A comparison of reported variation in the morphometrics of Xiphinema diversicaudatum (Nematoda: Dorylaimida) and the effects of some methods of preparing specimens for examination by optical microscopy

Abstract

The effect was examined of 28 combinations of different methods of killing, fixing and mounting specimens in glycerol on the morphometrics of Xiphinema diversicaudatum. Fixation of specimens, after killing, caused significant morphometrical differences when compared with specimens prepared by a standard method (= heat killed in water at 60°C for 5 min). The fixatives caused significant swelling of the body diameters and a shrinkage in length. Mounting specimens in glycerol frequently reduced the effects caused by fixation, but many significant morphometric differences remained after mounting specimens in glycerol when compared with specimens prepared by a standard method. Only the length of body of nematodes appeared not to be affected significantly by killing, fixation or mounting specimens in glycerol. This seemed to be the result of an extension of the anterior to oesophageal-intestinal length counteracting shrinkage occurring in the remaining body length. I t is not practical to recommend the adoption of a procedure for killing, fixing and mounting specimens in glycerol as all methods appeared to affect at least one, if not several, morphometries. However, to identify correctly specimens to the specific rank, especially when morphometrie criteria are being used, some specimens should be processed using the methods employed for type specimens of the most similar species.