Inside the Womb: Sand Tiger Shark Embryos Prey on Siblings

Sand tiger sharks (Carcharias taurus) possess one of the most unusual reproductive methods among vertebrates. When multiple embryos develop together in the mother's uterus, the faster-growing embryo attacks and consumes its siblings before birth. This phenomenon is known as intrauterine cannibalism, with two technical terms: embryophagy and adelphophagy, literally meaning to eat one's own siblings. The behavior was first discovered accidentally in 1948 when a researcher examining the uterus of a near-term sand tiger shark was bitten by an embryo inside. To date, this extreme form of cannibalism is only known to occur in this species, although milder forms of intrauterine cannibalism, such as eating unfertilized eggs without preying on siblings, are found in several other shark species. Process Inside the Uterus A female shark has two separate uteri and produces eggs gradually over several months. Therefore, in early pregnancy, one uterus can contain more than one embryo from different egg capsules. Fertilized eggs enter both uteri, but they do not always develop at the same time. Embryos that hatch earlier from their egg capsules gain an advantage of faster growth and earlier development of teeth and eyes compared to other embryos in the same uterus, enabling them to move and attack first before their siblings have developed that far. Sand tiger sharks (Carcharias taurus) swim in shallow waters. Their nearly equally sized double dorsal fins and brownish-gray bodies are characteristic of this species. Photo: D Ross Robertson/Smithsonian…This article was originally published on Mongabay