Search

Analyses of the dimensions and morphology of spermatozoa can be useful in the identification of mammalian species. We compared and contrasted sperm morphology and dimensions in 9 genera and 18 species of the family Cricetidae. Spermatozoa were obtained from the cauda epididymes of animals previously fixed in 10% formalin, and stained with Giemsa or silver-nitrate staining methods. At least 50 spermatozoa from different specimens were examined for each species. Discriminant function analysis was used to distinguish between the spermatozoa of different species and to identify the best discriminating characteristics. MANOVA revealed that differences between species were significant. Species in the same genus tended to group together. Qualitative characteristics that discriminate between species are discussed. Fil: Rossi, Luis Francisco. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: De La Sancha, Noé U.. Chicago State University; Estados Unidos. The Field Museum of Natural History; Estados Unidos Fil: Luaces, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Investigaciones Cardiológicas. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Investigaciones Cardiológicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina Fil: Estevez, Daniela Yael. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina Fil: Merani, Maria Susana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina

Different concentrations of a glyphosate formulation, Roundup® Full II (66.2% glyphosate) were tested in culture peripheral blood of armadillo Chaetophractus villosus with cytogenetic biomarkers like mitotic index (MI), chromosomal aberrations (CA), sister chromatid exchange (SCE) and cell proliferation kinetics (CPK) by means of replication index. Adults animals of both sexes were exposed to RU at four concentrations ranging from 0.026 mL RU solution to 0.379 mL RU daily in oral treatment with the same volume (0.2 mL) during 7 days. We analyzed the induced damage at different times considering T0 as control value, one (T1), seven (T7) and 30 days (T30). One day after, only the higher concentration shows MI significant differences (p

For brown howler monkeys (Alouatta guariba clamitans), diploid chromosome numbers varying from 2n = 45 to 2n = 52, with XX/XY, X1X1X2X2/X1X2Y, and X1X1X2X2X3X3/X1X2X3Y1Y2 sex chromosome systems have been described by mitotic studies but still await confirmation by meiotic analyses. We analyzed 3 male individuals sampled in the wild (in the municipality of Santa Maria, RS, Brazil) as well as 1 male and 1 female individual in captivity at the São Braz breeding center. Peripheral blood samples and testicular biopsies were taken. We found different diploid numbers for both sexes in somatic cells, 2n = 45,X1X2X3Y1Y2 in males and 2n = 46,X1X1X2X2X3X3 in females, with 4 metacentric (9-12), 7 submetacentric (1-6, 8), and 9 acrocentric autosomal chromosome pairs (13-20, 22). X1 and X2 were submetacentric chromosomes, while X3, Y1, and Y2 were acrocentric ones. Spermatocyte microspreads were examined for synaptonemal complexes. Pachytene spermatocyte analysis was done to verify the chromosome number and morphologies observed in mitotic karyotypes. Immunodetection was performed using anti-SMC3 and anti-CREST antibodies. The presence of a sex chromosome pentavalent X1X2X3Y1Y2 in the males was confirmed by C-banding in metaphase I and by immunodetection in prophase I by the clear identification of 5 centromeres. The G-banded karyotype corresponded to that previously described for A. g. clamitans in the south of Brazil (Curitiba, Parana State, and Blumenau, Santa Catarina State) and for the Misiones Province, Argentina.

Sentinel species are useful tools for studying the deleterious effects of xenobiotics on wildlife. The large hairy armadillo (Chaetophractus villosus) is the most abundant and widely distributed mammal in Argentina. It is a long-lived, omnivorous, burrowing species, with fairly restricted home ranges. To evaluate the level of spontaneous genetic damage in this mammal, we determined the baseline values of several genotoxicity biomarkers. The study included 20 C. villosus adults of both sexes from eight pristine localities within its geographic distribution range. Genotoxicity analysis was performed on 72-h lymphocyte cultures, using mitomycin C as positive control. We obtained the baseline values of mitotic index (MI=10.52±0.30 metaphases/total cells, n=20), chromosome aberrations (CA=0.13±0.22, n=20), sister chromatid exchanges (SCE)=6.55±0.26, n=6) and replication index (RI=1.66, n=6). MI and CA did not show significant differences (P>0.05) among localities or between sexes. No significant differences in MI, CA, SCE, and RI (P>0.05) were found between values from the pristine localities and historical data. There were significant differences in CA, SCE, and RI (P

In Nature, mammalian seasonal breeders undergo spermatogenetic arrest during the non-breeding season. In the large hairy armadillo Chaetophractus villosus, testis regression initiates with immature post-meiotic germ cells sloughing into the tubule lumen and continues with the death of the remaining spermatocytes. At the end of the regression period, only spermatogonia and Sertoli cells persist in the seminiferous epithelium. It has been suggested that cell sloughing is determined by changes in the adhesion complexes between Sertoli cells and spermatids, which are mediated by low intra-testicular testosterone levels. By immunofluorescence and western blotting we studied key proteins of the N-cadherin/N-cadherin and α6β1-integrin/laminin interlocks that contribute to the complex Sertoli/spermatid adhesion system throughout the eight stages of the seminiferous epithelium cycle in the comparison between active and regressing testes. In active testis, β1-integrin, Laminin G3, N-cadherin, β-catenin, P-β-catenin-Tyr654, FAK, P-FAK-Tyr397, Src, P-Src-Tyr416 proteins present a spermatogenetic cycle-dependent localization pattern, unmaintained in regressing testes. In the latter, quantitative variations and changes in the phosphorylation state of protein FAK, Src, and β-catenin contribute to the disassembly of the N-cadherin/N-cadherin and α6β1-integrin/laminin interlocks, thus promoting the massive release of immature spermatids.

In Argentina, Chaetophractus villosus has a wide distribution that overlaps with agricultural areas where soybean is the predominant crop. In such areas the pesticide Roundup Full II® (RU) is widely applied. The genotoxic effect of its active ingredient glyphosate (RU is 66.2% glyphosate) on the peripheral blood lymphocytes of C. villosus was tested over a range of concentrations (280, 420, 560, 1120 μmol/L). Culture medium without glyphosate served as negative control, while medium containing mitomycin C served as positive control. Genetic damage was characterized in terms of the percentage of cells with chromosome aberrations (CA), the mean number of sister chromatid exchanges (SCE) per cell, and the modification of cell proliferation kinetics via the calculation of the replication index. Significant increases (p < 0.0001) were seen in the CA frequency and the mean number of SCEs per cell compared to negative controls at all the RU concentrations tested. Chromatid breaks, the only form of CA observed, under the 560 μmol/L RU conditions and in presence of mitomycin C were four to five times more common than at lower concentrations, while no viable cells were seen in the 1120 μmol/L treatment. The mean number of SCEs per cell was significantly higher under the 280 μmol/L RU conditions than the 420 or 560 μmol/L RU conditions; cells cultivated in the presence of MMC also showed significantly more SCEs. All the RU concentrations tested (except in the 1120 μmol/L RU treatment [no viable cells]) induced a significant reduction in the replication index (p > 0.0001). The present results confirm the genotoxic effects of RU on C. villosus lymphocytes in vitro, strongly suggesting that exposure to RU could induce DNA damage in C. villosus wildlife. Fil: Luaces, Juan Pablo. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Rossi, Luis Francisco. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Chirino, Monica Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Browne, Melanie. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Merani, Maria Susana. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Mudry, Marta Dolores. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

The karyotype of the giant anteater Myrmecophaga tridactyla was studied throughout the species’ Argentine range. Images of the chromosome complement clearly revealed the karyotype and identified previously misinterpreted chromosomes. The peripheral blood lymphocytes of 26 adult animals (11 males and 15 females) were cultured and used to obtain mitotic metaphases. These preparations were subjected to conventional staining, G- and C-banding, and Fluorescent in situ Hibridization (FISH). Spermatocyte pachytene microspreads for one adult were examined for synaptonemal complexes. The karyotype (2n = 60 XX/XY; Fundamental Number (FN) = 110 without XY) showed an autosomal complement of six metacentric, 18 submetacentric, and six acrocentric chromosome pairs. The X chromosome (4.67 ± 0.29% of the haploid set) was shown to be large and submetacentric, similar in size to autosomes 3–5. The Y chromosome was submetacentric (2.60 ± 1.08% of the haploid set). It is, however, larger than the Y chromosome of the ...

Karyotype and cytotype variations for the large hairy armadillo (Chaetophractus villosus) were studied throughout the species' Argentine distribution. Peripheral blood lymphocyte cultures of 421 animals were used to obtain mitotic metaphases. Preparations were subjected to conventional staining, G- and C-banding, and FISH involving a telomeric probe. Meiotic analysis was performed on testis material from 10 adults. Spermatocytes were examined for synaptonemal complexes in microspreads. The karyotype (2n = 60 XX/XY; FN = 84 without XY) showed an autosomal complement of 6 metacentric and 7 submetacentric chromosomes; the remainder was acrocentric. The X chromosome was submetacentric and the Y acrocentric. Centromeric C+ marks were observed in all chromosomes except pair 16. Three NOR signals were detected in 6q, 12p, and 26p. Two chromosomal rearrangements were characterized in chromosome pair 1 a pericentric inversion seen in the material from Jacinto Aráuz, General Madariaga and Pellegrini and a deletion in the material from Loma Verde. Interstitial telomeric signals were observed in chromosome pairs 4, 12, 16, and 26. Pachytene spermatocyte analysis confirmed the basic chromosome number and morphologies observed in mitotic karyotypes. The evolution of C. villosus involved chromosomal rearrangements as recorded for other species of its superorder. The present results establish the basis for the cytogenetic characterization of this species.

The anatomy and histology of the male genital tract of the lesser anteater were studied. Fine details of spermatozoa regarding their genesis and morphology were also studied in six adult specimens. The testes lie in the pelvic cavity. The deferent duct emerges from the epididymis and opens into the ejaculatory duct, which drains into the membranous urethra. Accessory glands (prostate, seminal vesicle and bulbourethral gland) are histologically similar to those described in other mammals. The short penis presents an urethral orifice, while the corpus spongiosum becomes thinner at the end indicating the absence of a histologically defined glans. The seminiferous epithelium shows: (1) Sertoli cells with deep nuclear indentations, (2) spermatogonia with crusty-like chromatin, (3) spermatocytes at different stages of maturation and (4) three morphologi- cally distinct stages of spermatid differentiation according to nuclear shape, acrosome development and chromatin condensation. Sperm heads appear oval. The length of the spermatozoa averages 67.33 ± 1.60 lm. Two specimens with inactive spermatogenesis were azoospermic. Their testes and epididymis pre- sented sizes smaller than those with active spermatogenesis. These studies together with others in anteaters may contribute to successful breeding in conservation programmes. Fil: Rossi, Luis Francisco. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina Fil: Luaces, Juan Pablo. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina Fil: Aldana Marcos, Hernan Javier. Universidad de Belgrano. Facultad de Ciencias Exactas y Naturales; Argentina Fil: Cetica, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Veterinarias. Instituto de Investigacion y Tecnología en Reproducción Animal; Argentina Fil: Perez Jimeno, Guillermo. Proyecto Conservacion Oso Hormiguero; Argentina Fil: Merani, Maria Susana. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; Argentina

Armadillos constitute a neotropical endemic mammalian group in the American continent and the main diversity is distributed in Argentina. Several species of this family are in danger of extinction. Blood collection in armadillos is difficult because of their anatomy. In the present work, in latex-perfused material, the rete mirabile of the coccygeal artery of the tail was recognized as an appropriate venipuncture site for sterile blood collection. From cadaveric material, histological sections of the tail of six species of five genera of armadillos were used to determine the diameter and the distance to access the main artery of the rete mirabile ventrodorsally. Field studies were carried out in wild animals. A total of 232 blood samples were obtained from the following species: Chaetophractus villosus (70), C. vellerosus (105), Zaedyus pichiy (15), Euphractus sexcinctus (8), Dasypus hybridus (25), and Tolypeutes matacus (9). The animals were restrained with the thumbs pressing the abdomen ventro...

Knowledge of armadillo reproductive physiology is essential for developing ex situ and in situ assisted reproductive techniques for propagating and/or controlling populations of these animals. The present study included assessment of fecal sex steroids by radioimmunoassay, determining reproductive status via monitoring ovarian activity (in the wild) and therefore reproductive status, in wild females of the large hairy armadillo (Chaetophractus villosus) and the crying armadillo (Chaetophractus vellerosus) in the southern hemisphere. Plasma and fresh fecal progesterone concentrations were not significantly correlated in either species. However, in both species, there was a significant positive correlation between plasma progesterone and dry fecal progesterone concentrations (r = 0.82, P < 0.05 and r = 0.60, P < 0.05, respectively). Dry fecal progesterone and estradiol concentrations were measured in one captive C. villosus (average baseline progesterone and estradiol concentrations 28.72 ± 11.75 ng/g dry feces and 3.04 ± 0.80 ng/g dry feces, respectively) and one captive C. vellerosus (average baseline progesterone and estradiol concentrations 14.05 ± 3.03 ng/g dry feces and 3.46 ± 1.20 ng/g dry feces, respectively) to detect hormonal peaks over 1 y; these occurred from late fall to early summer. Feces from wild C. villosus and C. vellerosus were also collected over 1 y to determine progesterone peaks, which occurred in winter and spring in both species (with no peaks during the summer or fall). Accordingly, C. villosus and C. vellerosus had a seasonal reproductive pattern. The significant correlations between dry fecal and plasma progesterone concentrations validated this method for monitoring reproductive status in these species.

Species of Polybetes are known exclusively from South America. Currently there are 13 described species, 9 occurring in Argentina. Cytogenetic studies in spiders are scarce; the cytogenetics of only about 1% of nearly 39,500 described species are known. Within the Sparassidae, 38 species out of 1,009 (< 4%) have been cytogenetically analyzed; the most frequent chromosome number is 2n = 43/46 (male/female), n = 20 + X1X2X3, present in almost half of the species studied. Female diploid chromosome number is only known for four species: Heteropoda venatoria (Linnaeus 1767) (2n = 44); Pediana regina (L. Koch 1875), Isopeda sp. and Olios sp. (2n = 46). Within the genus Polybetes, only P. pythagoricus (Holmberg 1875) had been previuosly cytogenetically analyzed. In the present work, the karyotype, heterochromatin content and distribution, and silver stained nucleolus-organizer regions of P. pythagoricus, P. rapidus (Keyserling 1880) and P. punctulatus Mello-Leitao 1944 are described and compared. In P. ...

The karyotypes of Lucilia cluvia (Walker, 1849) and L. sericata (Meigen, 1826) from Argentina were characterized using conventional staining and the C- and G-like banding techniques. Besides, nucleolus organizer regions (NORs) were detected by fluorescent in situ hybridization (FISH) and silver staining technique. The chromosome complement of these species comprises five pairs of autosomes and a pair of sex chromosomes (XX/XY, female/male). The autosomes of both species have the same size and morphology, as well as C- and G-like banding patterns. The X and Y chromosomes of L. cluvia are subtelocentric and easily identified due to their very small size. In L. sericata, the X chromosome is metacentric and the largest of the complement, showing a secondary constriction in its short arm, whereas the Y is submetacentric and smaller than the X. The C-banding patterns reflect differences in chromatin structure and composition between the subtelocentric X and Y chromosomes of L. cluvia and the biarmed sex chromosomes of L. sericata. These differences in the sex chromosomes may be due to distinct amounts of constitutive heterochromatin. In L. cluvia, the NORs are placed at one end of the long-X and of the long-Y chromosome arms, whereas one of the NORs is disposed in the secondary constriction of the short-X chromosome arm and the other on the long-Y chromosome arm in L. sericata. Although the G-like banding technique does not yield G-bands like those in mammalian chromosomes, it shows a high degree chromosomal homology in both species because each pair of autosomes was correctly paired. This chromosome similarity suggests the absence of autosomal rearrangements during karyotype evolution in the two species studied. Fil: Chirino, Monica Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina Fil: Rossi, Luis Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina Fil: Bressa, Maria Jose. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina Fil: Luaces, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina Fil: Merani, Maria Susana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Laboratorio de Biología Cromosómica; Argentina

Previous works about comparative spermatology in Dasypodidae determined that sperm morphology is a striking variable among genera. It was suggested that this sperm feature may be related to specific morphologies of the female reproductive tract. The present comparative study of the morphology of the female genital tract from seven species corresponding to six genera of Dasypodidae is aimed to determine the main similarities and differences between the species and to establish a possible correlation with the sperm shapes and sizes. Genital tracts were studied macroscopically and histologically. Dasypus hybridus has disk-shaped ovaries and the cortex occupies almost all the organ with a single oocyte in each follicle. Tolypeutes matacus, Chaetophractus villosus, Chaetophractus vellerosus, Zaedyus pichiy, Cabassous chacoensis and Clamyphorus truncatus possess ovoid and elongated ovaries, with both longitudinally polarized cortex and medulla, and the peculiar presence of several oocytes in the same follicle. D. hybridus and T. matacus have a simple pear-shaped uterus, but in the other species the uterus is pyramid shaped and bicornuate. The uterine cervix is very long in all studied species. Only T. matacus presents a true vagina as in most eutherian mammals; on the other hand, in the other species a urogenital sinus is observed. The structure of female reproductive tracts in Dasypodidae contains a mixture of assumedly primary and other derived features. According to the different morphologies of the regions analyzed, a classification of the female genital tracts in three groups can be performed (group 1: Dasypus; group 2: Tolypeutes; group 3: Chaetophractus, Zaedyus, Cabassous, Clamyphorus) and a correlation between each group and a specific sperm morphology can be established.

We quantitatively analyzed the spermatogenic process, including evaluation of seminiferous tubules with defective cycles, rates of germ cell death and sperm morphology, in adult male mice with standard telocentric chromosomes (2n = 40, CD1 strain), homozygous (2n = 24, Mil II population) and heterozygous (2n = 24 × 40) for Robertsonian (Rb) rearrangements. The animals were analyzed at three different ages: three, five and seven months after birth. The number and position of crossover events were also determined by chiasmata counting and immunostaining with an antibody against mouse MLH1 protein. Our analysis of spermatogenesis confirms the impairment of the spermatogenic process in multiple simple heterozygotes due to both germ cell and abnormal sperm morphology. The detrimental effects exerted by Rb heterozygosities were found to be at least partially buffered with time: the frequency of defective tubules was lower and germ cell survival and sperm morphology better in 7-month-old animals than in the 3- and 5-month-old mice. While there are previously published data on germ cell death in multiple simple heterozygotes, this is the first report of a partial rescue of spermatogenesis with time. The mean frequency of MLH1 foci was lower in Rb homozygous and heterozygous mice than in mice carrying all telocentric chromosomes. The lower number of foci in Rb mice can be ascribed to a decrease in the number of multiple chiasmata and the maintenance of single chiasmata preferentially located in the terminal region of both the telocentric and metacentric chromosomes.

The armadillo Chaetophractus villosus is a seasonal breeder whose seminiferous epithelium undergoes rapid regression with massive germ cell loss, leaving the tubules with only Sertoli cells and spermatogonia. Here, we addressed the question of whether this regression entails 1) the disassembly of cell junctions (immunolocalization of nectin-3, Cadm1, N-cadherin, and beta-catenin, and transmission electron microscopy [TEM]); 2) apoptosis (immunolocalization of cytochrome c and caspase 3; TUNEL assay); and 3) the involvement of Sertoli cells in germ cell phagocytosis (TEM). We showed a dramatic reduction in the extension of vimentin filaments associated with desmosomelike junctions at the interface between Sertoli and germ cells, and an increased diffusion of the immunosignals of nectin-3, Cadm1, N-cadherin, and beta-catenin. Together, these results suggest loss of Sertoli-germ cell adhesion, which in turn might determine postmeiotic cell sloughing at the beginning of epithelium regression. Then, loss of Sertoli-germ cell adhesion triggers cell death. Cytochrome c is released from mitochondria, but although postmeiotic cells were negative for late apoptotic markers, at advanced regression spermatocytes were positive for all apoptotic markers. Transmission electron microscopy analysis showed cytoplasmic engulfment of cell debris and lipid droplets within Sertoli cells, a sign of their phagocytic activity, which contributes to the elimination of the residual meiocytes still present in the latest regression phases. These findings are novel and add new players to the mechanisms of seminiferous epithelium regression occurring in seasonal breeders, and they introduce the armadillo as an interesting model for studying seasonal spermatogenesis.

The armadillo Chaetophractus villosus is a seasonal breeder whose seminiferous epithelium undergoes rapid regression with massive germ cell loss, leaving the tubules with only Sertoli cells and spermatogonia. Here, we addressed the question of whether this regression entails 1) the disassembly of cell junctions (immunolocalization of nectin-3, Cadm1, N-cadherin, and beta-catenin, and transmission electron microscopy [TEM]); 2) apoptosis (immunolocalization of cytochrome c and caspase 3; TUNEL assay); and 3) the involvement of Sertoli cells in germ cell phagocytosis (TEM). We showed a dramatic reduction in the extension of vimentin filaments associated with desmosomelike junctions at the interface between Sertoli and germ cells, and an increased diffusion of the immunosignals of nectin-3, Cadm1, N-cadherin, and beta-catenin. Together, these results suggest loss of Sertoli-germ cell adhesion, which in turn might determine postmeiotic cell sloughing at the beginning of epithelium regression. Then, loss of Sertoli-germ cell adhesion triggers cell death. Cytochrome c is released from mitochondria, but although postmeiotic cells were negative for late apoptotic markers, at advanced regression spermatocytes were positive for all apoptotic markers. Transmission electron microscopy analysis showed cytoplasmic engulfment of cell debris and lipid droplets within Sertoli cells, a sign of their phagocytic activity, which contributes to the elimination of the residual meiocytes still present in the latest regression phases. These findings are novel and add new players to the mechanisms of seminiferous epithelium regression occurring in seasonal breeders, and they introduce the armadillo as an interesting model for studying seasonal spermatogenesis.

Three xenarthrans species Chaetophractus villosus, Chaetophractus vellerosus, and Zaedyus pichiy have been used for the analysis of the structure, behavior, and immunochemical features of the XY body during pachytene. In all these species, the sex chromosomes form an XY body easily identifiable in thin sections by the special and regular packing of the chromatin fibers of the internal region of the XY body ("differential" regions) and those of the peripheral region (synaptic region). Spermatocyte spreads show a complete synapsis between the X- and the Y-axis, which lasts up to the end of pachytene. From the early pachytene substages to the late ones, the X-axis develops prominent branches, which in late pachytene span the synaptic region. Synapsis is regular as shown by SYCP1 labeling. Axial development is followed by SYCP3 labeling and in the asynaptic region of the X-axis by BRCA1. Gamma-H2AX labels exclusively the differential (asynaptic) region of the X chromosome. A single focus is labeled by MLH1 in the synaptic region. The location of this MLH1 focus spans from 0.3 to 1.6 μm from the telomere in the analyzed xenarthrans, covering approximately half of the Y-axis length. It is concluded that xenarthrans, as basal placental mammals, harbor the largest pseudoautosomal regions of presently analyzed mammals, and shows the typical features of meiotic sex chromosome inactivation (MSCI).

The morphological and histological features of the unusual reproductive tract of the female lesser anteater, Tamandua tetradactyla (Myrmecophagidae, Xenarthra), are described for the first time. The present study aimed to establish the main similarities and differences between this species and other xenarthrans. The populations of this species are declining rapidly for a number of reasons and our study is relevant to diverse programs related to its conservation. Studies were carried out on five female genital tracts of adult specimens. Ovaries were ovoid, presenting a medulla completely surrounded by the cortex, differently from that described in other xenarthans. Like in Dasypus but different from all other armadillos studied, single oocyte follicles were observed and a simple the uterus. The uterovaginal canal connects the uterus with the urogenital sinus. The simple columnar epithelium of the uterovaginal canal ends abruptly at a septum which resembles a hymen, where the transitional epithelium of the urogenital sinus appears. This ancestral feature is shared with that of other armadillos, except Tolypeutes matacus, which has a true vagina. Characteristics of the reproductive tract and sperm morphology of other Xenarthra are comparatively discussed. These observations suggest that important reproductive features are shared between the family Myrmecophagidae and the genus Dasypus, a basal group in the phylogeny of Xenarthra.

The response to infection with Junin virus, wild strain Cba An 9446, and the antenatal and postnatal transmission of the pathogen in its natural host, Calomys musculinus, were studied. Intranasal infection in adult animals (90–120 days) did not produce mortality or illness during the 150-day period of observation. From day 21 to 150 after infection, 50% of the animals showed viral persistence with shedding of virus in both urine and saliva. The remaining half became seropositive, and no infectious virus was recovered from them. Although the virus did not infect fetuses during gestation, 50% of weaned pups nursed by viremic mothers were infected. Neither persistence nor immunologic response altered the reproductive pattern of the animals. The absence of reproductive failure in the infected host and the efficiency of postnatal transfer of Junin virus indicate that vertical transmission could contribute to the viral maintenance over time.

The aim of this work was to assess the effect of metronidazole (MTZ) on the stages of the seminiferous epithelial cycle and spermatozoa morphology when the drug is administered in human therapeutic doses to 60-day-old CFW male mice. The frequency of the stages was established by counting spermatocytes in pachytene and spermatids. Abnormalities in the flagellum or the head, lack of maturity and multiple malformations, were considered in the morphological analysis. Murine control strain was compared with MTZ treated group (v.ip 130 mg/kg/bw) both kept in standard captivity conditions. Cellular composition or number of stages in the seminiferous tubules were not altered in MTZ exposed animals, though the number of cells in stages I, V and XII was increased. The sperm cell morphology was severely affected by the treatment with potentially serious consequences on the normal fertilization process. Thus, the MTZ has to be considered as a conceivable thread regarding male fertility.

The distribution of the vertebrate telomeric sequence (TTAGGG)(n) in four species of armadillos (Dasypodidae, Xenarthra), i.e. Chaetophractus villosus (2n = 60), Chaetophractus vellerosus (2n = 62), Dasypus hybridus (2n = 64) and Zaedyus pichiy (2n = 62) was examined by FISH with a peptide nucleic acid (PNA) probe. Besides the expected telomeric hybridization, interstitial (centromeric) locations of the (TTAGGG)n sequence were observed in one chromosome pair of Chaetophractus vellerosus and Zaedyus pichiy, suggesting chromosome fusion of ancestral chromosomes occurring during the evolution of Dasypodidae. In addition, all the species analysed showed one to four apparently telocentric chromosomes, exhibiting only two telomeric signals. However, the immunodetection study of kinetochore proteins on synaptonemal complex spreads from C. villosus showed that the apparently telocentric chromosomes have a tiny short arm that can be resolved only in the more elongated pachytene bivalents. This finding suggests that none of the species of armadillos possess true telocentric chromosomes. Our present results support a reduction in the diploid number by fusion of acrocentrics with loss of chromosome material as a tendency in Dasypodidae.

Akodon molinae (with 2n = 42-43-44 and an FN = 44) shows a remarkable polymorphism of chromosome 1 in natural and laboratory populations. Specimens 2n = 42, named single homozygotes (SH), have a chromosome pair 1 formed by two large metacentric chromosomes. Specimens 2n = 3, heterozygotes (Ht), have one chromosome 1 and two medium-sized subtelocentric chromosomes, 1a and 1b, which are homologous with the long and short arms of chromosome 1 respectively. Specimens 2n = 44 are double homozygotes (DH), with just two pairs of medium-sized subtelocentric chromosomes, 1a and 1b. Analysis of meiotic metaphases I and II showed that anomalous segregation occurs more frequently in spermatocytes carrying the 1a and 1b chromosomes. This would disturb gametogenesis and other reproductive and developmental processes, producing a marked decrease in viability of DH individuals. There is, as yet, no satisfactory explanation for these phenomena. To investigate structural elements which might explain such segregational anomalies, we have studied bivalent and trivalent synapsis in pachytene spermatocytes from SH, Ht and DH specimens. Of a total of 80 spermatocyte nuclei microspreads, the following results were obtained: of 16 microspreads from two SH individuals, 20 autosomic bivalents plus the XY bivalent were observed; of 48 microspreads from three Ht individuals, 19 autosomic bivalents, 1 trivalent and an XY bivalent were seen; and of the 16 microspreads from two DH individuals, 21 autosomic bivalents plus the XY bivalent were found. Trivalents analysed showed complete pairing between the short arms of 1a and 1b, and having an apparently normal synaptonemal complex (SC) with lengths of 1 and 2.8 µm. The trivalent SC showed three telomeric ends, corresponding to arms: q1 and q1a; p1 and q1b; and p1a and p1b, with attachment plates to the nuclear envelope of normal organisation. None of the trivalents showed asynapsis or desynapsis between p1a and p1b, nor an association with the XY bivalent. In 70 % of spermatocytes studied, the XY bivalent showed complete pairing between X and Y, with SC formation along the whole length of the Y chromosome. The remaining 30 % showed partial pairing, with an SC length which varied from the common end. Based on these findings and those of previous studies, we discuss: 1.- that the obliged configuration of the trivalent, with SC formation between the short arms of 1a and 1b, helps to assure a quasi normal segregation between 1, 1a and 1b in anaphase I of Ht meiosis; and 2.- that co-existence in trivalents of chromosomes 1, 1a and 1b in Ht individuals, breaks down the structural and functional integrity of the short arms of 1a and 1b, producing an accumulative damage which would also explain the decreased viability of individuals bearing these chromosomes Akodon molinae con 2n = 42-43-44 y FN = 44 presenta un notable polimorfismo en el cromosoma 1 en poblaciones naturales y de laboratorio, los individuos 2n = 42 tienen un par 1 formado por dos cromosomas metacéntricos grandes y son denominados homocigotos simples (SH); los individuos 2n = 43, heterocigotos (Ht), presentan un cromosoma 1 y dos cromosomas subtelocéntricos de tamaño medio 1a and 1b, que son homólogos con los brazos largo y corto del 1, respectivamente; y los individuos 2n = 44 que son los doble homocigotos (DH) y presentan dos pares de cromosomas subtelocéntricos 1a y 1b. Análisis de la metafases I y II meióticas han demostrado que se producen segregaciones anómalas con una alta frecuencia en los espermatocitos portadores de los cromosomas 1a and 1b. Ello alteraría a otros procesos, como la gametogénesis, la reproducción y el desarrollo, disminuyendo la viabilidad individual y poblacional de los DH. No ha habido una explicación satisfactoria para estos fenómenos. Para investigar elementos estructurales que pudiesen explicar tales alteraciones segregacionales, se estudió la sinapsis de bivalentes y trivalentes en espermatocitos en paquiteno de ejemplares SH, Ht y DH. De un total de 80 microesparcidos de núcleos de espermatocitos: en 16 núcleos de ejemplares SH se observaron 20 bivalentes autosómicos más el bivalente XY; en 48 núcleos de Ht se observaron 19 bivalentes autosómicos, 1 trivalente y un bivalente XY; y en 16 núcleos de DH se observaron 21 bivalentes autosómicos más el bivalente XY. Los trivalentes analizados mostraron apareamiento completo entre los brazos cortos de 1a y 1b conformándose un complejo sinaptonémico (CS) aparentemente normal con una longitud entre 1 µm y 2,8 µm. El CS de los trivalentes presentó tres extremos teloméricos correspondientes a los brazos: q1 y q1a, p1 y q1b y p1a y p1b, con placas de inserción a la envoltura nuclear de organización normal. En ninguno de los trivalentes se observó asinapsis o desinapsis entre p1a y p1b, ni asociaciones con el bivalente XY. En el 70 % de los espermatocitos estudiados el bivalente XY mostró apareamiento completo entre X e Y, con formación de CS en toda la longitud del cromosoma Y. El 30 % restante presentó apareamiento parcial con un CS de longitud variable a partir del extremo común. Sobre la base de los resultados de este trabajo y los antecedentes existentes, se discute: 1.- que la configuración obligada del trivalente con formación de CS entre los brazos cortos de 1a y 1b, contribuye a asegurar la segregación cuasi normal entre 1, 1a y 1b en la I anafase de la meiosis de los Ht; y 2.- que la coexistencia en los trivalentes de los cromosomas 1, 1a y 1b en los Ht, erosiona la integridad estructural y funcional de los brazos cortos de 1a y 1b, daño que sería acumulativo y que explicaría la viabilidad disminuída de los individuos portadores de estos cromosomas

Most primates studied have the usual XX/XY sex-chromosome system. However, exceptions to this rule among howler monkeys have been suggested by several authors. Recently a quadrivalent was discovered in male meiosis of Alouatta caraya and it was established that this species has an X1X2Y1Y2 sex chromosome system. On that basis, a cytogenetic analysis of 25 males of this species is described. showing the corrected karyotype of this species. Each chromosome involved in the particular sex-chromosome system of this species is identified on the basis of mitotic chromosome measurements. G and C-banding patterns as well as on the relative measurements of synaptonemal complexes. It is now established that A. caraya has a karyotype with 2n = 52 in both sexes, and that the male one shows a single autosome 7 (X2) besides the X (X1) and the two products of the reciprocal translocation between the second autosome #7 and the Y chromosome (Y1 and Y2), while females show a homomorphic pair #7 (X2) and a pair of X1. The evolutionary implications of the exceptional primate species having composite sex-chromosome systems are discussed. Fil:Mudry, M.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Gorostiaga, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Very little is known about the distinct reproductive biology of armadillos. Very few studies have investigated armadillo spermatogenesis, with data available only for Euphractus sexcinctus and Dasypus novemcinctus. In the present study, we analysed male germ cell differentiation in the large hairy armadillo Chaetophractus villosus throughout the year, describing a cycle of the seminiferous epithelium made of eight different stages. Evaluation of the testis/body mass ratio, analysis of the architecture of the seminiferous epithelium and the frequency of defective seminiferous tubules allowed identification of a temporal interruption of spermatogenesis during the period between mid-May to July (mid–end autumn) in correlation with very low testosterone levels. Overall, these results suggest that spermatogenesis is seasonal in C. villosus.

A multiple sex chromosome system was found in three unrelated individuals of the primate Alouatta caraya. This mechanism is originated by a translocation between the Y chromosome and one of the autosomes (A7). Mitotic karyotypes show two small, acrocentric chromosomes (AY and YA), which are the translocation products. In metaphase I of male meiosis, there is a very long chain quadrivalent in which the order of the element is: X-YA-A7-AY. Segregation in the quadrivalent is alternate and gives balanced products. Synaptonemal complex karyotypes at pachytene show the structure of the quadrivalent made by the four axes. There is a slight difference in the relative length of AY and YA and the kinetochore of A7 aligns with that of AY. The synaptic pattern and changes in the quadrivalent during pachytene are described. Thin sections of the quadrivalent body show that the chromatin packing in the sex chromosome region is different from that of the autosomal region. This X1X2Y1Y2/X1X1XX2 sex chromosome system may be extended among other members of the genus Alouatta.

Sperm morphology was studied in 10 species of the caviomorph rodent Ctenomys. Ctenomys argentinus, C. conoueri, C. dorbigny and C.perrensis had symmetric spermatozoa with paddle-like heads. Ctenomys australis, C. mendocinus, C. porteousi, C. rionegrensis and Ctenomys sp., on the other hand, had spermatozoa with paddle-like heads but with the tail inserted at one side of the central axis and a nuclear caudal extension originating from the base of the head at the opposite side of the insertion of the tail and running parallel to the flagellum; these spermatozoa are referred to as simple-asymmetric. In C. yolandae, a complex-asymmetric morphological type not previously described for the genus was found. This type is characterized by the presence of two nuclear caudal extensions. Symmetric spermatozoa (total length = 52 pm) were shorter than asymmetric (both simple and complex) ones (total length = 87 pm). In spite of these differences, the relative size of heads, midpieces and tails were maintained in the three groups, representing 12%, I I YO and 88% of the average total length, respectively. Within each group of species bearing the same sperm type, a low interspecific variability both in morphological patterns and dimensions of sperm cells was observed. This low interspecific variability associated with the north to south geographical distribution of species having, respectively, symmetric and asymmetric spermatozoa, suggests that these characters appeared at an early stage in evolution of the group, and probably played an important role in the first steps of speciation by promoting reproductive isolation.

The husbandry and breeding of Calomys laucha (Rodentia, Cricetidae) in captivity are described. Growth curves based on body weight and length showed statistical differences between sexes after 45 days, males being heavier than females. The overall reproductive efficiency was 53·4% but birth rate was depressed during winter. Gestation length was 21±1 days and females exhibited postpartum oestrus with a 3-7 day implantation delay (51%). Litter size was 5·3×1·1 ( n=34). Pup survival at weaning was 84·9%. Mean life span in laboratory conditions was 13·5 months and a cumulative mortality of 90% was reached at 27-28 months of age.

The effect of infection with Junin virus on growth and reproduction of its natural reservoir, Calomys musculinus, was studied. Eighty-five C. musculinus were inoculated intranasally at birth with 100 TCID50 of Cba An 9446 strain of Junin virus and observed for 480 days. No clinical signs of neurologic illness were registered. Infected animals showed an increased mortality rate of up to 70% between days 24–40 post-infection. This period of high mortality was preceded by low weight gain during lactation and registered until 60 days. From day 14 post-infection until day 480, Junin virus was recovered from blood, urine, and oral swab in all animals checked at any time. By day 480 post-infection, 100% of survivors showed widespread viral dissemination in brain, spleen, kidneys, and salivary glands. There was marked reduction in reproductive efficiency among infected animals. Out of 15 mating pairs, 2 (13.3%) littered at least once compared to 60% in the control group. The reduction of fertility and the altered survival rate of Junin virus-infected C. musculinus indicate that vertical transmission mechanisms per se are insufficient to maintain the infection in successive generations in the absence of horizontal transmission.

Argentine hemorrhagic fever (Junin virus) is a human viral disease for which immune therapy proves effective, though a late neurologic syndrome is occasionally associated with the treatment. We attempted to determine in the infected marmoset Cullithrix jacchus whether immune therapy leads to protection and/or CNS damage. Fifteen C jacchus were inoculated with 103 tissue culture infectious dose 50% (TCID50) of the XJ strain of Junin virus. On day 6 post infection (pi), 12 primates were treated with homologous immune serum. Animals were observed daily; and hematologic, serologic, virologic, and histologic studies were performed. All primates, both treated and controls, presented leukopenia, thrombocytopenia, anemia, and weight loss from day 14 pi onward. The three control animals died on days 22, 25, and 32 pi. Among the 12 treated monkeys, 3 died on days 21, 22, and 29. Hematologic values returned to normal during the second month; initial weight was recovered by the fourth month. Three out of the nine survivors showed neurologic alterations of various degrees, with hind-limb paralysis in the most severe case. Among treated monkeys, viremia and viral titers in the lungs, kidney, and lymph nodes were lower than in controls. Neutralizing antibodies were present in high titers in all treated marmosets, except in the one presenting paralysis in which values were minimal and viral persistence was detected in CNS. In conclusion, immune serum treatment of Junin virus-infected marmosets was found to reduce mortality from 100% to 25%. Viremia and viral titers in organs were lowered, and late neurologic signs appeared in 30% of treated survivors.

The meiotic behavior of sex chromosomes has been investigated in variant females of Akodon azarae, both in pachytene oocytes and metaphase I. In somatic cells, these females have a heteromorphic sex pair, in which the minor chromosome has been previously interpreted as a major deletion of the long arm of the X chromosome (dX). After microspreading for synaptonemal complex analysis, pachytene oocytes show two axes of very different lengths (100:17.1), which correspond to the sex chromosomes X and dX. True synapsis is abnormally restricted (43.3%) between these sex chromosomes; on the other hand, self-synapsis of both the X and dX chromosomes is frequent (60%). Single, nonsynapsed axes or axial segments are thickened. Strong chromatin condensation occurs around nonsynapsed axes or axial segments, giving many of these sex pairs an appearance similar to an XY body (“sex vesicle”). The minor gonosome axis differs from that of the Y chromosome of male meiosis, as the former is shorter (relative to the X) and has a different synaptic behavior. In 17 metaphases I from XdX variant females, only heteromorphic, end-to-end joined sex pairs were observed. These variant females differ from the variant females of the wood lemming Myopus schisticolor in several respects, but a similar mechanism seems to be prevalent in other species of the genus Akodon. Self-synapsis of unequal gonosomes in oocytes is assumed as an escape from functional deterioration, following the hypothesis put forward by others.

Cytogenetic analysis was performed in Akodon (Akodon) puer (= Akodon coenosus ) , Akodon azarae bibianae, Akodon ( Hypsimys ) budini, Bolomys temchuki elioi, Bolomys temchuki liciae, Oxymycterus rufus rufus, Oxymycterus ruf us platensis , and Oxymycterus paramensis . Diploid numbers, chromosomal morphology, and lengths and banding patterns (G and C) were determined for each taxon. Chromosomal number and gross morphology are also described in topotypical specimens of Akodon ( Akodon ) arenicola (= Akodon ( Akodon ) azarae azarae ) and Oxymycterus nasutus . A 2n = 34 karyotype, similar to one previously reported as Akodon coenosus , was confirmed in Akodon puer. A. budini showed a 2n = 38 karyotype peculiar within the genus as regards chromosomal morphology and C bands. A. a. bibianae has a 2n = 38 karyotype closely related with that of A. a. azarae . The two subspecies of B. temchuki , which differ strikingly in fur color, showed an identical 2n = 34 karyotype, which was quite similar in diploid number, chromosomal morphology, and banding patterns to that reported for B. lasiurus , but was different in the morphology of the Y and in G and C bands when compared with B. obscurus from the south of Buenos Aires Province. The three species of Oxymycterus , which markedly differ in morphometric character states, showed an identical 2n = 54 karyotype, and no banding differences were observed between O. rufus and O. paramensis .

Akodon azarae (Rodentia Cricetidae) has a sex chromosome polymorphism which gives rise to XX females and females with a partial or total deletion of one X chromosome. Two hypotheses have been proposed to explain the findings in A. azarae. In the first it is assumed that XX, Xx and XO females are fertile and able to produce X, x and 0 ova to give XX, Xx and XO females after fertilization by a X-bearing sperm. The second hypothesis proposes and extreme mechanism of sex dosage compensation ranging from X-chromosome inactivation, to partial or total X chromosome elimination. These hypotheses are tested by analysing the chromosome complement in the offspring derived from mating pairs of A. azarae of known chromosome constitution.The offspring obtained from XX x XY mating pairs showed: a) a sex ratio of 0.67 females per male, b) an average litter size of 3.8 pups, c) the lack of Xx or XO females. The offspring derived from Xx females had: a) a sex ratio of 1.73 females per male, b) a ratio of 0.64 XX females per each Xx female, c) an average litter size of 4.8 pups. The results obtained do not fit the predictions of the fertilization or the sex dosage compensation hypothesis. However, they can be explained by combining the fertilization hypothesis with a rate of lethality of XX zygotes. The possible cause of the XX zygote lethality and the eventual relationship between sex chromosomal polymorphism and density cycles in natural populations of A. azarae are discussed. Moreover, it is presented evidence stressing the instability of deleted X chromosomes.

Cross fertilization was tested between oocytes of Calomys callidus and spermatozoa from C. callidus, C. musculinus and C. laucha by both in vivo and in vitro insemination. After in vivo and in vitro insemination, respectively, percentages of oocytes fertilized were 68.8 and 46.6 (C. callidus X C. callidus), 20.3 and 12.7 (C. callidus X C. musculinus), 26.7 and 4.3 (C. callidus X C. laucha). Thus, the percentages obtained after in vitro insemination were always lower than those obtained with in vivo insemination. It was found that 23.9% and 44.4% of two-cell hybrid embryos were present in oviducts 30 hr after in vivo insemination of C. callidus females with C. musculinus or C. laucha spermatozoa, respectively. At a later stage (56 hr postinsemination), development did not progress further, and abnormal embryos were found both at 30 and 56 hr postinsemination, suggesting some kind of cleavage arrest or degeneration of the embryos. We suggest that fertilization is not strictly species-specific, at least among the species we studied, but that there are some factors that reduce the efficiency of interspecific fertilization.

In order to assess the effect of the antiviral Ribavirin on the course of Junín virus infection in Callithrix jacchus, seven inoculated monkeys were treated with 15 mg of the drug, twice a day, starting 6 days after infection when all animals were viremic. The three untreated controls showed typical signs of Junín virus infection at 14 days pi and their mean time of death was 18 days. In contrast, no signs of illness were detected in Ribavirin-treated animals until 24 days pi, when marmosets showed signs of neurological involvement: 5 of these animals died (mean day of death: 36) but the two remaining treated monkeys improved and survived infection without sequelae. The comparison of survival rates (0% vs 28%) and the delay of the mean day of death observed indicates that the Ribavirin treatment used has therapeutic effect on Junín virus infection in vivo.

Akodon molinae, a vole mouse widely distributed in central Argentina, shows remarkable chromosome polymorphisms. It is one of the natural reservoirs of the actiologic agent of haemorrhagic fever, and a laboratory colony could be of great help in investigating this disease. Pregnancy lasted 23 (range 21-25) days. Litters of 4-5 young were born to monogamous breeding pairs about every 30 days, with weaning at 26 days post partum. The sex ratio at birth was 505 males to 500 females: at weaning it was 460 to 440. Sexual maturity was attained at about 16 weeks of age in males and 12-20 weeks in females. Akodon molinae is easy to handle, but fighting and killing or neglect of young are problems.

The quantitative contribution of vertical transmission to the prevalence rate of Junin virus infection in subsequent generations of its natural reservoir, Calomys musculinus, was analysed. Data on mortality and reproduction of C. musculinus infected at birth with a wild strain of Junin virus were used to estimate the infection-dependent relative survival rate (beta = 0.4849) and relative fertility of the infected host (alpha = 0.2088). Prevalence rates of infection, obtained by mathematical simulation in optimal conditions of vertical transfer, dropped steadily to zero in a few generations. Vertical transmission was found to be insufficient to overcome the effect of highly depressed survival and fertility of the infected host and maintain a stabilized prevalence of Junin virus infection in successive generations; this suggested that viral maintenance is mainly dependent upon horizontal transmission.

Growth and reproduction of Akodon molinae (A.m.), A. dolores (A.d.) (Rodentia: Cricetidae), and their hybrids are described. A.d. showed less fertility under animal room conditions, fewer "successful" matings, similar litter sizes, and an altered sex proportion as compared to A.m.; A.d. ovulatory index is supposed to be higher than mean litter size. X-linked lethal gene(s) and chromosome polymorphisms are possible causes of these variations. Interspecific crosses showed a marked seasonal (summer) tendency in parturitions. Intraspecific matings also produced young during winter. F1 hybrids showed a reversed tendency, while F2 matings returned to the parental pattern. A.d. male X A.m. female and F1 crosses presented larger litter sizes than the other pairings. A.m. exhibited sexual differences in weight after 60 days of age. A.d. and F1 hybrids did not show significant differences in weight of both sexes at any age. A.m. males and females were heavier than A.d. individuals except 12 months after birth. F1 hybrids born to A.m. male were heavier at birth than the A.d. female s interspecific offspring, and may be interpreted as a maternal influence of the A.m. females. Hybrids were heavier than their parents at birth and some of them were also heavier at 21 days, and probably is due to pseudoheterosis. The comparison of body measurements between sexes of both species did not give conclusive results. A.m. females were larger than females of A.d. Males of both species showed similar total lengths; A.m. males had larger body lengths and shorter tails. Body measurements were not related to weight variations. However, differences in weight and measurements between sexes appeared simultaneously at 2-6 months. This probably reflected the attainment of maturity.