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 (e.g., lions, deer, some primates, and many systems where there is an alpha male). [1] A common example of polyandrous mating can be found in the field cricket ( Gryllus bimaculatus ) of the invertebrate order Orthoptera (containing crickets, grasshoppers, and groundhoppers). Polyandrous behavior is also prominent in many other insect species, including the red flour beetle, the adzuki bean weevil, 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,[ citation needed ] such as jacanas and dunnocks, insects such as honeybees, and fish such as pipefish.
It is theorized that polyandry is more prevalent in organisms where incompatibility is more costly, and where this incompatibility is more likely. [2] The former is especially true in viviparous organisms. [3] Where the cost of having a low-quality father is significant, however, an organism is less likely to be polyandrous. [2]
The adaptive significance of polyandry in animals is controversial. Polyandry has direct benefits for females allowing fertilization assurance, provision of resources, and parental care for their offspring. [4] House mice (Mus musculus musculus) have shown indirect, genetic benefits, where females have increased offspring survival through multiple mating, showing that practicing polyandry mating results in an increase in offspring viability. [5] In a meta analysis, including 10 different orders of insects, polyandry increased the production of eggs by females specifically in Lepidopterans and Orthopterans. [6] Indirect benefits of mating for females can be gained through sperm competition to attain "good genes", cryptic female choice, increased genetic quality, and genetic diversity. [7] Females spiders ( Pisaura mirabilis ) store more sperm from gift-giving males suggesting that sperm storage is under female control through cryptic sperm choice. [8] The increase in sperm storage from the gift giving males might allow females to produce "sexy sons" that also give gifts and increase the fitness of offspring. Sperm storage and fertilization success increased with copulation duration, suggesting an advantage in sperm competition. [8]
Many reptile species also demonstrate polyandry, especially among members of the tortoise family (Testudinidae). Through polyandry and long-term sperm storage, recent studies have found evidence for the ability of female tortoises to produce clutches of eggs that demonstrate multiple paternity. [9] [10] Predictably, these hatchlings showed an increase in genetic variability compared to those sired by a single male. [10] Potential for multiple paternity within a clutch is primarily a result of sperm storage across reproductive cycles, since studies have confirmed the presence of multiple males' sperm in the female tortoise reproductive tract simultaneously. [10] As a result of clutches with greater variation in paternal genes and increased sperm competition, females can maximize both the genetic quality and number of offspring. [11] Multiple paternities within a single clutch is therefore considered an effective strategy to increase the reproductive success and fitness of female tortoises. [9]
Acorn woodpeckers provide substantial information on breeding systems because they practice monogamy, polyandry, and polygyny. In polyandry the presence of more male breeders in acorn woodpeckers has shown that females reproduce the optimal clutch size and that with paternity sharing between males it is behaviorally more stable increasing male and female fitness. [12] As opposed to polygyny, where it has been observed that polygynous females that lay a large number of eggs exceeding the optimal clutch size reduces the fitness of the group. [12] Polygynous trios compared to polyandrous trios showed that having more eggs lowered the group fitness. Chao (1997) studies using acorn woodpeckers suggest that other mating systems are practiced at a lower rate when compared to polyandry because it is polyandry that can maximize the fitness of males and females when obtaining optimal clutch size. In polyandrous mating, optimal clutch size is obtained because there is only one female and it becomes more stable when all members remain together. [12]
Multiple mating is also seen in wattled jacanas where females have a group of males close by for mating. Copulations are easily seen in jacanas, facilitating the observation of females copulating continuously with various males. [13] The continuous copulations and the close proximity to mates have allowed the females to fly in within minutes leading to the expected sperm mixing [13] and allowing the most viable sperm to fertilize most of the clutch or to increase genetic diversity for benefits in disease resistance. [14] Snow and Andrade (2005) concluded that the redback spider (Latrodectus hasselti) increases their ability to manipulate the paternity of their offspring by using the spermathecae to store multiple sperms. Additionally, a study on leaf-cutting ants ( Acromyrmex echinatior ) supported the hypothesis that sperm mixing indeed occurs in polyandrous social insects. It was further found that the eggs in the queen ants showed to be completely mixed and used randomly during egg laying. [14]
According to Gordon G. Gallup, as a form of adapting to multiple mating in females, human penile shape is indicative of an evolutionary history of polyandry. Male humans evolved to have a wedge- or spoon-shaped glans and to perform repeated thrusting motions during copulation in order to draw foreign semen back away from the cervix and thus to compete with sperm of other males. [15]
Polyandry may also impose costs on females, exposing them to diseases, increased predation risk, time and energy costs, and even physical harm due to sexual harassment. [4] Polyandrous females encounter sexual harassment when courted by males resulting to be costly to females. In order to reduce the costs to the females, females will take part in polyandry. For example, in the bee species Anthidium maculosum , like in many other species, the high cost of resisting mating may exceed the cost of accepting numerous males in a breeding if copulating takes a short time, and therefore females in some species are inclined to being polyandrous. [16] In the polyandrous system, sexual coercion has been observed to be one of the major reasons for why females begin to mate with multiple males to outweigh the cost under different circumstances. [17] The sexual conflict hypothesis suggest that polyandry can occur due to sexual coercion [18] preventing females from obtaining any benefits. Sexual coercion has been seen in three different forms: forced copulation, sexual harassment, and intimidation. Forced copulation is seen in those males that cannot gain access to females for mating. As a result of the lack of access to mates, males are more likely to engage in sexually aggressive behaviors that could result in physical harm and death for females, as has been observed in elephant seals and ducks. Intimidation was seen in social primates, who coerce females into mating, therefore, pushing them to mate with their own aggressor. Males use intimidation as a method of punishment in females that do not mate with them. [17]
Sexual coercion has many benefits to males allowing them to mate, but their strategies pose high cost for females. [17] This has been observed in vertebrates like green turtles. [19] The green turtles is an example of a species that does not receive any possible benefit from polyandry and only uses it to reduce the cost of mating. [19] As for house mice, multiple male mating was observed even when females had the opportunity to select their mate without sexual coercion, showing that it was due to female choice. [18] In the fly Dryomyza anilis , females favor matings with quick oviposition. [20] D. anilis females can store sperm for at least two egg batches without their fertilization rate decreasing. Therefore, mating before each oviposition is not necessary. There is no significant overall benefit for females in multiple matings; large females are at an advantage due to their ability to resist unnecessary matings. [21]
As a result of multiple male mating, multiple paternities were observed in species as a result of convenience polyandry. [4] Convenience Polyandry Hypothesis is the assumption that there is a greater cost for females when, refusing male mating attempts than in choice mating. [22] It is the situation in which females adjust their mating rate to balance the costs of male harassment. It has been suggested that convenience polyandry would increase when females are weaker than males, decreasing the costs of sexual aggression. Convenience polyandry is seen in several arthropod species, like water striders ( Gerris buenoi ). [22]
Males that compete for more mating opportunities are the ones that have shown less cooperation in breeding. However, there are other males that in order to gain access to females and mating opportunities practice parental care. Such parental care is mostly seen in polyandrous mating systems; but they must go through the cost of sharing paternity and parental care. This has been observed in avians like acorn woodpeckers (Melanerpes formicivorus), [12] and fishes as the cichlid fish (Julidochromis transcriptus). [23] Observations that show male relatedness suggest the importance for male social relationships in taking care of offspring. These social relationships in males are seen in primates, Geoffroy's tamarins, Saguinus geoffroyi. [24] High proportions of related males at the half sibling or higher were found. [24]
As for frog species, rhacaphorid frog ( Kurixalus eiffingeri ), is one of the few that is polyandrous and exhibits parental care of eggs. The male frogs sit on the egg clutches, maintaining contact with the eggs. [25] Parental care and males genetic contribution were found significantly correlated meaning that male frogs with a higher paternity attended their eggs far more significantly than those of partial paternity for the clutch. [25] Females that mate with more than one male obtain the aid of both and as a result of all three parents providing food and care to the offspring there is an increase in the survival of their young. The amount of help is determined based on mating share and paternity share. (Mating Systems, p 275)
In polyandrous mating it has been suggested that male cooperation may outweigh the costs of sharing paternity in situations of scarcity, of foods and of high competition levels for land or females. Female size and a large breeding territory defended by more males may force male cooperation. For males, such factors can promote an increase in reproductive success, leaving behind the cost of paternity share (Mating Systems, p277). Comb-crested jacana's (Irediparra gallinacea) has shown genetic evidence for paternity assurance. [26] The comb-crested jacana females had one to three more mates available for copulation. In order to guarantee paternity to their male mates, the females would spend time in the territory of the male, laying her eggs. [26]
Some taxa with high social organization are eusocial, meaning that a single female (e.g., the queen bee) or caste produces offspring while the other organisms (e.g., non-reproductive female worker bees) cooperate in caring for the young. Examples of mammalian eusociality include Damaraland mole-rats and naked mole-rats, [27] [28] among whom polyandry is the norm and polygyny has never been observed. [29]
Infanticide avoidance is one of the major reasons animals, like mammals, are inclined to choose polyandry. [30] Infanticide is observed to be the major cause of mortality in various mammals. Polyandry is thought to evolve from their offspring's vulnerability to infanticide. [31] There is evidence that polyandry is an effective strategy that is adapted by many to increase their offspring survival through the avoidance of male infanticide. Bank voles (Myodes glareolus) has supported the infanticide avoidance hypothesis where polyandrous females' offspring have a higher survival than monandrous females' offspring. [32]
High levels of multiple paternity have widely been seen and reported in snakes, marine turtles, [33] and lizards. [18] However, Lee and Hayes (2004) have evidence that suggests that there is no set data in green turtles that significantly shows that there are potential fitness gains through polyandry. Instead, it is suggested that the multiple mating is a result of male aggression. Both Wright [4] and Lee and Hayes studies exhibit similar results that show a lack of support of the indirect benefits of polyandry. In addition, they pose that there is no relationship between multiple paternity and reproductive success. Multiple male paternity is present in green turtles, but no significant fitness benefits have been found. Observations done on clutches showed that there was no correlation of reproductive success when mating with multiple males. [19]
Current research suggests that polyandry is the dominant social structure in the New World monkey family Callitrichidae. The Callitrichidae includes marmosets and tamarins, two groups of small New World monkeys found in South America. Wild groups usually consist of three to ten individuals, with one reproductively active female, one or more reproductive males, and several nonreproductive helpers that can be either male or female. Cooperative polyandry is not the only mating system found in these primates. Polyandrous, monogamous, and polygynous groups can be found within the same population, and a group can even change mating systems, making it the most flexible mating system of any non-human primate. [34] Unlike most primates who typically give birth to single young, twins are the average litter size for tamarins and marmosets. The entire group participates in raising the offspring, sharing the responsibilities of infant carrying, feeding, and grooming. The presence of nonreproductive helpers appears to be the most important factor in determining which mating system is used, as ecological and environmental variability have not been found to have a significant impact. Goldizen (1987) proposed the hypothesis that monogamy in Callitrichidae should develop only in groups with nonreproductive helpers to help raise the young, and in the absence of these helpers, both polyandrous males and females would have higher reproductive success than those in lone monogamous pairs. Indeed, in studies of Saguinus fuscicollis, common name saddle-back tamarin, no monogamous lone pairs have ever been seen to attempt a breeding cycle. [35]
The green-veined white is a butterfly of the family Pieridae.
Polygynandry is a mating system in which both males and females have multiple mating partners during a breeding season. In sexually reproducing diploid animals, different mating strategies are employed by males and females, because the cost of gamete production is lower for males than it is for females. The different mating tactics employed by males and females are thought to be the outcome of stochastic reproductive conflicts both ecologically and socially.
A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to animals, the term describes which males and females mate under which circumstances. Recognised systems include monogamy, polygamy, and promiscuity, all of which lead to different mate choice outcomes and thus these systems affect how sexual selection works in the species which practice them. In plants, the term refers to the degree and circumstances of outcrossing. In human sociobiology, the terms have been extended to encompass the formation of relationships such as marriage.
Sperm competition is the competitive process between spermatozoa of two or more different males to fertilize the same egg during sexual reproduction. Competition can occur when females have multiple potential mating partners. Greater choice and variety of mates increases a female's chance to produce more viable offspring. However, multiple mates for a female means each individual male has decreased chances of producing offspring. Sperm competition is an evolutionary pressure on males, and has led to the development of adaptations to increase male's chance of reproductive success. Sperm competition results in a sexual conflict between males and females. Males have evolved several defensive tactics including: mate-guarding, mating plugs, and releasing toxic seminal substances to reduce female re-mating tendencies to cope with sperm competition. Offensive tactics of sperm competition involve direct interference by one male on the reproductive success of another male, for instance by mate guarding or by physically removing another male's sperm prior to mating with a female. For an example, see Gryllus bimaculatus.
Animal sexual behaviour takes many different forms, including within the same species. Common mating or reproductively motivated systems include monogamy, polygyny, polyandry, polygamy and promiscuity. Other sexual behaviour may be reproductively motivated or non-reproductively motivated.
Monogamous pairing in animals refers to the natural history of mating systems in which species pair bond to raise offspring. This is associated, usually implicitly, with sexual monogamy.
Sexual conflict or sexual antagonism occurs when the two sexes have conflicting optimal fitness strategies concerning reproduction, particularly over the mode and frequency of mating, potentially leading to an evolutionary arms race between males and females. In one example, males may benefit from multiple matings, while multiple matings may harm or endanger females, due to the anatomical differences of that species. Sexual conflict underlies the evolutionary distinction between male and female.
Sexual cannibalism is when an animal, usually the female, cannibalizes its mate prior to, during, or after copulation. It is a trait observed in many arachnid orders, several insect and crustacean clades, gastropods, and some snake species. Several hypotheses to explain this seemingly paradoxical behavior have been proposed. The adaptive foraging hypothesis, aggressive spillover hypothesis and mistaken identity hypothesis are among the proposed hypotheses to explain how sexual cannibalism evolved. This behavior is believed to have evolved as a manifestation of sexual conflict, occurring when the reproductive interests of males and females differ. In many species that exhibit sexual cannibalism, the female consumes the male upon detection. Females of cannibalistic species are generally hostile and unwilling to mate; thus many males of these species have developed adaptive behaviors to counteract female aggression.
The sexy son hypothesis in evolutionary biology and sexual selection, proposed by Patrick J. Weatherhead and Raleigh J. Robertson of Queen's University in Kingston, Ontario in 1979, states that a female's ideal mate choice among potential mates is one whose genes will produce males with the best chance of reproductive success. This implies that other benefits the father can offer the mother or offspring are less relevant than they may appear, including his capacity as a parental caregiver, territory and any nuptial gifts. Fisher's principle means that the sex ratio is always near 1:1 between males and females, yet what matters most are her "sexy sons'" future breeding successes, more likely if they have a promiscuous father, in creating large numbers of offspring carrying copies of her genes. This sexual selection hypothesis has been researched in species such as the European pied flycatcher.
Drosophila pseudoobscura is a species of fruit fly, used extensively in lab studies of speciation. It is native to western North America.
The red flour beetle is a species of beetle in the family Tenebrionidae, the darkling beetles. The red flour beetle, and other closely related beetles like the Gnatocerus cornutus, are a worldwide pest of stored products, particularly food grains, and a model organism for ethological and food safety research.
Monogyny is a specialised mating system in which a male can only mate with one female throughout his lifetime, but the female may mate with more than one male. In this system, the males generally provide no paternal care. In many spider species that are monogynous, the males have two copulatory organs, which allows them to mate a maximum of twice throughout their lifetime. As is commonly seen in honeybees, ants and certain spider species, a male may put all his energy into a single copulation, knowing that this will lower his overall fitness. During copulation, monogynous males have adapted to cause self genital damage or even death to increase their chances of paternity.
Bateman's principle, in evolutionary biology, is that in most species, variability in reproductive success is greater in males than in females. It was first proposed by Angus John Bateman (1919–1996), an English geneticist. Bateman suggested that, since males are capable of producing millions of sperm cells with little effort, while females invest much higher levels of energy in order to nurture a relatively small number of eggs, the female plays a significantly larger role in their offspring's reproductive success. Bateman's paradigm thus views females as the limiting factor of parental investment, over which males will compete in order to copulate successfully.
Polygyny is a mating system in which one male lives and mates with multiple females but each female only mates with a single male. Systems where several females mate with several males are defined either as promiscuity or polygynandry. Lek mating is frequently regarded as a form of polygyny, because one male mates with many females, but lek-based mating systems differ in that the male has no attachment to the females with whom he mates, and that mating females lack attachment to one another.
Sexual selection in mammals is a process the study of which started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, consisting of male–male competition and mate choice that mold the development of future phenotypes in a population for a given species.
Sexual selection in scaled reptiles studies how sexual selection manifests in snakes and lizards, which constitute the order Squamata of reptiles. Each of the over three thousand snakes use different tactics in acquiring mates. Ritual combat between males for the females they want to mate with includes topping, a behavior exhibited by most viperids in which one male will twist around the vertically elevated fore body of its opponent and forcing it downward. It is common for neck biting to occur while the snakes are entwined.
Sexual selection in amphibians involves sexual selection processes in amphibians, including frogs, salamanders and newts. Prolonged breeders, the majority of frog species, have breeding seasons at regular intervals where male-male competition occurs with males arriving at the waters edge first in large number and producing a wide range of vocalizations, with variations in depth of calls the speed of calls and other complex behaviours to attract mates. The fittest males will have the deepest croaks and the best territories, with females making their mate choices at least partly based on the males depth of croaking. This has led to sexual dimorphism, with females being larger than males in 90% of species, males in 10% and males fighting for groups of females.
Polyandry in fishes is a mating system where females mate with multiple males within one mating season. This type of mating exists in a variety of animal species. Polyandry has been found in both oviparous and viviparous bony fishes and sharks. General examples of polyandry occur in fish species, such as green swordtails and Trinidadian guppies. Specific types of polyandry have also been classified, such as classical polyandry in pipefish cooperative polyandry in cichlids and convenience polyandry in sharks.
Extended female sexuality is where the female of a species mates despite being infertile. In most species, the female only engages in copulation when she is fertile. However, extended sexuality has been documented in Old World primates, pair bonded birds and some insects. Extended sexuality is most prominent in human females who exhibit no change in copulation rate across the ovarian cycle.
Primate sociality is an area of primatology that aims to study the interactions between three main elements of a primate social network: the social organisation, the social structure and the mating system. The intersection of these three structures describe the socially complex behaviours and relationships occurring among adult males and females of a particular species. Cohesion and stability of groups are maintained through a confluence of factors, including: kinship, willingness to cooperate, frequency of agonistic behaviour, or varying intensities of dominance structures.