Topic 11. Mating Systems and BehaviorMating systems are not the same thing as mating behavior. Mating system: The social associations and number of sexual partners an individual has during one breeding season.Mating systems have been categorized as follows:Monogamy – 1 male and 1 femalePolygyny – 1 male and multiple femalesPolyandry – 1 female and many malesPolygynandry – many males and many females with social associationsPromiscuity – many males and many females without social associationsRemember: We avoid the term “polygamy” in animal behavior.The type(s) of mating systems shown by animals is very much the result of sexual conflict and resource distribution.Sexual conflict: differential selection on males and females to maximize fitness. This is summarized by the general observation that male reproductive success is limited by access to females, whereas female reproductive success is limited by her ability to produce gametes – translating usually in her ability to acquire resources to support health and safety. This is the so-called “trickle down” effect of reproductive success.Resource distribution: Depending on how resources are distributed in an environment, and given that females are accessing or in close proximity to resources, males might be able to monopolize the reproductive output of many females simultaneously (resources clumped) underlying the evolution of a polygynous mating system. Conversely, if resources are distributed homogenouslythroughout the environment and females are attracted to the resources, males mightnot be able to monopolize multiple females simultaneously, and this could lead to the evolution of monogamy or at least mate guarding.The importance of resource distribution in the evolution of mating systems was exemplified by the Grey-sided Vole experiment in Norway.MONOGAMY. Favored to evolve when:Biparental care is present and increases reproductive success (many bird species)Territorial or mate guarding increases reproductive success. (snapping shrimp example)POLYGYNY. Can result if males are defending either females directly (Female defense polygyny), and/or resources (Resource defense polygyny), in which case they can monopolize females who are attracted to the resources. (In some cases, male dominance hierarchies will result in the dominant male receiving the majorityof reproductive opportunities. This is the case in lekking behavior where males aredefending neither females nor resources. Remember that, unlike territories, leks donot have resources necessary for sustained living.)Female defense polygyny. Male wild horses defend 3-12 females simultaneously, but bands of horses occupy the same home ranges. Thus showing that the males are defending the females directly and sharing resources.Resource defense polygyny. Large male carrion beetles that were capable of defending larger or more resources had greater reproductive success than small males. Female fitness was not affected by whether she was large or small.Females will sometimes have a “choice” about whether they enter into a monogamous relationship or share a male with another female in a polygynous relationship. This is shown by the Polygyny threshold model. A monogamous female can have the same fitness level as a polygynous female if the territory quality is significantly better in the polygynous mating system. The Lark Buntingsand Prothonotary Warblers can switch from monogamy to polygyny and vice versadepending on the territory quality.POLYANDRY. (Much less common than polygyny). Since in many cases the males are left to take care of the offspring, this system may be favored to evolve in resource-poor environments or where predation on offspring is high. The Wattled Jacana bird is one of the best examples of polyandry. Eusocial insects such as bees, wasps, and ants that have a “queen” also show polyandry.Thornhill and Alcock (1983) list a number of possible advantages to adopting a polyandrous mating system. (They are primarily insect researchers.)Sperm replenishmentMaterial benefits (They consider this to be the most likely reason)Genetic benefitsConveniencePOLYGYNANDRY. Social associations are formed between multiple males and multiple females. European badgers show this mating system. Dunnock birds can change their mating systems from year to year because female territory size varies depending on the availability or quality of resources. In a goodyear with abundant resources, females will have small territories; conversely, in a bad year, females will have large territories in order to have all the resources necessary for sustained living. Males, who show up to the breeding grounds after the females, generally will always have the same sized territories. So the male territories can encompass 1 female (monogamy), multiple females (polygyny), overlap other male territories with only 1 resident female (polyandry), or multiple males and multiple female territories overlap (polygynandry).PROMISCUITY (Scramble Competition). Likely evolves when costs exceed benefits in defense of mates or resources, and there is no need for biparental care. Garter snakes emerging from hibernacula is an example.SOCIAL mating systems are not the same thing as GENETIC mating systems. When DNA paternity testing is done, it is obvious that there is a considerable amount of Extra-Pair Copulations (EPCs) occurring. This is especially seen in supposedly monogamous species, such as birds. (Remember that swallow males can break up EPCs by producing false alarm calls.)Sperm Competition. The most direct example of male-male competition since it specifically results in the fertilization of an egg. Some males have an advantage infertilizing eggs by being the last to copulate with a female (dungflies) or the first (chickens and some other bird species).Primate sperm competition or male-male conflict competition affects sexualdimorphism and the mating system or vice versa. Species differences can be seen in the testes/body size ratios. Testes size is positively correlated with the amount of sperm a male can produce. In primates with polygynous mating systems (Gorillas), the males engage in combat with each other to monopolize the reproduction of several females – this has resulted in a large sexual dimorphism in body size, but reduced testes size since they do NOT compete on the level of the sperm and thus do not need copious amounts of sperm. On the other