Sex-based trade-offs in the innate and acquired immune systems of Sternotherus minor

Corticosterone treatment results in fat deposition and body mass maintenance without effects on feeding behaviour or immunity in female lizards (Tropidurus catalanensis)

Throughout life, animals must maintain homeostasis while coping with challenging events. The period after reproduction can be challenging for oviparous females to maintain homeostasis since they direct most of their energy stores to vitellogenesis, possibly increasing the vulnerability to stressors. Changes in glucocorticoids' (GC) secretion promote various behavioural and physiological adjustments daily and to restore balance after facing stressors. However, when GC are elevated for extended periods, which usually occurs in response to chronic exposure to stressors, they can affect feeding behaviour and suppress the immune function. We aim to elucidate the effects of chronic corticosterone (CORT) exposure on feeding behaviour, body condition and immune function in female lizards, Tropidurus catalanensis, in the post-reproductive period. Thirty animals were divided into three groups: 1. Control (no experimental procedure performed); 2. Empty Implant (animals implanted with empty silastic tube); and 3. CORT Implant (animals implanted with silastic tube filled with CORT, with a chronic continuous release for at least a week). CORT plasma levels feeding behaviour, body condition (body index [BI] and fat index [FI]), leukocyte count, and several immune function variables (bacterial killing ability [BKA], hemagglutination titer, phytohemagglutinin [PHA] immune challenge and leukocyte count) were evaluated. After implantation, CORT treated animals maintained stable body mass through the experiment, while Control and Empty Implant groups displayed weight loss. In the CORT treated animals, there was also a positive relation between BI and FI, and higher FI when compared to groups 1 and 2. No effects of CORT were observed on feeding behaviour nor on the immune function.

Testing androgen-induced immunosuppression: Environmental androgens as a model system for steroid-immune interaction

It is well known that hormones influence and direct most facets of physiology; however, there is still contention regarding the directions of certain relationships, for example, between gonadal hormones and immunity. Among the many proposed relationships relating to gonadal-immune interactions, support for immunosuppressive effects of androgens remains prominent within physiological literature. Although ample study has been directed toward the immunosuppressive effects of androgens, considerable disagreement remains regarding their influence on immune function. In this study, we test the hypothesis that androgens inhibit immunocompetence in the American alligator (Alligator mississippiensis). Developing alligators were incubated at female-producing temperatures with a subset of individuals being exposed to 17-α-methyltestosterone (MT) before sexual determination. 17-α-methyltestosterone is a potent androgen, not aromatizable by crocodilians, that has been found to exert masculinizing effects in exposed crocodilian populations in vivo and in vitro. Additionally, a subset of animals was exposed to a novel antigen to quantify innate and acquired immune function. We recovered no significant differences in leukocyte ratios or proportions between groups and found no significant differences in innate immune function as measured by hemolysis-hemagglutination. However, we did find significant differences in acquired immune function, where masculinized individuals expressed greater antibody titers. Our findings reject the hypothesis that androgens suppress immune function; rather, androgens may be immunoenhancing to acquired humoral responses and neutral to innate humoral immunity in crocodilians.

Sex-specific effects of immune challenges on green anole lizard metabolism

Immune responses can increase survival, but they can also incur a variety of costs that may lead to phenotypic trade-offs. The nature of trade-offs between immune activity and other components of the phenotype can vary and depend on the type and magnitude of immune challenge, as well as the energetic costs of simultaneously expressing other traits. There may also be sex-specific differences in both immune activity and trade-offs, particularly with regard to energy expenditure that might differ between males and females during the breeding season. Females are generally expected to invest less in nonspecific immune responses compared to males due to differences in the allocation of resources to reproduction, which may lead to sex differences in the metabolic costs of immunity. We tested for sex-specific differences in metabolic costs of different types of immune challenges in Anolis carolinensis lizards, including lipopolysaccharide (LPS) injection and wounding. We also tested for differences in immune prioritization by measuring bacterial killing ability (BKA). We predicted males would show a greater increase in metabolism after immune challenges, with combined immune challenges eliciting the greatest response. Furthermore, we predicted that metabolic costs would result in decreased BKA. LPS injection increased the resting metabolic rate (RMR) of males but not females. Wounding did not affect RMR of either sex. However, there was an inverse relationship between BKA and wound healing in LPS-injected lizards, suggesting dynamic tradeoffs among metabolism and components of the immune system.

Sex-specific innate immunity and ageing in long-lived fresh water turtles (Kinosternon flavescens: Kinosternidae)

BACKGROUND

The progressive deregulation of the immune system with age, termed immunosenescence, has been well studied in mammalian systems, but studies of immune function in long-lived, wild, non-mammalian populations are scarce. In this study we leverage a 38-year mark-recapture study to quantify the relationships among age, sex, survival, reproductive output and the innate immune system in a long-lived reptile, yellow mud turtles (Kinosternon flavescens; Testudines; Kinosternidae).

METHODS

We estimated rates of survival and age-specific mortality by sex based on mark-recapture data for 1530 adult females and 860 adult males over 38 years of captures. We analyzed bactericidal competence (BC), and two immune responses to foreign red blood cells - natural antibody-mediated haemagglutination (NAbs), and complement-mediated haemolysis ability (Lys) - in 200 adults (102 females; 98 males) that ranged from 7 to 58 years of age captured in May 2018 during their emergence from brumation, and for which reproductive output and long-term mark-recapture data were available.

RESULTS

We found that females are smaller and live longer than males in this population, but the rate of accelerating mortality across adulthood is the same for both sexes. In contrast, males exhibited higher innate immunity than females for all three immune variables we measured. All immune responses also varied inversely with age, indicating immunosenescence. For females that reproduced in the preceding reproductive season, egg mass (and therefore total clutch mass) increased with age,. In addition to immunosenescence of bactericidal competence, females that produced smaller clutches also had lower bactericidal competence.

CONCLUSIONS

Contrary to the general vertebrate pattern of lower immune responses in males than females (possibly reflecting the suppressive effects of androgens), we found higher levels of all three immune variables in males. In addition, contrary to previous work that found no evidence of immunosenescence in painted turtles or red-eared slider turtles, we found a decrease in bactericidal competence, lysis ability, and natural antibodies with age in yellow mud turtles.

Reptilian Innate Immunology and Ecoimmunology: What Do We Know and Where Are We Going?

Reptiles, the only ectothermic amniotes, employ a wide variety of physiological adaptations to adjust to their environments but remain vastly understudied in the field of immunology and ecoimmunology in comparison to other vertebrate taxa. To address this knowledge gap, we assessed the current state of research on reptilian innate immunology by conducting an extensive literature search of peer-reviewed articles published across the four orders of Reptilia (Crocodilia, Testudines, Squamata, and Rhynchocephalia). Using our compiled dataset, we investigated common techniques, characterization of immune components, differences in findings and type of research among the four orders, and immune responses to ecological and life-history variables. We found that there are differences in the types of questions asked and approaches used for each of these reptilian orders. The different conceptual frameworks applied to each group has led to a lack of unified understanding of reptilian immunological strategies, which, in turn, have resulted in large conceptual gaps in the field of ecoimmunology as a whole. To apply ecoimmunological concepts and techniques most effectively to reptiles, we must combine traditional immunological studies with ecoimmunological studies to continue to identify, characterize, and describe the reptilian immune components and responses. This review highlights the advances and gaps that remain to help identify targeted and cohesive approaches for future research in reptilian ecoimmunological studies.

Immune activation affects whole-organism performance in male but not female green anole lizards (Anolis carolinensis)

Immune responses are intuitively beneficial, but they can incur a variety of costs, many of which are poorly understood. The nature and extent of trade-offs between immune activity and other components of the integrated phenotype can vary, and depend on the type of immune challenge, as well as the energetic costs of simultaneously expressing other traits. There may also be sex differences in both immune activity and immunity-induced trade-offs, particularly in the case of trade-offs involving functional traits such as whole-organism performance capacities that might be of different fitness value to males and females. We tested the response of three performance traits (sprinting, endurance, and biting) to two different immune challenges (LPS injection and wound healing) in both male and female Anolis carolinensis lizards. We found clear differences in how male and female performance capacities were affected by immune activation. LPS injection and wound healing had interactive effects on all three performance traits in males, but immune activation did not affect female performance. We also found that the degree of wound healing exhibited complex interactive effects involving sex and type of immune activation that varied depending on the performance trait in question. These results demonstrate that male and female green anoles experience different consequences of immune responses, and also that the type and extent of that activation can drive trait-specific performance trade-offs.