Chromosome numbers in antlions (Myrmeleontidae) and owlflies (Ascalaphidae) (Insecta, Neuroptera)

Abstract

A short review of main cytogenetic features of insects belonging to the sister neuropteran families Myrmeleontidae (antlions) and Ascalaphidae (owlflies) is presented, with a particular focus on their chromosome numbers and sex chromosome systems. Diploid male chromosome numbers are listed for 37 species, 21 genera from 9 subfamilies of the antlions as well as for seven species and five genera of the owlfly subfamily Ascalaphinae. The list includes data on five species whose karyotypes were studied in the present work. It is shown here that antlions and owlflies share a simple sex chromosome system XY/XX; a similar range of chromosome numbers, 2n = 14-26 and 2n = 18-22 respectively; and a peculiar distant pairing of sex chromosomes in male meiosis. Usually the karyotype is particularly stable within a genus but there are some exceptions in both families (in the genera Palpares and Libelloides respectively). The Myrmeleontidae and Ascalaphidae differ in their modal chromosome numbers. Most antlions exhibit 2n = 14 and 16, and Palparinae are the only subfamily characterized by higher numbers, 2n = 22, 24, and 26. The higher numbers, 2n = 20 and 22, are also found in owlflies. Since the Palparinae represent a basal phylogenetic lineage of the Myrmeleontidae, it is hypothesized that higher chromosome numbers are ancestral for antlions and were inherited from the common ancestor of Myrmeleontidae + Ascalaphidae. They were preserved in the Palparinae (Myrmeleontidae), but changed via chromosomal fusions toward lower numbers in other subfamilies.

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

“…1), confirming the chromosome number, 2n = 26 (24 + XY), reported by Kuznetsova et al (2015). FISH with “insect” telomeric probe (TTAGG) n produced strong hybridization signals on the chromosome ends at metaphase I (Figs 2, 3) and other stages of meiosis (not shown).…”

“…An additional univalent, most likely a B-chromosome, which precociously segregates together with one of the sex chromosomes, was occasionally observed in first metaphase nuclei (not shown). The data obtained suggest a diploid karyotype of 2n = 16 (14 + XY) in contrast to 2n = 18 (16 + XY) reported by Kuznetsova et al (2015). FISH with (TTAGG) n probe has detected no hybridization signals in the first metaphase nuclei (Fig.…”

“…As summarized recently (Kuznetsova et al 2015), the karyotypes are currently known for 37 species of the Myrmeleontidae representing about 2.2% of the extant antlion species. The studied species belong to 21 genera and 9 subfamilies ( sensu Krivokhatsky 2011) and were shown to have an XY-sex chromosome system as well as diploid chromosome numbers ranging from 14 to 26.…”

“…FISH with (TTAGG) n and 18S rDNA probes was applied as previously reported for some other insects (Kuznetsova et al 2015, Maryańska-Nadachowska et al 2016, Golub et al 2016). In brief, chromosome preparations were treated with 100 µg/ml RNase A and 5 mg/ml Pepsin solution to remove excess RNA and proteins.…”

“…Until now, the cytogenetic studies in the Myrmeleontidae have been carried out on 37 species from 21 genera, and were focused exclusively on the basic features of the karyotypes such as chromosome numbers and sex determination systems (reviewed in Kuznetsova et al 2015). …”