Highlighting chromosomal rearrangements of five species of Galliformes (Domestic fowl, Common and Japanese quail, Barbary and Chukar partridge) and the Houbara bustard, an endangered Otidiformes: banding cytogenetic is a powerful tool

Abstract

Birds are one of the most diverse groups among terrestrial vertebrates. They evolved from theropod dinosaurs, are closely related to the sauropsid group and separated from crocodiles about 240 million years ago. According to the IUCN, 12% of bird populations are threatened with potential extinction. Classical cytogenetics remains a powerful tool for comparing bird genomes and plays a crucial role in the preservation populations of endangered species. It thus makes it possible to detect chromosomal abnormalities responsible for early embryonic mortalities. Thus, in this work, we have provided new information on part of the evolutionary history by analysing high-resolution GTG-banded chromosomes to detect inter- and intrachromosomal rearrangements in six species. Indeed, the first eight autosomal pairs and the sex chromosomes of the domestic fowl Gallusgallusdomesticus Linnaeus, 1758 were compared with five species, four of which represent the order Galliformes (Common and Japanese quail, Gambras and Chukar partridge) and one Otidiformes species (Houbara bustard). Our findings suggest a high degree of conservation of the analysed ancestral chromosomes of the four Galliformes species, with the exception of (double, terminal, para and pericentric) inversions, deletion and the formation of neocentromeres (1, 2, 4, 7, 8, Z and W chromosomes). In addition to the detected rearrangements, reorganisation of the Houbara bustard chromosomes mainly included fusions and fissions involving both macro- and microchromosomes (especially on 2, 4 and Z chromosomes). We also found interchromosomal rearrangements involving shared microchromosomes (10, 11, 13, 14 and 19) between the two analysed avian orders. These rearrangements confirm that the structure of avian karyotypes will be more conserved at the interchromosomal but not at intrachromosomal scale. The appearance ofa small number of inter- and intrachromosomal rearrangements that occurred during evolution suggests a high degree of conservatism of genome organisation in these six species studied. A summary diagram of the rearrangements detected in this study is proposed to explain the chronology of the appearance of various evolutionary events starting from the ancestral karyotype.

Keywords: Avian cytogenetics; GTG-banding; Galliformes; Otidiformes; chromosomal reshuffling; evolution.

Figure 1.

Comparison of chromosome (A) 1, (B) 2, (C) 4, (D) 7, (E) 8, (F) Z, and (G) W in GTG bands between the six species studied. The dotted lines indicate similarities, the full ones and the red circls/frames show the differences. GGA: Domestic chicken, CCO: Common quail, CJA: Japanese quail, ABA: Gambra partridge, ACH: Chukar partridge, CUN: Houbara bustard.

Figure 2.

Representation of chromosomal rearrangements that could have occurred during the chromosomes formation of the six studied species A appearance of a neocentromere (NC) on the ancestral CJA1 and CUN1 B double inversion that could have occurred on chromosome 2 between GGA and CCO/CJA (left). Appearance of a possible terminal fission on ancestral GGA2, which would be at the origin of the formation of CUN2 and microchromosome CUN10 (right) C possible formation of a neocentromere during the evolution of GGAW and CCOW D appearance of several fissions on the ancestral chromosome 4, which would be at the origin of the formation of chromosomes 4, 11, 14 and 19 of the Houbara bustard (left). Appearance of paracentric inversion between GGA4 and ACH4 (right) E formation of a neocentromere between GGA7 and ABA7 (left) or the course of a pericentric inversion between GGA7 and CUN7 (in the middle), deletion of the short arm p of GGA7 and CJA7 could have occurred between during evolution (right) F pericentric inversion could have occurred between GGA8 and (CCO8, CJA8, CUN8) (left), possible formation of a NC between GGA8 and CUN8 as well as the both partridge species (right) G formation of CUNZ following a possible interstitial deletion (fragment corresponding to CUN13) occurring on the ancestral Z chromosome accompanied by a terminal inversion (left). A terminal inversion in Zq2.1 is observed in ABA (right).

Figure 3.

Evolutionary representation of partial karyotypes of some galliforms and of an otidiform as well as the inter and intrachromosomal rearrangements that would have occured during speciation, compared to the presumed ancestral avian karyotype.