He Marsupial of the tlacuaches Is the main characteristic that distinguishes these animals. It is by this bag that belong to the subclass Marsupialis .
Tlacuaches, so known in Mexico and Central America and called opossums in the rest of the Spanish speaking countries, are omnivorous mammals that usually inhabit trees and burrows.
Marsupio open, species Didelphis virginiana. Image via Konrad Wothel / Minden Pictures
They are characterized by the marsupi, a kind of bag or fold of the skin, within which the period of development of the pups ends. These are born before having completed all phases of it.
This feature is present in other animals of the same subclass, such as kangaroos, koalas, etc., although there are smaller genera, such as the tlacuache mouse or Mexican marmosa, which lacks a marsupial pouch.
The development and definition of the marsupi is also a variable characteristic between the different genera, since it can go from a very rudimentary bag to a completely shaped and observable to the naked eye.
The gestation form of tlacuache or opossum does not include a placenta and barely lasts 12 days and a half inside the uterus while the rest of the development process takes place in the marsupi. It is the shortest breeding season among all mammals.
This fact is an advantage for the study of the species and for the advancement of biology as a science, since it allows direct observation of the growth of newborns and their behavior within the marsupi. In fact, much of the existing information about tlacuache is due to such studies of development and morphology.
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What is the poultry marsupi? Physical characteristics
This fold of the skin of the females of the tlacuaches is located on the mammary glands, although in the case of the category Didelphidae , Does not cover them in full, from where they will feed the young.
Usually, it is better developed in species that inhabit the trees than in the terrestrial species and can have the opening in the front or back.
The picture below shows an open marsupi, although it belongs to the species Didelphis Virginiana (Also known as American opossum) is very similar to the tarsus marsupi.
The hair that is observed around the marsupio of the female that is feeding to its young, usually turns of an amber color, product of secretions of sweat glands located inside the marsupio.
There are three differentiable regions in the tarsal marsupi, one dorsal, one located between the thorax and the abdomen and the one closest to the genital apparatus, called Pars pudenda .
Females can open or close the marsupi voluntarily, as it is provided with a sphincter or set of musculo-skeletal fibers that, when contracted, make this function possible, which is necessary before delivery.
It is a way to regulate the temperature and prepare the internal environment of the bag. It is also useful at the time of delivery, since it allows relaxing the marsupi so that the embryos can reach it more easily.
The role of the marsupi: development and protection
The marsupial acts basically as an incubator, as the newborn marsupials are so small that their weight is never more than 1 gram, even a complete litter does not exceed 1% of the body weight of the mother.
Although it is a species that is born almost embryonic by the immaturity of its body, the limbs and muscles above are sufficiently developed and already have small claws in the front legs.
In this way, they are able to crawl from the vagina (when they are born) helping themselves from the mother's coat, to the marsupi, to begin the breastfeeding period by adhering to the mother's breasts.
The time the pups will last in the marsupial is variable. It will depend on such factors as the mother's body mass, litter size and number of litters per year, but it is known that the lactation period lasts about two months.
Gradually, after this time, the offspring will be fed less of the breast milk until they leave the poultry. However, they will return to it to shelter and suck the milk intermittently, although in some cases, nursing offspring have been observed outside the poultry.
Since the litter will spend considerable time inside the marsupi, the marsupi is sufficiently expandable for all pups to fit into it.
They can even move as they grow, as the mother's nipple gradually lengthens as well to compensate for the growth of the offspring. This expansion of the skin is only temporary.
Once the weaning of the offspring has occurred, the marsupial is reduced in size but never again has the same dimensions as it had before pregnancy.
In addition to providing the right environment to complete the last stage of development of newborns, the marsupio serves as a protection against potential threats from the outside world.
In addition, it allows the pups to maintain an adequate temperature, since they are not yet able to control their own body temperature.
Of course, the absence or presence of the marsupi indicates whether it is a male or female tlacuache specimen.
Interestingly enough, it has been observed in experiments conducted by biologists that female tlacuaches and, in general, those belonging to the category Didelphia They accept offspring from other litters that are placed on their marsupials.
In short, this modality of non-placental gestation has always been a subject of study for researchers and biologists, being the marsupio the point of interest for what happens inside it, its functions and the accessibility that offers to carry out The observations of the specimens.
References
- Feldhammer et al. (2015). Mammalogy: Adaptation, Diversity, Ecology . Baltimore, Johns Hopkins University Press.
- Feldhammer et al (2003). Wild Mammals of North America: Biology, Management, and Conservation . Baltimore, Johns Hopkins University Press.
- Hunsaker, D. (1977). The Biology of Marsupials . London, Academic Press Inc.
- Jones et al. (2003). Predators with Pouches: The Biology of Carnivorous Marsupials. Australia, Csiro Publishing.
- Krause, W, and Krause W. (2006). The Opossum: Its Amazing Story . Columbia, Department of Pathology and Anatomical Sciences.