Rapid chromosomal evolution in the bush-cricket Gonatoxia helleri Hemp, 2016 (Orthoptera, Phaneropterinae)

Abstract

Gonatoxia helleri Hemp, 2016 is one of the most widespread bush-crickets of the genus Gonatoxia Karsch, 1889 in East Africa. This species with seven large chromosomes (2n♂ = 7) differs from other representatives of the genus Gonatoxia drastically by its reduced chromosome number, the asymmetrical karyotype including karyomorphs rarely found in tettigoniids, as well as in irregularities in the course of meiosis. To better understand the origin of such an exceptional karyotype, chromosomes of 29 specimens from four populations/localities were studied using classical techniques, such as C-banding, silver impregnation, fluorochrome double staining and fluorescence in situ hybridization (FISH) technique with 18S rDNA and (TTAGG)n telomeric probes. FISH showed many 18S rDNA loci as well as interstitial telomeric sequences, where chromosome morphology varied in these components in terms of quantity and distribution. The 18S rDNA loci coincided with active NORs and C-banding patterns. We suggest that a combination of Robertsonian rearrangements and/or multiple common tandem fusions involving the same chromosomes contributed to the formation of this karyotype/karyomorphs. The results are the first step towards a better understanding of chromosomal reorganization and evolution within the genus Gonatoxia. Low chromosome number, together with the incidence of chromosomal polymorphism that is higher in G. helleri than previously reported in bush-crickets, implies that this species can be a valuable new model for cytogenetic and speciation studies. Our findings suggest that chromosomal translocations lead to diversification and speciation in this species and could be the driving force of adaptive radiation.

Karyotypes diversity in some Iranian Pamphagidae grasshoppers (Orthoptera, Acridoidea, Pamphagidae): new insights on the evolution of the neo-XY sex chromosomes

“…These features indicate that the Nocarodeini tribe demonstrate the advanced stage of the neo-Y chromosome evolution in Pamphaginae (Bugrov and Grozeva 1998;Bugrov et al 2016;Jetybayev et al 2017a, b). The fluorescence in situ hybridization (FISH) with telomeric probe and rDNA genes is a very useful tool for comparative analysis of karyotype in Orthoptera insects (Warchałowska-Śliwa et al 2020). In addition, the determination of the position of telomeric and rDNA repeats in chromosomes of many groups of insects made it possible to identify the mechanisms of structural rearrangements (Kuznetsova et al 2019).…”

Highly divergent karyotypes and barcoding of the East African genus Gonatoxia Karsch (Orthoptera: Phaneropterinae)

“…Genomes of three Phaneropterinae genera have uniform karyotypes, with respective chromosome numbers of 2n♂ = 30 + X0 in Parapyrrhicia Brunner von Wattenwyl, 1891 63 and in Plangia Stål, 1873 43 , and 2n♂ = 28 + X0 in Eurycorypha Stål, 1873 37 . In contrast to this apparent uniformity, an extreme case of rapid chromosome evolution was detected in Gonatoxia Karsch, 1889 species 3 , 46 . Gonatoxia is a very fascinating African genus characterized by a high chromosome variability rarely observed in tettigoniids (both in chromosome number and structure, 2n♂ = 28 + X0, 26 + X0 or 6 + X0) and chromosomal polymorphism within and between species.…”

“…Differences in chromosome number (karyotype variability) or chromosomal polymorphism within species are seen in many plant and animal groups, and may be involved in adaptation e.g. 1 – 3 . In closely related taxa that differ in many structural features of their chromosomes, either numerically or morphologically, these changes may reveal reproductive isolation 4 .…”

“…These bushcrickets are fully alate Phaneropterinae, perfectly adapted to the foliage of forests. Only in the last couple of years more information on the bioacoustics 64 and cytogenetics 3 of this genus became available, and new species were described 46 . Gonatoxia maculata Karsch, 1889 (2n♂ = 28 + X0 and 2n = 26 + X0), a species of savanna woodlands and deciduous dry forests, has the most widespread distribution of the genus, with individuals recorded from Somalia, Kenya and Tanzania while G. furcata Hemp, 2016 (2n♂ = 26 + X0) and G. immaculata Karsch, 1889 (2n♂ = 26 + X0) are endemics occurring in wet lowland and submontane forests and coastal and lowland wet forests, respectively.…”

“…Gonatoxia helleri is an especially interesting species because it has the lowest number of chromosomes (2n♂ = 6 + X0) both within its genus and among the Phaneropterinae. Thus, even the most basic characteristics of karyotypes seem to be useful tools to apply in the taxonomy of Gonatoxia 3 , 46 .

Figure 1 Map of geographical distribution and so far known localities (empty circles) and sampling points for Gonatoxia populations in East Africa.

…”