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Geographical variability of the chigger species Neotrombicula autumnalis and its interrelationships with N. caucasica stat. nov. (Trombiculidae)

A.A. Stekolnikov

Parazitologiya, 31(5): 397-413 (1997) (In Russian, English summary).


Morphological differences between two chigger mite species, Neotrombicula autumnalis and N. caucasica stat. nov., are studied. New localities are reported for both species, for the second - also new hosts. Typical N. autumnalis from Moldova precisely differed from the type series of N. caucasica from Georgia, but our collection on Western Caucasus included large number of intermediate forms. Attempts to draw a boundary between the two species by the linear discriminant analysis were not produced taxonomically reliable result. Thereby we decided to construct a picture of overall dissimilarities between all specimens and to classify them according to the positions of points on the diagram. The method of multidimensional scaling with preliminary selection of characters was applied to produce such picture. The selection was carried out on the basis of cluster analysis, revealed a structure of correlations between standard measurements. The boundary drawn in this way was formalized by the construction of discriminant function.

After that, it has become possible to consider a pattern of variation for different characters. Obvious tendency of a clinal variability, with increase of the sample means from west to east was observed in the majority of characters. And the cline included frequently the samples of both species. Serious taxonomical difficulties arose also from the strong difference between type series and other materials of N. caucasica. However, the basic diagnostic character of N. caucasica, the scutal width, does not correlate with Ip and lengths of setae and, consequently, it cannot be considered as just a "size" character subject to obvious intraspecific ecologically dependent variability. On the contrary, the difference between type and western N. caucasica could be easily interpreted as a result of ecologically caused diminution in the Georgian population of the species.

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