The cytology and arval morphology of the Victorian representatives of the subgenus Kiefferulus of the genus Chironmus (Diptera: Nematocera)

Abstract

The larvae of C. martini, C. intertinctus, and the Botanic Gardens species can be distinguished from other Victorian "blood worms" by the structure of the hypostomial plate and the presence of only one pair of blood gills. It is also the case that the larvae of any one species differ from those of the other two in the average length of the fullgrown larva, the length of the blood gills, and the presence of a feeding brush in C. martini. In the adult form the Botanic Gardens species is taxonomically identical with C. intertinctus. All three species possess the usual four salivary gland chromosomes and each species is quite polymorphic. Twelve inversions are known from C. intertinctus, six from the Botanic Gardens species, and nine from C. martini, which is unusual in being polymorphic for three duplications or deficiencies. It is suggested that the similarity between C. intertinctus and the Botanic Gardens species is due to convergence because of their similar ecology.

Biometrical Effects of the Inversion Polymorphism of Kiefferulus Intertinctus (Skuse)

“…Although the two characters studied are both length measures, it is evident that the results observed are not due to a single effect since, as has been shown previously (Martin 1963), these characters are independent during the seasonal changes in larval size. Thus it is not unduly surprising that the inversions apparently have a different effect on larval and ventral tubule length.…”

“…Ventral tubule length was measured to the nearest micrometer unit at x 25 magnification, which represents measurement to the nearest 0·04 mm. As pointed out by Martin (1963), the length of fixed larvae is about 20% greater than that of living larvae, but this difference should be consistent in all specimens. Late prepupae, or larvae which were obviously damaged and therefore not fully extended, were not utilized for measurement.…”

“…The major problem in this study was that the various samples were too small to show any but the most extreme effects, and the results from different samples could not be pooled because of the seasonal variations in size which occur (Martin 1963). Therefore a non-parametric test suggested by Dr. R. E. Blackith (now of Trinity College, Dublin) was used.…”

“…The material utilized in this study came from the localities previously listed by Martin (1962Martin ( , 1963Martin ( , 1965. Fixed larvae were used for measurements because they are easier to handle and are almost straight, requiring very little manipulation to obtain an accurate measurement.…”

“…In the course of cytological studies on the inversion systems of the midge Kiefferulus intertinctus (Skuse), previously called Chironomus intertinctus (Martin 1962(Martin , 1963(Martin , 1965, measurements were made on the fixed larval bodies before dissection to determine whether the inversions have any effect on the size of the 'larva carrying them.…”