Filial cannibalism

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Filial cannibalism occurs when an adult individual of a species consumes all or part of the young of its own species or immediate offspring. Filial cannibalism occurs in many species ranging from mammals to insects, and is especially prevalent in various species of fish. [1] The exact evolutionary purpose of the practice in those species is unclear and debated among zoologists, though there is consensus that it may have, or may have had at some point in species' evolutionary history, certain evolutionary and ecological implications.

Contents

Types

Total

Total or whole clutch cannibalism occurs when a parent consumes its entire brood. This usually occurs when a brood is small or of lower quality. The most obvious purpose of total or whole clutch cannibalism is the termination of care for the parents. The main benefit of this action can only be an investment in the future reproduction of potentially larger or healthier broods. [2]

Partial

Partial clutch cannibalism occurs when a parent consumes a part of its offspring. "Parental manipulation of brood size may allow the parent the maximize lifetime reproductive output by adjusting current reproductive costs in favour of future survival and subsequent opportunities for reproduction." [3] Unlike total or whole clutch cannibalism, partial clutch cannibalism invests in both current and future reproduction. [2] Male parents, particularly male fish, may eat some of their offspring to complete their "current parental cycle, and remain in sufficiently good condition to engage in further breeding cycles." [4]

Benefits

The following potential benefits of filial cannibalism have been suggested by zoologists:

Costs

Suggested costs are the loss of immediate fitness [9] and the risk of transmission of diseases and parasites. [3]

Social factors

Competition among a species for resources, mating opportunities, and reproductive dominance are all promoters for filial cannibalism. To compete well in a certain species' social structure, a parent may be compelled to practice filial cannibalism to limit the amount of energy and time they spend raising their young.

Males may compete for mating opportunities by eating the offspring of a female to make that female more sexually receptive or to re-mate. By doing this, a male might be able to prolong its lifetime mating opportunities. [3]

Female fish may compete for mating opportunities with males by raiding the male's nest and eating the eggs inside. Females may also use cannibalism – particularly birds and bees that live in a joint-nesting social structure – as a way to establish reproductive dominance by eating the eggs of a co-breeder. [3]

In some animal cultures, competition may lead to instances of egg thievery, nest takeovers, and cuckoldry. However, the consumption of an animal's brood is often more beneficial than the consumption of unrelated conspecifics, since it takes less energy to eat their own offspring and lessens the chance of getting their own brood raided when getting food while away from their offspring. [10]

Filial cannibalism in fish

Many species of fish with paternal care exhibit total or partial clutch cannibalism. This is likely in order to gain additional energy and nutrients, which might ultimately increase their future reproductive success. [11] Cannibalized offspring can act as a food source for the male fish guarding them. [12]

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 the reproductive benefits. [11] 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). [13]

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 the amount of care that would have to be 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. [11]

Filial cannibalism 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 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. [14]

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 serve 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. [15]

Infanticidal cannibalism among humans

Among humans, cases of newborns or infants being killed because they are "considered unwanted or unfit to live" and then "consumed by the mother, father, both parents or close relatives" are known as infanticidal cannibalism or cannibalistic infanticide. [16] [17] Infanticide followed by cannibalism was practiced in various regions, but is particularly well documented among Aboriginal Australians. [17] [18] [19]

See also

Related Research Articles

<span class="mw-page-title-main">Burying beetle</span> Genus of beetles

Burying beetles or sexton beetles, genus Nicrophorus, are the best-known members of the family Silphidae. Most of these beetles are black with red markings on the elytra (forewings). Burying beetles are true to their name—they bury the carcasses of small vertebrates such as birds and rodents as a food source for their larvae, this makes them carnivorous. They are unusual among insects in that both the male and female parents take care of the brood.

<span class="mw-page-title-main">Behavioral ecology</span> Study of the evolutionary basis for animal behavior due to ecological pressures

Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when studying animal behaviors: What are the proximate causes, ontogeny, survival value, and phylogeny of a behavior?

<span class="mw-page-title-main">American coot</span> Species of bird

The American coot, also known as a mud hen or pouldeau, is a bird of the family Rallidae. Though commonly mistaken for ducks, American coots are only distantly related to ducks, belonging to a separate order. Unlike the webbed feet of ducks, coots have broad, lobed scales on their lower legs and toes that fold back with each step which facilitates walking on dry land. Coots live near water, typically inhabiting wetlands and open water bodies in North America. Groups of coots are called covers or rafts. The oldest known coot lived to be 22 years old.

<span class="mw-page-title-main">Damselfish</span> Group of fishes

Damselfish are those within the subfamilies Abudefdufinae, Chrominae, Lepidozyginae, Pomacentrinae, and Stegastinae within the family Pomacentridae. Most species within this group are relatively small, with the largest species being about 30cm in length. Most damselfish species exist only in marine environments, but a few inhabit brackish or fresh water. These fish are found globally in tropical, subtropical, and temperate waters.

<span class="mw-page-title-main">Blue-footed booby</span> Species of bird

The blue-footed booby is a marine bird native to subtropical and tropical regions of the eastern Pacific Ocean. It is one of six species of the genus Sula – known as boobies. It is easily recognizable by its distinctive bright blue feet, which is a sexually selected trait and a product of their diet. Males display their feet in an elaborate mating ritual by lifting them up and down while strutting before the female. The female is slightly larger than the male and can measure up to 90 cm (35 in) long with a wingspan up to 1.5 m (5 ft).

Parent–offspring conflict (POC) is an expression coined in 1974 by Robert Trivers. It is used to describe the evolutionary conflict arising from differences in optimal parental investment (PI) in an offspring from the standpoint of the parent and the offspring. PI is any investment by the parent in an individual offspring that decreases the parent's ability to invest in other offspring, while the selected offspring's chance of surviving increases.

<span class="mw-page-title-main">Pipefish</span> Subfamily of fishes

Pipefishes or pipe-fishes (Syngnathinae) are a subfamily of small fishes, which, together with the seahorses and seadragons, form the family Syngnathidae.

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<i>Odontotaenius disjunctus</i> Species of beetle

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<span class="mw-page-title-main">Siblicide</span>

Siblicide is the killing of an infant individual by its close relatives. It may occur directly between siblings or be mediated by the parents, and is driven by the direct fitness benefits to the perpetrator and sometimes its parents. Siblicide has mainly, but not only, been observed in birds.

<span class="mw-page-title-main">Cannibalism</span> Consuming another individual of the same species as food

Cannibalism is the act of consuming another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded in more than 1,500 species. Human cannibalism is well documented, both in ancient and in recent times.

<span class="mw-page-title-main">Scissortail sergeant</span> Species of fish

The scissortail sergeant or striptailed damselfish is a large damselfish. It earns its name from the black-striped tail and sides, which are reminiscent of the insignia of a military Sergeant, being similar to those of the sergeant major damselfish. It grows to a length of about 16 centimetres (6.3 in).

<span class="mw-page-title-main">Infanticide (zoology)</span> Killing of young offspring by an adult animal of the same species

In animals, infanticide involves the intentional killing of young offspring by a mature animal of the same species. Animal infanticide is studied in zoology, specifically in the field of ethology. Ovicide is the analogous destruction of eggs. The practice has been observed in many species throughout the animal kingdom, especially primates but including microscopic rotifers, insects, fish, amphibians, birds and mammals. Infanticide can be practiced by both males and females.

<span class="mw-page-title-main">Parental care</span> Behavior in animals of taking care of offspring

Parental care is a behavioural and evolutionary strategy adopted by some animals, involving a parental investment being made to the evolutionary fitness of offspring. Patterns of parental care are widespread and highly diverse across the animal kingdom. There is great variation in different animal groups in terms of how parents care for offspring, and the amount of resources invested by parents. For example, there may be considerable variation in the amount of care invested by each sex, where females may invest more in some species, males invest more in others, or investment may be shared equally. Numerous hypotheses have been proposed to describe this variation and patterns in parental care that exist between the sexes, as well as among species.

Mate desertion occurs when one or both parents abandon their current offspring, and thereby reduce or stop providing parental care. Often, by deserting, a parent attempts to increase breeding opportunities by seeking out another mate. This form of mating strategy behavior is exhibited in insects, birds and mammals. Typically, males are more likely to desert, but both males and females have been observed to practice mate desertion.

<i>Microspathodon chrysurus</i> Species of fish

The yellowtail damselfish is a species of damselfish native to tropical areas such as the Caribbean coast of Panama. Damselfish are abundant in coral reef environments. The International Union for Conservation of Nature lists this fish as being of “least concern”. The species is exploited on a minor scale, for fisheries and the aquarium trade. It may be threatened by the invasive lionfish.

<span class="mw-page-title-main">Polyandry in animals</span> Class of mating system in non-human species

In behavioral ecology, polyandry is a class of mating system where one female mates with several males in a breeding season. Polyandry is often compared to the polygyny system based on the cost and benefits incurred by members of each sex. Polygyny is where one male mates with several females in a breeding season . A common example of polyandrous mating can be found in the field cricket of the invertebrate order Orthoptera. Polyandrous behavior is also prominent in many other insect species, including the red flour beetle and the species of spider Stegodyphus lineatus. Polyandry also occurs in some primates such as marmosets, mammal groups, the marsupial genus' Antechinus and bandicoots, around 1% of all bird species, such as jacanas and dunnocks, insects such as honeybees, and fish such as pipefish.

<span class="mw-page-title-main">Parental care in birds</span>

Parental care refers to the level of investment provided by the mother and the father to ensure development and survival of their offspring. In most birds, parents invest profoundly in their offspring as a mutual effort, making a majority of them socially monogamous for the duration of the breeding season. This happens regardless of whether there is a paternal uncertainty.

<span class="mw-page-title-main">Matriphagy</span>

Matriphagy is the consumption of the mother by her offspring. The behavior generally takes place within the first few weeks of life and has been documented in some species of insects, nematode worms, pseudoscorpions, and other arachnids as well as in caecilian amphibians.

Vertebrate maternal behavior is a form of parental care that is specifically given to young animals by their mother in order to ensure the survival of the young. Parental care is a form of altruism, which means that the behaviors involved often require a sacrifice that could put their own survival at risk. This encompasses behaviors that aid in the evolutionary success of the offspring and parental investment, which is a measure of expenditure exerted by the parent in an attempt to provide evolutionary benefits to the offspring. Therefore, it is a measure of the benefits versus costs of engaging in the parental behaviors. Behaviors commonly exhibited by the maternal parent include feeding, either by lactating or gathering food, grooming young, and keeping the young warm. Another important aspect of parental care is whether the care is provided to the offspring by each parent in a relatively equal manner, or whether it is provided predominantly or entirely by one parent. There are several species that exhibit biparental care, where behaviors and/or investment in the offspring is divided equally amongst the parents. This parenting strategy is common in birds. However, even in species who exhibit biparental care, the maternal role is essential since the females are responsible for the incubation and/or delivery of the young.

References

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