Karyotype and putative chromosomal inversion suggested by integration of cytogenetic and molecular data of the fungus-farming ant Mycetomoellerius iheringi Emery, 1888

Comparative cytogenetic analyses are being increasingly used to collect information on species evolution, for example, diversification of closely related lineages and identification of morphologically indistinguishable species or lineages. Here, we have described the karyotype of the fungus-farming ant Mycetomoellerius iheringi Emery, 1888 and investigated its evolutionary relationships on the basis of molecular and cytogenetic data. The M. iheringi karyotype consists of 2n = 20 chromosomes (2K = 18M + 2SM). We also demonstrated that this species has the classical insect TTAGG telomere organization. Phylogenetic reconstruction showed that M. iheringi is phylogenetically closer to M. cirratus Mayhé-Nunes & Brandão, 2005 and M. kempfi Fowler, 1982. We compared M. iheringi with other congeneric species such as M. holmgreni Wheeler, 1925 and inferred that M. iheringi probably underwent a major pericentric inversion in one of its largest chromosomes, making it submetacentric. We discussed our results in the light of the phylogenetic relationships and chromosomal evolution.

Presence of the canonical TTAGG insect telomeric repeat in the Tenthredinidae (Symphyta) suggests its ancestral nature in the order Hymenoptera

Telomeric repeats in two members of the sawfly family Tenthredinidae (Hymenoptera), namely, Tenthredo omissa (Förster, 1844) and Taxonus agrorum (Fallén, 1808) (both have n = 10), were studied using fluorescence in situ hybridization (FISH). Chromosomes of both species were demonstrated to contain the canonical TTAGG insect telomeric repeat, which constitutes the first report of the (TTAGG)_n telomeric motif for the Tenthredinidae as well as for the clade Eusymphyta and the suborder Symphyta in general. Taken together with the presence of this repeat in many other Holometabola as well as in the hymenopteran families Formicidae and Apidae from the suborder Apocrita, these results collectively suggest the ancestral nature of the (TTAGG)_n telomeric motif in the Hymenoptera as well as its subsequent loss within the clade Unicalcarida and independent reappearance in ants and bees. If this is true, the loss of the TTAGG repeat can be considered as a synapomorphy of the corresponding clade.

Are the TTAGG and TTAGGG telomeric repeats phylogenetically conserved in aculeate Hymenoptera?

Despite the (TTAGG)_n telomeric repeat supposed being the ancestral DNA motif of telomeres in insects, it was repeatedly lost within some insect orders. Notably, parasitoid hymenopterans and the social wasp Metapolybia decorata (Gribodo) lack the (TTAGG)_n sequence, but in other representatives of Hymenoptera, this motif was noticed, such as different ant species and the honeybee. These findings raise the question of whether the insect telomeric repeat is or not phylogenetically predominant in Hymenoptera. Thus, we evaluated the occurrence of both the (TTAGG)_n sequence and the vertebrate telomere sequence (TTAGGG)_n using dot-blotting hybridization in 25 aculeate species of Hymenoptera. Our results revealed the absence of (TTAGG)_n sequence in all tested species, elevating the number of hymenopteran families lacking this telomeric sequence to 13 out of the 15 tested families so far. The (TTAGGG)_n was not observed in any tested species. Based on our data and compiled information, we suggest that the (TTAGG)_n sequence was putatively lost in the ancestor of Apocrita with at least two subsequent independent regains (in Formicidae and Apidae).

Cytogenetic study on antlions (Neuroptera, Myrmeleontidae): first data on telomere structure and rDNA location

Myrmeleontidae, commonly known as "antlions", are the most diverse family of the insect order Neuroptera, with over 1700 described species (in 191 genera) of which 37 species (in 21 genera) have so far been studied in respect to standard karyotypes. In the present paper we provide first data on the occurrence of the "insect-type" telomeric repeat (TTAGG) _n and location of 18S rDNA clusters in the antlion karyotypes studied using fluorescence in situ hybridization (FISH). We show that males of Palpares libelluloides (Linnaeus, 1764) (Palparinae), Acanthaclisis occitanica (Villers, 1789) (Acanthaclisinae) and Distoleon tetragrammicus (Fabricius, 1798) (Nemoleontinae) have rDNA clusters on a large bivalent, two last species having an additional rDNA cluster on one of the sex chromosomes, most probably the X. (TTAGG) _n - containing telomeres are clearly characteristic of Palpares libelluloides and Acanthaclisis occitanica; the presence of this telomeric motif in Distoleon tetragrammicus is questionable. In addition, we detected the presence of the (TTAGG) _n telomeric repeat in Libelloides macaronius (Scopoli, 1763) from the family Ascalaphidae (owlflies), a sister group to the Myrmeleontidae. We presume that the "insect" motif (TTAGG) _n was present in a common ancestor of the families Ascalaphidae and Myrmeleontidae within the neuropteran suborder Myrmeleontiformia.