Honest signals and sexual conflict: Female lizards carry undesirable indicators of quality.

Sex differences in animal coloration often result from sex-dependent regulatory mechanisms. Still, some species exhibit incomplete sexual dimorphism as females carry a rudimentary version of a costly male trait, leading to intralocus sexual conflict. The underlying physiology and condition dependence of these traits can inform why such conflicts remain unresolved. In eastern fence lizards (Sceloporus undulatus), blue iridophore badges are found in males and females, but melanin pigmentation underneath and surrounding badges is male-exclusive. We track color saturation and area of badges across sexual maturity, and their relationship to individual quality (body condition and immunocompetence) and relevant hormones (testosterone and corticosterone). Saturation and testosterone were positively correlated in both sexes, but hormone and trait had little overlap between males and females. Saturation was correlated with body condition and immunocompetence in males but not in females. Co-regulation by androgens may have released females from resource allocation costs of color saturation, even when in high condition. Badge area was independent of testosterone, but associated with low corticosterone in females, indicating that a nonsex hormone underlies incomplete sexual dimorphism. Given the evidence in this species for female reproductive costs associated with ornamentation, this sex-nonspecific regulation of an honest signal may underlie intralocus sexual conflict.

Effects of temperature on plasma corticosterone in a native lizard.

The glucocorticoid stress response is frequently used to indicate vertebrate response to the environment. Body temperature may affect glucocorticoid concentrations, particularly in ectotherms. We conducted lab manipulations and field measurements to test the effects of body temperature on plasma corticosterone (predominant glucocorticoid in reptiles) in eastern fence lizards (Sceloporus undulatus). First, we acclimated lizards to one of 4 treatments: 22 °C, 29 °C, 33 °C, or 36 °C, and measured cloacal temperatures and plasma corticosterone concentrations at baseline and after exposure to a standardized stressor (cloth bag). Both baseline and stress-induced corticosterone concentrations were lower in lizards with lower body temperatures. Second, we acclimated lizards to 22 °C or 29 °C and exposed them to a standardized (cloth bag) stressor for 3 to 41 min. Lizards acclimated to 29 °C showed a robust increase in plasma corticosterone concentrations with restraint stress, but those at 22 °C showed no such increases in corticosterone concentrations. Third, we measured lizards upon capture from the field. There was no correlation between body temperature and baseline plasma corticosterone in field-caught lizards. These results suggest body temperature can significantly affect plasma corticosterone concentrations in reptiles, which may be of particular concern for experiments conducted under laboratory conditions but may not translate to the field.

Ecoimmune reallocation in a native lizard in response to the presence of invasive, venomous fire ants in their shared environment.

Exposure to stressors over prolonged periods can have fitness-relevant consequences, including suppression of immune function. We tested for effects of presence of an invasive species threat on a broad panel of immune functions of a coexisting lizard. Eastern fence lizards (Sceloporus undulatus) have been exposed to invasive fire ants (Solenopsis invicta) for over 80 years. Fire ants sting and envenomate lizards, causing physiological stress, but we do not have a comprehensive understanding of the broad immune consequences of lizard exposure to fire ant presence. We conducted a suite of immune measures on fence lizards caught from areas with long histories of fire ant invasion and lizards from areas not yet invaded by fire ants. The effect of fire ant presence on immunity varied depending on the immune component measured: within fire ant invaded areas, some portions of immunity were suppressed (lymphocytic cell-mediated immunity, complement), some were unaffected (phagocytic respiratory burst, natural antibodies), and some were enhanced (anti-fire ant immunoglobulin M, basophils) compared to within uninvaded areas. Rather than fire ants being broadly immunosuppressing, as generally assumed, the immune response appears to be tailored to this specific stressor: the immune measures that were enhanced are important to the lizards' ability to handle envenomation, whereas those that were unaffected or suppressed are less critical to surviving fire ant encounters. Several immune measures were suppressed in reproductive females when actively producing follicles, which may make them more susceptible to immunosuppressive costs of stressors such as interactions with fire ants.

Obtaining plasma to measure baseline corticosterone concentrations in reptiles: How quick is quick enough?

There is growing interest in the use of glucocorticoid (GC) hormones to understand how wild animals respond to environmental challenges. Blood is the best medium for obtaining information about recent GC levels; however, obtaining blood requires restraint and can therefore be stressful and affect GC levels. There is a delay in GCs entering blood, and it is assumed that blood obtained within 3 min of first disturbing an animal reflects a baseline level of GCs, based largely on studies of birds and mammals. Here we present data on the timing of changes in the principle reptile GC, corticosterone (CORT), in four reptile species for which blood was taken within a range of times 11 min or less after first disturbance. Changes in CORT were observed in cottonmouths (Agkistrodon piscivorus; 4 min after first disturbance), rattlesnakes (Crotalus oreganus; 2 min 30 s), and rock iguanas (Cyclura cychlura; 2 min 44 s), but fence lizards (Sceloporus undulatus) did not exhibit a change within their 10-min sampling period. In both snake species, samples taken up to 3-7 min after CORT began to increase still had lower CORT concentrations than after exposure to a standard restraint stressor. The "3-min rule" appears broadly applicable as a guide for avoiding increases in plasma CORT due to handling and sampling in reptiles, but the time period in which to obtain true baseline CORT may need to be shorter in some species (rattlesnakes, rock iguanas), and may be unnecessarily limiting for others (cottonmouths, fence lizards).

Contrasting Responses of Lizards to Divergent Ecological Stressors Across Biological Levels of Organization.

It is frequently hypothesized that animals employ a generalized "stress response," largely mediated by glucocorticoid (GC) hormones, such as corticosterone, to combat challenging environmental conditions. Under this hypothesis, diverse stressors are predicted to have concordant effects across biological levels of an organism. We tested the generalized stress response hypothesis in two complementary experiments with juvenile and adult male Eastern fence lizards (Sceloporus undulatus). In both experiments, animals were exposed to diverse, ecologically-relevant, acute stressors (high temperature or red imported fire ants, Solenopsis invicta) and we examined their responses at three biological levels: behavioral; physiological (endocrine [plasma corticosterone and blood glucose concentrations] and innate immunity [complement and natural antibodies]); and cellular responses (gene expression of a panel of five heat-shock proteins in blood and liver) at 30 or 90 min post stress initiation. In both experiments, we observed large differences in the cellular response to the two stressors, which contrasts the similar behavioral and endocrine responses. In the adult experiment for which we had innate immune data, the stressors affected immune function independently, and they were correlated with CORT in opposing directions. Taken together, these results challenge the concept of a generalized stress response. Rather, the stress response was context specific, especially at the cellular level. Such context-specificity might explain why attempts to link GC hormones with life history and fitness have proved difficult. Our results emphasize the need for indicators at multiple biological levels and whole-organism examinations of stress.

Local and systemic immune responses to different types of phytohemagglutinin in the green anole: Lessons for field ecoimmunologists.

The phytohemagglutinin (PHA) skin test is commonly used by ecologists to assess cell-mediated immune function of wild animals. It can be performed quickly and easily in the field, involving injection of PHA and measurement of the resultant swelling. There are multiple formulations of PHA used in ecological studies, with potentially differing outcomes that could produce inconsistent results. We tested two common types of PHA in the green anole (Anolis carolinensis) to identify local and systemic immune responses underlying the resultant swelling at 6, 18, 24, and 48 hr post injection. There were differences in both local (injection site) and systemic (blood) leukocyte responses to PHA-L versus PHA-P. PHA-P injection produced a greater overall increase in local heterophil count at the injection site compared with PHA-L, and this response was greatest at 6 and 24 hr post injection. Systemically, heterophil percentage was higher in the blood of PHA-P- versus PHA-L-injected anoles at 24 hr post injection; the time point at which heterophil percentage peaked in PHA-P-injected anoles. These results indicate that although both PHA types are effective tests of immune function in green anoles, the PHA-P swelling response invokes a much stronger heterophilic response. PHA-L is a more specific test of lymphocyte function, particularly at 24 hr post injection, making it preferable for ecoimmunology studies.