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Mating Systems

• Mating systems in animals are highly variable with several types observed.
• Monogamous mating system: one male mates with one female, and one female mates with one male during a breeding season.
• Raises a question: Why would males exhibit monogamous behavior?
  • This is considered a Darwinian puzzle, as typically males would maximize their reproductive success by mating with multiple partners.

Extrapair Paternity (EPP)

• Defined as offspring conceived with another male outside the primary mate relationship.
• Over 30 years of research has yielded more than 500 studies across 300+ bird species.
• EPP rates vary widely (0% to >80% EPF or extra-pair fertilization, and 0% to >90% EPB or extra-pair broods).

Examples of Extra-Pair Paternity Rates

• Hooded Warbler: 40% EPP
• Common Yellowthroat: 30% EPP
• Superb Fairy-wren: 70% EPP

Genetic Mating Systems

• Social monogamy does not equal genetic monogamy: a socially monogamous pair may not necessarily be genetically monogamous due to practices like extrapair mating.
• High costs of infidelity can occur, including reduced reproductive success and potential relationship breakdown (divorce).
• Factors influencing female choice to mate with multiple males include:
  • Compatible genes hypothesis: offspring fitness may increase with diverse parental gene combinations.
  • Good genes hypothesis: females may seek males with superior genetic qualities to improve offspring fitness.

Polygyny

• Defined as when a male has more than one social mate (e.g., elephant seals, elk).
• Males' ability to monopolize multiple females depends on female distribution and resource availability. This can be influenced by:
  • Predation pressure
  • Distribution of food sources
  • Aggregation of females at certain resource patches.

Costs and Benefits of Polygyny for Females

• Females may share a male to access better quality territories or resources, leading to the Polygyny Threshold Model's predictions:
  • A female may choose to accept sharing a male if the benefits outweigh the costs.
  • Costs may include reduced reproductive outcomes when another female is present in the territory.
• A female’s choice may hinge on having a superior territory compared to other unmated males.

Polygyny Threshold Model Assumptions and Predictions

• Assumptions:
  • There is a cost to polygyny, affecting the reproductive success of females sharing males.
  • Female success is related to the quality of territory or male resources.
• Predictions:
  • Females will trade off the costs against the possible benefits of superior territories.
  • They will accept polygyny only if compensated with a better territory than that of unmated alternatives.

Red-Winged Blackbird Case Study

• In marshy habitats, male Red-winged Blackbirds establish territories where females build nests among cattail shoots, with deeper water providing better protection from predators.
• When faced with polygyny, a female must choose between:
  • Sharing a male on a high-quality territory (A) or
  • Mating monogamously on a lower-quality territory (B).
• Females maximize reproductive success by selecting the better option based on territory quality.

Quality of Breeding Situations

• Females assess the territory quality in relation to available males when choosing a mate.
• Inevitably, it can lead to scenarios where both polygynous and monogamous males coexist in a breeding context, causing variations in female reproductive strategies based on available resources and territorial advantages.