Cytotaxonomy of four European species in the Eusimulium vernum group (Diptera: Simuliidae)

Abstract

The polytene chromosomes of four closely related Eusimulium (Roubaud) morphospecies from Europe have been examined. These are Eusimulium vernum (Macquart), E. costatum (Friedrichs), E. cryophilum (Rubtzov), and E. carpathicum (Knoz). Interspecific comparisons indicate that vernum and costatum are homosequential in chromosomal banding pattern; however, costatum does differ from vernum in possessing a conspicuous chromocenter. Both species may have B chromosomes, but these are not identical. Three kinds of vernum populations are found: pure X₀Y₀ (with undifferentiated X and Y chromosomes), pure X₀Y₁ (with males heterozygous for IIS-1 ve), and mixed X₀Y₀/X₀Y₁ populations. Only two European vernum cytotypes are indicated. Eusimulium cryophilum and E. carpathicum share a suite of autosomal polymorphisms as well as a fixed paracentric (IL-2) and a fixed pericentric (IIIP-1) inversion with respect to the vernum "Knebworth" standard. They differ from one another by three fixed inversions (IIS-1, IIIS-3, and IIIS-4). It is argued that at least two siblings, cryophilum A and cryophilum B, exist within cryophilum s.l. Sections 86B and 91C in the long arm of chromosome III appear to be extremely labile for breakage and reunion phenomena because several tandem or near-tandem inversions occur in this area. A cytophylogeny of the taxa under study is presented.