“Divorce in an island bird population: causes, consequences, and lack of inheritance”

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Nathaniel T. Wheelwright and Céline Teplitsky

Adult Savannah sparrow.
(Credit: Drew Fulton)

In birds that form pair bonds, divorce occurs when both members of a pair survive to breed again but no longer remain social mates. What drives mate-switching? Does rejecting one’s partner in favor of another improve a bird’s lifetime reproductive success? Is divorce a heritable trait whose transmission is influenced by genes or culture? Nat Wheelwright (Bowdoin College, Brunswick, ME, USA) teamed up with Céline Teplitsky (Centre d’Écologie Fonctionnelle et Évolutive, Montpellier, France) to try to answer these questions in a wild bird population, taking advantage of a long-term study of Savannah sparrows (Passerculus sandwichensis) breeding on Kent Island, New Brunswick, Canada.

Eight-day-old nestling Savannah sparrow.
(Credit: Nat Wheelwright)

Divorce is commonplace among Savannah sparrows: Over an 18-year period, nearly half of all pairs split. One female sparrow accumulated five divorces over her lifetime (only two fewer than the legendary American film actress Elizabeth Taylor). Females who had received relatively little parental assistance from their mates were more likely to divorce if they had had a poor breeding season or been paired with a small male. Divorce did not necessarily result in improved reproductive success for young females, although it did for older females. Young males (but not older males) suffered lower reproductive success following a divorce. Overall, the researchers found that natural selection for divorce was weak or non-existent. Although divorce was repeatable in females, a quantitative genetic analysis found no additive genetic variance underlying the trait or evidence of maternal or paternal effects. Divorce in Savannah sparrows appears to be a non-heritable, flexible behavior whose expression and consequences depend upon an individual’s sex, mating status, size, and age. Read the Article