Trunk movements during locomotion in the marsupial Monodelphis domestica (didelphidae)

The small didelphid cmarsupial, Monodelphis domestica, uses a lateral sequence walk during slow treadmill locomotion and gradually shifts to a trot as speed increases. At higher speeds it changes abruptly to a half-bound. Cinematographic records suggest significant lateral bending but no sagittal bending of the trunk during the slow walk and a reduced amount of lateral bending during the fast walk. There is slight lteral, but no sagittal, bending during the trot. Sagittal bending is obvious during the half-bound, but no lateral bending is evident. Cineradiography confirms that the vertebral column of the trunk bends laterally during the slow walk. Bending occurs throughout the trunk region, but seems to be most pronounced in the anterior lumbar region. Associated with this bending of the trunk is substantial rotation of the pelvic girdle in the plane of yaw. Pelvic rotation is synchronized with the locomotor cycle of hindlimbs. Each side of the pelvis rotates forward during the recovery phase of the ipsilateral hindlimb and backward during the contact phase of this limb. Information on locomotor trunk movements in other limbed tetrapods is limited. The pattern of trunk bending found in Monodelphis, however, is consistent with that reported in the placental mammal Felis catus and in some lepidosaurian reptiles. This suggests that sagittal bending did not replace lateral bending during the evolution of mammals, as is sometimes suggested. Rather, bending in the vertical plane seems to have been added to lateral bleeding when the ancestors of extant mammals acquired galloping and bounding capabilities.     

Carpal ontogeny in Monodelphis domestica and Caluromys philander (Marsupialia)

Carpal bones have experienced numerous changes during marsupial evolution, even though their diversity and development remain poorly studied. The aim of this work was to document adult form and the pattern of mesenchymal tissue condensation and formation of chondrification and ossification centers in the hand of two marsupials. Two fundamental questions were asked: whether the loss of embryonic precursors was associated with the loss of adult elements, or whether there were developmental signs of ancestral mammalian elements that have been fused or lost in marsupial taxa. We were also interested to find out whether there is sexual dimorphismus in the carpals, as has been reported for some didelphids. Histological sections, cleared and stained specimens and macerated skeletons representing an ontogenetic series of Monodelphis domestica were used to document carpal development. Comparisons were made with perinatal stages of Caluromys philander and with adult specimens of other marsupials. A prenatal M. domestica in the 13th day after conception has a cell condensation that because of its position is homologized with a centrale, which is at birth already lost or fused. Neonatal M. domestica and C. philander have the number and arrangement of their adult carpal anatomy. Trapezium and trapezoid start ossification later than most other carpals, while pisiform and prepollex are the last to do so. Adult males of M. domestica have relatively larger and more robust pisiforms, compared to other carpals, than females. This sexual dimorphism develops relatively late as it was not recorded in male specimens around 160 days old. An extra sesamoid bone located just distal to the radius and proximo-palmar to the scaphoid was recorded in specimens of C. philander, C. derbianus and Didelphis virginiana.     

Plasma protease inhibitor (PI) system in the laboratory opossum,Monodelphis domestica

Protease inhibitor (PI) polymorphism was observed in the laboratory opossum,Monodelphis domestica, by either one-dimensional acid polyacrylamide gel electrophoresis (PAGE; pH 4.6) or isoelectric focusing (pH 3.5-5.0) followed by immunoblotting with rabbit antiserum to human α₁-antitrypsin; but acid PAGE produced superior resolution of the PI proteins. Family studies demonstrated an inheritance of nine codominant autosomal alleles,PI ^D ,PI ^E ,PI ^F ,PI ^G ,PI ^H ,PI ^I ,PI ^J ,PI ^K , andPI ^M , and a population study revealed frequencies of 0.411, 0.010, 0.341, 0.034, 0.023, 0.071, 0.035, 0.020, and 0.055, respectively.     

Food preferences of captive gray short-tailed opossums (Monodelphis domestica)

The gray short-tailed opossum has been a subject in behavioral and biomedical studies for the last quarter century, but researchers know little about its preferred diet. The authors describe a study designed to determine food preferences of this species for the purpose of identifying suitable rewards to be used in behavioral studies.     

Cranial osteogenesis in Monodelphis domestica (Didelphidae) and Macropus eugenii (Macropodidae)

The pattern of onset and general rate of cranial ossification are compared in two marsupials, Monodelphis domestica (Didelphidae) and Macropus eugenii (Macropodidae). In both species a similar suite of bones is present at birth, specifically those surrounding the oral cavity and the exoccipital, and in both postnatal events follow a similar course. The facial skeleton matures more rapidly than the neurocranium, which is characterized by an extended period of ossification. Most dermal bones begin ossification before most endochondral bones. Endochondral bones of the neurocranium are particularly extended in both the period of onset of ossification and the rate of ossification. These data confirm suggestions that morphology at birth is conservative in marsupials and we hypothesize that the pattern of cranial osteogenesis is related to two distinct demands. Bones that are accelerated in marsupials are correlated with a number of functional adaptations including head movements during migration, attachment to the teat, and suckling. However, the very slow osteogenesis of the neurocranium is probably correlated with the very extended period of neurogenesis. Marsupials appear to be derived relative to both monotreme and placental mammals in the precocious ossification of the bones surrounding the oral cavity, but share with monotremes an extended period of neurocranial osteogenesis. © 1993 Wiley-Liss, Inc.     

Reproduction, development and physiology of the gray short-tailed opossum (Monodelphis domestica)

The gray short-tailed opossum (Monodelphis domestica) has become a useful marsupial for biomedical research since it breeds reliably in the laboratory. During a 3 year period (1983-1986), a total of 129 litters were born in the colony at NJMS resulting in five generations of captive-born animals. Litter size ranged from 2 to 13 and the average sex ratio at weaning was 1:1. Mean body temperature of M. domestica was approximately 32.3 degrees C and respiratory rate approximately 54 breaths/minute. Systolic blood pressures of approximately 188 mmHg and heart rates of 345 beats/minute were found. Techniques of blood collection, anesthesia, implanting of hormones, ovariectomies and castrations, and treatment of neonates are described as well as current practices of colony management.     

The organization of somatosensory cortex in the short-tailed opossum ( Monodelphis domestica )

The organization of neocortex in the short-tailed opossum ( Monodelphis domestica ) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.     

The organization of somatosensory cortex in the short-tailed opossum (Monodelphis domestica)

The organization of neocortex in the short-tailed opossum (Monodelphis domestica) was explored with multiunit microelectrode recordings from middle layers of cortex. Microelectrode maps were subsequently related to the chemoarchitecture of flattened cortical preparations, sectioned parallel to the cortical surface and processed for either cytochrome oxidase (CO) or NADPH-diaphorase (NADPHd) histochemistry. The recordings revealed the presence of at least two systematic representations of the contralateral body surface located in a continuous strip of cortex running from the rhinal sulcus to the medial wall. The primary somatosensory area (S1) was located medially while secondary somatosensory cortex (S2) formed a laterally located mirror image of S1. Auditory cortex was located in lateral cortex at the caudal border of S2, and some electrode penetrations in this area responded to both auditory and somatosensory stimulation. Auditory cortex was outlined by a dark oval visible in flattened brain sections. A large primary visual cortex (V1) was located at the caudal pole of cortex, and also consistently corresponded to a large chemoarchitecturally visible oval. Cortex just rostral and lateral to V1 responded to visual stimulation, while bimodal auditory/visual responses were obtained in an area between V1 and somatosensory cortex. The results are compared with brain organization in other marsupials and with placentals and the evolution of cortical areas in mammals is discussed.     

Evidence for spontaneous postlactational estrus in gray short-tailed opossums (Monodelphis domestica)

Previous studies of the gray short-tailed opossum have shown that ovarian activity and estrus are induced by male pheromones, but we recently documented urogenital sinus (UGS) estrus in postlactational females despite their isolation from the male stimuli known to be associated with induced estrus. Body weights and UGS smears were collected after removal of pups in midlactation (19-37 days postpartum), after weaning (55-61 days postpartum), or after pheromone exposure. Estradiol was measured by RIA in plasma samples collected from dams during lactation, after separation from pups, and at estrus. Average days to UGS estrus from pup removal or initial pheromone exposure differed (P<0.05) only between the midlactation and pheromone exposure groups. Postlactational females showed a decrease in body weight from the time of pup removal or weaning to estrus, which contrasts with the increase seen in pheromonally stimulated females. Plasma estradiol was elevated at estrus in all groups, and females that were paired with males at postlactational estrus mated and produced litters. This study demonstrates that gray short-tailed opossums consistently experience estrus within 2 wk of weaning their young and that postlactational estrus appears to be hormonally and behaviorally equivalent to estrus induced by direct exposure to male pheromones.     

Milk composition in an American marsupial (Monodelphis domestica).

1. Twenty one sequential milk samples from an American marsupial (Monodelphis domestica) were analyzed. 2. The solids fraction was relatively low initially (10% w/w) and then increased to about 30% at mid-lactation where it remained until lactation ceased. 3. During the first 50 days of lactation the relative proportions of protein, fat and carbohydrate were 36, 28 and 34%, respectively, of the solids fraction. 4. Sodium and magnesium concentrations were constant; however levels of potassium and magnesium varied substantially. 5. The milk of M. domestica exhibits a similar pattern of quantitative and qualitative changes to that seen in Australian marsupials.     

Absence of a significant mixed lymphocyte reaction in a marsupial (Monodelphis domestica)

Previously we reported preliminary results suggesting that the marsupial Monodelphis domestica fails to exhibit a mixed lymphocyte reaction with allogeneic lymphocytes. To test whether this observation is simply a matter of a response too weak to detect, but capable of being augmented by immunization, we performed mixed lymphocyte culture tests on 23 of these animals that had been immunized with lymphocytes. Despite the fact that all recipients were sensitized to the lymphocytes of the donors, none of the animals had a substantial mixed lymphocyte response. Significant stimulation was noted with the mitogen concanavalin A; thus, the T cells were immunologically competent. It seems likely that the failure of this species to exhibit a significant mixed lymphocyte response is due to T cells whose ontogeny differs from that of the T cells of eutherian mammals.     

Water balance in Monodelphis domestica (Didelphidae) from the semiarid Caatinga of Brazil

1. Water conservation and energy metabolism in a semiarid-area, neotropical marsupial (Monodelphis domestica) were studied in the laboratory. 2. The rate of energy consumption in this species is low, corresponding with results reported for Australian and other neotropical marsupials. 3. Evaporative water loss rate is low and comparable to that of several desert small rodents, when body size differences are taken into account; however, the ratio of metabolic water production-to-evaporative water loss is lower than in the rodents. 4. Urine osmotic, urea, and chloride concentrations in water-stressed animals are within the range of values reported for some arid-area granivorous rodents, for insectivorous/carnivorous Australian marsupials, and for a North American insectivorous desert rodent. 5. Water-balance computations indicate that this species should be able to maintain water balance at 25 degrees C on a high-protein diet with a water content of about 60% without access to drinking water; this water requirement is comparable to that of ecologically similar marsupials and placentas in arid areas of other continents.     

Gonadal sex differentiation in the neonatal marsupial, Monodelphis domestica

A quantitative and histological study of the gonads of newborn grey short-tailed opossums, Monodelphis domestica, is described. The pups were karyotyped, and comparisons were made within litters segregating for XX and XY sex chromosomes. A total of four litters including 25 pups were available. On the day of birth, developing testes were significantly larger than the ovaries of litter mates, and testes could be histologically distinguished by the formation of sex cords and a tunica albuginea. The data suggest that in this marsupial species gonadal differentiation may be initiated in utero.     

Timetable of in vivo embryonic development in the grey short-tailed opossum (Monodelphis domestica)

The timing of development was examined in 496 embryos from female Monodelphis domestica, collected at known time intervals after video recorded mating. Ovulation occurred approximately 20 hr (day 1) after mating, and fertilization was observed by 24 hr. Transport through the oviducts was rapid, and pronuclear stage embryos were recovered from the uterus as early as 24 hr after mating. Second cleavage had occurred by 55 hr after mating. Three-celled embryos were among those collected on day 3 after mating, indicating that asynchronous cleavage of blastomeres can occur from the two-cell stage. The four-cell stage persisted for approximately 24 hr, and embryos that had undergone third cleavage were first recovered 74 hr after mating. Embryos that had undergone fourth to fifth cleavage were found 96–100 hr (4 days) after mating and complete unilaminar blastocysts by 5.5 days after mating. Primary endoderm formed from an already distinct embryonic area of the unilaminar blastocyst early on day 7 after mating. Formation of the bilaminar blastocyst was completed rapidly, on day 7 after mating. The primitive streak appeared on day 10 after mating, and organogenesis rapidly ensued on a timetable similar to that reported for Didelphis virginiana (McCrady, 1938). Close contact with the maternal circulation was established on day 11 and by day 12 maternal and embryonic tissues could not be separated without damage. The length of the gestation period from fertilization to birth was approximately 13.5 days. These observations provide the basis for further embryological cellular and molecular studies of this species as a laboratory model for marsupial development.© 1994 Wiley-Liss, Inc.     

Aldolase C polymorphism in the laboratory opossum, Monodelphis domestica

A two-allele polymorphism in aldolase C was identified in brain extracts of grey short-tailed opposums, Monodelphis domestica , by electrophoresis in starch or cellulose acetate gels. Pedigree data were consistent with autosomal codominant inheritance. The polymorphism was present in two of the six genetically distinct laboratory populations that have been established for this species.     

Biochemical genetics of alcohol dehydrogenase isozymes in the gray short-tailed opossum (Monodelphis domestica)

Polyacrylamide gel-isoelectric focusing (PAGE-IEF) methods were used to examine the multiplicity, tissue distribution, and biochemical genetics of alcohol dehydrogenase (ADH) isozymes among gray short-tailed opossums (Monodelphis domestica). Seven ADH isozymes were resolved and distinguished on the basis of their isoelectric points, tissue distributions, and substrate and inhibitor specificities. ADH1 and ADH2 exhibited Class I properties and were observed in liver (and intestine) extracts. ADH3, ADH4, and ADH5 showed “high-K _m ” (possibly Class IV) properties, with ADH3 and ADH4 exhibiting high activity in cornea, ear, stomach, and esophagus extracts. ADH6 and ADH7 exhibited Class III properties, including activities as formaldehyde dehydrogenases, with each showing different tissue distribution characteristics; ADH6 was widely distributed, and ADH7 was restricted to prostate extracts. An additional form of formaldehyde dehydrogenase (FDH) was observed, which was inactive with hexenol and ethanol as substrates. Isoelectric point variants were observed for ADH3 (three forms) and for ADH4 (two forms), and the inheritance of ADH3 was studied in 15 families ofM. domestica. The data were consistent with codominant inheritance of two alleles (ADH3*A andADH3*B) at a single autosomal locus (designatedADH3) and with a model involving a dimeric ADH isozyme: ADH3 (γ₂ isozyme, forming three dimers designated γ ₂ ¹ , γ¹ γ², and γ ₂ ² in heterozygous individuals).