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). A common example of polyandrous mating can be found in the field cricket (Gryllus bimaculatus) of the insect order Orthoptera (containing crickets, grasshoppers, and groundhoppers). Polyandrous behavior is also prominent in many other insect species, including honeybees, the red flour beetle, the adzuki bean weevil, and the species of spider Stegodyphus lineatus. Polyandry also occurs in some mammals including primates such as marmosets and the marsupial genera Antechinus and bandicoots, and in around 1% of all bird species, such as jacanas and dunnocks, and in fish such as pipefish.
Predictors of polyandry It is theorized that polyandry is more prevalent in organisms where incompatibility is more costly, and where this incompatibility is more likely. The former is especially true in viviparous organisms. Where the cost of having a low-quality father is significant, however, an organism is less likely to be polyandrous.
Benefits and costs of mating for females 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. 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. In a meta analysis, including 10 different orders of insects, polyandry increased the production of eggs by females specifically in Lepidopterans and Orthopterans. Indirect benefits of mating for females can be gained through sperm competition to attain "good genes" (Good-sperm hypothesis), cryptic female choice, increased genetic quality, and genetic diversity. Females spiders (Pisaura mirabilis) store more sperm from gift-giving males suggesting that sperm storage is under female control through cryptic sperm choice. 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. Polyandry also works as evolutionary bet-hedging to avoid extinction of female lineage due to male infertility or mating failure (bet-hedging polyandry hypothesis). 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. Predictably, these hatchlings showed an increase in genetic variability compared to those sired by a single male. 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. 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. Multiple paternities within a single clutch is therefore considered an effective strategy to increase the reproductive success and fitness of female tortoises.
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