Research Article |
Corresponding author: Yasmine Kartout-Benmessaoud ( kartout_yasmine@yahoo.fr ) Academic editor: Nina Bulatova
© 2018 Yasmine Kartout-Benmessaoud, Kafia Ladjali-Mohammedi.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kartout-Benmessaoud Y, Ladjali-Mohammedi K (2018) Banding cytogenetics of chimeric hybrids Coturnix coturnix × Coturnix japonica and comparative analysis with the domestic fowl. Comparative Cytogenetics 12(4): 445-470. https://doi.org/10.3897/CompCytogen.v12i4.27341
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The Common quail Coturnix coturnix Linnaeus, 1758 is a wild migratory bird which is distributed in Eurasia and North Africa, everywhere with an accelerating decline in population size. This species is protected by the Bonn and Berne conventions (1979) and by annex II/1 of the Birds Directive (2009). In Algeria, its breeding took place at the hunting centre in the west of the country. Breeding errors caused uncontrolled crosses between the Common quail and Japanese quail Coturnix japonica Temminck & Schlegel, 1849. In order to help to preserve the natural genetic heritage of the Common quail and to lift the ambiguity among the populations of quail raised in Algeria, it seemed essential to begin to describe the chromosomes of this species in the country since no cytogenetic study has been reported to date. Fibroblast cultures from embryo and adult animal were initiated. Double synchronization with excess thymidine allowed us to obtain high resolution chromosomes blocked at prometaphase stage. The karyotype and the idiogram in GTG morphological banding (G-bands obtained with trypsin and Giemsa) corresponding to larger chromosomes 1–12 and ZW pair were thus established. The diploid set of chromosomes was estimated as 2N=78. Cytogenetic analysis of expected hybrid animals revealed the presence of a genetic introgression and cellular chimerism. This technique is effective in distinguishing the two quail taxa. Furthermore, the comparative chromosomal analysis of the two quails and domestic chicken Gallus gallus domesticus Linnaeus, 1758 has been conducted. Differences in morphology and/or GTG band motifs were observed on 1, 2, 4, 7, 8 and W chromosomes. Neocentromere occurrence was suggested for Common quail chromosome 1 and Chicken chromosomes 4 and W. Double pericentric inversion was observed on the Common quail chromosome 2 while pericentric inversion hypothesis was proposed for Chicken chromosome 8. A deletion on the short arm of the Common quail chromosome 7 was also found. These results suggest that Common quail would be a chromosomally intermediate species between Chicken and Japanese quail. The appearance of only a few intrachromosomal rearrangements that occurred during evolution suggests that the organization of the genome is highly conserved between these three galliform species.
Avian cytogenetics, cell culture, chimeric hybrids, Coturnix coturnix × Coturnix japonica, GTG-banding, intrachromosomal rearrangements.
Birds represent a class of tetrapod vertebrates which contains a vast diversified variety of species (
The avian genome is characterized by very high chromosome number, with an average of 2N=76 - 80 (
Taxonomically, the majority of avian karyotypes are exceptionally stable and present conserved synteny regions (
Like the domestic fowl Gallus gallus domesticus Linnaeus, 1758, the Common quail Coturnix coturnix Linnaeus, 1758 and the Japanese quail Coturnix japonica Temminck & Schlegel, 1849 are the representative species of the ancestral order Galliformes. The Japanese quail originates from the eastern Palearctic (Siberia, Mongolia, Korea, Northeastern China and Japan) but has lost migratory behavior, normal in its wild type (
In Algeria, a global strategy of preservation of the Common quail was organized thanks to collaborations between National research stations and Hunting Centre. The breeding of this species was kept in the form of reduced numbers at the Tlemcen Hunting Centre in the west of the country. The strong phenotypic resemblance between the European and the Japanese quail originated from errors committed during the breeding stage brought about as a result of uncontrolled crossings between these species and the appearance of hybrids (information supplied by the Tlemcen Hunting Centre).
Indeed, the Japanese quail is different from the European quail although they were considered for a long time as two subspecies (
However, the hybridization has negative consequences on the evolution of the genetic heritage of the species concerned and their preservation (
Thus, the introgressive hybridization caused by the uncontrolled release of Japanese quails seems to induce a very worrying genetic shift. In fact, a more or less complete loss of the migratory ability of hybrid subjects has been noted with the appearance of a hybrid song and the assignment of morphological and behavioral characters (
Interspecific chimeras can be also met with at an early development stage, resulting from a crossing between closely related species especially in birds (
Although high resolution molecular techniques are well advanced, chromosome banding remains an effective method for delineating chromosome homologies between phylogenetically related species. Indeed, banding colorations allow participation, in an important way, in the studies of taxonomy and phylogenetics and reveal the ancestral chromosome rearrangements of vertebrates (
The purpose of this study is to establish the karyotype of the Common quail Coturnix coturnix at high resolution level with morphological banding techniques. So far, no study of the chromosomes of this species has been reported. Also, considering the possibility of an introgressive hybridization between the Common quail and the Japanese quail, it was necessary to analyze the individuals expected to be the hybrid animals (Coturnix coturnix × Coturnix japonica) in order to remove the ambiguity within the quail populations bred in Algeria. Comparative chromosome analysis by GTG banding of both species of quails and the domestic fowl Gallus gallus domesticus has been conducted to detect certain rearrangements that would have occurred during speciation and to estimate the degree of conservation between these species.
Common quail Coturnix coturnix: Five fertile eggs and an adult, 6-month-old male brought during the reproduction period from the Tlemcen Hunting Centre, Algeria (34°53'24"N, 1°19'12"W) have been analyzed in the present study.
Japanese quail Coturnix japonica: Five fertile eggs resulting from animals raised in the Hunting Centre of Zeralda, Algeria (36°42'06"N, 2°51'47"E) were also cultivated.
Hybrid animals: The Tlemcen Hunting Centre us to analyze eggs resulting from animals expected to be hybrid and resulting of an uncontrolled crossing between the Common quail and the Japanese quail. So, seven fertile eggs obtained at the 15th generation have been cultured.
The age of all the embryos put in cultures in the present study varies between 8 and 12 days. The eggs were incubated in a ventilated incubator where the conditions of hygrometry (55%) and temperature (39.5 °C) are maintained. For the embryos and the adult animal, the cellular cultures were carried out under sterile conditions in a chamber of cellular culture equipped with a vertical laminary flow hood (Polaris72 N°19311). The fibroblast primary cultures were carried out after samples were taken from fragments of various body parts (lung, heart, liver, kidneys and muscles). The cells were put in suspension in medium of RPMI 1640 supplemented by 20mm of HEPES, 1% of L-Glutamine (Gibco ref.: 22409-015, batch: 695608), 10% of foetal calf serum (FCS, Gibco ref.: 10270-106, batch: 41Q4074K), Penicillin-Streptomycin 1% and 1% of Fungizone (Gibco ref.: 15160-047, Batch: S25016D). The cells in culture were incubated at 41 °C (
Cultures were synchronized with a double thymidine block (10mg /ml, Sigma) during S phase in order to increase the yield of metaphase and early metaphase cells as described by
The method of
Chromosome preparations were screened under a photonic microscope (Zeiss Scope A1, Axio) equipped with a digital black-and-white camera (Cool cube 1). Images have been captured by metasystem processing software. Photos were treated by ADOBE PHOTOSHOP 7.0 software.
The establishment of karyotypes is based upon nomenclature taking into account the morphology and size of chromosomes according to the International System for Standardized Avian Karyotypes (ISSAK) (
The IMAGE J software was used to integrate the scale bar on the photos (
The fibroblast cultures derived from wild quail proved to be very sensitive to the various treatments (thymidine, BrdU and FdU). Indeed, cell culture follow-up showed fibroblast set up after two to five days, but after trypsination (0,05%) and synchronization, most cells died both in the embryos and adult. However, in Japanese quails and hybrids, the cells showed good viability after incorporation of different treatments. The cells from embryos provide a higher mitotic index and a greater potential for cell division compared to adult animal. The mitotic index observed in wild quail averaged one to two metaphases per a field (G×10). On the other hand, in Japanese quails and expected hybrids, the mitotic index was approximately 10 metaphases.
The control of the cell cycle by synchronization seems to be the best and most suitable procedure for blocking the so-called high-resolution chromosomes. The duration of the cell half cycle was estimated at 6 hours for both quail species. The majority of cells, dividing the two quail species, obtained in this experiment were at the metaphase and prometaphase stages.
Forty-five metaphases which showed well-distributed chromosomes were selected to count the diploid number of the Common quail, thus estimated at 2N=78 and represented by 38 pairs of autosomes and one pair of sex chromosomes (Figure
Prometaphase spreads following the GTG-banded chromosomes of A the Common quail Coturnix coturnix B Japanese quail Coturnix japonica (Black bars indicate the centromere positions of the chromosomes 1).
The GTG staining technique revealed clear G-banding patterns in all macrochromosomes and microchromosomes to size number 12 at least. Only the first 12 pairs and ZW sex chromosomes of the Common quail were described in this study (Figure
Size of the mitotic chromosomes of the Common quail Coturnix coturnix (n=14) p: short arm, q: long arm, p+q: relative length, CI: Centromeric index=p/(p+q) × 100.
Chromosomes | p (µm) | q(µm) | q/p | p+q(µm) | CI% |
---|---|---|---|---|---|
1 | 1.71 | 2.29 | 1.32 | 4 | 42 |
2 | 1.25 | 1.66 | 1.32 | 2.91 | 42.95 |
3 | 0.12 | 2.15 | 17.91 | 2.27 | 5.28 |
4 | 0.30 | 1.85 | 6.16 | 2.15 | 13.95 |
5 | 0.10 | 1.40 | 8.25 | 1.50 | 6.7 |
6 | 0.11 | 0.9 | 8.18 | 1.01 | 10.89 |
7 | 0.18 | 0.79 | 4.38 | 0.97 | 18.55 |
8 | 0.26 | 0.51 | 1.96 | 0.77 | 33.76 |
9 | 0.1 | 0.65 | 6.5 | 0.75 | 13.33 |
10 | 0.08 | 0.58 | 7.25 | 0.66 | 12.12 |
11 | 0.1 | 0.55 | 5.5 | 0.65 | 15.38 |
12 | 0.08 | 0.48 | 6 | 0.56 | 14.28 |
Z | 1.06 | 1.08 | 0.49 | 2.14 | 49.53 |
W | 0.16 | 0.8 | 5 | 0.96 | 16.66 |
A GTG-banded karyotype for pairs 1 to 12 and sex chromosomes of the Common quail Coturnix coturnix. B Idiogram corresponding to A.
Chromosomes 1 and 2 are submetacentric. Their arm ratios are quite similar (q/p = 1,32) (Table
In this study, we confirmed the diploid number of chromosomes of the Japanese quail, 2N=78 (Figure
The GTG-banded karyotype and corresponding idiogram of the Japanese quail are illustrated in Figures
Morphometry of the first twelve macrochromosomes and gonosomes of the Japanese quail Coturnix japonica (n=16) p: short arm. q: long arm. p+q: relative length. CI: centromeric index=p/(p+q) × 100.
Chromosomes | p(µm) | q(µm) | q/p | p+q(µm) | CI% |
---|---|---|---|---|---|
1 | 1.3 | 2.8 | 2.15 | 4.1 | 31.70 |
2 | 1.25 | 1.66 | 1.32 | 2.91 | 42.95 |
3 | 0.14 | 2 | 14.28 | 2.14 | 8.18 |
4 | 0.32 | 1.7 | 5.31 | 2.02 | 15.84 |
5 | 0.15 | 1.11 | 7.4 | 1.26 | 11.90 |
6 | 0.08 | 0.76 | 9.5 | 0.84 | 9.52 |
7 | 0.1 | 0.66 | 6.6 | 0.76 | 13.16 |
8 | 0.24 | 0.47 | 1.95 | 0.71 | 33.80 |
9 | 0.07 | 0.56 | 8.56 | 0.63 | 11.11 |
10 | 0.09 | 0.49 | 5.44 | 0.58 | 15.51 |
11 | 0.08 | 0.46 | 5.75 | 0.54 | 14.81 |
12 | 0.05 | 0.48 | 9.6 | 0.53 | 9.43 |
Z | 0.96 | 1.05 | 1.09 | 2.01 | 47.76 |
W | 0.18 | 0.92 | 5.11 | 1.1 | 16.36 |
Of the seven expected hybrid quails cultivated in this project, only two cell cultures have succeeded. These hybrids were analyzed in the 15th generation, were all viable and derived from fertile parents. The homologous chromosomes of the same pair were designated “Cc” for Common quail and “Cj” for Japanese quail (Figure
A, C Prometaphase spreads following the GTG-banded chromosomes of hybrid quail B, D Black traits indicate the centromere positions of the homologous chromosomes 1 which are morphologically different.
A Prometaphase spread following the GTG-banded chromosomes of hybrid quail B patterns of pairs 1 to 8 and sex chromosomes corresponding to A showing the differences on chromosomes 1, 2 and 7 of both species. Scale bar: 5µm.
The two analyzed hybrid embryos showed a coexistence of three cell types that we have identified as chimeric hybrids (Figure
Chimera embryo showing A the cohabitation of the Common and Japanese quail cells B gynandromorphism corresponding karyotypes to A with ZZ/ZW chromosomes indicated by the arrows.
Another anomaly has also been detected concerning sex chromosomes, which is a kind of chimerism called gynandromorphism. Thus, one of the two chimeric preparations corresponded to a gynandromorphic individual that corresponds to the presence of two distinct cell populations at a same time: male and female (Figure
The chromosome comparison by GTG banding analysis of three species (Common quail, Japanese quail and Chicken Gallus gallus domesticus “GGA”) confirms the presence of chromosomal rearrangements already described for Japanese quail and Chicken (
Important homology was observed on chromosome 1 of the Common quail compared to its homologs in domestic chicken, while a perfect correspondence of the GTG band profiles is observed on chromosomes 1 of the two quail species, a difference in the ratio q/p was found (Figure
Even though the cells of birds remain among the most difficult species to maintain in culture, the prometaphase cells are particularly suitable for bird analysis because the chromosomes are thin and elongate, making the structure of the smaller elements more distinct (
The high sensibility observed in cells cultures of wild quail corroborate with the vulnerability of this species in breeding areas unlike the Japanese quail because of its easy practical prolificacy in captivity (Caballero de la Calle et Peña Montañés 1997, personal communication of the Tlemcen Hunting Centre). This is the case for the Barbary and Chukar partridges (
The diploid number of 2N=78 estimated in Common quail and then in Japanese quail, emphasizes the exceptional conservation of karyotypes in the order of Galliformes (
The karyotypes of Common and Japanese quail show 8–10 pairs of macrochromosomes and 30–28 pairs of microchromosomes which are very difficult to distinguish. This is quite similar to that in most Galliformes (
While the GTG band karyotype of the Japanese quail Coturnix japonica was described up to the eighth chromosome pair only (
Comparative chromosomal analysis of both quails with domestic chicken allowed us to discover high conservation as well as differences in the karyotypes. The Common quail karyotype shares more similarities with chicken chromosomes than that of Japanese quail with Chicken. However, the Chicken karyotype is considered as the most similar to the putative ancestral bird karyotype (
In fact, the high conservation of GTG banding patterns of chromosomes 1 in these three Galliformes species is observed, whereas difference in the q/p arm ratio is detected on chromosomes 1 of the two quails. This result could be explained by a formation of an evolutionary new centromere (ENC) (Figure
Evolutionary new centromere (ENC) formation on chromosome 1 of the Common and the Japanese quails.
Double pericentric inversion is demonstrated in some G-band motifs when chromosome 2 of Common quail and Japanese quail are compared as was reported in previous studies (Figure
Double inversion that could have occurred during evolution on chromosome 2 between the Common and the Japanese quails.
In the present work, we observed perfect conservation patterns in chromosome 4 of the three species. Furthermore, a morphological difference was noted between Chicken and the both quails. This result could suggest repositioning of the centromere during the speciation event (Figure
However, the fourth avian chromosome pair is quite complex in the history of bird evolution (Chowdhary and Raudsepp, 2000). Multiple hypotheses were proposed to explain the differences in chromosome 4 of Japanese quail and domestic Chicken (
Comparative chromosome 7 mapping of Common quail highlighted a large conservation with domestic fowl (Figure
In both quails, the 8 chromosomes were highly similar but differences in the disposition of the GTG bands were observed comparing them to Chicken (Figure
We observed high conservation between the Z chromosomes of the Chicken and the two quails. This result suggests no presence of pericentric inversion in the common ancestor of the three species, as previously described by
However, W chromosomes of both quails presented similarities. They have a small short arm, unlike the longer one in the Chicken. This morphological difference could be the result of formation of neocentromere (ENC) during the evolution. Moreover, the difference in size observed in the two species of quails could be explained by the fact that the ZW sex chromosomes would undergo unequal condensation/decondensation of the chromosomal arms (
The observed differences between the Common and Japanese quail chromosomes dealt with chromosomes 1, 2 and 7. All of the rearrangements described probably occurred in the evolutionary process before the separation of the two quail species. The important chromosomal similarity between these two species could allow to obtain a fertile and highly prolific progeny (
The presence of different cell types (Cc and Cj) within the same hybrid individual may be due to double fertilization of the ovule and its polar globule from sperms of different origins. Indeed, surviving spermatozoa from anterior mating can be preserved in the female genital tract at the infundibulum and could then be released into the oviduct lumen (
Chimerism is an extremely rare abnormality in animals. The proportions of the three cell types obtained represented a micro-chimerism which is defined by the number of cells affected. It is when a genetically foreign population represents less than 5% of the nucleated cells of an individual or organ (
Gynandromorphism is an anomaly that is not very well answered in birds (
The analysis of hybrid animals bred in western Algeria showed us that introgressive hybridization affected the genetic heritage of the Common quail Coturnix coturnix and would be a threat to its preservation. Although the wild quail and Japanese quail are phylogenetically very close, the chromosome banding method allowed us to propose the karyotype of the Common quail and to distinguish these two taxa. The comparative cytogenetic study allowed us to detect ancestral intrachromosomic rearrangements that could have accompanied the speciation and evolution of the karyotypes of the three species of Galliformes. Common quail would be an intermediate species between the Chicken and Japanese quail, which would be more recent in appearance. As a result, cytogenetics is a very important element in taxonomy and phylogeny studies.
In addition, for better knowledge of the Common quail genome, Fluorescence In Situ Hybridization (FISH) will be performed for individual microchromosome identification (
Authors would like to thank collaborators from the National Hunting Centres of Tlemcen and Zeralda (General Direction of Forests) for kindly providing the adult animal and the quail eggs. We would like to thank also the Tlemcen Hunting Federation who participated in the capture of wild common quails. We especially thank Mr MENAD Houari and Miss Larinouna Fatiha for support, as well as to Dr BELHAMRA (University of Biskra, Algeria) who provided us with data on Common quail and for contribution to this work.
We acknowledge Zeiss company (in particular Mr LAGUEL), Mrs Ouchia-Benissad Siham, the Laboratory of Cytogenetic in particular Dr Ait Abdelkader (Pierre and Marie Curie Centre, Algeria), the whole team of Biological Engneering of Cancer Laboratory (Faculty of Medicine, University of Bejaia, Algeria), for the precious help.
Finally, the authors also wish to thank Dr Kelani-Atmani Dina and Mister Aissanou Mourad who helped us with the English translation.
The authors are most grateful to the Ministry of Territory Planning and Environment (project 223), Ministry of Higher Education and Scientific Research (project 209), Ministry of the Interior, in the framework of Post-Graduation Specialized, which provided financial support.