The metabolic response to an immune challenge in a viviparous snake, Sistrurus miliarius

Glucocorticoid and glycemic responses to immune challenge in a viviparous snake afflicted with an emerging mycosis

Disease may be both a cause and a consequence of stress, and physiological responses to infectious disease may involve stress coping mechanisms that have important fitness consequences. For example, glucocorticoid and glycemic responses may affect host fitness by altering resource allocation and use in hosts, and these responses may be affected by competing stressors. To better understand the factors that affect host responses to infection, we challenged the immune system of field-acclimatized pygmy rattlesnakes, Sistrurus miliarius, with a sterile antigen, lipopolysaccharide (LPS), and measured the glucocorticoid and glycemic response in healthy non-reproductive snakes, snakes afflicted with an emerging mycosis (ophidiomycosis) and pregnant snakes. We hypothesized that LPS challenge would result in a glucocorticoid and glycemic response typical of the vertebrate acute phase response (APR), and therefore predicted that LPS challenge would result in an acute increase in plasma corticosterone (CORT) and a decline in plasma glucose in all individuals. Additionally, we hypothesized that the APR would be attenuated in individuals simultaneously coping with additional challenges to homeostasis (i.e. disease or reproduction). As predicted, the immune challenge elicited an acute increase in plasma CORT and a decrease in plasma glucose. Snakes coping with ophidiomycosis and pregnant snakes were able to mount a robust glucocorticoid and hypoglycemic response to LPS challenge, which was contrary to our hypothesis. Our findings clarify directions of causality linking infection, glucocorticoids and glucose, and emphasize the importance of future research examining the fitness consequences of interactions between stress and disease in wildlife threatened by emerging pathogens.

Anthropogenic and climatic factors interact to influence reproductive timing and effort

Reproduction, although absolutely essential to a species' persistence, is in itself challenging. As anthropogenic change increasingly affects every landscape on Earth, it is critical to understand how specific pressures impact the reproductive efforts of individuals, which directly contribute to the success or failure of populations. However, organisms rarely encounter a single burden at a time, and the interactions of environmental challenges can have compounding effects. Understanding environmental and physiological pressures is difficult because they are often context-dependent and not generalizable, but long-term monitoring across variable landscapes and weather patterns can improve our understanding of these complex interactions. We tested the effects of urbanization, climate, and individual condition on the reproductive investment of wild side-blotched lizards (Uta stansburiana) by measuring physiological/reproductive metrics from six populations in urban and rural areas over six consecutive years of variable precipitation. We observed that reproductive stage affected body condition, corticosterone concentration, and oxidative stress. We also observed that reproductive patterns differed between urban and rural populations depending on rainfall, with rural animals increasing reproductive investment during rainier years compared to urban conspecifics, and that reproductive decisions appeared to occur early in the reproductive process. These results demonstrate the plastic nature of a generalist species optimizing lifetime fitness under varying conditions.

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.

Parasitism in viviparous vertebrates: an overview

The reproductive mode of viviparity has independently evolved in various animal taxa. It refers to the condition in which the embryos or young develop inside the female's body during gestation, providing advantages such as protection, nutrition, and improved survival chances. However, parasites and diseases can be an evolutionary force that limit the host's resources, leading to physiological, morphological, and behavioral changes that impose additional costs on both the pregnant female and her offspring. This review integrates the primary literature published between 1980 and 2021 on the parasitism of viviparous hosts. We describe aspects such as reproductive investment in females, offspring sex ratios, lactation investment in mammals, alterations in birth intervals, current reproductive investment, variations between environments, immune system activity in response to immunological challenges, and other factors that can influence the interaction between viviparous females and parasites. Maintaining pregnancy incurs costs in managing the mother's resources and regulating the immune system's responses to the offspring, while simultaneously maintaining an adequate defense against parasites and pathogens. Parasites can significantly influence this reproductive mode: parasitized females adjust their investment in survival and reproduction based on their life history, environmental factors, and the diversity of encountered parasites.

Relationships between hormone levels, metabolism and immune response in toads from a semi-arid region

Steroid hormones (e.g. androgens [AN] and corticosterone [CORT]) modulate complex physiological functions such as reproduction, energy mobilization, metabolism, and immunity. Fluctuations in environmental resource availability along with other factors, such as parasitism, can interact with the effects of these steroids, modifying aspects of immunocompetence and its metabolic costs. To understand these possible interactions, we studied AN and CORT, immune response [swelling response to phytohemagglutinin (PHA) injection and bacterial killing ability (BKA)], parasite load, resting metabolic rate (RMR) and rates of oxygen consumption after PHA injection, in two different phases of the annual cycle of a toad (Rhinella jimi) from a highly seasonal environment (Brazilian semi-arid, Caatinga). We observed increased rates of O₂ consumption after both PHA and the control (saline) injection, indicating a metabolic response to adverse stimuli but not the immune challenge. Toads showing higher RMR and VO₂ after the adverse stimuli (PHA/saline injection) had lower field AN and CORT plasma levels, suggesting these hormones might mediate a metabolic energy conservation strategy both at baseline levels and after adverse stimuli. Parasite load seem to impose an energetic constrain to the metabolic response to PHA and saline injection. Also, individuals showing higher PHA swelling response had higher field CORT plasma levels (particularly when males are breeding) which opposes the idea of a possible trade-off between reproductive activity and other physiological traits and indicate the immunoenhancing effects CORT elevated at physiological levels. BKA did not show a seasonal variation or correlation with body condition nor hormone levels, indicating that the immune surveillance mediated by the complement remains constant despite other ecological and physiological changes.

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.

Experimental ectoparasite removal has a sex-specific effect on nestling telomere length

Parasites are a strong selective force that can influence fitness-related traits. The length of chromosome-capping telomeres can be used to assess the long-term costs of parasitism, as telomere loss accelerates in response to environmental stressors and often precedes poorer survival prospects. Here, we explored the sex-specific effects of ectoparasite removal on morphology and telomere length in nestling tree swallows (Tachycineta bicolor). To do so, we experimentally removed blow fly (Protocalliphora spp.) larvae from nests using Permethrin, a broad-spectrum insecticide. Compared to water-treated controls, insecticide treatment of nests had a sex-biased effect on blood telomere length: ectoparasite removal resulted in significantly longer telomeres in males but not females. While this treatment did not influence nestling body mass, it was associated with reduced feather development regardless of sex. This may reflect a relaxed pressure to fledge quickly in the absence of parasites, or alternatively, could be a negative side effect of permethrin on morphology. Exploring robust sex-specific telomere dynamics in response to early-life environmental pressures such as parasitism will shed light on sexual dimorphism in adult life histories and aging.

Past, Present, and Future of Naturally Occurring Antimicrobials Related to Snake Venoms

This review focuses on proteins and peptides with antimicrobial activity because these biopolymers can be useful in the fight against infectious diseases and to overcome the critical problem of microbial resistance to antibiotics. In fact, snakes show the highest diversification among reptiles, surviving in various environments; their innate immunity is similar to mammals and the response of their plasma to bacteria and fungi has been explored mainly in ecological studies. Snake venoms are a rich source of components that have a variety of biological functions. Among them are proteins like lectins, metalloproteinases, serine proteinases, L-amino acid oxidases, phospholipases type A₂, cysteine-rich secretory proteins, as well as many oligopeptides, such as waprins, cardiotoxins, cathelicidins, and β-defensins. In vitro, these biomolecules were shown to be active against bacteria, fungi, parasites, and viruses that are pathogenic to humans. Not only cathelicidins, but all other proteins and oligopeptides from snake venom have been proteolyzed to provide short antimicrobial peptides, or for use as templates for developing a variety of short unnatural sequences based on their structures. In addition to organizing and discussing an expressive amount of information, this review also describes new β-defensin sequences of Sistrurus miliarius that can lead to novel peptide-based antimicrobial agents, using a multidisciplinary approach that includes sequence phylogeny.

The acute phase response in bats (Carollia perspicillata) varies with time and dose of the immune challenge

The acute phase response (APR) is a core component of the innate immune response and represents the first line of immune defense used in response to infections. Although several studies with vertebrates reported fever, a decrease in food intake and body mass, and an increase in neutrophil/lymphocyte ratio and total white blood cell count after lipopolysaccharide (LPS) inoculation, there was great variability in the magnitude of these responses. Some of these differences might reflect, to some extent, differences in the time of endotoxin inoculation (during active or rest periods) and dose. Therefore, our study tested the interplay between LPS dose and time of injection on selected physiological (fever and increase in total white blood cell count and neutrophil/lymphocyte ratio) and behavioral (food intake) components of the APR using a Neotropical fruit-eating bat (Carollia perspicillata) as a model organism. We predicted that LPS would trigger a dose- and time-dependent response in APR components. APR components were assessed in rest and active periods after injection of three doses of LPS (5, 10 and 15 mg kg-1 LPS). The results indicate a more robust decrease in food intake at higher doses during the active period, while increased neutrophil/lymphocyte ratio was more robust during the active period regardless of dose. Furthermore, the skin temperature increase lasted longer at higher doses regardless of the timing of injections. Our study offers important insights into the dependence of time as well as the LPS dosage effect in the APR of bats, and how they deal with the magnitude of infections at different times of day.

Energy expenditure across immune challenge severities in a lizard: consequences for innate immunity, locomotor performance and oxidative status

Reptiles, like other vertebrates, rely on immunity to defend themselves from infection. The energetic cost of an immune response is liable to scale with infection severity, prompting constraints on other self-maintenance traits if immune prioritization exceeds energy budget. In this study, adult male side-blotched lizards (Uta stansburiana) were injected with saline (control) or high (20 µg g-1 body mass) or low (10 µg g-1 body mass) concentrations of lipopolysaccharide (LPS) to simulate bacterial infections of discrete severities. The costs and consequences of the immune response were assessed through comparisons of change in resting metabolic rate (RMR), energy metabolites (glucose, glycerol, triglycerides), innate immunity (bactericidal ability), sprint speed and oxidative status (antioxidant capacity, reactive oxygen metabolites). High-LPS lizards had the lowest glucose levels and greatest sprint reductions, while their RMR and bactericidal ability were similar to those of control lizards. Low-LPS lizards had elevated RMR and bactericidal ability, but glucose levels and sprint speed changes between those of high-LPS and control lizards. Levels of glycerol, triglycerides, reactive oxygen metabolites and antioxidant capacity did not differ by treatment. Taken together, energy expenditure for the immune response varies in a non-linear fashion with challenge severity, posing consequences for performance and self-maintenance processes in a reptile.

The reptilian perspective on vertebrate immunity: 10 years of progress

Ten years ago, ‘Understanding the vertebrate immune system: insights from the reptilian perspective’ was published. At the time, our understanding of the reptilian immune system lagged behind that of birds, mammals, fish and amphibians. Since then, great progress has been made in elucidating the mechanisms of reptilian immunity. Here, I review recent discoveries associated with the recognition of pathogens, effector mechanisms and memory responses in reptiles. Moreover, I put forward key questions to drive the next 10 years of research, including how reptiles are able to balance robust innate mechanisms with avoiding self-damage, how B cells and antibodies are used in immune defense and whether innate mechanisms can display the hallmarks of memory. Finally, I briefly discuss the links between our mechanistic understanding of the reptilian immune system and the field of eco-immunology. Overall, the field of reptile immunology is poised to contribute greatly to our understanding of vertebrate immunity in the next 10 years.

Endurance and sprint training affect immune function differently in green anole lizards (Anolis carolinensis)

Limited resources must be partitioned among traits that enhance fitness. Although survival-related traits often trade off with reproduction, survival-related traits themselves may trade off with each other under energy limitations. Whole-organism performance and the immune system both enhance survival, yet are costly, but it is unclear how the two might trade off with each other under energy-limited conditions. Resources can be allocated to very different types of performance (e.g. aerobic endurance versus anaerobic sprinting), just as they can be allocated to different components of the immune system (e.g. innate versus acquired) to maximize survival. We forced allocation to different performance traits in green anole lizards (Anolis carolinensis) using specialized exercise training, to determine how different components of the immune system would be impacted by shifts in energy use. We measured immunocompetence in endurance-trained, sprint-trained and untrained control lizards by evaluating swelling response to phytohemagglutinin (cell-mediated immunity), antibody response to sheep red blood cells (acquired humoral immunity) and wound healing (integrated immunity). Endurance-trained lizards had reduced cell-mediated immunity, whereas sprint-trained lizards had reduced rates of wound healing. The acquired immune response was not affected by either type of training. Because each immune measure responded differently to the different types of training, our results do not support the hypothesis that simple energy limitation determines overall investment in immunity. Instead, different components of the immune system appear to be affected in ways specific to how energy is invested in performance.