Inbreeding as a strategy in subdivided populations.

Conditions that would favor inbreeding are developed for: 1) nonfamilial inbreeding within a deme versus outbreeding; 2) altruistic inbreeding by females versus outbreeding; 3) sib-mating versus outbreeding; and 4) sib-mating versus nonfamilial breeding within a deme. Inbreeding behavior is advantageous under certain conditions but depends on the types of mating, previous breeding history of the deme, rate of accumulation of inbreeding depression, and the cost of migration. In polygynous mating systems it is genetically more advantageous for males to migrate, because female emigration may 1) leave a related male with no mate or one fewer mate, or 2) force both male and female to risk the cost of migration. Nonfamilial breeding is always a better strategy than sib-mating given previous inbreeding within the deme. Even when the cost of migration is zero, inbreeding is favored if the coefficient of relationship among relatives is greater than the ratio of the probabilities of offspring inviability to offspring viability. -from Authors