Biodiversity of Simulium metallicum sensu lato (Diptera: Simuliidae), a complex of Neotropical vectors associated with human onchocerciasis

- Three new cytoforms were discovered in the Simulium metallicum species complex.
- The complex now includes a total of 17 cytoforms.
- At least three morphologically corroborated cytoforms are full species.
- None of the new cytoforms is known from current or historical onchocerciasis foci.
- Two groupings, the S. horacioi complex and S. metallicum complex, are recognized.

The polytene chromosomes of 130 larvae of the Neotropical Simulium metallicum complex from Brazil, Costa Rica, and Ecuador revealed five cytoforms, including three ('M', 'N', and 'O') that are new and two ('B' and 'J') that represent range extensions of up to 850 km. The discovery of three new cytoforms brings the total number in the complex to 17. Cytoforms 'B', 'J', and 'N' are reproductively isolated from one another, and their species status is corroborated by morphological evidence. None of the three new cytoforms is known from current or historical onchocerciasis foci, although 'M' inhabits the periphery of the former Ecuadorian Santiago onchocerciasis focus a mere 30 km to the west. The number of fixed chromosomal differences, as many as 24, separating some members of the S. metallicum complex far exceeds that known between members of any other simuliid species complex. Two distinct groupings can be diagnosed within the S. metallicum complex, based on at least eight fixed chromosomal rearrangements and structural characters in the larval stage. Consequently, a recommendation is made to recognize the S. horacioi complex and the S. metallicum complex sensu stricto. Recognition of two separate complexes provides potential phylogenetic content with predictive power for understanding biological phenomena such as vector potential.

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