title: Why are incubation periods longer in the tropics? A common-garden experiment with house wrens reveals it is all in the egg.
abstract: Incubation periods of Neotropical birds are often longer than those of related species at temperate latitudes. We conducted a common-garden experiment to test the hypothesis that longer tropical incubation periods result from longer embryo development times rather than from different patterns of parental incubation behavior. House wrens, one of few species whose geographic range includes tropical equatorial and temperate high latitudes, have incubation periods averaging 1.2 days longer at tropical latitudes. We incubated eggs of house wrens in Illinois and Panama under identical conditions in mechanical incubators. Even after factoring out differences in egg size, tropical house wrens still required 1.33 days longer, on average, to hatch. We conclude that parental attendance patterns do not account for latitudinal differences in incubation period but that some other as yet unmeasured factor intrinsic to the egg or embryo, or both, extends development time in the tropics.
authors.affiliation: Oak Creek Lab of Biology, Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331, USA. douglas.robinson@oregonstate.edu
authors.forename: W Douglas
authors.initials: WD
authors.lastname: Robinson
authors.forename: John D
authors.initials: JD
authors.lastname: Styrsky
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Payne
authors.forename: R Given
authors.initials: RG
authors.lastname: Harper
authors.forename: Charles F
authors.initials: CF
authors.lastname: Thompson
mesh_terms: D000818:Animals; D047108:Embryonic Development; D010063:Ovum / Q000502:physiology*; D020308:Songbirds / Q000196:embryology*; D014329:Tropical Climate