Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 8306
Title: Natural selection on morphology varies among years and by sex in Magellanic penguins (Spheniscus magellanicus)
Author: Laura E. Koehn, Jeffrey J. Hard, Elaine P. Akst, P. D. Boersma
Publication Year: 2016
Journal: The Auk: Ornithological Advances
Volume: 133
Pages: 783-805
DOI: 10.1642/AUK-16-50.1
Keywords: morphology, heritability, selection, Magellanic penguins, animal model, reproductive success,

The evolution of morphology in a population reflects several factors, including the influence of environmental variability on natural selection. We estimated natural selection on and heritability of four individual morphological traits: bill length, bill depth, flipper length, and foot length, and two multivariate morphological traits, in adult Magellanic Penguins (Spheniscus magellanicus) at Punta Tombo, Argentina from 1983­–2010. We estimated heritability of morphology with parent-offspring regression and animal models, conditioning on sex because these penguins are sexually dimorphic. For the analysis of selection on each trait, we estimated both linear and quadratic selection gradients, based on the number of fledglings produced, for breeding males and females in each year. Estimates from animal models indicated that all six traits were heritable; in parent-offspring regressions, corresponding heritabilities were significantly higher in sons than daughters in 100% of tests. Over 28 years, we could not detect selection in 21 years for males and 21 years for females. For the years we did detect selection, the direction and intensity of selection on traits varied, and was especially variable for females. We detected selection on primarily multivariate body size but also on male bill sizes and female bill and foot length. Selection on male flipper and foot length and female bill depth was detectable only in relation to selection on body size. When there was selection in males, selection on body and bill sizes was mainly toward larger sizes and occurred in four of six years with high chick starvation. The absence of detectable selection on morphology in most years suggests that it is not tightly linked to fitness and that the dynamic environment where Magellanic Penguins live helps maintain morphological variation. The temporal variability in selection likely fosters stability of morphology through time, a pattern that might not be evident in short term studies.

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Theme: Recovery and rebuilding of marine and coastal species
Foci: Characterize the population biology of species, and develop and improve methods for predicting the status of populations.