Chapter 6-7

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  • Topic: Reproduction, Sexual dimorphism, Kin selection
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Chapter 6: Primate Mating Systems
A. The language of Adaptive Explanations
Biologists often use the term “Strategy” to describe the behavior of animals. However, “strategy” refers to a set of behaviors occurring in a specific functional context (such as mating, parenting, or foraging). This led to greater reproductive success in ancestral populations have been favored by natural selection and represent adaptations. Costs and Benefits of some Strategies

(+) If they increase the genetic fitness of individuals
(-) If they reduce the genetic fitness of individuals
B. The Evolution of Reproductive Strategies
Primates provide much more resources to their young (males in some species). In species without parental care, females produce large, nutrient rich gametes. Males produce small gametes and supply only genes. Many males do not care for their offspring

They can have more offspring if they have sex with more females When caring for young, it does not increase their fitness
These males are either the “investing” or “non-investing” type of father Primate females have to commit in their offspring
In primates, and other mammals, selection tends to favor low male investment because females lactate and males don’t. C. Reproductive Strategies of Females
Primates have considerably longer pregnancies than smaller animals This is because brain tissue develops extremely slowly.
Females reproductive success depends on the ability to acquire resources They must achieve a minimum nutrition level in order to ovulate and conceive. Limited amount of resources in habitat which can allow them to: grow faster, mature early, and give birth at shorter intervals Sources of variation in female reproductive performance

Primiparous= primates who give birth for the first time
Very young and very old females do not have a high reproductive rate as middle aged females. Younger females may lack experience in handling newborn infants and may not provide proper care for them. High ranking females reproduce more

At times, females form dominance hierarchies (regulate access to resources). This might enable high ranking females to obtain larger quantities or higher quality than lower ranking females. These females are more vulnerable to predators. Some Multi-male/female groups of Old World monkeys, female dominance rank are correlated with various aspects of females’ reproductive performance. In captive, vervet groups, high ranking females have shorter birth intervals than lower ranking females. Marmoset and Tamarin groups in the wild have more than one adult female but the dominant one is the one who breeds successfully. Quality of Social Bonds Influence Reproduction

Social bonds matter to females because studies show they tend to: live longer, reproduce successfully, protection from predators, and reduced stress levels. Reproductive Trade-offs
Since mothers have a limited amount of effort into offspring, they can’t max quality and quantity of young they produce because infants need time and effort to develop. D. Sexual Selection and Male Mating Strategies

Males can produce progeny (offspring) from many females which makes males compete for females Darwin called this “sexual selection” because it favors traits that increase the animals’ attractiveness to potential mates. Sexual Selection is often stronger than natural selection

Has a greater effect on mammalian males on behavior and morphology because their reproductive success is different from females. Successful females might give birth to 5 to 10 offspring. Two types of Sexual Selection

Intersexual- when female chooses their mate (not too common). Intrasexual- favors traits that enhances success in male/male competition Most intense among males. The basic form of male/male competition is when males drive other males away from females. Males who win fights win females and female groups.

Sexually dimorphic- 2 sexes consistently differ in size or appearance Males compete over...