Embryonic Cannibalism in Sand Tiger Sharks Explained

Running head: EMBRYONIC CANNIBALISM AND COMPETITION 1 Embryonic Cannibalism and Competition in Sand Tiger Sharks Student’s Name Institutional Affiliation

EMBRYONIC CANNIBALISM AND COMPETITION 2 Embryonic Cannibalism and Competition in Sand Tiger Sharks Animals can exhibit unique but interesting mating systems and reproduction behavior, some of which are worth exploring. For example, a sand tiger shark, or Carcharius Taurus , has attracted the attention of many scientists due to its remarkable reproductive behavior. According to Chapman et al. (2013), sang tiger sharks’ embryo cannibalizes their littermates to establish supremacy in the uterus. When females’ ova get fertilized, their offspring are most likely from different male sharks. The researchers indicated that the first hatchling exhibits a cannibalistic behavior by feeding on other embryos so that no other hatchling will survive. Female sand tiger sharks mostly give birth to two siblings, one from each side of the uterus. Therefore, sand tiger sharks' embryonic cannibalism is a peculiar strategy to determine the genetic makeup of the offspring. In most cases, the game of sexual selection ends when the egg gets fertilized, meaning that the first male to fertilize the egg has won the right to sire the next generation. However, Chapman et al. (2013) have proved that the same strategy may not be replicable in the sand tiger sharks world. Female sand tiger sharks have two uteri, one on the left and one on the right, each carrying fertile eggs. They can reproduce with a variety of male sand tiger sharks when they are fertile. However, the female sand tiger sharks, only have two pups after a year, one from each side of the uterus. Such a situation would be literary impossible to comprehend without further research to determine how it happens. As a result, a study by Chapman et al. (2013) revealed that the battle for supremacy starts in the uterus. The first embryo to hatch from the encapsulated fertilized egg grows bigger than the rest of the siblings. Once it reaches about 100mm, the hatchling attacks, kills, and consumers the others, achieving exponential growth. What started as hundreds of eggs waiting to be fertilized becomes a single sibling, having all the necessary

EMBRYONIC CANNIBALISM AND COMPETITION 3 ingredients to grow having eliminated competition. Chapman and his six co-researchers analyzed 15 pregnant sand tiger sharks taken in Richards Bay, South Africa, after almost five years of scientific research. After genetic studies, the researchers found that 60% of the cases, about 9 sand tiger sharks, carried babies from the same father. Such results suggested that offspring from all other fathers were killed. Moreover, the results indicated that even if the female mated with various males, there is no guarantee that the male succeed in successfully passing their genes to the next generation. The researchers further explain that some behavioral and physiological patterns that male sand tiger sharks portray could also contribute to sexual selection. Male sand tiger sharks indulge in mate guarding behavior, where the dominant male, who is high in testosterone, keeps other males out until copulation is complete. Such a conduct enhances the likelihood of such males fertilizing the first egg while postponing subsequent fertilization by other males. When embryos of the same size are approaching hatching, the competitive embryos win. Female sand tiger sharks do not have a choice of the male sand tiger sharks they want as the father of their babies. The embryos killed become crucial resources to support the growth of the dominant embryo, reducing the energy and investment the mother would require supporting multiple babies. Therefore, embryonic cannibalism appears to be an effective strategy to sire healthier babies from a preferred father, mostly the first mating partner. The research highlights that sexual selection and competition can exist after fertilization. The study reveals that although the first embryo implanted has higher chances of surviving than the rest, it may still be replaced through competition. However, more research is required to delve deeper into competition and the role it plays in contributing to the cannibalistic behavior in the uterus ( Nishank & Swain, 2018 ). Besides, female sand tiger sharks can select mates that

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EMBRYONIC CANNIBALISM AND COMPETITION 4 exhibit particular characteristics, such as aggressiveness, dominance, strength, size, and mating behavior. In this system, the quality and fitness of the sperm are critical in determining the overall winner and the quality of the embryo. Therefore, embryonic cannibalism is a remarkable genetic behavior that explains how sexual selection and competition can determine the genetic formation of the offspring.

EMBRYONIC CANNIBALISM AND COMPETITION 5 References Chapman, D. D., Wintner, S. P., Abercrombie, D. L., Ashe, J., Bernard, A. M., Shivji, M. S., & Feldheim, K. A. (2013). The behavioral and genetic mating system of the sand tiger shark, Carcharias taurus, an intrauterine cannibal. Biology Letters , 9 (3), 20130003. Nishank, S. S., & Swain, S. (2019). Cannibalism in animals. Science Horizon , 4 , 33-39.

Biology

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