How do marsupials reproduce while an older offspring is still in the pouch?

In many marsupial species, such as certain macropodids, reproduction can occur while an older offspring is still residing in the marsupium (pouch).1

Following the birth of the first joey, the female often enters heat and mates within a few days. After conception, the resulting microscopic embryo enters a state of suspended development known as diapause. This embryo remains dormant until the older offspring begins to leave the pouch or environmental conditions become favorable. Once development resumes, the embryo proceeds to birth after a gestation period of approximately 30 days.1

During this transition, the mother is capable of supporting young at different developmental stages simultaneously. To accommodate their varying nutritional needs, the mother’s teats can produce different compositions of milk at the same time. This reproductive strategy is considered an adaptation that allows populations to recover quickly following periods of environmental stress, such as a drought.1