Abstract
Changes in the mean and variance of phenotypic traits like wing and head morphology are frequently used as indicators of environmental stress experienced during development and may serve as a convenient index of urbanization exposure. To test this claim, we collected adult western honey bee (Apis mellifera Linnaeus 1758, Hymenoptera, Apidae) workers from colonies located across an urbanization gradient, and quantified associations between the symmetries of both wing size and wing shape, and several landscape traits associated with urbanization. Landscape traits were assessed at two spatial scales (three km and 500 m) and included vegetation and anthropogenic land cover, total road length, road proximity and, population and dwelling density. We then used geometric morphometric techniques to determine two wing asymmetry scores—centroid size, a measure of wing size asymmetry and Procrustes distance, a measure of wing shape asymmetry. We found colony dependent differences in both wing size and shape asymmetry. Additionally, we found a negative association between wing shape asymmetry and road proximity at the three km buffer, and associations between wing shape asymmetry and road proximity, anthropogenic land cover and vegetation cover at the 500 m buffer. Whilst we were unable to account for additional variables that may influence asymmetry including temperature, pesticide presence, and parasitism our results demonstrate the potential usefulness of wing shape asymmetry for assessing the impact of certain landscape traits associated with urbanization. Furthermore, they highlight important spatial scale considerations that warrant investigation in future phenotypic studies assessing urbanization impact.
Highlights
The unique interplay between humans and the environment in cities generates novel anthropogenic stressors such as artificial lighting, air pollution, and elevated temperatures that can profoundly affect organisms at multiple levels of biological organization (Johnson & Munshi-South, 2017; Williams, Hahs & Vesk, 2015; Alberti, Marzluff & Hunt, 2017)
Measurement error and directional asymmetry Technical error of measurement was small for both wing size and shape
Overall the present results indicate wing shape asymmetry in western honey bees may be related to how proximal colonies are to roads and depending on the spatial scale considered (e.g. 500 m vs. three km), other habitat variables including vegetation area and anthropogenic land area
Summary
The unique interplay between humans and the environment in cities generates novel anthropogenic stressors such as artificial lighting, air pollution, and elevated temperatures that can profoundly affect organisms at multiple levels of biological organization (Johnson & Munshi-South, 2017; Williams, Hahs & Vesk, 2015; Alberti, Marzluff & Hunt, 2017). Such anthropogenic stressors can induce physiological responses such as cell death (Lodovici & Bigagli, 2011), and elevate stress hormone concentrations Given the large number of anthropogenic stressors present in cities and the magnitude with which they affect species, it is imperative we find sensitive indicators (i.e. biomarkers) that can detect detrimental effects before populations are irreversibly impacted
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