Recherches sur la phylogénie du genreSaga(Orthoptera: Tettigoniidae): données chromosomiques

Abstract

Abstract. Studies on the phylogeny of the genus Saga (Orthoptera: Tettigoniidae): chromosomic data. Combining the fi rst cytogenetic analysis of four European Saga species, and the re-assessment of the karyotype of Saga pedo (Pallas 1771), with published data and the results of investigations in the fi eld, a phylogeny of the species included is proposed. The most ancestral karyotypes seem to be those of Saga ornata Burmeister 1839 and Saga cappadocica Werner 1903, with all autosomes being acrocentrics. The merge of two pairs of their chromosomes resulted in the karyotypes of Saga natoliae Serville 1839 and Saga hellenica Kaltenbach 1967, including one pair of large submetacentrics. These two karyotypes differ by a pericentric inversion on these large chromosomes, that probably took place in S. natoliae. Saga campbelli Uvarov 1921 and Saga rammei Kaltenbach 1965, got an additional chromosomic merge and therefore include two pairs of large submetacentrics. The karyotype of S. rammei has an additional distinctive feature in its heterochromatin. The karyotype of S. pedo is tetraploid, probably the result of juxtaposition of two diploid genomes as a result of hybridisation. The distinctive feature in heterochromatin of S. rammei is found on S. pedo into two distinct chromosomes. Although one could expect quadruplets or doublets of chromosomes, a wide diversity of single chromosomes was noted. This demonstrates that a high rate of chromosomal restructuring has modifi ed the karyotype of S. pedo, after its transition to tetraploidy. These accumulated restructuring, resulting in a high heterozygocity, can be explained by the lack of meiotic barrier for this parthenogenetic species. During our recent research in the fi eld in the south of Balkans, an area with a possible intergradation between Saga pedo and some bisexual closely related species was discovered . The chromosome analysis of specimens from this area will be a main subject for the continuation of our research.

Chromosomal differentiation among bisexual European species of Saga (Orthoptera: Tettigoniidae: Saginae) detected by both classical and molecular methods

“…For both subspecies of S. campbelli it is hypothesized that two Robertsonian translocations and one pericentric inversion, resulted in 2n = 27 (FN = 32) (two metacentric/submetacentric L1, L2 pairs and a subacrocentric X chromosome). The chromosome number of S. campbelli accords with the number recently reported by Lemonnier-Darcemont et al (2008). However, in our study an unexpected chromosome number of 2n = 23 was revealed in S. rammei.…”

“…Cytogenetic differences between these species suggest that chromosomal divergence occurred during their speciation (Warcha owska-liwa et al, 2007). Lemonnier-Darcemont et al (2008) reached the same conclusion after studying of S. campbelli and S. rammei, which both have a chromosome number of 2n = 27%.…”

“…The mechanism that led to the further reduction in the diploid chromosome number remains unclear. Such a significant difference in the chromosome number for a single species, bearing in mind the karyotype variation in the genus, cannot exclude the possibility that the specimens we studied and those studied by Lemonnier-Darcemont et al (2008) belong to two different species. These differences may be caused too by inter-species hybridization or population polymorphism, but this remains to be resolved and additional samples from Macedonia need to be analyzed.…”

“…However, in our study an unexpected chromosome number of 2n = 23 was revealed in S. rammei. Lemonnier-Darcemont et al (2008) describe S. rammei as having 2n = 27. Our data indicate a tendency for a further reduction in chromosome number in this taxon.…”

Hybridation entreSaga campbelliKaltenbach 1965 etSaga hellenicaKaltenbach 1967 (Orthoptera: Tettigoniidae)

“…Les autres paires formées, bien que provenant d'espèces diff érentes, ne montrent pas plus de diff érences que s'il s'agissait d'une espèce pure. Ceci montre bien que seule, une translocation robertsonienne sépare les caryotypes de S. hellenica et S. campbelli, comme déjà proposé (Lemonnier-Darcemont et al 2008).…”