title: Geographic variation and within-individual correlations of physiological stress markers in a widespread reptile, the common garter snake (Thamnophis sirtalis).
abstract: Characterizing the baseline and stress-induced hormonal, metabolite, and immune profiles of wild animals is important to assess the impacts of variable environments, including human-induced landscape changes, on organismal health. Additionally, the extent to which these profiles are coordinated across physiological systems within individuals remains an important question in understanding how stressors can differentially affect aspects of an individual's physiology. Here, we present data from wild populations of the common garter snake (Thamnophis sirtalis) on both baseline and stress-induced biomarkers: plasma corticosterone (CORT) concentration, plasma glucose concentration, and whole blood heterophil:lymphocyte ratio. Using a standardized restraint protocol with individuals from populations in disparate portions of this species' range - the Sierra Nevada Mountains of California and the plains of Iowa - we collected blood plasma samples at nine time points over three days. Both CORT and glucose response curves differed between georegions, with Iowa snakes attaining higher glucose concentration and maintaining elevated CORT and glucose levels for a longer duration. Additionally, both the total amount and proportional increases of CORT and glucose were lower in larger and therefore older snakes, suggesting ontogenetic shifts in stress perception or response. Within-individual correlation among the three physiological indicators was significant at the time of capture, absent after 3h in captivity, and partially restored after 3days in captivity, demonstrating the effect of stress on the relationships among these physiological systems. Together, these results provide further evidence for the great physiological flexibility of ectothermic tetrapods in maintaining homeostasis across a range of factors.
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA. Electronic address: gangloff@iastate.edu.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Gangloff
authors.affiliation: Department of Biology, Westmont College, Santa Barbara, CA 93108, USA.
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Sparkman
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Kaitlyn G
authors.initials: KG
authors.lastname: Holden
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Caitlyn J
authors.initials: CJ
authors.lastname: Corwin
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Madeline
authors.initials: M
authors.lastname: Topf
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Bronikowski
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000097:blood / Q000502:physiology; D015415:Biomarkers / Q000097:blood; D001786:Blood Glucose / Q000378:metabolism; D002140:California; D017812:Colubridae / Q000097:blood / Q000502:physiology*; D003345:Corticosterone / Q000097:blood; D017753:Ecosystem; D005843:Geography; D007484:Iowa; D007958:Leukocyte Count; D013312:Stress, Physiological
chemical_list: D015415:Biomarkers; D001786:Blood Glucose; D003345:Corticosterone
keywords: Allostasis; Corticosterone; Geographic variation; Glucose; Homeostasis; Hormones; Leukocyte