Chromosomal relationships of Simulium suzukii, an Old World member of the Simulium tuberosum species group (Diptera: Simuliidae)

Abstract

The banding patterns of polytene chromosomes from the larval silk glands of the black fly Simulium suzukii from Taiwan are resolved relative to other species in the Simulium tuberosum group. Simulium suzukii is chromosomally most similar to the Simulium tani complex, sharing 11 fixed inversions, relative to the standard map for the Simulium tuberosum group, but di#ering by three fixed inversions and by having unique sex chromosomes and autosomal polymorphisms.

Macrogenomic Evidence for the Origin of the Black Fly Simulium suzukii (Diptera: Simuliidae) on Okinawa Island, Japan

“…2–9), and all inversions are numbered. Previously recognized inversions carry the same numbers as those previously recognized for the S. tuberosum group [21], [22], whereas novel inversions within a chromosomal arm bear new, sequential numbers. Fixed inversions are underlined on the maps and italicized in the text; autosomal and sex-linked inversions are in standard type.…”

“…Although Taiwanese material originally was identified morphologically as S. suzukii [34], it is chromosomally more similar to the S. tani complex in Malaysia and Thailand by virtue of the shared IIIL-5 inversion [22] than it is to any analyzed population of the S. suzukii lineage. We, therefore, reassign the Taiwanese material to the S. tani complex and apply a new cytoform designation, ‘L.’ The Taiwan cytoform might represent a distinct species, differing from its closest relatives by three fixed inversions and unique sex chromosomes and autosomal polymorphisms [22].…”

“…The polytene chromosomes were characterized relative to the standard maps for the subgenus Simulium , the S. tuberosum group, and the S. tani complex, according to procedures and terminology previously outlined [21], [22]. Chromosome arms with novel band sequences were photographed under oil immersion (1600x) on an Olympus BX40 compound microscope, and scanned into Adobe® Photoshop® Elements 8 to assemble chromosome maps.…”

“…Simulium suzukii also is known from Amamioshima Island and Tokunoshima Island [18], both in the central island group of the Ryukyus and within about 165 km north of Okinawa Island. Simulium suzukii and the isomorphic, chromosomally similar S. tani Takaoka & Davies of tropical Asia form a subgroup of more than 10 chromosomally differentiated forms in the S. tuberosum species group, some of which might represent distinct species [21], [22].…”

“…The wealth of chromosomal rearrangements in the S. suzukii / tani lineage [21], [22] suggests that a signature of the source population(s) might be found. In addition to using comparative populations of S. suzukii and S. tani previously characterized chromosomally (i.e., from China, Taiwan, and Thailand), we cast a wide net to include new material from Japan, Malaysia, and South Korea.…”