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J Insect Sci
2010 Jan 01;10:87. doi: 10.1673/031.010.8701.
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Karyotype plasticity in crickets: numerical, morphological, and nucleolar organizer region distribution pattern of Anurogryllus sp.
Cristina Schneider M
,
Ariza Zacaro A
,
Ferreira A
,
Cella DM
.
Abstract
Within the Orthopteran species, those of the suborder Ensifera have been rarely studied from the cytogenetic point of view, mainly due to the difficulties for taxonomic identification of its species. The Gryllidae is the second largest family of this suborder and possesses some genera, such as Anurogryllus, that occur only on the American continents. The aim of this work was to determine the karyotype characteristics, the meiotic chromosome behaviour, and the nucleolar organizer region (NOR) pattern of Anurogryllus sp (Orthoptera: Gryllidae). In the analyzed sample, high levels of numerical, morphological, and NORs polymorphisms were detected. Within five distinct karyotypes that were found, the basic karyotype of Anurogryllus sp. showed 2n(male symbol) = 22 + X0 with acrocentric autosomes and a metacentric X sex chromosome; furthermore, a conspicuous secondary constriction related to the NOR was present along the entire short arm on pair 5. The other four types of karyotypes arose from centric fusions between elements of pairs 1/3, 2/6, 4/7 and a NOR partial translocation from pair 5 onto the long arm terminal region of one element of the fused pair 2/6. Such intraspecific variability and the consequences of high levels of polymorphism are discussed, leading to conjectures about the mechanisms that led to these chromosome rearrangements.
Figure 1. . Karyotypic diversity of Anurogryllus sp. detected in mitotic cells stained with Giemsa. A: Karyotype 1, 2n (♂) = 22 + X0. B: Karyotype II, 2n (♂) = 21 + X0, showing the heterozygous state for the centric fusion 1/3. C: Karyotype III, 2n (♀) = 17 + XX, demonstrating the homozygous form for the centric fusion 1/3 and 2/6, and the heterozygous condition for the centric fusion 4/7. D–E: Karyotype IV and V, respectively, 2n (♀) = 16 + XX, revealing the homozygous condition for the centric fusion 1/3, 2/6, and 4/7. In E, observe the heteromorphic secondary constriction on the long arm distal region of the 2nd metacentric pair (arrow). In all karyotypes, the pair 5 showed a secondary constriction on the whole short arm. Scale bar = 5 µm. High quality figures are available online.
Figure 2. . Meiotic cells of Anurogryllus sp. standard stained. A–B: Early and late metaphase I, respectively, 2n = 8II + X0. In A, note the autosomal bivalents with one (small arrow) or two (large arrow) terminal chiasmata. C–D: Metaphase II, with n = 8 + X and n = 8, respectively. Scale bar = 5 µm. High quality figures are available online.
Figure 3. . NOR pattern in mitotic cells of Anurogryllus sp. submitted to both standard staining (A, C, E, G, I) and silver nitrate impregnation (B, D, F, H, J). A–B: Female, 2n = 22 + XX. C–D: Male, 2n = 21 + X0. E–F: Female, 2n = 17 + XX. G–H: Male, 2n = 16 + X0. I–J: Female, 2n = 16 + XX. The small arrow indicates secondary constriction and the large arrow shows NOR. Scale bar = 5 µm. High quality figures are available online.
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