Shark embryos can move around the mother’s womb and eat their “brothers”

The science already knows that embryos of some species of sharks eat their relatives in the womb. However, the new device gave biologists fresh information about this widespread act of cannibalism, showing that the embryos do not just eat each other, but can travel between the uterus in search of a victim.

In most animals, embryonic movements are limited to small fluctuations and an occasional coup. Therefore, researchers from the Churaumi Aquarium, Japan, were extremely surprised to find that the unborn young Indian nanny shark (Nebrius ferrugineus) is not only moving through its womb, but can also move to the next one. The research results are published in the journal Ethology.

These scientists have shown the frequent migration of embryos between the right and left uterus, this discovery was made thanks to a new ultrasound equipment designed to scan for human pregnancy. Portable scanners have been used for several years, even to look inside sharks, but this was made difficult by the fact that the fish was removed from their habitat.

To study them in a more natural state, scientists improved their device, making it resistant to moisture and pressure. For several years, researchers studied three pregnant sharks, making more than 40 ultrasound clips on which up to four sharks could be seen squirming inside each mother.
 
 
Image of shark embryos / © Ethology
 
In one mother, the embryos changed places three times. In another case, the movement was much more intense: a total of 24 migrations were recorded during the entire pregnancy. One of the pictures showed how the actual exchange of the uterus occurred, and one of the embryos hastily moved from one uterus to another. His speed was eight centimeters per second, which struck scientists. Another shark in the early stages of pregnancy had two embryos in each uterus. After some time, they became one less. After two more months, only two embryos remained, and by the end of the pregnancy there was only one winner.

Previously, biologists suspected that shark embryos could move between the queen bees and absorb their competitors, but those observations were made during an invasive surgical procedure, leaving open the question of whether the same processes occur under natural conditions. Researchers believe that this unique behavior may be one of the ways in which some shark species provide food for their developing embryos.