page_title: Sexual selection in mammals
section_title: Male-male competition
hierarchical_section_title: Sexual selection in mammals / Precopulatory mechanisms / Male-male competition
caption_attribution_description: A mating plug in a female Richardson's ground squirrel (Spermophilus richardsonii)
context_page_description: Sexual selection in mammals 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.
context_section_description: Male-male competition to copulate with the opposite sex is 
  often seen in mammals. African elephants strongly promote male-male competition. Elephants continuously grow throughout their lifetime. As males grow older, they also experience increasing lapses of musth, a violent sexual excitement, and most reproductive success happens to males in musth as it helps them win fights. A fight between a male in musth and one not can result in the death of the latter.
  Species with intense male-male competition are known to exhibit the most size dimorphism. For example, female American black bears (Ursus americanus) are 20–40% smaller than males.
  Male mammals can compete for harems as well with elephant seals competing fiercely for harems. As mammals reach sexual maturity, secondary sexual characteristic arise. Elephant seals have a proboscis in the adult male, which is used to project loud noises, frequently heard during the mating season. Elephant seals with a bigger proboscis emit lower sounds than males with a smaller proboscis and are the bigger of the males in a colony.
  Mate-guarding is an important factor in male-male competition to ensure fertilization of an offspring, and, when successful, helps to overlook and court the female. It especially prevents sperm competition from occurring as it ensures reproductive success. This process can be engaged when a post-coital signal is sent to a male to keep guard by the female. Mating plugs are a form of mate-guarding that have proved to show precopulatory female choice. Copulatory plugs are commonly acellular and thought to be made by proteins from the seminal vesicles. DNA taken from copulatory plugs show females deter from mating with close relatives.
caption: Mating plug
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