Three decades of studies on chromosomal polymorphism of Drosophila willistoni and description of fifty different rearrangements

Abstract

Drosophila willistoni (Insecta, Diptera) is considered a paradigm for evolutionary studies. Their chromosomes are characterized by multiple paracentric inversions that make it hard to identify and describe chromosomal polymorphisms. In the present report we attempted to systematize the description of all the 50 inversions found in the last three decades, since we have been studying the chromosomes of several individuals of 30 different populations, including the one used in the genome sequencing project (Gd-H4-1). We present the photographic register of 11 arrangements in the left arm of the X chromosome (XL), eight in the right arm (XR), 10 in the left arm of chromosome II (IIL), eight in its right arm (IIR) and 13 in chromosome III. This information also includes their breakpoints on the reference photomap. A clear geographic difference was detected in XL and XR, with different fixed arrangements depending on the origin of the population studied. Through the comparison of all X arrangements it was possible to infer the putative ancestral arrangements, i.e., those related to all the remaining arrangements through the small number of inversions that occurred in the past, which we will call XL-A and XR-A. In the autosomes (IIL/IIR and III), fixed inversions were detected, but most are segregating in different frequencies along the geographical distribution of the D. willistoni populations.

Drosophila Chromosomal Polymorphism: From Population Aspects to Origin Mechanisms of Inversions

“…The authors founded up to eight breakpoints at the same band in certain chromosomal segments. Similar results were observed in D. subobscura [56], Hawaiian Drosophila [57], and D. willistoni [58].…”

Reassignment of Drosophila willistoni Genome Scaffolds to Chromosome II Arms

“…This strain comes from Guadeloupe Island in the Caribbean, and it was used for sequencing the complete genome of this species ( Drosophila 12 Genomes Consortium 2007 ). For that purpose, the high degree of polymorphism for inversions naturally present in this species ( Rohde and Valente 2012 ) was virtually solved by successive inbreeding ( Drosophila 12 Genomes Consortium 2007 ). The stock was purchased from the UC San Diego Stock Center and maintained at 21° in standard cornmeal−agar−yeast culture medium.…”

“…Drosophila willistoni belongs to the willistoni species group of the subgenus Sophophora . With a widespread geographic distribution in the Neotropical region ( Val et al 1981 ; Bächli 2015 ), it is one of the most polymorphic species for chromosomal inversions in the entire genus Drosophila ( Sperlich and Pfriem 1986 ; Rohde and Valente 2012 ) and is a classic model organism for research in population and evolutionary genetics, speciation, ecological genetics, and molecular evolution ( Ehrman and Powell 1982 ; Krimbas and Powell 1992 ; Markow and O’Grady 2007 ). The karyotype of this species consists of two metacentric chromosomes (X and II) and a rod chromosome (III) ( Dobzhansky and Pavan 1943 ).…”

“…Subsequently, scaffolds were anchored to the polytene chromosomes based on a handful of genetic markers, mainly enzyme loci and other genes taken from classical studies ( Ayala et al 1972 ; Lakovaara and Saura 1972 ; Dobzhansky and Powell 1975 ), and less than 10 gene markers mapped by in situ hybridization (ISH). There is scarcity of gene markers occurring in the metacentric chromosome II, which shows a high level of segregating inversions, mainly in the IIL arm ( Rohde and Valente 2012 ). This chromosome has two similarly sized arms named IIL and IIR ( Dobzhansky 1950 ), which have been traditionally considered homologous to Muller elements C and B, respectively ( Lakovaara and Saura 1972 ; review in Sorsa 1988 ).…”

Characterizing the transcriptional expression and in situ localization of the Dnmt2 gene in Drosophila willistoni

“…In addition to the peculiarity of having sex-specific methylation [15,25], D. willistoni is known to have extensive gene arrangement polymorphisms on all chromosomes [29][30][31][32] willistoni. Most phylogenetic reconstruction software tends to force D. willistoni as an outgroup, based on the high evolutionary rates.…”