Published: July 6, 2015

New Discoveries in How Animal Moms-to-Be Feed Their Babies

Kate Golembiewski, PR and Science Communications Manager, Public Relations


Pop quiz—what kinds of animal mothers feed their babies before birth? The first (and maybe only) ones to come to mind are probably mammals like us—moms-to-be funnel nutrients from their blood supply right to their developing embryos through an organ called the placenta; the moms literally “eat for two.” That’s a different kind of nourishment than you see in most other animals—the majority lay eggs with a nutritious yolk for the embryo to use as it develops.

However, Field Museum scientists have helped discover that there are a lot more kinds of animals whose mothers directly and continuously feed their embryos than we originally thought. Mammals are far from the only ones to practice what scientists call matrotrophy (“mother feeding”)—it turns out that there are at least some moms feeding their embryos in 21 of the 34 big groups of animals (phyla). The biggest surprise in this study was how many different kinds of invertebrate animals seem to have independently evolved ways to feed their embryos directly. Certain kinds of insects, sea stars, and flatworms display matrotrophy—in fact, there are more species of flatworms that feed their young through matrotrophy than there are species of mammals.

Scott Lidgard, the Field Museum scientist who helped lead the team that made the discovery, explained, “There’s lots of information out there about animals that are similar to us, but by not focusing on invertebrates, we’re missing parts of the story. There are all these different ways to deliver nutrients to developing embryos. Our paper sets a baseline for bringing together the detailed and sometimes obscure work of hundreds of scientists in an cohesive picture to inform future studies.”

The study illuminates these different kinds of ways that mothers feed their embryos. Some sharks feed their young directly through an organ that’s similar to mammals’ placentas, while certain scorpions have uterine “milk glands.” Coral-like creatures called bryozoans don’t have uteri—the embryos often develop in hollow buds on the parent's body, where again, a placenta-like organ supplies them with nourishment. Meanwhile, some sea stars species get the “Mother of the Year” award—the embryos feed on their mom’s body from the inside.

Lidgard and a colleague at St. Petersburg State University in Russia led the international team, who made their discovery about the widespread use of matrotrophy by poring over scientific papers and databases to find examples of mother-feeding like the ones above. By looking at the relationships between species that use matrotrophy and those that don’t, they estimate that the mechanism has evolved at least 140 separate times across the tree of life.

Lidgard is interested in the big picture of life on Earth, and this study on matrotrophy will help scientists make connections about parentage and evolution throughout the animal kingdom, including species that are often overlooked. Lidgard explained, “In order to understand how the cycle of life occurs and evolves, we can’t just look at one tiny group of animals and extrapolate—there’s a wider diversity here that can help us understand life.”


Photo credit: Flickr user Arthur Chapman