Corresponding author: Bernard Dutrillaux (
Academic editor: Robert Angus
The mitotic karyotypes of 17 species of African
Dutrillaux A-M, Dutrillaux B (2016) Chromosome comparison of 17 species / sub-species of African Goliathini (Coleoptera, Scarabaeidae, Cetoniinae). Comparative Cytogenetics 10(2): 269–282. doi:
At first glance, this apparent karyotype homogeneity might indicate that chromosome rearrangements rarely occurred during the multiple speciation events having originated more than 30,000
Here, we report mitotic and meiotic chromosome data of 17 species of African species belonging to
All but one species studied here were obtained by breeding developed by amateur entomologists from whom we obtained larvae. We pursued the breeding until imagine stage using oak leaf-mould. Diagnoses were performed according to
- C-banding: fairly large juxta-centromeric C-band on pairs 1-8, smaller on pair 9 and X, absent on the Y. Presence of a faint C-band at the telomeric region of the chromosome 4p arm (4pter).
- After LG staining, a banding differentiates all chromosome pairs (Fig.
- Silver staining: at pachynema of meiotic prophase, nucleoli are always next to the sex bivalent; at metaphase I, strong staining of the space between the X and Y. NOR location: Xp (p=short arm, according to ISCN, 1985)).
- Chromosome morphology: pairs N°1-4 metacentric; pairs N° 5 and 6 acrocentric; X acrocentric with two frequent gaps and Y punctiform.
- C-banding: quite discrete at all centromeric regions, and also at intercalary regions of chromosomes 1–4.
- Silver staining: present at mitotic metaphase on short arms of acrocentrics (N° 5, 6 and X). At pachynema, the sex bivalent is intensely stained, as well as the centromeric regions of bivalents 5 and 6. Nucleoli are associated with the sex bivalent and bivalent 6 short arm. At metaphase I, there is an intense staining of the space between the X and Y. NOR location: Xp, 5p, 6p.
- Chromosome morphology: all the autosomes but N° 3 appear to be meta- or sub-metacentric after Giemsa staining. The X is sub-metacentric and the Y punctiform.
- C-banding: very faint or absent on most autosomes. Only the acrocentric N° 3 is clearly C-banded at centromeric region. Large additional heterochromatic segments are present at 7p terminal region and on Xp.
- Silver staining: intense on the Xp arm and on the Y at mitotic metaphase. At pachynema, nucleoli are alongside the sex bivalent. The heterochromatic region of bivalent 7 is frequently close or at contact with the sex bivalent. At metaphase I, intense staining of the space between the X and Y. NOR location: Xp, Y?
- Chromosome morphology: all the autosomes are meta- or sub-metacentric; the X is metacentric and the Y punctiform.
- C-banding: large juxta-centromeric C-bands on centromeric regions of all chromosomes, including the X and Y, with only slight variations. Discreet C-bands are present at terminal or sub-terminal regions of the 4p arm, and occasionally other chromosome arms.
- LG staining: a discreet banding differentiates all chromosome pairs.
- NOR staining: at pachynema, nucleoli are located alongside the short arm of a small bivalent, N° 7 or 8.
- Chromosome morphology: all autosomes but pair N° 8 are meta- or sub-metacentric. Pair N° 8 is acrocentric, the X is sub-metacentric and the Y punctiform.
- C-banding: large juxta-centromeric bands in pairs N° 1-7, smaller in pairs N° 8 and 9 and sex chromosomes.
- Silver staining: at pachynema, nucleoli are located on the short arm of bivalent N° 8. NOR location: 8p arm
- Chromosome morphology: all autosomes are meta- or sub-metacentric. The X is sub-metacentric and the Y punctiform.
- C-banding: fairly large juxta-centromeric C-bands on pairs N° 1, 3, 4 and 9, small on pairs 2, 7, 8 and X, and very small on pairs N° 5 and 6 and Y.
- Silver staining: intense on the Xp arm and the Y at mitotic metaphase; presence of nucleoli in association with the intensely stained X component of the sex bivalent at pachynema; and intense at the X and Y junction of the Xyp bivalent at metaphase I. NOR location: Xp arm.
- Chromosome morphology: all autosomes meta- or sub-metacentric; X acrocentric or sub-metacentric (inter-individual variation?), Y almost punctiform.
- C-banding: large C-bands at all juxta-centromeric regions, except for pair N° 8 and chromosome Y. Frequent small C-band on chromosome 3pter. The Xp arm may be either C-banded (acrocentric form) or not (sub-metacentric form).
- Silver staining: as for
- Chromosome morphology: all autosomes and the X meta- or sub-metacentric and the Y punctiform.
- C-banding: large and variable juxta-centromeric C-bands on pairs N° 1–8, smaller on pair N° 9 and sex chromosomes. A dispensable C- band exists on chromosome 2pter.
- NOR staining: as for
- Chromosome morphology: the X chromosome and all autosomes but pair no 9 are acrocentric. The Y is punctiform.
- C-banding: intense C-bands are present at the centromere regions of most chromosomes. Faint C-bands are also distally located on the long arms of chromosomes1 to 5.
- LG staining: all chromosome pairs could be identified.
- NOR staining: At pachynema, the sex bivalent is intensely stained, and nucleoli are associated with the short arm of an acrocentric, presumably bivalent 7. At metaphase I, the space between the X and Y is intensely stained. NOR location: 7p arm.
- Chromosome morphology: all autosomes meta- or sub-metacentric; X metacentric, Y punctiform.
- C-banding: fairly intense at all juxta-centromeric regions of all autosomes and sex chromosomes; presence of a C-band on 3pter.
- LG staining: all chromosome pairs could be identified (Fig.
- Silver staining: at pachynema, nucleolus are alongside the terminal region of bivalent 3; intense staining of the sex bivalent in the space between X and Y at metaphase I. NOR location: 3p arm.
- Chromosome morphology: all autosomes meta- or sub-metacentric; X metacentric, Y small.
- C-banding: moderately large C-bands at juxta-centromeric regions of pairs N° 1–4 and 6–8, small on pairs 5 and 9, and almost inexistent on sex chromosomes; presence of a small C-band on 3pter.
- LG staining: identification of all chromosome pairs.
- Silver staining: intense at the proximal region of chromosome 6p arm at mitotic metaphase and on the Xyp bivalent at metaphase I. NOR location: 6p arm.
- Chromosome morphology: all the autosomes and the X appear to be meta- or sub-metacentric after Giemsa staining, and the Y is quite small.
- C-banding: large or very large juxta-centromeric C-bands on all chromosomes but the Y. On pairs N° 8 and 9 and the X, one arm is entirely heterochromatic. Thus, these chromosomes must be regarded as acrocentric, although they look metacentric. Large variations of heterochromatin lead to a marked polymorphism. For instance, the size of the X may vary by twofold among individuals.
- LG staining: identification of all chromosome pairs (Fig.
- Silver staining: at pachynema, the sex bivalent is intensely stained, and nucleoli are at contact with the short arm of bivalent 9. At metaphase I, the space between X and Y is stained, as usual in Xyp bivalents. NOR location: 9 p arm
Comparison of autosomes from gonocytes of 5 species after Giemsa light staining:
- Chromosome morphology: pairs N° 1, 2, 4, 5, 7 and 9 meta- or sub-metacentric, pairs N° 3, 6 and 8 acrocentric. The X is acrocentric and the Y punctiform.
- C-banding: fairly intense at all juxta-centromeric regions of all autosomes and faint on sex chromosomes.
- LG staining: identification of all chromosome pairs.
- Silver staining: at pachynema, nucleoli are associated with the centromeric region of the acrocentric bivalent 6. NOR location: 6p arm.
- Chromosome morphology: all autosomes are metacentric or sub-metacentric, the X is a large sub-metacentric, and the Y is a small metacentric.
- C-banding: limited to centromeric regions on autosomes, it stains most of the X and Y.
- LG staining: identification of all chromosome pairs (Fig.
- NOR staining: at pachynema, nucleoli are located alongside the sex bivalent, which is unusually large, due to the presence of a large heterochromatic fragment on the X chromosome. This heterochromatin prevents to accurately locate both centromere and NOR on this chromosome.
- Chromosome morphology: all the autosomes are meta- or sub-metacentric. The X is unusually large and sub-metacentric; the Y is acrocentric.
- C-banding: very large C-bands at all juxta-centromeric regions of all chromosomes, representing 30-40% of their whole length. The large size of the X is principally related to the presence of heterochromatin. X and Y form a large parachute bivalent at metaphase I.
- Silver staining: at pachynema, nucleoli are recurrently located near the centromere region of a large metacentric, which could not be identified. At metaphase I, the large parachute sex bivalent is deeply stained between the X and the Y. NOR location: autosomal.
- Chromosome morphology: all the autosomes and the X appear to be metacentric or sub-metacentric (chromosomes 1, 3, 6 and 8) or sub-metacentric after Giemsa staining, and the Y is quite small.
- C-banding: in addition to non-remarkable juxta-centromeric C-bands, presence of a small C-band on the terminal region of the 5p arm. The small Xp arm is heterochromatic and the Y remains unstained.
- LG staining: identification of all chromosome pairs (Fig.
- Silver staining: nucleoli remain alongside the sex bivalent at pachynema and the space between X and Y is intensely stained at metaphase I. NOR location: probably on the heterochromatic short arm of the X.
- Chromosome morphology: all the autosomes and the X appear to be metacentric or sub-metacentric after Giemsa staining, and the Y is quite small.
- C-banding: in addition to juxta-centromeric heterochromatin on all chromosomes, large additional and polymorphic heterochromatic segments occur on chromosomes 5,6, 8 and the X.
- LG staining: identification of all chromosome pairs.
The karyotypes of all species except
The 16 other karyotypes comprise nine pairs of autosomes of gradually decreasing size. Their similar sizes among the different karyotypes may have the following interpretations:
– neither translocations nor other inter-chromosomal exchanges occurred during evolution/speciation processes;
– exchanges occurred, but involved very small fragments, hard to detect;
– exchanges involved large fragments of similar sizes, preserving chromosome size.
Exchanges of very small fragments are unlikely. They are harmful because they lead to deleterious, but viable chromosomal imbalances, in progeny of heterozygote translocation carriers, as shown in human pathology. Thus, they should have been strongly counter-selected during evolution. Exchanges of large fragments may exist, but it would be very unlikely that they systematically involved fragments of similar size. Thus, the more likely interpretation is that speciation and evolution processes have occurred with few or without inter-chromosomal rearrangements in this tribe of beetles. Then, either chromosome rearrangements rarely occurred, or they were mostly of the intra-chromosomal type such as inversions. This last interpretation is, by far, the most likely (
The X chromosome exhibits four different morphologies: acrocentric, sub-metacentric, metacentric and more or less sub-metacentric, with one euchromatic and another heterochromatic arm (C-banded). The two former morphologies were observed in species of
Large amounts of heterochromatin are present in the X chromosome of six species belonging to five genera (
As in many other
On the whole, it remains very difficult to propose undisputable phylogenetic relationships by using these classical cytogenetic data. The detected rearrangements are too few, and the species studied probably represent a too small and heterogenous sample of the sub-family. If inversions are in cause, it is not certain that molecular cytogenetics (FISH) would significantly improve the results, at least by the use of chromosome painting.
Finally, an improvement could come from chromosome banding, but a major problem remains: the difficulty for inducing a consistent banding of euchromatin. Beetle chromosomes are apparently not composed of large heterogeneous DNA fragments, as ALU and LINE sequences, associated to R- and G-banding in mammalian chromosomes (
All the karyotypes of the 17 studied species differ from each other in some respects by inversions, heterochromatin variations and translocations. As expected, congeneric species possess more similar karyotypes than species from different genera, but it remains impossible to propose a phylogeny based on chromosome changes. It is noteworthy that