Casilla , Santiago 7, Chile. Cavia tschudii Fitzinger, is a wild guinea pig species living in South America that according to the analysis of mitochondrial genes is the closest wild form of the domestic guinea pig. To investigate the genetic divergence between the wild and domestic species of guinea pigs from a cytogenetic perspective, we characterized and compared the C, G and AgNOR banded karyotypes of molecularly identified Cavia tschudii and Cavia porcellus Linnaeus, specimens for the first time. Both species showed 64 chromosomes of similar morphology, although C.
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Casilla , Santiago 7, Chile. Cavia tschudii Fitzinger, is a wild guinea pig species living in South America that according to the analysis of mitochondrial genes is the closest wild form of the domestic guinea pig.
To investigate the genetic divergence between the wild and domestic species of guinea pigs from a cytogenetic perspective, we characterized and compared the C, G and AgNOR banded karyotypes of molecularly identified Cavia tschudii and Cavia porcellus Linnaeus, specimens for the first time.
Both species showed 64 chromosomes of similar morphology, although C. Differences in the C bands size and the mean number of AgNOR bands between the karyotypes of the two species were detected. Most of the two species chromosomes showed total G band correspondence, suggesting that they probably represent large syntenic blocks conserved over time.
Partial G band correspondence detected among the four submetacentric chromosomes present only in the C. The role of the chromosomal and genomic differences in the divergence of these two Cavia species is discussed. Cavia tschudii Fitzinger, is a wild species of guinea pig Rodentia , Caviidae which inhabits northern Chile, southern Peru and Bolivia and northwestern Argentina Weir , Woods and Kilpatrick The domestic guinea pig Cavia porcellus Linnaeus, has a cosmopolitan distribution and is an experimental animal, pet, and even is consumed as food in countries of the Andean Altiplano Tello There is a consensus that Cavia porcellus is a domestic form derived from one of the five currently recognized wild species of guinea pigs that inhabit South America Woods and Kilpatrick By contrast, the crosses between Cavia porcellus and Cavia aperea sensu Erxleben, Pictet and Ferrero , Rood and between Cavia porcellus and Cavia cutleri Tschudi, sensu Bennet, Castle produced hybrids which were fertile in both sexes.
Later, molecular analyses of the mitochondrial cytochrome b and 12S RNA genes clearly showed that the closest species to Cavia porcellus is Cavia tschudii and not the genetically related Cavia aperea Spotorno et al.
Based on these molecular results and on the analysis of mummified guinea pig remains found in archeological sites, Spotorno et al. Considering that the karyotype provides useful characters in taxonomic and systematic studies and that changes in the number and structure of chromosomes may contribute to speciation King , Searle , Capanna and Redi , Capanna and Castiglia , Marques-Bonet and Navarro , Faria and Navarro , we describe and compare now for the first time the G, C and AgNOR banded karyotypes in molecularly identified specimens of the wild montane guinea pig Cavia tschudii and the domestic guinea pig Cavia porcellus.
Our objective is to discover the chromosomal and genomic differences between these two species of Cavia in relation to the divergence associated with the domestication process. Chromosomes were obtained from marrow cells using conventional in vivo colchicine, hypotonic method, preceded by yeast injection to improve the mitotic index Lee and Elder Metaphase cells were G-banded and C-banded by the methods described by Chiarelli et al.
At least 10 good-quality metaphases for each of the staining methods per taxon were selected under a light microscope and digitally captured and stored. The centromeric indexes calculated by measuring the chromosomal arms in 12 metaphases of each species, allowed the classification of the chromosomes as metacentric, submetacentric, subtelocentric and telocentric Levan et al.
Male and female G-banded karyotypes from each species were compared and the chromosomes were classified as having totally corresponding, partially corresponding or unique G band patterns Spotorno , Walker et al. The statistical significance of the differences was estimated using a Chi squared test.
Conventional stained karyotypes: a Cavia tschudii male b Cavia porcellus female. Cavia tschudii showed five pairs of submetacentric chromosomes group D, Fig. The X chromosome of Cavia tschudii was a large submetacentric similar to that of Cavia porcellus and the Y chromosome was a subtelocentric larger than that of Cavia porcellus Fig.
The four submetacentric chromosomes present only in the Cavia tschudii karyotype showed partial G band correspondence with four Cavia porcellus subtelocentric chromosomes Fig. Only the Y chromosomes and two autosomal pairs Cavia tschudii chromosomes 12, 13 and Cavia porcellus chromosomes 14, 18 were unique of each species karyotype Table 1. G-banded karyotypes: a Cavia tschudii male b Cavia porcellus female. Chromosomes numbered according to original karyotype descriptions see Fig.
Cts chromosomes are at the left and Cpo at the right of each chromosomal group. Note that the long arms of subtelocentric St and telocentric T forms of pair 1 show total G band correspondence inset. Correspondence of Cavia tschudii and Cavia porcellus chromosomes according to their G band patterns 1. Rough simulation of the changes associated with the occurrence of pericentric inversions in Cavia tschudii chromosomes. The chromosomal distribution of the C bands was similar in the karyotypes of the two species, being located preferentially in the centromeres and the short arms of the chromosomes Fig.
However, the amount of constitutive heterochromatin was appreciably greater in Cavia tschudii than in Cavia porcellus , spreading over most of the short arms in several subtelocentric chromosomes Fig. Both Y chromosomes were completely heterochromatic, being larger the Y chromosome of Cavia tschudii than the Cavia porcellus one Fig. C-banded karyotypes: a Cavia tschudii male b Cavia porcellus male, showing heteromorphism for chromosome 1. Most of the chromosomes of both species were tentatively identified according size and morphology.
Multiple AgNOR bands were detected in the karyotypes of both species, consistently located in the telomeres of several chromosomal pairs Fig. The analysis of some AgNOR banded metaphases per species indicated that the number of AgNOR bands was different between the two species and also among the individuals. Thus, the results showed that in Cavia porcellus the mean and maximum numbers of chromosomes with active NORs 5. Moreover, when we examined all the 3. AgNOR-banded karyotypes: a Cavia tschudii male with four nucleolar chromosomal pairs 4, 11, 14 and 29 b Cavia porcellus male with five nucleolar chromosomal pairs 1, 3, 5, 7 and The nucleolar chromosomes of both species were tentatively identified according to their size and morphology.
The FNa variability of guinea pig species may be due to polymorphisms for the presence of short arms in the chromosomes described as subtelocentric or telocentric in these species. The polymorphism for chromosome 1 short arms detected previously for Cavia cobaya Pallas, , a synonym of Cavia porcellus , Ohno et al. The number and morphology of Cavia tschudii and Cavia porcellus chromosomes were similar to those reported for other subspecies and species of the genus Cavia.
The analysis of the C bands showed that although they had a similar distribution in the chromosomes of the two species, they were smaller in size in the autosomes and in the Y chromosome of Cavia porcellus than in the Cavia tschudii ones, suggesting that a loss of heterochromatin occurred during the domestication process. In accordance with this result, measurements of the genome sizes of 31 hystricognath rodent species Gallardo et al.
Five chromosomal pairs bearing NOR at the short arm telomeres were found by Zenzes et al. Using a double-staining procedure they could identify those chromosomes as numbers 1, 3, 9, 12 and 14 of the quinacrine banded stained karyotype.
An accurate identification of the Cavia porcellus and Cavia tschudii nucleolar chromosomes described here would require the use of a similar double-staining procedure to allow the comparisons with other descriptions. The differences in the number of AgNOR bands found between the two Cavia species analyzed here and among the individuals in each of them, confirmed the tendency to variability in NOR expression usually described for mammals.
It has been proposed that this variability would depend mainly on the specific metabolic demands of cells and individuals Mikelsaar et al.
The greater number of AgNOR bands found in the Cavia porcellus karyotype than in the Cavia tschudii one would reveal a greater transcriptional activity of the ribosomal genes in the genome of the domestic form. One possible functional explanation of this result is that since Cavia porcellus has been selected for productive purposes, it would require higher rates of protein synthesis than the wild form. Comparison of the G-banded karyotypes of the two Cavia species included in this study revealed that most of the autosomal pairs and the X chromosomes showed total G band correspondence, suggesting that these chromosomes constitute large syntenic blocks present in the common ancestor of both species and conserved over time.
The differences in morphology and the partial G band correspondences detected between four chromosomal pairs of these two species, suggest that the four submetacentric chromosomes present only in the Cavia tschudii karyotype would have suffered pericentric inversions originating the four subtelocentric chromosomes of Cavia porcellus Fig.
Cavia porcellus would be the domestic successor of Cavia tschudii from which it would have originated more than and possibly years ago Wing by a process of domestication and artificial selection in the Cavia tschudii populations which inhabit southern Peru and northern Chile Spotorno et al. While being domesticated, those populations must have been small in size and with only a few individuals participating as parents in the reproductive process, which over many generations would have produced high levels of endogamy.
These characteristics would have facilitated the fixation of the pericentric inversions which must have emerged spontaneously and frequently in the populations.
Specifically, the heterozygotes for the pericentric inversions would have decreased their fertility since their gametes would be unbalanced as a result of crossing-over in the inverted segment Coyne et al. As a consequence, gene flow between the original homozygotes and the homozygotes for the inversion would have been reduced, originating genetic divergence between the two chromosomal forms.
Nevertheless, it has been demonstrated recently that the fertility of the inversion carriers is not always reduced Muss and Schwanitz In some cases and depending on the size, genetic content, and chromosomal location of the inversion, the chromosomal inverted region pairs non-homologously with its normal partner forming a straight bivalent which does not present any loop, so causing crossing-over suppression Torgasheva and Borodin If that is the case, the absence or reduced recombination between the inverted and non inverted genomic regions in the Cavia pericentric inversions, would be the cause of genetic divergence accumulation and reduction of gene flow between the two chromosomal forms, as it was proposed as a general model of speciation by several authors Noor et al.
A critical assessment of reproductive isolation in crosses between Cavia species as previously reported, confronts the appropriate identification of specimens, the reliability of the taxonomy at the time, and the nature of the differences eventually found.
By contrast, other wild specimens from Ica, Peru that also received the name Cavia cutleri by Tschudi in , were finally renamed as Cavia tschudii by Fitzinger in see Weir ; the latter is now the usually accepted name for the wild montane guinea pig Woods and Kilpatrick Therefore, Cavia cutleri Bennet, is now considered a synonym of Cavia porcellus Woods and Kilpatrick In any case, the assignation of the individuals from Arequipa to Cavia cutleri Bennet was not well documented in that study, since it was based only on the smaller body size of those individuals with respect to domestic Cavia porcellus Castle In sum, if the chromosomal and nucleolar differences we are reporting here in molecularly identified specimens of Cavia tschudii and Cavia porcellus were also found in other populations, we predict that their eventual hybrids will show some degree of genomic incompatibility.
Reproduction of wild mammal species in captivity is a difficult and not always successful task. It is even more difficult to obtain descendants from crosses between different chromosomal races or species in the laboratory Walker et al. Although we repeatedly tried to cross our specimens of Cavia tschudii with Cavia porcellus in our laboratory, we have had no success yet.
If the analysis of the crosses realized between chromosomal races of Mus and Sorex rodents Hauffe and Searle , Castiglia and Capanna , Franchini et al. To estimate fertility, specific reproductive aspects must be studied, such as the success obtained in crosses between the parental forms and some hybrid characters, i. Specifically, the fertility of the heterozygotes for the pericentric inversions described here should be further investigated to evaluate the contribution of those chromosomal changes to the divergence of the two Cavia species.
Comparative Cytogenetics 8 2 : — National Center for Biotechnology Information , U. Journal List Comp Cytogenet v. Comp Cytogenet. Published online Jul Laura I. Walker , 1 Miguel A. Spotorno 1. Miguel A. Author information Article notes Copyright and License information Disclaimer.
Corresponding author: Laura I. Walker moc. Received Mar 13; Accepted Jun Copyright Laura I. Walker, Miguel A. This article has been cited by other articles in PMC.
Abstract Cavia tschudii Fitzinger, is a wild guinea pig species living in South America that according to the analysis of mitochondrial genes is the closest wild form of the domestic guinea pig. Introduction Cavia tschudii Fitzinger, is a wild species of guinea pig Rodentia , Caviidae which inhabits northern Chile, southern Peru and Bolivia and northwestern Argentina Weir , Woods and Kilpatrick Open in a separate window.
Figure 1. Figure 2. Figure 3.
Montane guinea pig
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The montane guinea pig Cavia tschudii is a species of caviid rodent found in the Andes in South America. The montane guinea pig is the likely ancestor of Cavia porcellus , the domestic cavy or domestic guinea pig. Peruvian wild guinea pigs were first described by E. Bennett in , who termed them Cavia cutleri. Johann Jakob von Tschudi , in an publication, used the term Cavia cutleri to refer to what are now considered two separate entities - the first, Bennett's Cavia cutleri , which was later by Oldfield Thomas in identified as probably a differently pigmented version of Cavia porcellus , and the second, a wild Peruvian guinea pig that was clearly different from the animal Bennett described. The colour varies in different parts of the range; in Peru, the dorsal fur is dark reddish-brown mixed with black, and the underparts are dark buffy-grey; in Chile, the dorsal surface is pale agouti brown with paler underparts; in Bolivia, the upper parts are agouti olive and the underparts creamy-white or white. The montane guinea pig is native to the high Andes in South America.