Wet- and Dry-Season Steroid Hormone Profiles and Stress Reactivity of an Insular Dwarf Snake, the Hog Island Boa (Boa constrictor imperator)

Abstract

Field endocrine studies providing new comparisons for inference into the evolutionary and ecological factors shaping organismal physiology are important, often yielding novel physiological insights. Here, we explored factors associated with the sex steroid hormone concentrations and adrenocortical response to capture stress in Hog Island boas (Boa constrictor imperator) in the Cayos Cochinos archipelago of Honduras to generate comparative field hormone data from a tropical reptile and test the island tameness hypothesis. Baseline concentrations of testosterone, corticosterone, estradiol, and progesterone were measured during the wet and dry seasons, and an acute stressor of 1 h in a cloth bag was used to assess the stress response. Plasma steroid concentrations in these snakes were generally low in comparison to other taxa. Higher testosterone concentrations in males and higher estradiol and corticosterone concentrations in females were observed during the wet season compared to the dry season, which may be indicative of mating activities and vitellogenesis during this period. Snakes displayed a 15-fold increase in corticosterone concentrations in response to capture stress, a rise that was not impacted by whether a snake had been captured during previous years. The adrenocortical stress response was greater in males and positively related to body temperature. We suggest that this system merits future inquiries into the physiology and behavior of B. c. imperator, particularly as a model for studying insular impacts on diverse life history characters.

No island-effect on stress for a rodent from a near-shore archipelago

“…White-footed mice do not display island syndrome in the Thousand Islands Despite the tendency for island wildlife to display morphological and physiological adaptations to insularity (Matson et al, 2014;Holding et al, 2014;Spencer et al, 2017), white-footed mice in the Thousand Islands did not differ in any of these characteristics from their mainland conspecifics. White-footed mice on islands did not display higher relative abundance than mainland mice in disagreement with the general prediction that rodents exhibit particularly high densities on islands (Adler & Levins, 1994;Crespin, Duplantier & Granjon, 2012;, which has been observed for other small vertebrates as well (Novosolov, Raia & Meiri, 2013;Sale & Arnould, 2013).…”

Effects of temperature on plasma corticosterone in a native lizard

“…It is also possible that lizard body temperature, even within the range observed in the field, may affect the stress-induced plasma CORT concentrations, which we did not measure. For example, rattlesnakes and boa constrictors show no correlation between body temperature and baseline plasma CORT, but a positive correlation between body temperature and stress-induced CORT 37,41 . This may indicate that the stress-response is more sensitive to differences in body temperature, and may be affected by temperature even when baseline CORT is unaffected.…”

“…Baseline plasma CORT concentrations in some reptile species are known to vary considerably between seasons 27,36 . This is often attributed to changes in reproductive activity throughout the year 27,36,37 , but unmeasured temperature changes between seasons may also contribute to this variation. Ambient temperature is rarely considered when discussing CORT concentrations in ectothermic species, but may be extremely important given its strong effect on body temperature and physiologic processes in ectotherms 38 .…”

Stress Ecology of the Pacific Rattlesnakes (Crotalus Oreganus and Crotalus Helleri)

“…Sometimes, as in this study, no relationship between time-to-bleed and CORT is observed (Holding et al, 2014b;Hopkins & DuRant 2011), which is likely because samples were collected within an adequate timeframe before circulating CORT increased due to stress response to handling (Schuett et al 2004). …”

“…One possibility is that the snakes were stressed by the initial vibrator activation but had acclimated or habituated to vibrations by mid-treatment, so baseline CORT was not affected. It is also possible the vibrator device may have acted as a multiple-exposure acute stressor (see Lutterschmidt et al 2009;Holding et al 2014a;Holding et al 2014b) rather than a chronic stressor, with snakes' CORT elevating after a vibration bout and returning to baseline before blood was sampled. A recent study exposed captive garter snakes (Thamnophis elegans) to multiple-exposure acute stressors as a "chronic stress" treatment and also observed no change in baseline CORT, but observed differences in physiological responses such as wound healing and circulating metabolites in the "chronic stress" group compared to non-stressed controls (Neuman-Lee et al 2015).…”