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1. Effect of dietary macronutrients and immune challenge on gut microbiota, physiology and feeding behaviour in zebra finches

   https://doi.org/10.1111/mec.17428  

   Love, Ashley C; Tabb, Victoria; Youssef, Noha H; Wilder, Shawn M; DuRant, Sarah E (July 2024, Molecular Ecology)

   Bonneaud, Camille (Ed.)

   Abstract Macronutrients play a vital role in host immunity and can influence host–pathogen dynamics, potentially through dietary effects on gut microbiota. To increase our understanding of how dietary macronutrients affect physiology and gut microbiota and investigate whether feeding behaviour is influenced by an immune threat, we conducted two experiments. First, we determined whether zebra finches (Taeniopygia guttata) exhibit shifts in physiology and gut microbiota when fed diets differing in macronutrient ratios. We found the type and amount of diet consumed affected gut microbiota alpha diversity, where microbial richness and Shannon diversity increased with caloric intake in birds fed a high‐fat diet and decreased with caloric intake in birds fed a high protein diet. Diet macronutrient content did not affect physiological metrics, but lower caloric intake was associated with higher complement activity. In our second experiment, we simulated an infection in birds using the bacterial endotoxin lipopolysaccharide (LPS) and quantified feeding behaviour in immune challenged and control individuals, as well as birds housed near either a control pair (no immune threat), or birds housed near a pair given an immune challenge with LPS (social cue of heightened infection risk). We also examined whether social cues of infection alter physiological responses relevant to responding to an immune threat, an effect that could be mediated through shifts in feeding behaviour. LPS induced a reduction in caloric intake driven by a decrease in protein, but not fat consumption. No evidence was found for socially induced shifts in feeding behaviour, physiology or gut microbiota. Our findings carry implications for host health, as sickness‐induced anorexia and diet‐induced shifts in the microbiome could shape host–pathogen interactions. 

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2. Decoupling the effects of food and density on life‐history plasticity of wild animals using field experiments: Insights from the steward who sits in the shadow of its tail, the North American red squirrel

   https://doi.org/10.1111/1365-2656.13341  

   Dantzer, Ben; McAdam, Andrew_G; Humphries, Murray_M; Lane, Jeffrey_E; Boutin, Stan; Pelletier, ed., Fanie (October 2020, Journal of Animal Ecology)

   Abstract Long‐term studies of wild animals provide the opportunity to investigate how phenotypic plasticity is used to cope with environmental fluctuations and how the relationships between phenotypes and fitness can be dependent upon the ecological context.Many previous studies have only investigated life‐history plasticity in response to changes in temperature, yet wild animals often experience multiple environmental fluctuations simultaneously. This requires field experiments to decouple which ecological factor induces plasticity in fitness‐relevant traits to better understand their population‐level responses to those environmental fluctuations.For the past 32 years, we have conducted a long‐term integrative study of individually marked North American red squirrelsTamiasciurus hudsonicusErxleben in the Yukon, Canada. We have used multi‐year field experiments to examine the physiological and life‐history responses of individual red squirrels to fluctuations in food abundance and conspecific density.Our long‐term observational study and field experiments show that squirrels can anticipate increases in food availability and density, thereby decoupling the usual pattern where animals respond to, rather than anticipate, an ecological change.As in many other study systems, ecological factors that can induce plasticity (such as food and density) covary. However, our field experiments that manipulate food availability and social cues of density (frequency of territorial vocalizations) indicate that increases in social (acoustic) cues of density in the absence of additional food can induce similar life‐history plasticity, as does experimental food supplementation.Changes in the levels of metabolic hormones (glucocorticoids) in response to variation in food and density are one mechanism that seems to induce this adaptive life‐history plasticity.Although we have not yet investigated the energetic response of squirrels to elevated density or its association with life‐history plasticity, energetics research in red squirrels has overturned several standard pillars of knowledge in physiological ecology.We show how a tractable model species combined with integrative studies can reveal how animals cope with resource fluctuations through life‐history plasticity. 

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3. High sugar diet alters immune function and the gut microbiome in juvenile green iguanas ( Iguana iguana )

   https://doi.org/10.1242/jeb.246981  

   Ki, Kwanho C; Lewis, Erin L; Wu, Elizabeth; Oliaro, Francis J; Aubry, Lise M; Knapp, Charles R; Kapheim, Karen M; DeNardo, Dale; French, Susannah S (July 2024, Journal of Experimental Biology)

   ABSTRACT The present work aimed to study whether a high sugar diet can alter immune responses and the gut microbiome in green iguanas. Thirty-six iguanas were split into four treatment groups using a 2×2 design. Iguanas received either a sugar-supplemented diet or a control diet, and either a lipopolysaccharide (LPS) injection or a phosphate-buffered saline (PBS) injection. Iguanas were given their respective diet treatment through the entire study (∼3 months) and received a primary immune challenge 1 and 2 months into the experiment. Blood samples and cloacal swabs were taken at various points in the experiment and used to measure changes in the immune system (bacterial killing ability, lysis and agglutination scores, LPS-specific IgY concentrations), and alterations in the gut microbiome. We found that a sugar diet reduces bacterial killing ability following an LPS challenge, and sugar and the immune challenge temporarily alters gut microbiome composition while reducing alpha diversity. Although sugar did not directly reduce lysis and agglutination following the immune challenge, the change in these scores over a 24-h period following an immune challenge was more drastic (it decreased) relative to the control diet group. Moreover, sugar increased constitutive agglutination outside of the immune challenges (i.e. pre-challenge levels). In this study, we provide evidence that a high sugar diet affects the immune system of green iguanas (in a disruptive manner) and alters the gut microbiome. 

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4. Quantifying the Autonomic Response to Stressors—One Way to Expand the Definition of “Stress” in Animals

   https://doi.org/10.1093/icb/icaa009  

   Gaidica, Matt; Dantzer, Ben (April 2020, Integrative and Comparative Biology)

   null (Ed.)

   Abstract Quantifying how whole organisms respond to challenges in the external and internal environment (“stressors”) is difficult. To date, physiological ecologists have mostly used measures of glucocorticoids (GCs) to assess the impact of stressors on animals. This is of course too simplistic as Hans Seyle himself characterized the response of organisms to “noxious stimuli” using multiple physiological responses. Possible solutions include increasing the number of biomarkers to more accurately characterize the “stress state” of animal or just measuring different biomarkers to more accurately characterize the degree of acute or chronic stressors an animal is experiencing. We focus on the latter and discuss how heart rate (HR) and heart rate variability (HRV) may be better predictors of the degree of activation of the sympathetic–adrenal–medullary system and complement or even replace measures of GCs as indicators of animal health, welfare, fitness, or their level of exposure to stressors. The miniaturization of biological sensor technology (“bio-sensors” or “bio-loggers”) presents an opportunity to reassess measures of stress state and develop new approaches. We describe some modern approaches to gathering these HR and HRV data in free-living animals with the aim that heart dynamics will be more integrated with measures of GCs as bio-markers of stress state and predictors of fitness in free-living animals. 

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5. Population‐level variation of digestive physiology costs of mounting an immune response in damselflies

   https://doi.org/10.1111/een.12837  

   Tye, Simon_P; Blaske, Benjamin_K; Siepielski, Adam_M (January 2020, Ecological Entomology)

   1. Trade‐offs are often predicted to occur between energetically costly activities, such as somatic growth and eliciting immune responses to parasites. Although parasitism frequently reduces growth via lowered consumption, it remains unclear if the energetic demands of generating immune responses also affect the digestive physiological processes necessary for growth. Moreover, as local environmental conditions affect energetic investment towards growth and immune responses, the extent of any digestive–immune response trade‐offs may vary among populations and not be fixed at the species‐level. 2. To test these ideas, melanisation – a general innate immune response – was first induced in damselfly larvae (Enallagma vesperum) from two populations. The study then quantified growth and consumption rates, assimilation and production efficiencies, and daily metabolic rates to determine if digestive–immune response trade‐offs were present and, if so, whether they differed between populations. 3. There was no evidence of any trade‐offs between immune responses and digestive physiology components in either population. However, the results did show that populations differentially allocated energy towards different digestive physiology components after an immune response was elicited: one population increased their relative consumption and daily metabolic rates, while the other population had lower assimilation efficiencies and consumption rates. 4. Although researchers lack a mechanistic understanding of the observed population‐level differences, these results suggest that accounting for population‐level variation in digestive physiology and immune responses is critical to inferences about how immunological defences to parasitism may affect the ability for organisms to both acquire and utilise resources. 

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