Lactation Versus Placentation: Diverse Reproductive Strategies of Mammals

Speaker: Marilyn B Renfree

Venue: Zijingang Hall, Alumni Building, Zijingang Campus

Abstract: Viviparity is widespread among animals, with many species nurturing their offspring in the uterus via a placenta. This process requires adaptive modifications to ensure the embryo’s development within the mother. However, only **mammals** further extend maternal protection through lactation.  In eutherians (placental mammals), the **lactation period ranges from days to years, whereas marsupials (e.g., kangaroos) give birth to underdeveloped young that mature during lactation. Eutherian milk composition remains stable, while marsupial milk dynamically adjusts its nutritional profile to regulate offspring growth.  Notably, we found that multiple genes expressed in the mammary glands of the tammar wallaby (a marsupial) overlap with key placental genes in eutherians. This suggests that marsupials use lactation—rather than a placenta—to regulate the postnatal development of their "external fetuses" until independence, effectively completing an evolutionary shift from umbilical nourishment to nipple-based sustenance.