Polygyny in animals

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. 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. ==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. 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. A polygynous leader male will always be the best mating choice before he is beaten by another male, so it is harder for females to find a partner better than their mate in polygyny as compared to monogamy. This might reduce the number of females at risk for EPC once their mate finds out. ==Polygyny threshold model==

graph An explanation for why polygynous systems persist is explained by the polygyny threshold model. This model demonstrates the link between female reproductive success and territory quality or the quality of a breeding situation. The polygyny threshold model also shows the effects of female reproductive success when multiple females in the same territory mate with one male. In this situation, the female has the option of breeding with an unmated male in a poor-quality territory or with an already-mated male in a high-quality territory. The second breeding female will receive fewer resources from the male than the first breeding female. However, if the bigamous threshold is higher than the second female's original resource threshold, the female will enter into a polygynous mating system, since she would still benefit from acquiring more resources. The polygyny threshold model can be applied to more than two females, provided there are enough resources to support them. Although highly debated, female choice in the great reed warbler may be explained by the good genes theory. False paternity and decreased offspring survival are two factors which might contribute to a decrease in male fitness. ==Evolutionary significance==

From an evolutionary standpoint, the most predominant characteristic that is often found in polygynous mating systems is extreme sexual dimorphism. Sexual dimorphism, or the difference in size or appearance between males and females, gives males an advantage in fights against each other to demonstrate dominance and win over harems. Sexual dimorphism can present in larger body size and canine size. Female Coquerel's sifaka (Propithecus coquereli) mate with the winners of battles for the harem because the male has shown that he is stronger than another, potentially offering more protection from predators. Female red-winged blackbirds (Agelaius phoeniceus) exhibit aggression toward other females upon intrusion into the harem, usually heightened around breeding season. This behavior demonstrates that the females are protecting their breeding male from intruding females, suggesting they are preventing female access to a desirable mate. ==See also==