Mating Systems ZOL 313 June 11, 2008

Mating Systems Objectives Be able to characterize a given mating system as monogamy, polygyny, or polyandry. Understand how differences in the distribution of females and resources lead to different types of polygyny. Become familiar with hypotheses about the adaptive value of monogamy and polyandry and be able to generate hypotheses and predictions. ZOL 313 June 11, 2008

Types of Mating Systems Monogamy: One male mates with 2. Polygamy: One gender has multiple partners of the other gender. A. Polygyny: One male mates with B. Polyandry: One female mates with

Polygyny Most common mating system Types of Polygyny: Female defense polygyny Resource defense polygyny Scramble competition polygyny Lek polygyny The spatial distribution of _________ and __________ determines what type of polygyny a species will have.

Polygyny Female defense polygyny: One male directly defends several females. Occurs when: Example: Yellow-bellied marmot females live in groups of female relatives, one male will defend a group of females from other males. Prediction:

Polygyny Resource defense polygyny: One male acquires several mates that are attracted to resources he controls. Occurs when: What types of resources might males defend? Example: In an African cichlid fish, territorial males bring shells to their middens that females use as nest sites.

Polygyny Scramble competition polygyny: One male acquires several widely scattered mates by finding them before other males do. Occurs when: Example: Male ground squirrels have to search widely for females who are only receptive for 4-5 hours during the breeding season. Prediction: Males will spend more time searching for missing females

Example: Sage grouse lek Polygyny Lek polygyny: Groups of males gather at a common display site (lek) that females visit to select a mate. Occurs when: Why not just use scramble competition polygyny? Hotspot hypothesis Hotshot hypothesis Female preference hypothesis Example: Sage grouse lek

Polygyny Lek polygyny: Groups of males gather at a common display site (lek) that females visit to select a mate. Hotspot hypothesis: Males cluster at leks because Prediction: Leks should be located in areas with higher concentrations of nesting females.

Polygyny Lek polygyny: Groups of males gather at a common display site (lek) that females visit to select a mate. Hotshot hypothesis: Males cluster at leks because Prediction: The most successful location within a lek will change from year to year.

Polygyny Lek polygyny: Groups of males gather at a common display site (lek) that females visit to select a mate. Female preference hypothesis: Males cluster at leks because Prediction: Larger leks will attract more receptive females.

Polyandry Why might it be adaptive for a female to mate with more than one male? Polyandry provides females with ________ benefits. Fertility insurance hypothesis Good genes hypothesis Genetic compatibility hypothesis More resources hypothesis Better protection hypothesis Infanticide reduction hypothesis Not mutually exclusive. Polyandry may be adaptive in different species for different reasons.

Polyandry Polyandry provides females with genetic benefits. Fertility assurance hypothesis: Mating with multiple males Prediction: Gunnison’s prairie dog females who are more polyandrous will be more likely to become pregnant.

Polyandry Polyandry provides females with genetic benefits. Good genes hypothesis: Mating with multiple males Prediction: Yellow-toothed cavy females who mate with more than one male will have more surviving offspring. Prediction: Sons of sexually successful field crickets will be more attractive to females.

Polyandry Polyandry provides females with genetic benefits. Genetic compatibility hypothesis: Mating with multiple males It is usually better for offspring to be heterozygous. Prediction: In sand lizards, there should be a negative relationship between the genetic similarity of the male and female (bandsharing) and the amount of offspring a male sires.

Polyandry Polyandry provides females with material benefits. More resources hypothesis: Mating with multiple males Prediction: Female leaf beetles who mate multiply will lay the same number of eggs whether they mate with the same male or with different males.

Polyandry Polyandry provides females with material benefits. Better protection hypothesis: Mating with multiple males Male damselflies will protect females from harassment by other males after they have mated. Prediction: Female damselflies will mate with more males when they experience more harassment (at higher male densities).

Polyandry Polyandry provides females with material benefits. Infanticide reduction hypothesis: Mating with multiple males Example: Female langurs will copulate with multiple males, even when they are not ovulating. Infanticidal males that have copulated with a female generally leave her offspring alone.

Monogamy Why might it be adaptive for a male to mate with only one female? Mate assistance hypothesis Mate guarding hypothesis Female-enforced monogamy (monogamy is not adaptive for males) Not mutually exclusive. Monogamy may be adaptive in different species for different reasons.

Monogamy Mate assistance hypothesis: Monogamy is adaptive because Prediction: Male care greatly increases offspring survival in the California mouse.

Monogamy Mate guarding hypothesis: Monogamy is adaptive because Prediction: In bank swallows, males will be most attentive to their mates when they are fertile.

Monogamy Female enforced monogamy hypothesis: Monogamy is not adaptive for males Prediction: Male burying beetles will spend more time releasing mate-attracting pheromones when their first mates are prevented from stopping them.

Monogamy Example: Researchers exposed socially monogamous yellow-breasted chats to models of males and females of their own species and, as a control, a wren model. They measured the relative aggression of male and female yellow-breasted chats toward each of these models. Which of the three hypotheses for monogamy are the results consistent with?

Monogamy Social monogamy does not necessarily imply ________________. Extra pair copulations (EPCs) by both genders are very common. (Only 14% of bird species tested have true monogamy.) Benefits to males of EPCs: Benefits to females of EPCs: