title: Corticosteroid responses of snakes to toxins from toads (bufadienolides) and plants (cardenolides) reflect differences in dietary specializations.
abstract: Toads are chemically defended by cardiotonic steroids known as bufadienolides. Resistance to the acute effects of bufadienolides in snakes that prey on toads is conferred by target-site insensitivity of the toxin's target enzyme, the Na+/K+-ATPase. Previous studies have focused largely on the molecular mechanisms of resistance but have not investigated the physiological mechanisms or consequences of exposure to the toxins. Adrenal enlargement in snakes often is associated with specialization on a diet of toads. These endocrine glands are partly composed of interrenal tissue, which produces the corticosteroids corticosterone and aldosterone. Corticosterone is the main hormone released in response to stress in reptiles, and aldosterone plays an important role in maintaining ion balance through upregulation of Na+/K+-ATPase. We tested the endocrine response of select species of snakes to acute cardiotonic steroid exposure by measuring circulating aldosterone and corticosterone concentrations. We found that Rhabdophis tigrinus, which specializes on a diet of toads, responds with lower corticosterone and higher aldosterone compared to other species that exhibit target-site resistance to the toxins but do not specialize on toads. We also found differences between sexes in R. tigrinus, with males generally responding with higher corticosterone and aldosterone than females. This study provides evidence of physiological adaptations, beyond target-site resistance, associated with tolerance of bufadienolides in a specialized toad-eating snake.
authors.affiliation: Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322-5305, United States; Ecology Center, Utah State University, 5205 Old Main Hill, Logan, UT 84322-5205, United States. Electronic address: shab.mohammadi@gmail.com.
authors.forename: Shabnam
authors.initials: S
authors.lastname: Mohammadi
authors.affiliation: Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322-5305, United States; Ecology Center, Utah State University, 5205 Old Main Hill, Logan, UT 84322-5205, United States.
authors.forename: Susannah S
authors.initials: SS
authors.lastname: French
authors.affiliation: Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322-5305, United States.
authors.forename: Lorin A
authors.initials: LA
authors.lastname: Neuman-Lee
authors.affiliation: Ecology Center, Utah State University, 5205 Old Main Hill, Logan, UT 84322-5205, United States.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Durham
authors.affiliation: Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kojima
authors.affiliation: Department of Zoology, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Mori
authors.affiliation: Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322-5305, United States; Ecology Center, Utah State University, 5205 Old Main Hill, Logan, UT 84322-5205, United States.
authors.forename: Edmund D
authors.initials: ED
authors.lastname: Brodie
authors.affiliation: Department of Biology, Utah State University, 5305 Old Main Hill, Logan, UT 84322-5305, United States; Ecology Center, Utah State University, 5205 Old Main Hill, Logan, UT 84322-5205, United States.
authors.forename: Alan H
authors.initials: AH
authors.lastname: Savitzky
mesh_terms: D000450:Aldosterone / Q000097:blood; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002018:Bufanolides / Q000737:chemistry / Q000633:toxicity*; D002298:Cardenolides / Q000737:chemistry / Q000633:toxicity*; D017812:Colubridae / Q000097:blood / Q000502:physiology*; D003345:Corticosterone / Q000378:metabolism*; D004032:Diet; D005260:Female; D008297:Male; D010042:Ouabain / Q000633:toxicity
chemical_list: D002018:Bufanolides; D002298:Cardenolides; D000450:Aldosterone; D010042:Ouabain; D003345:Corticosterone
keywords: Aldosterone; Bufadienolide; Corticosteroids; Corticosterone; Na(+)/K(+)-ATPase; Snake