Polygyny (; from Neo-Greek πολυγυνία, from πολύ- (polú-) 'many' and γυνή (gunḗ) 'woman, wife') is a mating system in which one male lives and mates with multiple females but each female only mates with a few males. 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. Polygyny is typical of one-male, multi-female groups and can be found in many species including: elephant seal, spotted hyena, gorilla, red-winged prinia, house wren, hamadryas baboon, common pheasant, red deer, Bengal tiger, Xylocopa sonorina, Anthidium manicatum and elk. Often in polygynous systems, females will provide the majority of parental care.
Mating systems
When two animals mate, they both share an interest in the success of the offspring, though often to different extremes. Unless the male and female are perfectly monogamous, meaning that they mate for life and take no other partners, even after the original mate's death, the amount of parental care will vary. Instead, it is much more common for polygynous mating to happen. Polygynous structures (excluding leks) are estimated to occur in up to 90% of mammals. Polygyny in birds occurs infrequently when compared to mammals, as monogamy is most commonly observed. Evolutionarily speaking, polygyny in birds might have evolved because many females do not require male support to care for their offspring. Because females do not need extra help raising their nests, males can afford to invest in multiple females. Nonetheless, male parental care is often found in many polygynous territorial bird species, leading to female competition for male assistance. Most often, males will seek a second female to impregnate, once the first female has laid her eggs. Strongly polygynous or monogamous species display increased female–female aggression. Many factors affect female aggression including predator density, habitat quality, nest spacing, and territory size. Often, females will fight for resources from the male, such as food and nest protection. The female disadvantages of mating with an already-mated male bird can be overcome with ample resources provided by the male, resulting in female choice.
Emlen and Oring mating systems model In 1977, Stephen T. Emlen and Lewis W. Oring created a mating systems model that shows how resource distribution affects female living patterns and subsequently, mating systems. In a mating system, the limiting sex (usually females) is the one that the limited sex (usually males) tries to monopolize. The combination of resource distribution, parental care, and female breeding synchrony determines what mating strategies the limited sex will employ. Polygyny will occur when resources are localized and females form clusters, making it easier for males to control them. The various types of polygyny result because of the differential access individuals have to resources.
Types of polygyny When females continually move and are not spatially stable, males pursue a mate defense strategy. When the females are clumped, four types of polygyny occur.
(Adapted from Dr. Susan Alberts) When females are spatially stable in and around a resource, males pursue a resource defense strategy and polygyny occurs when the females are clumped and the offspring require little to no parental care (e.g. yellow-bellied marmots, orange-rumped honeyguides).
Costs and benefits for males
Costs In polygynous systems there is less genetic diversity due to the fact that one male sires all of the offspring. Additionally, it is difficult for males to monopolize many females at once, leading to extra-pair copulations in which a few females are able to mate with another male, while not being watched by the breeding male. (Some studies also show that EPC is less common in polygyny compared to monogamy.) These breeding males also have short tenure, and it is common for groups of males who do not have harems to attack a breeding male in order to gain reproductive access to his females. In some cases, polygyny can lead to aggression between males. An example of species that exhibit male-male aggression under polygynous system is Allobates femoralis. Physical aggression can be induced by territorial defense and competition in courtship. Especially, during the courtship march, a competing male can intercept the female while the male who originally courted the female searches for an oviposition site. In this case, the physical aggression between males can last about 15 minutes until one of the males leave the site.
Benefits The largest advantage for males in a polygynous mating system is the increased fitness and reproductive success of the lone male because he will father all the offspring. Being the sole male of a harem is highly advantageous for the male because he has a much higher chance of his progeny surviving, which means he is passing on his genes to more individuals.
Costs and benefits for females
Costs Due to the fact that one male sires all of the offspring there is less genetic diversity in the community, which is disadvantageous to females. Additionally, females sometimes encounter infanticide, which is when a breeding male is overthrown and a new breeding male becomes dominant and kills all of their current offspring, as he has not fathered them. Because the females no longer have offspring to nurse, they will go into estrous sooner, which allows the new breeding male to mate with the females earlier.
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