Chromosomal relationships among the native rodents (Cricetidae: Oryzomyini) of the Galápagos Islands, Ecuador

Although the Galápagos Islands are recognized for their contribution to our understanding of evolutionary theory and have received the attention of scientists for over 185 years, our understanding of the native rodents there has been minimal relative to many other groups of organisms. Much of what we knew through most of the 20th century was based solely on species descriptions. Chromosome data has been limited to only Nesoryzomys narboroughi (2n = 32, FN (number of autosomal arms) = 50) and Aegialomys galapagoensis (2n = 56; FN = 58). We present the karyotypes of the only remaining extant species in the genus, N. swarthi (2n = 56; FN = 54) and N. fernandinae (2n = 44; FN = 54). Chromosomal banding reveals that extensive rearrangement has occurred within Nesoryzomys, including Robertsonian fusion and tandem fusion events but these alone cannot account for the diverse diploid numbers found within the genus. We propose that 1) N. swarthi represents the ancestral karyotype for the genus, similar to A. galapagoensis, 2) N. swarthi and N. fernandinae share the same fundamental number, suggesting divergence by Robertsonian fusions, and 3) N. narboroughi has the most derived karyotype, based on banding morphology and low diploid number.

Evolution of the Proto Sex-Chromosome in Solea senegalensis

Solea senegalensis is a flatfish belonging to the Soleidae family within the Pleuronectiformes order. It has a karyotype of 2n = 42 (FN = 60; 6M + 4 SM + 8 St + 24 T) and a XX/XY system. The first pair of metacentric chromosomes has been proposed as a proto sex-chromosome originated by a Robertsonian fusion between acrocentric chromosomes. In order to elucidate a possible evolutionary origin of this chromosome 1, studies of genomic synteny were carried out with eight fish species. A total of 88 genes annotated within of 14 BACs located in the chromosome 1 of S. senegalensis were used to elaborate syntenic maps. Six BACs (BAC5K5, BAC52C17, BAC53B20, BAC84K7, BAC56H24, and BAC48P7) were distributed in, at least, 5 chromosomes in the species studied, and a group of four genes from BAC53B20 (grsf1, rufy3, slc4a4 and npffr2) and genes from BAC48K7 (dmrt2, dmrt3, dmrt1, c9orf117, kank1 and fbp1) formed a conserved cluster in all species. The analysis of repetitive sequences showed that the number of retroelements and simple repeat per BAC showed its highest value in the subcentromeric region where 53B20, 16E16 and 48K7 BACs were localized. This region contains all the dmrt genes, which are associated with sex determination in some species. In addition, the presence of a satellite “chromosome Y” (motif length: 860 bp) was detected in this region. These findings allowed to trace an evolutionary trend for the large metacentric chromosome of S. senegalensis, throughout different rearrangements, which could be at an initial phase of differentiation as sex chromosome.

Multicolor Spectral Analyses of Mitotic and Meiotic Mouse Chromosomes Involved in Multiple Robertsonian Translocations. II. The NMRI/CD and CD/TA Hybrid Strains

Multicolor spectral analyses (spectral karyotyping) were performed on mitotic chromosomes of NMRI, CD, and TA mice and on male meiotic chromosomes (diakineses) of NMRI/CD and CD/TA hybrids. All chromosomes, including the various centric (robertsonian) fusions, could be unequivocally identified. Apart from the robertsonian translocations, which were previously detected by conventional banding analyses, no other interchromosomal rearrangements were found in these mice. In both the CD and TA mice, the autosomes 19 and the XY sex chromosomes are not involved in robertsonian translocations. In diakineses of male meiosis of the NMRI/CD hybrid, the 9 expected trivalents were present, whereas in those of the CD/TA hybrids a stable large meiotic multivalent, formed by 15 robertsonian fusion chromosomes and 2 terminally located normal chromosomes, was observed. The specific sequential order of the robertsonian fusion chromosomes found within this meiotic chain was as theoretically predicted. In the majority of diakineses of the NMRI/CD and CD/TA hybrids, the free autosomal bivalent 19 and the XY sex bivalent formed noticeable tight spatial associations.

EXPANSION OF CYTOGENETICALLY MODIFIED FORM OF OPISTHORCHIS FELINEUS IN THE TOM RIVER BASIN

In 1993, karyotyping of Opisthorchis felineus sporocysts, isolated from aquatic mollusks Bithynia inflat a in the industrial wastewater of the Siberian Chemical Combine discovered cytogenetically modified 12-chromosome specimens. In 2012-2013, a repeated study of the spread of these mutant trematodes in the lower course of the river Tom was carried out. It was established that specimens with sporocysts of O. felineus having 2n=12 were found in 8 of 10 places of catching. The caught goldfish were used to isolate metacercariae to infest golden hamsters in the experimental conditions. After 5 months, the hamster livers were processed to extract marita specimens and the number of chromosomes in their ovaries and testes was cytogenetically determined. The results of analysis of the spread of O. felineus carried out by this method showed the presence of 12-chromosome form of the Opisthorchis marita in all places of fishing out in the lower course of the river Tom. Analysis of the 12-chromosome karyotype allows to conclude that this mutation was a result of Robertsonian fusion of chromosomes 3 and 6 of 14-chromosome form of karyotype.