Rearrangement hotspots in the sex chromosome of the Palearctic black fly Simulium bergi (Diptera, Simuliidae)

Abstract

An extreme example of nonrandom rearrangements, especially inversion breaks, is described in the polytene chromosomes of the black fly Simulium bergi Rubtsov, 1956 from Armenia and Turkey. A total of 48 rearrangements was discovered, relative to the standard banding sequence for the subgenus Simulium Latreille, 1802. One rearrangement, an inversion (IIS-C) in the short arm of the second chromosome, was fixed. Six (12.5%) of the rearrangements were autosomal polymorphisms, and the remaining 41 (85.4%) were sex linked. More than 40 X- and Y-linked rearrangements, predominantly inversions, were clustered in the long arm of the second chromosome (IIL), representing about 15% of the total complement. The pattern conforms to a nonrandom model of chromosome breakage, perhaps associated with an underlying molecular mechanism.

Sympatric speciation in the Simulium arcticum s. l. complex (Diptera: Simuliidae): The Rothfels model updated

“…If break points appeared similar in these regions they were scored as positives. Molecular studies of the basal portion of the IIL region might reveal why so many inversions are located there (Adler et al, ). Such an approach should reveal potential epigenomic/genomic interactions as they may apply to gene regulation where topologically associating domains (TAD's; Spielmann, Lupiáñez, & Mundlos, ) have been shown to play a functional role in gene expression/regulation and where rearrangement break points across vertebrate species are strongly enriched at TAD boundaries and depleted within TAD's across species (Krefting, Andrade‐Navarro, & Ibn‐Salem, ).…”

Geographic structure of sibling species and cytotypes of the Simulium arcticum complex (Diptera: Simuliidae) in rivers of central Idaho and southeastern Washington, United States of America

“…This study also confirms that the proximal region of the long arm of chromosome II is a hot spot for chromosome change (Shields 2013; Adler et al . 2016).…”

When and how do sex‐linked regions become sex chromosomes?

“…Moreover, a Y-or W-linked region's lack of recombination in might reflect rearrangements that spread by genetic drift in a small population (reviewed by Ironside 2010;Ponnikas et al 2018). This cannot explain an overrepresentation on sex chromosomes unless some further mechanism creates a higher rearrangement input rate on these chromosomes (such as the remarkable apparent difference in the Dipteran blackflies; see Adler et al 2016). Unfortunately, comparative tests of whether chromosomes carrying sex-determining loci have a special tendency to subsequently evolve nonrecombining regions are hampered by a reporting bias: sex chromosome differences are readily detectable cytologically, without laborious surveys of all chromosomes in multiple individuals of a species.…”