Search tips
Search criteria

Results 1-4 (4)

Clipboard (0)
Year of Publication
Document Types
1.  Human disturbance alters endocrine and immune responses in the Galapagos marine iguana (Amblyrhynchus cristatus) 
Hormones and behavior  2010;58(5):792-799.
Anthropogenic disturbance is a relevant and widespread facilitator of environmental change and there is clear evidence that it impacts natural populations. While population-level responses to major anthropogenic changes have been well studied, individual physiological responses to mild disturbance can be equally critical to the long-term survival of a species, yet they remain largely unexamined. The current study investigated the impact of seemingly low-level anthropogenic disturbance (ecotourism) on stress responsiveness and specific fitness-related immune measures in different breeding stages of the marine iguana (Amblyrhynchus cristatus). Specifically, we found stress-induced elevations in plasma corticosterone among tourist-exposed populations relative to undisturbed populations. We also found changes in multiple immunological responses associated with stress-related effects of human disturbance, including bacterial killing ability, cutaneous wound healing, and hemolytic complement activity, and the responses varied according to reproductive state. By identifying health-related consequences of human disturbance, this study provides critical insight into the conservation of a well-known species that has a very distinct ecology. The study also broadens the foundation of knowledge needed to understand the global significance of various levels of human disturbance.
PMCID: PMC2982938  PMID: 20708010
Corticosterone; reproduction; immunity; tourism
2.  Exogenous insulin enhances humoural immune responses in short-day, but not long-day, Siberian hamsters (Phodopus sungorus) 
Many animals experience marked seasonal fluctuations in environmental conditions. In response, animals display adaptive alterations in physiology and behaviour, including seasonal changes in immune function. During winter, animals must reallocate finite energy stores from relatively costly, less exigent systems (e.g. reproduction and immunity) to systems critical for immediate survival (e.g. thermoregulation). Seasonal changes in immunity are probably mediated by neuroendocrine factors signalling current energetic state. One potential hormonal candidate is insulin, a metabolic hormone released in response to elevated blood glucose levels. The aim of the present study was to explore the potential role of insulin in signalling energy status to the immune system in a seasonally breeding animal, the Siberian hamster (Phodopus sungorus). Specifically, exogenous insulin was administered to male hamsters housed in either long ‘summer-like’ or short ‘winter-like’ days. Animals were then challenged with an innocuous antigen and immune responses were measured. Insulin treatment significantly enhanced humoural immune responses in short, but not long days. In addition, insulin treatment increased food intake and decreased blood glucose levels across photoperiodic treatments. Collectively, these data support the hypothesis that insulin acts as an endocrine signal integrating seasonal energetic changes and immune responses in seasonally breeding rodents.
PMCID: PMC2880144  PMID: 20236973
immunity; energy balance; insulin; antibody response
3.  The glutamate agonist, NMDA blocks gonadal regression and enhances antibody response to an immune challenge in Siberian hamsters (Phodopus sungorus) 
Seasonal variation in behavior and physiology, including changes in immune function, are common. This variability is elicited by changes in photoperiod and often covaries with fluctuations in both energy reserves and reproductive state. It is unclear, however, whether changes in either variable alone drive seasonal changes in immunity. We investigated the relative contributions of reproduction and energy balance to changes in immune function. To accomplish this, we uncoupled seasonal changes in reproduction from those related to energy balance via daily injections of N-methyl-D-Aspartate (NMDA) in Siberian hamsters (Phodopus sungorus). NMDA is a glutamatergic agonist that blocks short-day induced gonadal regression while leaving short-day declines in body mass unaffected. In Experiment 1, we examined the effect of differing doses of NMDA on testosterone production as a proxy for NMDA effects on reproduction; a dose-dependent rise in testosterone was observed. In Experiment 2, animals were maintained on long or short days and received daily injections of NMDA. After eight weeks all animals underwent a humoral immune challenge. Short-day animals receiving daily injections of NMDA maintained long-day-like gonads, however contrary to our predictions, no trade-off between reproduction or energy balance and immune function was observed. Unexpectedly, NMDA treatment increased immunoglobulin levels in all groups, suggesting NMDA may provide an immunomodulatory signal, presumably through actions on peripheral glutamate receptors. These results support a previous finding that NMDA blocks reproductive regression. In addition, these findings demonstrate a general immunoenhancing effect of NMDA that appears independent of changes in reproductive or energetic state of the animal.
PMCID: PMC2809793  PMID: 19820951
4.  Leptin increases maternal investment 
The primary goal of virtually all organisms is to produce genetic offspring, thereby passing on their genes to future generations. Offspring production, however, is limited by available resources within an environment. Moreover, distributing sufficient energy among competing physiological systems is challenging and can result in trade-offs between self-maintenance and offspring investment when resources are limited. In the current study, we tested the hypothesis that the adipose hormone leptin is involved in mediating energetic trade-offs between competing physiological systems. Specifically, we tested the effects of elevated maternal leptin on investment into offspring production versus self maintenance (immune function), in the Siberian hamster (Phodopus sungorus). The current study provides the first evidence that leptin serves as a signal to mothers of available energy resulting in epigenetic effects. Therefore, elevated leptin allows females to retain more embryos to parturition, and rear more offspring to weaning via reduced maternal infanticide. Innate immune response was suppressed seemingly as a result of these enlarged litters, suggesting that the observed fitness increase is not without costs to the mother. Collectively, these findings suggest that leptin plays a critical role in allowing mothers to determine how much energy to invest in the production and care of young versus self-maintenance.
PMCID: PMC2825785  PMID: 19710064
energy; immunity; reproduction; trade-offs

Results 1-4 (4)