Abstract
Two orthopteran species belonging to the East African genus Spalacomimus, S. verruciferus and S. talpa (Tettigoniidae: Het- rodinae), were investigated using both molecular cytogenetic techniques, including fluorescence in situ hybridization with 18S rDNA and (TTAGG) n telomeric probes, and classical techniques, such as C-banding, fluorochrome CMA 3 /DAPI staining, and silver impreg- nation. These techniques allowed us to identify cytogenetic markers that were then used to elucidate chromosome organization and differences between species. Chromosomal complements are reported for the first time for both analyzed species, which showed the same chromosomal number of 2n = 24 and the neo-XY sex chromosome system; however, the morphology of neo-sex chromosomes differs between these species. A cluster of the major rDNA (i.e., the nucleolar organizer region, NOR) was found to be located in the interstitial region of the sex chromosomes of S. verruciferus, whereas it was on the long pair of autosomes in S. talpa. The difference between the karyotypes of the studied species indicate divergent origins of their neo-XY systems. A detailed description of the struc- ture and behaviour of the sex chromosome configuration in male meiosis is provided. In S. verruciferus, the neo-XY system is derived from a Robertsonian fusion between the original acrocentric X and an acrocentric long pair of autosomes bearing an rDNA/NOR locus, leading to a bi-armed X and an acrocentric neo-Y chromosome. The neo-XY in S. talpa arose due to complicated rearrangements, at- tributable to a tandem fusion between the original acrocentric X and part of a medium-sized autosome, and resulting in supernumerary chromosomes. In the latter case, behaviour of the neo-X and neo-Y demonstrates a post-reductional division of these chromosomes. Variation in the evolution of two neo-XY sex chromosome systems are novel phylogenetic markers for the Hetrodinae and seem to promote speciation as important aspect for taxonomy.
Highlights
Hetrodinae are listed as a subfamily of Tettigoniidae
We present the chromosomal pattern of two Spalacomimus species
In S. talpa, two ribosomal 18S DNA (rDNA) clusters, located interstitially on the long pair, were detected (Fig. 1d). 18S rDNA coincident with active nucleolus organizer regions (NORs) was visualized by Ag-NOR staining (Fig. 1e)
Summary
Hetrodinae are listed as a subfamily of Tettigoniidae. The group is restricted to Africa, the Arabian Peninsula, and parts of Mediterranean Europe. Two species belonging to the genus Spalacomimus Karsch, a genus with the highest diversity in East Africa, were investigated cytotaxonomically. We investigated S. talpa (Gerstaecker, 1965) known from the area of Mts Kilimanjaro and Meru (Hemp, 2013) and several other localities in East Africa. The species is nocturnal and males are found in small shrubs and trees at night, performing their calling song. In northern Tanzania, it is a common species found at submontane elevations in coffee-banana plantations on Mt Kilimanjaro, but occasionally occurs in savanna habitats (Hemp, 2013). S. verruciferus (Karsch, 1997) is known from several localities in East Africa but beside collection data no further information is available for this species. Similar to S. talpa, S. verruciferus males perform their calling songs hanging from low branches at night
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