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The Karyotype of the Yellow Dung Fly, Scathophaga Stercoraria, a Model Organism in Studies of Sexual Selection

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The Karyotype of the Yellow Dung Fly, Scathophaga Stercoraria, a Model Organism in Studies of Sexual Selection

Sonja H Sbilordo et al. J Insect Sci.

Abstract

Knowledge of karyotypical characteristics of a species is essential for understanding how sexually selected and sexually antagonistic traits evolve. The yellow dung fly Scathophaga stercoraria L. (Diptera: Scathophagidae) is an established model system for studies of sexual selection and sexual conflict, but karyotypical data are lacking to date. Here, the karyotype of S. stercoraria was characterized using conventional Giemsa-staining and C-banding techniques. The diploid chromosome set consists of 6 pairs of bi-armed meta- or submetacentric chromosomes. The sex chromosomes are the largest chromosomes and constitute 30% of the total length of the diploid set in females and about 25% in males. Males are the heterogametic sex, and the length of the Y chromosome is about three-quarters of that of the X chromosome. C-banding revealed that both sex chromosomes are largely heterochromatic. In contrast, in the five autosome pairs, heterochromatin is limited to narrow bands in the centromeric regions. This karyotypic information will help provide a more profound understanding of the inheritance of phenotypic variation in reproductive traits and the chromosomal locations of underlying genes.

Figures

Figure 1.
Figure 1.
Mitotic cell spreads of a male (A) and a female (B) Scathophaga stercoraria. The sex chromosomes marked with asterisks (*) stain more darkly with Giemsa. High quality figures are available online.
Figure 2.
Figure 2.
Diagrammatic representation of the Giemsa stained idiogram of the male (A) and the female (B) of Scathophaga stercoraria. Strong labeling is depicted in black, weaker labeling in grey. High quality figures are available online.
Figure 3.
Figure 3.
Mitotic cell spreads of the exceptional female Scathophaga stercoraria with three sex chromosomes (A) after Giemsa staining and (B) C-banding technique. The sex chromosomes are marked with asterisks. The sex chromosomes are stained over almost their entire length using both procedures. All autosomes showed small dark stained bands in the centromeric region after C-banding (B). High quality figures are available online.
Figure 4.
Figure 4.
C-banding of a representative mitotic cell spread of a male Scathophaga stercoraria. Both sex chromosomes are more darkly stained than the C-band negative regions of the autosomes, and the Y chromosome additionally exhibits extensive darkly stained blocks. The autosomes are C-banding negative except for narrow bands in the centromeric regions. High quality figures are available online.
Figure 5.
Figure 5.
Diagrammatic representation of the C-banding idiogram of a male Scathophaga stercoraria. Strongest labeling is depicted in black weaker labeling in grey and C-banding negative regions are depicted in white. High quality figures are available online.

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