An obvious resemblance between the karyotypes of Ochotona huangensis and Ochotona dauurica was seen by the routine staining, despite of some bigger size of the first pair of Ochotona huangensis. The first four meta-submetacentric pairs of Ochotona dauurica are similar to the 2nd – 5-th pairs of Ochotona huangensis autosomes. The remaining five meta-submetacentric pairs of Ochotona dauurica, except the 10-th pair, are similar to the last five pairs of the first group of Ochotona huangensis autosomes. The 11-th – 15-th autosomes of Ochotona dauurica are very similar to the second subtelocentric group of Ochotona huangensis by morphology and sizes, with a loss of the little part of the upper arm on the 20-th pair. The absence of G-stained chromosomes not allows us to do unambiguous conclusion about the relationship between the karyotypes of Ochotona dauurica and Ochotona huangensis. Such species as Ochotona alpina (2n=42), Ochotona hyperborea (2n=40), Ochotona pallasi (2n=38) and Ochotona argentata (2n=38) of the subgenus Pika (Vorontsov and Ivanitskaya 1973, Ivanitskaya 1991) are close to Ochotona huangensis by the diploid chromosome number. However, they have more significant differences in relation of morphological groups and sizes of chromosomes.
The C-banding patterns of Ochotona dauurica specimens from Transbaikalia (near the station Armagotuy) and Mongolia (Selenge aimag, near Shamar) (Ivanitskaya 1991) differs slightly from the specimen studied by us. Four pairs of subtelo-acrocentric autosomes have euchromatic material on the short arms in our pika. According to the data obtained by Ivanitskaya (1991), euchromatic material was on the short arms only on one pair. This pair is the largest and it corresponds to our 11-th pair. In addition, Ivanitskaya (1991) described three completely heterochromatic pairs, but according to our data, only last two pairs of autosomes have such features. These differences may be due to interpopulation variability as well as influence of different C-staining procedures of chromosomal slides. However, the reason of these differences remains unclear, because of the absence of sufficient material at present.
A tendency of heterochromatin decreasing is confirmed in row of pikas: from species with a large number of chromosomes to species with a smaller number, while comparing the overall C-banding pattern of Ochotona dauurica and Ochotona huangensis (Formozov et al. 2004). Perhaps, this indicates a loss of the heterochromatic material as a result of the chromosomal rearrangements.
The species Ochotona alpina (subgenus Pika) is similar to Ochotona huangensis by the diploid chromosome number, but it has another arrangement of heterochromatin. Pericentromeric heterochromatin is detected only on 6 submetacentric and 5 subtelocentric pairs of Ochotona alpina autosomes (Ivanitskaya 1991). Four submetacentric pairs of Ochotona alpina (especially the first pair) have the larger heterochromatic blocks than the corresponding pairs of Ochotona huangensis. Two large subtelocentric pairs of Ochotona alpina also have the larger blocks of heterochromatin in comparison with the subtelocentric pairs of Ochotona huangensis. The remaining three minor subtelocentric pairs of Ochotona alpina, which contain the pericentromeric heterochromatin, have no analogues in the karyotype of Ochotona huangensis. Besides, the X chromosome of Ochotona alpina has no heterochromatin unlike Ochotona huangensis. The Y chromosome of Ochotona alpina is composed of heterochromatin entirely (Ivanitskaya 1991).
The molecular studies of the genus Ochotona (Yu et al. 2000, Formozov et al. personal communication) showed division of pikas for three superspecies groups: 1. Pika – northern pikas and Mongolian pika; 2. Ochotona – shrub-steppe pikas except Mongolian, Ladak and Kozlov’s pikas; 3. Conothoa – mountain pikas with Ladak and Kozlov’s pikas. At present, the statuses of subgenera are given for these groups of pikas (Hoffmann and Smith 2005). Formozov et al. (personal communication) suggested the existence of variation of the diploid chromosome number for each subgenus (group) of pikas. The karyotypes of the subgenus Pika species have 38-42 chromosomes. The species of the subgenus Ochotona have the karyotypes with 46-50 chromosomes. The pikas of the subgenus Conothoa have 60-62 chromosomes in the karyotypes. Moreover, there are species with 2n=68 in each subgenus.
The position of Ochotona huangensis is ambiguous in this system. According to the data of study of the cytochrome b and the ND4 gene (Yu et al. 2000), Ochotona huangensis is very far distant from the group of shrub-steppe pikas. Also, Ochotona huangensis is allocated to a separate independent group by analysis of the cytochrome b of 27 pikas species (Niu et al. 2004). At present, Ochotona huangensis (2n=42) belongs to the subgenus Ochotona (Hoffmann and Smith 2005). If the view point of Hoffmann and Smith is true, our data extend the level of variation of the diploid chromosome number for the subgenus Ochotona. In this case, there is no border with the subgenus Pika by this indicator. Thus, Ochotona huangensis is significantly diverging from the main group of the subgenus Ochotona by main karyotypic characteristics that corresponds to the data of mtDNA study (Yu et al. 2000, Niu et al. 2004). The recent cytogenetic study of Ochotona forresti (2n=54) (Ye et al. 2011) also greatly expands karyotypic variability of the subgenus Conothoa. As yet, the karyotypes of eight species of the subgenus Conothoa and three species of the subgenus Ochotona are not investigated. It is not excluded that the new karyotypic data will changed the level of the diploid numbers variation between all subgenera of the genus. Thus, we assume that the karyotypic system of the genus Ochotona can not be constructed completely without studying cytogenetic characteristics of all species of pikas.
An obvious resemblance between the karyotypes of Ochotona huangensis and Ochotona dauurica was seen by the routine staining, despite of some bigger size of the first pair of Ochotona huangensis. The first four meta-submetacentric pairs of Ochotona dauurica are similar to the 2nd – 5-th pairs of Ochotona huangensis autosomes. The remaining five meta-submetacentric pairs of Ochotona dauurica, except the 10-th pair, are similar to the last five pairs of the first group of Ochotona huangensis autosomes. The 11-th – 15-th autosomes of Ochotona dauurica are very similar to the second subtelocentric group of Ochotona huangensis by morphology and sizes, with a loss of the little part of the upper arm on the 20-th pair. The absence of G-stained chromosomes not allows us to do unambiguous conclusion about the relationship between the karyotypes of Ochotona dauurica and Ochotona huangensis. Such species as Ochotona alpina (2n=42), Ochotona hyperborea (2n=40), Ochotona pallasi (2n=38) and Ochotona argentata (2n=38) of the subgenus Pika (Vorontsov and Ivanitskaya 1973, Ivanitskaya 1991) are close to Ochotona huangensis by the diploid chromosome number. However, they have more significant differences in relation of morphological groups and sizes of chromosomes.
The C-banding patterns of Ochotona dauurica specimens from Transbaikalia (near the station Armagotuy) and Mongolia (Selenge aimag, near Shamar) (Ivanitskaya 1991) differs slightly from the specimen studied by us. Four pairs of subtelo-acrocentric autosomes have euchromatic material on the short arms in our pika. According to the data obtained by Ivanitskaya (1991), euchromatic material was on the short arms only on one pair. This pair is the largest and it corresponds to our 11-th pair. In addition, Ivanitskaya (1991) described three completely heterochromatic pairs, but according to our data, only last two pairs of autosomes have such features. These differences may be due to interpopulation variability as well as influence of different C-staining procedures of chromosomal slides. However, the reason of these differences remains unclear, because of the absence of sufficient material at present.
A tendency of heterochromatin decreasing is confirmed in row of pikas: from species with a large number of chromosomes to species with a smaller number, while comparing the overall C-banding pattern of Ochotona dauurica and Ochotona huangensis (Formozov et al. 2004). Perhaps, this indicates a loss of the heterochromatic material as a result of the chromosomal rearrangements.
The species Ochotona alpina (subgenus Pika) is similar to Ochotona huangensis by the diploid chromosome number, but it has another arrangement of heterochromatin. Pericentromeric heterochromatin is detected only on 6 submetacentric and 5 subtelocentric pairs of Ochotona alpina autosomes (Ivanitskaya 1991). Four submetacentric pairs of Ochotona alpina (especially the first pair) have the larger heterochromatic blocks than the corresponding pairs of Ochotona huangensis. Two large subtelocentric pairs of Ochotona alpina also have the larger blocks of heterochromatin in comparison with the subtelocentric pairs of Ochotona huangensis. The remaining three minor subtelocentric pairs of Ochotona alpina, which contain the pericentromeric heterochromatin, have no analogues in the karyotype of Ochotona huangensis. Besides, the X chromosome of Ochotona alpina has no heterochromatin unlike Ochotona huangensis. The Y chromosome of Ochotona alpina is composed of heterochromatin entirely (Ivanitskaya 1991).
The molecular studies of the genus Ochotona (Yu et al. 2000, Formozov et al. personal communication) showed division of pikas for three superspecies groups: 1. Pika – northern pikas and Mongolian pika; 2. Ochotona – shrub-steppe pikas except Mongolian, Ladak and Kozlov’s pikas; 3. Conothoa – mountain pikas with Ladak and Kozlov’s pikas. At present, the statuses of subgenera are given for these groups of pikas (Hoffmann and Smith 2005). Formozov et al. (personal communication) suggested the existence of variation of the diploid chromosome number for each subgenus (group) of pikas. The karyotypes of the subgenus Pika species have 38-42 chromosomes. The species of the subgenus Ochotona have the karyotypes with 46-50 chromosomes. The pikas of the subgenus Conothoa have 60-62 chromosomes in the karyotypes. Moreover, there are species with 2n=68 in each subgenus.
The position of Ochotona huangensis is ambiguous in this system. According to the data of study of the cytochrome b and the ND4 gene (Yu et al. 2000), Ochotona huangensis is very far distant from the group of shrub-steppe pikas. Also, Ochotona huangensis is allocated to a separate independent group by analysis of the cytochrome b of 27 pikas species (Niu et al. 2004). At present, Ochotona huangensis (2n=42) belongs to the subgenus Ochotona (Hoffmann and Smith 2005). If the view point of Hoffmann and Smith is true, our data extend the level of variation of the diploid chromosome number for the subgenus Ochotona. In this case, there is no border with the subgenus Pika by this indicator. Thus, Ochotona huangensis is significantly diverging from the main group of the subgenus Ochotona by main karyotypic characteristics that corresponds to the data of mtDNA study (Yu et al. 2000, Niu et al. 2004). The recent cytogenetic study of Ochotona forresti (2n=54) (Ye et al. 2011) also greatly expands karyotypic variability of the subgenus Conothoa. As yet, the karyotypes of eight species of the subgenus Conothoa and three species of the subgenus Ochotona are not investigated. It is not excluded that the new karyotypic data will changed the level of the diploid numbers variation between all subgenera of the genus. Thus, we assume that the karyotypic system of the genus Ochotona can not be constructed completely without studying cytogenetic characteristics of all species of pikas.
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