Developmental staging in a marsupial Dasyurus hallucatus

Abstract

In a marsupial, Dasyurus hallucatus, pouch-young of various ages from newborn to 55 days were embedded in wax and serially sectioned. On the basis of the relative development of external and internal characteristics, they were placed in the Carnegie staging system developed by Streeter and elaborated by O'Rahilly and associates. Birth occurred at stage 15, and the end of embryogenesis (stage 23) was reached about day 33. Whereas stage 23 is characterised in all eutherians by the closure of the secondary palate, this occurs before stage 15 in D. hallucatus. Since most other characters of the newborn are at a stage 15 level of development, there has been a relative acceleration of development of the secondary palate (and forelimb) in D. hallucatus that allows it to suckle and breathe at the same time. Between D. hallucatus and eutherians, there is general agreement in the sequence of development and in the relative degree of most structures at each stage. Further marsupials should be examined to see if the minor differences noted are peculiar to D. hallucatus or apply to marsupials generally.

Features of the structural development of the inferior colliculus in relation to the onset of hearing in a marsupial: The Northern Quoll,Dasyurus hallucatus

“…Northern quolls are born at a stage of embryogenesis equivalent to stage 15 of the Carnegie series but with precociously developed forelimbs, nasal septa, and mouth (Nelson, 1992). Day 33 in the quoll corresponds to stage 23 of the Carnegie series, the end of embryogenesis, because all organ systems are formed by that time.…”

“…Connections from the cochlear nucleus to the inferior colliculus of quolls are present by about day 30, close to the time when embryogenesis is complete in the Northern quoll (Nelson, 1992). Neurites of cells of the dorsal cochlear nucleus, labelled by injections of horseradish peroxidase into the inferior colliculus, are demonstrable in opossums (Didelphis uirginiana) at day 15 (Willard and Martin, 1986).…”

“…Neurites of cells of the dorsal cochlear nucleus, labelled by injections of horseradish peroxidase into the inferior colliculus, are demonstrable in opossums (Didelphis uirginiana) at day 15 (Willard and Martin, 1986). This apparently earlier growth of axons compared with quolls contrasts with the relatively delayed development of claws on the forefeet, parts of the mouth, and membranes around the eyes and ears in Didelphis (McCrady, 1938;Nelson, 1992). At embryonic day 15 in rats (22 days gestation) fibers growing from the cochlear nucleus, traced using DiI, have reached the midline (Kandler and Friauf, 1993;Niblock et al, 1995).…”

“…It becomes accustomed to humans so that, because of its size, it is suitable as a laboratory species. It is valuable for developmental studies (Aitkin et al, 1991(Aitkin et al, , 1994aNelson, 1989, 1992;Nelson, 1987Nelson, , 1992Pellis et al, 1992) because it bears a litter of eight young which appear in a shallow pouch after 21-25 days in utero (Nelson, unpublished observations). After about 40 more days, the young move from one nipple to another and could be lost from the pouch, but the mother is able to retrieve the pouch-young because the latter emit characteristic isolation sounds which are closely matched in spectra to the best frequency of the mother's audiogram (Aitkin et al, 1994b) and would thus be highly audible to the mother.…”

Marsupial oocytes, fertilization and embryonic development can provide useful tools to study developmental mechanisms

“…Marsupials are born at an altricial (immature) stage of development, but nevertheless, most organ systems are formed by birth and growth and differentiation of the organs proceed post-natally during lactation (Table 2). Nelson (13). In D. hallucatus, Stage 23 occurs on Day 33 of lactation.…”