Classics revisited: Miguel Fernández on germ layer inversion and specific polyembryony in armadillos.

BACKGROUND: Miguel Fernández was an Argentinian zoologist who published the first account of obligate polyembryony in armadillos. His contribution is here discussed in relation to his contemporaries, Newman and Patterson, and more recent work. FINDINGS: Fernandez worked on the mulita (Dasypus hybridus). He was able to get early stages before twinning occurred and show it was preceded by inversion of the germ layers. By the primitive streak stage there were separate embryonic shields and partition of the amnion. There was, however, a single exocoelom and all embryos were enclosed in a common set of membranes comprising chorion towards the attachment site in the uterine fundus and inverted yolk sac on the opposite face. He showed that monozygotic twinning did not occur in another armadillo, the peludo (Chaetophractus villosus). CONCLUSIONS: Fernández's work represented a major breakthrough in understanding how twinning occurred in armadillos. His work and that of others is of intrinsic interest to zoologists and has a direct bearing on the origin of monozygotic twins and birth defects in humans.

Morphological study of the cervical salivary glands in the nine-banded armadillo / Estudio morfológico de las glándulas salivales cervicales en el armadillo de nueve-bandas

The cervical salivary glands of the armadillo Dasypus novemcinctus was examined by light microscopy. These glands are situated on either side of the neck, divide in lobes and show a presence of a salivary bladder, associated with the main ducts of the gland. This gland is histologically a typical mixed glands, containing both mucous and serous elements, with mucous acini as the predominant secretory unit. The bladder itself is composed of a wall made up of pseudostratified epithelium, skeletal muscle and connective tissue. In general, the morphology of the cervical salivary glands appears similar to that described in other species of the mammals.

Las glándulas salivales cervicales del armadillo Dasypus novemcinctus fueron examinadas por microscopía de luz. Estas glándulas se encuentran a ambos lados del cuello, divididas en lóbulos y muestran la presencia de una vejiga salival, asociada con los principales conductos de la glándula. Esta glándula es histológicamente una típica glándula mixta, que contiene tanto elementos mucosos y serosos, con acinos mucosos como la principal unidad secretora. La vejiga en sí se compone de una pared formada por epitelio pseudoestratificado, músculo esquelético y tejido conectivo. En general, la morfología de las glándulas salivales cervicales parece similar a la descrita en otras especies de mamíferos.

Morphology and histological annual changes of the oviduct of chaetophractus villosus (Mammalia, Xenarthra, Dasypodidae) / Morfología y cambios histológicos anuales del oviducto de Chaetophractus villosus (Mammalia, Xenarthra, Dasypodidae)

The morphological features of the oviduct in the armadillo Chaetophractus villosus (Desmarest, 1804) were studied. In the simple columnar epithelium, ciliated cells, secretory cells, and cells of the bottom of the folds are described. The most remarkable findings are the increase in number of ciliated cells, when present, from the fimbriae to the uterus, being the isthmus practically lined by ciliated cells, and that secretory cells are more abundant in the apical zone of the ampulla and fimbriae, than in the isthmus. Morphological changes along the year in the different portions are described.

Se estudiaron las características morfológicas del oviducto del armadillo Chaetophractus villosus (Desmarest, 1804). En el epitelio, columnar simple, se describen células ciliadas, secretoras y células del fondo de los pliegues. Las células ciliadas, cuando están presentes, aumentan en número desde las fimbrias hacia el útero, estando el istmo prácticamente tapizado por células ciliadas, las células secretoras son más abundantes en la zona apical de la ampolla y en las fimbrias, que en el istmo. Se describen los cambios morfológicos en las diferentes porciones a lo largo del año.

Especies locales, mercado y transporte en las investigaciones embriológicas: el estudio de la poliembrionía en armadillos a principios del siglo XX / Local species, the market, and transportation in embryological research: the study of polyembryony in armadillos in the early twentieth century

Se examina en un caso concreto la afirmación general de la importancia de las redes de comunicación y la movilidad de las cosas para la ciencia. De qué forma esto jugó un papel relevante en las investigaciones sobre la embriología de ciertas especies de armadillos a principios del siglo XX? Como intentamos mostrar, el acceso a las hembras preñadas de esas especies silvestres y los tiempos en el transporte hasta el laboratorio fueron cuestiones substanciales en los inicios de esas investigaciones. Las estrategias para obtener muestras en el campo y la temporalidad de ciertos fenómenos, los circuitos comerciales en los que participan los organismos estudiados y su trasformación en el laboratorio permiten vislumbrar aspectos de cómo trabajaron y qué problemas enfrentaron esos científicos.

The article examines the general affirmation that communication networks and mobility are important to science by examining how these factors played a relevant role in one specific case, that is, research on the embryology of certain species of armadillos in the early twentieth century. As we show, access to pregnant females of the species and transport time from the wild to the laboratory were significant issues in the early days of such research. The strategies used to obtain field samples, the temporality of certain phenomena, the commercial circuits of which the organisms under study were a part, and the transformations they underwent in the laboratory all afford a glimpse at some aspects of how these scientists approached their work and what problems they faced in producing new knowledge.

[Local species, the market, and transportation in embryological research: the study of polyembryony in armadillos in the early twentieth century]. / Especies locales, mercado y transporte en las investigaciones embriológicas: el estudio de la poliembrionía en armadillos a principios del siglo XX.

The article examines the general affirmation that communication networks and mobility are important to science by examining how these factors played a relevant role in one specific case, that is, research on the embryology of certain species of armadillos in the early twentieth century. As we show, access to pregnant females of the species and transport time from the wild to the laboratory were significant issues in the early days of such research. The strategies used to obtain field samples, the temporality of certain phenomena, the commercial circuits of which the organisms under study were a part, and the transformations they underwent in the laboratory all afford a glimpse at some aspects of how these scientists approached their work and what problems they faced in producing new knowledge.

On the possible cause of monozygotic twinning: lessons from the 9-banded armadillo and from assisted reproduction.

Available hypotheses proposed to explain the mechanism of zygotic splitting fail to explain why monozygotic twins are more prevalent after all methods of assisted reproduction and which structure is likely to control this phenomenon. Arguably, a small proportion of oocytes might have an inborn propensity to undergo splitting upon fertilization leading to the constant prevalence of spontaneous monozygotic conceptions among different populations. Ovarian stimulation would then predictably increase the number of available splitting-prone oocytes and consequently would increase the chance for such oocytes to develop into monozygotic twins, leading to a 'dose'-dependent relationship between monozygosity rates and the combined effect of infertility treatment. Embryonic division into 2 distinct cell lines begins and accommodates within an intact zona pellucida that controls the process by preventing ill-timed hatching. Human fertilized oocytes are able to undergo 2 binary fissions, just as is the case for the 9-banded armadillo (the only other mammal that produces monozygotic quadruplets) and to give rise to a variety of combinations of monozygotic pregnancies. This hypothetical explanation does not negate the already existing and genetically sound hypotheses, but places them into a broader perspective that respects recent observations from modern infertility treatment.

Osteoderm morphology and development in the nine-banded armadillo, Dasypus novemcinctus (Mammalia, Xenarthra, Cingulata).

Among modern mammals, armadillos (Xenarthra, Cingulata) are the only group that possesses osteoderms, bony inclusions within the integument. Along the body, osteoderms are organized into five discrete assemblages: the head, pectoral, banded, pelvic, and tail shields. The pectoral, banded, and pelvic shields articulate to form the carapace. We examined osteoderm skeletogenesis in the armadillo Dasypus novemcinctus using serial and whole-mount histochemistry. Compared with the rest of the skeleton, osteoderms have a delayed onset of development. Skeletogenesis begins as condensations of osteoblasts secreting osteoid, localized within the papillary layer of the dermis. Osteoderm formation is asynchronous both within each shield and across the body. The first osteoderms to mineralize are situated within the pectoral shield of the carapace, followed by elements within the banded, head, pelvic, and tail shields. In general, within each shield ossification begins craniomedially and proceeds caudally and laterally, except over the head, where the earliest elements form over the frontal and parietal bones. The absence of cartilage precursors indicates that osteoderms are dermal elements, possibly related to the all-encompassing vertebrate dermal skeleton (exoskeleton). The mode of development of D. novemcinctus osteoderms is unlike that described for squamate osteoderms, which arise via bone metaplasia, and instead is comparable with intramembranously derived elements of the skull.

Comparative morphologic placental types in Dasypodidae (Chaetophractus villosus, Cabassous chacoensis, Tolypeutes matacus and Dasypus hybridus).

Information about the morphology of placentas in armadillos is scarce, except for D. novemcinctus. A comparative study of morphologic placental types in armadillos is important in order to have a comprehensive view of the peculiar reproductive physiology in this family. The aim of this paper is to perform a comparative analysis of the morphological features of the placenta in Chaetophractus villosus, Cabassous chacoensis, Tolypeutes matacus and Dasypus hybridus in order to classify them in accordance with Grosser (1909). The placentas were studied macroscopically and histologically (light microscopy in 1 micron thick sections and electron microscopy for fine structure). The macroscopic study in the 4 studied species showed a similar pear-shaped placenta homogeneously villosus in almost all the surface. The histological analysis showed that the 4 studied species had a hemochorial type of placenta. This type of placenta was also found in D. novemcinctus (Dasypodidae), but it is different from those described for other xenarthrans. Hemochorial types of placenta have also been described in more modern mammals. Despite the many primitive features of the armadillos and the different anatomical and physiological features between the genuses of dasypodids, all the studied species share this structural type of placenta.

Comparative morphologic placental types in Dasypodidae (Chaetophractus villosus, Cabassous chacoensis, Tolypeutes matacus and Dasypus hybridus)

Information about the morphology of placentas in armadillos is scarce, except for D. novemcinctus. A comparative study of morphologic placental types in armadillos is important in order to have a comprehensive view of the peculiar reproductive physiology in this family. The aim of this paper is to perform a comparative analysis of the morphological features of the placenta in Chaetophractus villosus, Cabassous chacoensis, Tolypeutes matacus and Dasypus hybridus in order to classify them in accordance with Grosser (1909). The placentas were studied macroscopically and histologically (light microscopy in 1 micron thick sections and electron microscopy for fine structure). The macroscopic study in the 4 studied species showed a similar pear-shaped placenta homogeneously villosus in almost all the surface. The histological analysis showed that the 4 studied species had a hemochorial type of placenta. This type of placenta was also found in D. novemcinctus (Dasypodidae), but it is different from those described for other xenarthrans. Hemochorial types of placenta have also been described in more modern mammals. Despite the many primitive features of the armadillos and the different anatomical and physiological features between the genuses of dasypodids, all the studied species share this structural type of placenta.(AU)

Molecular documentation of polyembryony and the micro-spatial dispersion of clonal sibships in the nine-banded armadillo, Dasypus novemcinctus.

A battery of allelic markers at highly polymorphic microsatellite loci was developed and employed to confirm genetically, the clonal nature of sibships in nine-banded armadillos. This phenomenon of consistent polyembryony, otherwise nearly unknown among the vertebrates, was capitalized upon to describe the micro-spatial distributions of numerous clonal sibships in a natural population of armadillos. Adult clone mates were significantly more dispersed than were juvenile sibs, suggesting limited opportunities for altruistic behavioural interactions among mature individuals. These results, and considerations of armadillo natural history, suggest that evolutionary explanations for polyembryony in this species may not reside in the kinds of ecological and kin selection theories relevant to some of the polyembryonic invertebrates. Rather, polyembryony in armadillos may be associated evolutionarily with other reproductive peculiarities of the species, including delayed uterine implantation of a single egg.

Structural interactions of trophoblast and uterus during hemochorial placenta formation.

It is argued that the successful placental arrangements are those that decrease the exposure of the trophoblast to the efferent side of the cellular immune response. Examples are taken from three different groups with hemochorial placentation, to show that their placental morphology places most of the trophoblast in contact with maternal blood, not maternal connective tissue. In addition, maternal cells of the junctional area are modified either before contact with trophoblast (rat) or just after trophoblast invasion (primate), or the region of contact is limited as in the armadillo, in which maternal blood sinuses are expanded to form intervillous spaces.