Polyandrous mating systems are uncommon in the animal kingdom, particularly in primates. Females fight for access to several men in classic or serial polyandry, and after mating with a single male, they abandon the male and their children altogether. Several seahorse species use this mating strategy. Female mates with numerous guys stay with them for an extended time, and all parents raise the kids together in cooperative or simultaneous polyandry.
This is sometimes seen as a secondary mating strategy to monogamy in tamarins and marmosets. Several females will mate with multiple males in a few species, and all parents will raise the children jointly. These systems are known as polygynandrous, albeit this mating type is highly unusual.
The phrases polygamy, polygyny, and polyandry are frequently incorrectly used interchangeably. Nevertheless, the practice of having multiple husbands at once is referred to as polyandry. In its broadest sense, polyandry also refers to having numerous male companions at the same time while being unmarried to any of them. Much theoretical and empirical research on the development of polygamy and mate choice has been conducted in the last ten years.
The reproductive capability of females is more constricted, leading to an emphasis on offspring quality rather than quantity. At the same time, males benefit directly from multiple mating (e.g., a more significant quantity of offspring). So many theories have been put forth to explain polyandry in females.
Some contend that if being polyandrous enhances the likelihood of mating with a superior man, polyandrous females benefit genetically from having several mates, either through the genetic diversity of the kids produced or their improved quality. This justification suggests that women are picky and prefer polyandry. Others contend this could lead to a sexual dispute over the number of partners because the greater optimal level of polygyny will likely differ from the lower optimal level of polyandry. As a result, females evolve countermeasures to boost their fitness to the cost of males, and males gain fitness by manipulating females (hence decreasing the fitness of those manipulated females).
Women frequently look for casual partners. Why would a woman be married to a man who is not likely to assist her in giving birth and raising their children? Fisher (1930) suggested that men who could contribute high-quality genes encouraging health, attractiveness to the opposite sex, and ultimately reproductive success would benefit women's progeny.
According to the related "sexy son hypothesis," when getting a trustworthy father investment is improbable, women have evolved preferences for males with phenotypic markers of high genetic quality above those with cues of high potential parental investment.
In exchange for the provision of resources, women may also engage in brief sexual intercourse with males, particularly if they are raising children and require investment. Women frequently engage in sexual activity with men who are not their social partners in South America's Ache and Bar communities, particularly after becoming pregnant. The fact that these men now have a societal obligation to care for and support the woman's children as their secondary fathers may contribute to muddying the paternity issue. These efforts consequently increase the survival rate of the kids.
Although monogamy may lessen infanticide and predation in some situations, the benefits of having numerous partners include access to additional resources, such as getting multiple wedding gifts and improved protection against infanticide through paternity dilution. Some benefits of polyandry are −
Indirect genetic advantages of having numerous partners include, for instance, the potential to "trade-up" when meeting a higher quality partner and giving birth to offspring who are more viable, sexually alluring, or genetically varied. Also, having multiple partners lowers the likelihood of total reproductive failure brought on by exclusive mating with an infertile partner or a partner with bad genetics. Genetic benefits are the next-generation advantages of mating with several genetically diverse males.
In essence, polyandry may be a bet-hedging strategy whereby females deliberately seek out a range of males to increase genetic diversity and mean offspring fitness while decreasing the likelihood of mating with genetically inferior, sterile, or incompatible partners.
By providing direct benefits to females who mate with numerous males, bet-hedging has the potential to play a significant role in the evolution of polyandry. For instance, a mutation that makes a female more likely to reproduce frequently may result in acquiring a direct or genetic gain just by spreading the risk. This benefit of bet-hedging could be enjoyed by females who randomly mate with several males.
Multiple mating would guard against the risk of unsuccessful reproduction (zero fitness) brought on by male infertility issues or low genetic quality and genetic compatibility resulting in non-viable offspring. Multiple mating can provide these bet-hedging benefits to females without mate selection or male-male competition, either directly or genetically.
Polyandry can increase the viability of the progeny by bet-hedging, at least in terms of increased frequencies of fertilization when the gametes from various guys are combined. According to a study, polyandrous females' eggs hatched with a success rate that was 2.4 times higher than that of monandrous or control females. The coefficient of variation (CV) for polyandry was approximately 41% lower than the other treatments and had a higher hatching success, indicating that polyandry serves as a bet-hedging tactic to lessen the likelihood of an unsuccessful mating with infertile or genetically incompatible males.
Because polyandry expands the options for sexual selection (female choice and male-male rivalry) beyond mating, it has significant evolutionary and ecological ramifications. Polyandry creates a robust selection for male and female adaptations that let people overcome paternity biases by promoting post-copulatory sexual selection.
Understanding why females mate several times in the face of the well-established direct (and indirect ;) costs of mating remains a significant difficulty despite the extensive theoretical and empirical attention paid to polyandry, including its effects on population extinction and conservation. Most research on this issue examines whether females gain from several matings, either directly by boosting reproductive success or indirectly by increasing social status.
Contrarily, female mating rate variation may be nonadaptive if it originates from convenience polyandry brought on by interlocus sexual conflict or through indirect selection on males due to intersexual genetic connection in mating behaviour.
When females use a multiple mating bet-hedging approach, there is potential for them to gain fitness through genetic advantages. They also show that sexual selection can enhance these advantages. These findings indicate that more research is needed to determine the factors underlying sustained polyandrous behavior.
We hope that our research inspires more research combining the ecological principles, such as the function of environmental fluctuation, that underlie the evolution of polyandry.
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