Margarete S. Mattevi

KARYOTYPES OF NINETEEN MARSUPIAL SPECIES FROM BRAZIL

Abstract Karyotypes of 127 individuals, representing 19 species of 10 genera of Brazilian marsupials (Didelphidae) were determined, with karyotypes of Gracilinanus emiliae and G. microtarsus, Marmosops incanus, Thylamys velutinus, and Philander frenata being described for the 1st time. The specimens were collected from 24 localities, in an area between 4°N (Surumú, Roraima) and 31°S (Mostardas, Rio Grande do Sul), in Brazil. Only 3 diploid numbers were found, 2n = 14 in G. emiliae, G. microtarsus, G. agilis, Marmosa murina, Marmosops parvidens, M. incanus, Micoureus demerarae, and T. velutinus; 2n = 18 in Monodelphis dimidiata, M. brevicaudata, M. kunsi, and M. domestica; and 2n = 22 in Chironectes minimus, Lutreolina crassicaudata, Didelphis albiventris, D. aurita, D. marsupialis, Philander opossum, and P. frenata.

CHROMOSOME STUDIES OF SEVEN SPECIES OF OLIGORYZOMYS (RODENTIA: SIGMODONTINAE) FROM BRAZIL

Abstract Karyotypes of 7 taxa of the rodent genus Oligoryzomys trapped in 33 localities from an area ranging from 01°N to 32°S in Brazil were analyzed. Three species were trapped exclusively in the Cerrado biome: O. stramineus, diploid number (2n) = 52, fundamental number (herein, number of autosomal arms; FN) = 68; O. eliurus, 2n = 62, with 2 fundamental numbers, FN = 64 and 66; and Oligoryzomys sp., 2n = 70, FN = 74. In the Amazon, we caught O. cf. messorius, 2n = 56, FN = 58, and O. microtis, 2n = 66, FN = 74. Oligoryzomys nigripes (2n = 61, 62, FN = 80–82) was trapped in 24 localities in various biomes, and O. flavescens from several sites in southern Brazil presented the same karyotypes as those already described at other sites. The C- and NOR-banding were performed for all species, and the (T2AG3)n telomeric probe hybridized in situ to both the short and long arms of all pairs of karyotypes of O. cf. messorius, O. eliurus, and Oligoryzomys sp. An analysis performed with 11 microsatellite DNA heterologous primers improved differentiation of O. nigripes from O. eliurus individuals, 2 species that presented 2n = 62 and that were trapped at the same site.

Senescence and human chromosome changes.

SummaryChromosome counts and a search for structural abnormalities were performed in cultured leukocytes from 60 elderly subjects (ages 62–96) and 60 controls (ages 10–13). A total of 3900 cells were examined, 3600 in 3-day cultures and 300 in cultivations maintained for 2 days. Our results and those obtained by other investigators indicate clearly that there is an increase in the level of aneuploidy and of structural abnormalities in the blood of aged persons. There is an excess of missing C-group chromosomes in elderly females, but no consistent preferential loss was observed among the males. In contrast with two previous studies, we found a significant decrease of aneuploid cells in 3-day cultures, as compared to those cultivated for 2 days only.

DESCRIPTION OF A NEW SPECIES OF AKODON (RODENTIA: SIGMODONTINAE) FROM SOUTHERN BRAZIL

Abstract Cranial and external morphology of 54 specimens of rodents of the genus Akodon from southern Brazil was analyzed. The sample included 27 individuals with a karyotype of 2n = 44 and 13 with 2n = 46 and 14 nonkaryotyped animals. Principal components analysis separated individuals with 2n = 44 from those with 2n = 46. Individuals with 2n = 44 were distinguished from those with 2n = 46 by narrow and elongated molars, ectolophid present, narrow interorbital breadth, reduced tegmen tympani, and distal baculum with the central and lateral digit approximately equal in size and proportions, not enlarged in the extremity. Discriminant functions analyses including 6 A. sanctipaulensis individuals and holotypes of A. serrensis and A. s. leucogula resulted in 3 distinct groups. The 2n = 46 individuals were related to A. serrensis, but those with 2n = 44 were not assignable to any described species for Akodon. We describe and propose the recognition of a new species for the genus.

Effect of sex, age and cultivation time on number of satellites and acrocentric associations in man.

SummaryLymphocyte cultures of 120 normal persons evenly distributed in relation to sex and age groups were studied. A total of 3900 cells were examined, 3600 in 3-day cultures and 300 in cultivations maintained for 2 days. In both age groups (10–13; 62–96 years) men showed higher numbers of satellites per cell but less cells with D/G associations. Older subjects presented a lower number of cells with D satellites and acrocentric associations; the pattern of these associations, however, did not seem to vary with age. The mean number of associations per cell decreased significantly in 3-day as opposed to 2-day cultures.

Proposed chromosomal phylogeny for the South American primates of the Callitrichidae family (Platyrrhini)

Cytogenetic and cytotaxonomic studies (G, C, sequential G/C, and NOR banding) were performed on 110 specimens representing the four genera of South American primates of the family Callitrichidae: Cebuella (C. pygmaea), Callithrix, groups argentata (C. argentata, C. emiliae, C. chrysoleuca, C. humeralifera, C. mauesi), and jacchus (C. aurita, C. geoffroyi, C. jacchus, C. kuhli, C. penicillata), Leontopithecus (L. chrysomelas, L. rosalia), and Saguinus (S. midas midas, S. m. niger). Mitotic chromosomes are characterized, and the rearrangements distinguishing the karyotypes of the taxa are inferred from arm homologies. The results were then converted into numerical data and submitted to cladistic analysis. The following conclusions were achieved: 1) Five karyotypic classes were observed, which correspond to the five taxa studied. Differences between them are as follows: a) Cebuella (2n = 44, 10 acrocentrics, A + 32 bi‐armed autosomes, bi) and the argentata group (2n = 44, 10A + 32bi) are different from each other due to a reciprocal translocation; b) both can be distinguished from the jacchus group (2n = 46, 14A + 30bi) by a centric fusion/fission rearrangement and a paracentric inversion; c) Leontopithecus (2n = 46, 14A + 30bi) and Saguinus (2n = 46, 14A + 30bi) differ from the jacchus group by a reciprocal translocation and three paracentric inversions; and d) Saguinus is different from the others by one paracentric inversion and pericentric inversions in at least four pairs of acrocentric autosomes. 2) The cladistic analysis separates Cebus (used as an outgroup) from the Callitrichidae groups, which forms a clade. Among the Callitrichidae, marmosets (Cebuella and Callithrix) form a sub‐clade, Cebuella and the argentata group being more closely related to each other than both are to the jacchus group. Tamarins (Leontopithecus and Saguinus) are also quite close, so that if one was not derived from the other, they with the marmosets share a common ancestor. Among the tamarins, Leontopithecus is karyotypically closest to the marmosets, specifically to the jacchus group. 3) Based on the chromosome information and considering the possible direction of the evolutionary changes (primitivity or phyletic dwarfism hypothesis, previously advanced by other authors), it was possible to propose the ancestral karyotypes and to develop two alternatives for the origin, differentiation and dispersion of the callitrichid. Both proposals are plausible, but when the geographical distribution is considered, the phyletic dwarfism hypothesis seems to be the most probable. Am. J. Primatol. 49:133–152, 1999.

T2AG3)n telomeric sequence hybridization indicating centric fusion rearrangements in the karyotype of the rodent oryzomys subflavus.

Chromosome preparations of 30 specimens of Oryzomys subflavus trapped in eight Brazilian localities were C-, and G-banded and analyzed by fluorescence in situ hybridization (FISH). Two karyotypes were found, 2n = 50/FN = 64, at three coastal localities of the Atlantic Forest domain, and 2n = 58/FN = 70 at two sites located in the Cerrado biome, Brazil Central. Two fluorescence in situ hybridization (FISH) patterns of the telomeric sequence (T2AG3)n were observed: in both karyotypes the probes hybridized to the telomeres of all chromosomes and also a hybridization signal in the centromeric regions of two autosome pairs was seen in the 2n = 50 karyotype. These results, together with the occurrence of other diploid numbers described in the literature, suggest that O. subflavus is a complex species, bearing fusion/fission rearrangements proper to the different biomes which it inhabits.

T2AG3)n telomeric sequence hybridization suggestive of centric fusion in karyotype marsupials evolution.

It has been suggested that the karyotype of the marsupials derived from a low diploid number (2n = 14) which originated, through fissions of biarmed chromosomes, the karyotypes with a higher 2n. The telomeric sequence (T2AG3)nwas in situhybridized to the chromosomes of Gracilinanus microtarsusand G. emiliae, Micoureus demeraraeand Marmosa murina, species with 2n = 14, in Monodelphissp., M. domestica, M. kunsiand M. brevicaudatawith 2n = 18, and in Lutreolina crassicaudata, Didelphis albiventris, Chironectes minimus, Philander opossumand P. frenata, all of them with 2n = 22. The probe hybridization occurred in the telomeric regions of both arms, short and long, of all chromosomes of the complement of all individuals of all species analysed. However, in some pairs of the karyotypes of Gracilinanus microtarsusand Micoureus demerarae(with 2n = 14), and in Monodelphissp., M. domestica, M. kunsiand M. brevicaudata(2n = 18) ectopic signs of hybridization were detected proximal to the centromeres, suggesting the retention of this telomeric sequence in the centromeric regions of some chromosomes of these species. Based on these results, it is proposed that the karyotype of marsupials evolved from a 2n = 22 to a 2n = 14, by means of chromosomal fusions.

Comparative chromosomal study of five taxa of genus Callithrix, group Jacchus (Platyrrhini, primates)

The karyotypes of four marmoset species of the Callithrix jacchus group (C. aurita, C. kuhlii, C. geoffroyi, and C. penicillata) were investigated. The patterns of G‐, C‐, and NOR‐bands of these karyotypes were compared with those of C. jacchus, previously described, in order to clarify the taxonomic relationships of this species group. All species present 2n = 46, 14 uni‐ and 30 biarmed autosomes, a median size submetacentric X chromosome, and the same NOR‐band patterns. No rearrangement or constitutive heterochromatic variation differentiate these species, which differ only in the morphology of the Y chromosome. The data obtained indicate that, from the chromosomal point stand, the marmoset species of C. jacchus group constitute a homogeneous clade. Am J Primatol 41:53–60, 1997.

An X1X1X2X2/X1X2Y mechanism of sex determination in a South American rodent, Deltamys kempi (Rodentia, Cricetidae)

Chromosome studies on 14 specimens of Deltamys kempi disclosed six males with 2n = 37, NF = 38, six females with 2n = 38, NF = 38, and two females with 2n = 37, NF = 38. G- and C-band analyses revealed a Y-autosome translocation in the males leading to a multiple chromosome system of sex determination of the type X1X1X2X2/X1X2Y, this being the second case of such a mechanism described in rodents. At meiosis the males presented a trivalent in which C-banding studies showed an alternate orientation of the sex chromosomes due to end-to-end association of the X1 and Y chromosomes, the Y and the X2 being held together by interstitial chiasmata. At metaphase II both n = 17 + Y and n = 18 + X1 are regularly observed. The two females with 2n = 37, NF = 38, are heterozygous for an autosomal centric fusion involving chromosomes 1 and 13. The product of the Y-autosome translocation constitutes the largest element of the karyotype (9.4% of the haploid set); the X1 chromosome amounts to 7.8% of this set, including a large heterochromatic block. When only its euchromatic region is considered, this percentage decreases to 4.6%. From two to seven NORs were observed at the telomeres, with a mean of 4.4 +/- 1.1 per cell.