Dryad
Published February 17, 2023 | Version v1
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Decoupling pioneering traits from latitudinal patterns in a North American bird experiencing a southward range shift

Authors/Creators

  • 1. Appalachian State University
  • 2. Indiana University

Description

  1. Eco-geographic rules describe spatial patterns in biological trait variation and shed light on the drivers of such variation. In animals, a consensus is emerging that 'pioneering' traits may facilitate range shifts via a set of bold, aggressive, and stress-resilient traits. Many of these same traits are associated with more northern latitudes, and most range shifts in the northern hemisphere indicate northward movement. As a consequence, it is unclear whether pioneering traits are simply corollaries of existing latitudinal variation, or whether they override other well-trodden latitudinal patterning as a unique eco-geographic rule of phenotypic variation.
  2. The tree swallow (Tachycineta bicolor) is a songbird undergoing a southward range shift in the eastern United States, in direct opposition of the poleward movement seen in most other native species' range shifts. Because this organic range shift countervails the typical direction of movement, this case study provides for unique ecological insights on organisms and their ability to thrive in our changing world.
  3. We sampled female birds across seven populations, quantifying behavioral, physiological, and morphological traits. We also used GIS and field data to quantify a core set of ecological factors with strong ties to these traits as well as female performance.
  4. Females at more southern expansion sites displayed higher maternal aggression, higher baseline corticosterone, and more pronounced elevation of corticosterone following a standardized stressor, contrary to otherwise largely conserved latitudinal patterning in these traits. Microhabitat variation explained some quantitative phenotypic variation, but the expansion and historic ranges did not differ in openness, distance to water, or breeding density.
  5. This countervailing range shift therefore suggests that pioneering traits are not simply corollaries of existing latitudinal variation, but rather, they may override other well-trodden latitudinal patterning as a unique eco-geographic rule of phenotypic variation.

Notes

Excel

Funding provided by: National Institutes of Health
Crossref Funder Registry ID: http://dx.doi.org/10.13039/100000002
Award Number: T32HD049336

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