Individuals at the forefront of a range shift are likely to exhibit phenotypic traits that distinguish them from the population breeding within the historic range. Recent studies have examined morphological, physiological and behavioral phenotypes of individuals at the edge of their range. Several studies have found differences in the hypothalamic–pituitary–adrenal (HPA) axis activity in response to acute restraint stress in individuals at the range limits. HPA axis activation leads to elevations in glucocorticoids that regulate physiology and behavior. Here we compare the hormonal profiles and morphometrics from Gambel’s white-crowned sparrows (Zonotrichia leucophrys gambelii) breeding at the northern limit of the population’s range to those birds breeding within the historic population range. Birds breeding at the northern limit experienced a harsher environment with colder temperatures; however, we found no differences in arthropod prey biomass between the northern limit and more southern (historic) sites. Males at the northern limit had higher body condition scores (mass corrected for body size) compared to individuals within the historic range, but no differences were found in beak and tarsus lengths, wing chord, muscle profile or fat stores. In males during the pre-parental stage, before breeding commenced, HPA axis activity was elevated in birds at the northern limit of the range, but no differences were found during the parental or molt stages. Females showed no differences in HPA axis activity during the parental stage. This study suggests that “pioneering” individuals at the limits of their breeding range exhibit physiology and morphology that are distinct from individuals within the historic range.
Bibliographical noteFunding Information:
This work was supported by the National Science Foundation Office of Polar Programs ARC 0909133, ARC 0908444, and ARC 0908602 to John C. Wingfield, Natalie Boelman, and Laura Gough. Additionally, Jonathan H. P??rez was supported in part by a National Science Foundation Graduate Research Fellowship (NSF GFRP 1148897) and Simone L. Meddle acknowledges Roslin Institute strategic grant funding from the Biotechnology and Biological Sciences Research Council. We would like to thank Molly Timm, Jeb Timm, and Jake Schas for logistical support and sample collections in the field. We thank Douglas L. Kane, Robert Gieck, Ken Irving, and Emily Youcha from the University of Alaska Fairbanks for the weather data collected at Franklin Bluffs. We would also like to thank Tom P. Hahn and Marilyn Ramenofsky for valuable feedback on the manuscript. JSK, SLM and JCW orginally conceived the experiment. JSK, SLM, SKS, HEC, MAM, LNQ, AA, JHP, and JCW conducted the field work. Laboratory work was performed by JSK, HEC, AA, and LNQ. Data were analyzed and the paper was written by JSK, LNQ, and HEC with JSK performing most of the work. Editorial advice was provided by all authors listed.
© 2015, The Author(s).
- Allostatic load
- Climate change
- Hypothalamic–pituitary–adrenal axis