Meeting Abstract
61.5 Wednesday, Jan. 6 Maternally-induced developmental conditions predict the shape of a songbird’s bill, a sexually and naturally selected trait SOCKMAN, K.W.; Univ. of North Carolina, Chapel Hill kws@unc.edu
The bill is an adult songbird’s most important tool, but the underlying sources of the between-individual variation in this trait on which both natural and sexual selection act are largely unknown. Due to the possibility that the massive change in bill morphology between the nestling and adult life stages is limited by developmental plasticity and to the often strong individual differences in selective forces that characterize the nestling period of development, I predicted that adult bill shape reflects nestling bill shape and that variation between nestlings arises due to hatching order and the seasonal timing of development. Using Lincoln’s sparrows (Melospiza lincolnii), I measured individuals as free-living nestlings and later as free-living or as laboratory-housed adults for a metric of bill shape (height/width) that is associated with an adult Lincoln’s sparrow’s performance of vocal, sexual signals. I found that bill shape during the nestling stage positively correlated with that during the adult stage for both free-living and laboratory-housed adults. I also found that nestling bill shape declined with hatching order and that the bill shape of both nestlings and laboratory-housed adults declined with the individual’s seasonal timing of development. These findings suggest that maternally induced developmental conditions may influence the value of a sexually and naturally selected trait. Nestlings may vary in bill shape either for adaptive (e.g., wider bills may be more favored among later-hatching offspring as a means of competing for food with older brood mates) or non-adaptive (bill shape may reflect differences in developmental constraints, such as nutritional deprivation) reasons, and such variation may explain the persistence of suboptimal bill shapes among adult songbirds in the presence of strong stabilizing or directional selection.
