User:Bucketkitty/Filial cannibalism

Filial cannibalism in fish
Many species of fish with paternal care will exhibit total clutch cannibalism or partial clutch cannibalism. This is likely in order to gain additional energy and nutrients, which could ultimately benefit their future reproductive success. Cannibalized offspring can act as a food source for the male fish guarding them.

Often, male fish will consume their entire clutch if it is too small, as the energetic costs of caring for a small clutch may be greater than their reproductive benefits. In other fish, filial cannibalism has been observed to regulate male fish's endocrine systems. For example, in the blenniid fish Rhabdoblennius nitidus, males have an androgen-dependent brood cycle. However, the acquisition of eggs suppresses the secretion of androgen, preventing males from performing courtship displays and obtaining more offspring. As a result, R. nitidus males will cannibalize all their eggs when the clutch size is small, so they can reproduce and care for a larger clutch of eggs (and subsequently have more offspring).

In some cases, the size of the clutch seems to determine whether the male consumes the entire clutch or only part of it. For example, in the fantail darter, males seem to consume a fixed number of eggs regardless of clutch size, which may be in order to cover the energy costs of guarding the eggs. Since the cost of parental care does not increase significantly with a larger clutch size, having small clutch size may not be worth amount of care invested in it. This is further compounded by the fact that in the fantail darter, females prefer males who have already mated and are guarding young eggs, possibly because it would reduce the risk of her eggs being consumed by the male. Specifically, females prefer males with young eggs over old eggs, so caring for smaller broods of older eggs may have little to no net benefit to the male. As a result, smaller clutches may end up being entirely consumed.

In insects
Filial cannibalism can act in a way analogous to brood reduction in birds, in order to reduce competition between offspring for resources and maximize the survival of fully-developed healthy offspring. For example, the burying beetle Nicrophorus vespilloides exhibits partial filial cannibalism. Burying beetles bury the bodies of small vertebrates as a food source for their offspring; for N. vespilloides, eggs are scattered a few centimeters away from the corpse. Once they hatch, the larvae make their way to the corpse to feed while supervised by their parents. Clutch sizes can be much larger than the corpse can support, which researchers suggest is due to eggs being laid as insurance for unexpected mortalities, parents being unable to accurately estimate the food capacity of the corpse, or parents being physically constrained to to a minimum clutch size (though studies have shown that parents will vary the size of their clutch based on the amount of food available). At higher densities with insufficient food, larvae may not develop completely, resulting in smaller adults that are less likely to find a mate, as well as limiting the maximum clutch size that can be laid. The parents thus kill part of their brood at the earliest stage to maximize the food available for the others.

Filial cannibalism can also serve as a source of energy while simultaneously removing nonviable eggs, such as those that have been parasitized. In the assassin bug Rhinocoris tristis, males are more likely to consume eggs at the periphery of the brood, which are most likely to be parasitized by wasps and are also the easiest for the male to access. Although R. tristis cannot distinguish between parasitized eggs and nonparasitized eggs, their preference for feeding on peripheral eggs may be a general behavior to maximize the chances of feeding on nonviable, parasitized eggs. In addition, it would reduce the number of peripheral eggs available to parasitic wasps, forcing them into an inner egg where guarding males are more likely to see and fight them off, which could potentially kill the wasp. Furthermore, eggs served as a source of energy due to the costs of parental care, such as reduced efficiency in feeding and energy used to fend off attackers. R. tristis males also guard adopted broods without a higher rate of cannibalization, suggesting that they cannot discriminate between their own eggs and unrelated ones.