratus) over a period of 13 months is described. Extensive transmission experiments revealed strict host specificity for the. flicker virus. Flicker-to-flicker transmission was achieved, both by inoculation and by cage contact. All attempts to isolate the virus were unsuccessful. The diagnosis of pox virus infection was confirmed by electronmicroscopy.

Physiologic specialization in Rhynchosporium secalis

British isolates of Rhynchosporium secalis show strict host specialization. Five isolates from Argentina and one from Australia behave similarly. Differences in pathogenicity are not apparently correlated with morphological characters of the spores, nor, except to a limited degree, with cultural features.

Studies on the Helminth Fauna of Alaska. X. Morphological Variation in Hymenolepis horrida (Von Linstow, 1901) (Cestoda: Hymenolepididae)

Specific identification of hymenolepidid cestodes whose life cycles are unknown is, of necessity, based upon morphological characters which are frequently subject to variation. Cestodes of the genus Hymenolepis Weinland, 1858, parasitic in certain rodent groups, are especially difficult to differentiate if they do not possess scolex armature; such characters as number, size, and shape of hooks are relatively stable. Any attempt toward the establishment of valid differential taxonomic characters for these may present problems which often appear insurmountable because of intersegmental and interstrobilar morphological variation. With the possible exception of intersegmental variation in certain specimens, the differences between strobilae of the same occurring together in a single host individual are generally slight. However, differences may appear to be marked when comparisons are made of specimens from a large series of conspecific host animals. Individual differences often become apparent in such specimens if the hosts represent widely separated geographical localities. In cestode which do not evidence very strict host specificity, it is possible that morphological variation may be more pronounced than in with more rigid host specificity. The possible influence of the host species, however, cannot be evaluated at present, since the phylogenetic relationships of most unarmed hymenolepidid cestodes, together with their ecological associations within either the definitive or the intermediate host, are too poorly known to permit any judgment. In order to better understand the taxonomic status of a given and those forms most closely resembling it morphologically, it is essential to ascertain the significance of the morphological differences and determine the limits of variation. Only an abundance of material, collected from various host over a wide geographical range, affords the best opportunity for determination of the extent of variation, and the consequent recognition of a completely graded series. Results obtained through a critical analysis of variable may broaden the species-concept as established by the original description, making necessary a revision of the diagnosis. This knowledge should preclude the description of additional new species which are too often based on material representing only an unknown in the pattern of variation of an already described species. During the course of routine identification, certain morphological differences were observed in a number of specimens of Hymenolepis horrida (von Linstow, 1901). The writer has attempted to determine the significance of these differences with regard to speciation, through a critical study of a series of cestodes from various microtine rodents (Table 1) collected over a wide geographical range. It is the purpose of this paper to present data derived from this study and to apply resulting information toward the clarification of the taxonomic status of H. horrida.