Cytogenetics and morphotaxonomy of the Simulium (Gomphostilbia) ceylonicum species group (Diptera: Simuliidae) in Thailand

Abstract

The polytene chromosomes of 1,612 larvae of three described morphospecies in the Simulium (Gomphostilbia) ceylonicum species group—S. asakoae, S. inthanonense, and S. sheilae—were examined from 52 sites in Thailand. A standard map for the S. ceylonicum group was established. Ten cytoforms, plus an eleventh from the literature, are revealed on the basis of unique suites of fixed and floating inversions; sex chromosomes are microscopically undifferentiated in all cytoforms. A cytodendrogram, based on shared inversions, shows seven lineages in a polytomy derived from a hypothetical ancestor. Morphological descriptions of the known life stages of each cytoform and keys to larvae, pupae, and polytene chromosomes also are provided. Despite small sample sizes for some cytoforms, all segregates appear to be good species, supported by both chromosomal and morphological evidence. Three reproductively isolated cytoforms for which adequate material is available are formally described as new species. The existence of chromosomally distinct entities within established morphospecies of the S. ceylonicum group supports a recurrent trend of hidden biodiversity in Southeast Asian black flies. The differentiation of taxa that we found in the S. ceylonicum group between northern and southern Thailand conforms to a similar biogeographic trend in diverse organisms.