Some equatorial environments exhibit substantial within-location variation in environmental conditions throughout the year and yet have year-round breeding birds. This implies that breeding in such systems are potentially unrelated to the... more
Some equatorial environments exhibit substantial within-location variation in environmental conditions throughout the year and yet have year-round breeding birds. This implies that breeding in such systems are potentially unrelated to the variable environmental conditions. By breeding not being influenced by environmental conditions, we become sure that any differences in immune function between breeding and non-breeding birds do not result from environmental variation, therefore allowing for exclusion of the confounding effect of variation in environmental conditions. This create a unique opportunity to test if immune function is down-regulated during reproduction compared to non-breeding periods. We compared the immune functions of sympatric male and female chick-feeding and non-breeding Red-capped Calandrella cinerea and Rufous-naped Larks Mirafra africana in equatorial East Africa. These closely-related species occupy different niches and have different breeding strategies in th...
A phylogenetic analysis of basal metabolism, total evaporative water loss, and life-history among foxes from desert and mesic regions
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Nest attentiveness and egg temperature do not explain the variation in incubation periods in tropical birds
Nest attentiveness and egg temperature do not explain the
Physiological and behavioural correlates of life-history
SUMMARYDesert birds often experience a scarcity of drinking water and food and must survive episodes of high ambient temperature (Ta). The physiological mechanisms that promote survival during extended periods of high Ta have received... more
SUMMARYDesert birds often experience a scarcity of drinking water and food and must survive episodes of high ambient temperature (Ta). The physiological mechanisms that promote survival during extended periods of high Ta have received little attention. We investigated the physiological responses of wild-caught and captive-reared Houbara bustards, Chlamydotis macqueenii, to Ta values ranging from below 0°C to 55°C, well above those in most previous studies of birds. Captive-reared Houbara bustards (mass 1245±242 g, N=7, mean ± s.d.) in summer have a resting metabolic rate (RMR) of 261.4 kJ day–1, 26 % below allometric predictions, and a total evaporative water loss (TEWL) at 25°C of 25.8 g day–1, 31 % below predictions. When Ta exceeded body temperature (Tb), the dry heat transfer coefficient decreased, a finding supporting the prediction that birds should minimize dry heat gain from the environment at high Ta values. Houbara bustards withstand high Ta values without becoming hyperth...
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The ‘energy demand’ hypothesis for short-term adjustments in basal metabolic rate (BMR) posits that birds adjust the size of their internal organs relative to food intake, a correlate of energy demand. We tested this hypothesis on hoopoe... more
The ‘energy demand’ hypothesis for short-term adjustments in basal metabolic rate (BMR) posits that birds adjust the size of their internal organs relative to food intake, a correlate of energy demand. We tested this hypothesis on hoopoe larks (Alaemon alaudipes), inhabitants of the Arabian desert, by acclimating birds for 3 weeks at 15 °C and at 36 °C, then measuring their BMR and total evaporative water loss (TEWL). Thereafter, we determined the dry masses of their brain, heart, liver, kidney, stomach, intestine and muscles of the pectoral region. Although mean body mass did not differ initially between the two groups, after 3 weeks, birds in the 15 °C group had gained mass (44.1±6.5 g), whereas larks in the 36 °C group had maintained a constant mass (36.6±3.6 g; means ± S.D., N=6). Birds in the 15 °C group had a mean BMR of 46.8±6.9 kJ day−1, whereas birds in the 36 °C group had a BMR of 32.9±6.3 kJ day−1, values that were significantly different when we controlled for difference...
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Animals exhibit seasonal cycles in a variety of physiological and behavioral traits. Studies of these cycles can potentially offer new insights into the evolution of individual differences. For natural selection to act, a trait must be... more
Animals exhibit seasonal cycles in a variety of physiological and behavioral traits. Studies of these cycles can potentially offer new insights into the evolution of individual differences. For natural selection to act, a trait must be both distinctive within individuals and variable among individuals. The extent to which the amplitude and phase of seasonal cycles fulfill these requirements is not well documented. As a preliminary analysis, we investigated seasonal cycles in the body mass of pigeons, which we weighed quarterly over a period of six years. [Our work with these animals complied with all applicable institutional regulations (University of Groningen Animal Experimentation Committee, license no. 5095) and Dutch and European laws.] We employed several of statistical techniques aimed at 1) quantifying the repeatability of seasonality and 2) comparing within- and among-individual variation in seasonality. Our goal is to take what we have learned from our analyses of mass and...
Research Interests:
Some equatorial environments exhibit substantial within-location variation in environmental conditions throughout the year and yet have year-round breeding birds. This implies that breeding in such systems are potentially unrelated to the... more
Some equatorial environments exhibit substantial within-location variation in environmental conditions throughout the year and yet have year-round breeding birds. This implies that breeding in such systems are potentially unrelated to the variable environmental conditions. By breeding not being influenced by environmental conditions, we become sure that any differences in immune function between breeding and non-breeding birds do not result from environmental variation, therefore allowing for exclusion of the confounding effect of variation in environmental conditions. This create a unique opportunity to test if immune function is down-regulated during reproduction compared to non-breeding periods. We compared the immune functions of sympatric male and female chick-feeding and non-breeding Red-capped Calandrella cinerea and Rufous-naped Larks Mirafra africana in equatorial East Africa. These closely-related species occupy different niches and have different breeding strategies in th...
A phylogenetic analysis of basal metabolism, total evaporative water loss, and life-history among foxes from desert and mesic regions
Nest attentiveness and egg temperature do not explain the variation in incubation periods in tropical birds
Nest attentiveness and egg temperature do not explain the
Physiological and behavioural correlates of life-history
SUMMARYDesert birds often experience a scarcity of drinking water and food and must survive episodes of high ambient temperature (Ta). The physiological mechanisms that promote survival during extended periods of high Ta have received... more
SUMMARYDesert birds often experience a scarcity of drinking water and food and must survive episodes of high ambient temperature (Ta). The physiological mechanisms that promote survival during extended periods of high Ta have received little attention. We investigated the physiological responses of wild-caught and captive-reared Houbara bustards, Chlamydotis macqueenii, to Ta values ranging from below 0°C to 55°C, well above those in most previous studies of birds. Captive-reared Houbara bustards (mass 1245±242 g, N=7, mean ± s.d.) in summer have a resting metabolic rate (RMR) of 261.4 kJ day–1, 26 % below allometric predictions, and a total evaporative water loss (TEWL) at 25°C of 25.8 g day–1, 31 % below predictions. When Ta exceeded body temperature (Tb), the dry heat transfer coefficient decreased, a finding supporting the prediction that birds should minimize dry heat gain from the environment at high Ta values. Houbara bustards withstand high Ta values without becoming hyperth...
Research Interests:
The ‘energy demand’ hypothesis for short-term adjustments in basal metabolic rate (BMR) posits that birds adjust the size of their internal organs relative to food intake, a correlate of energy demand. We tested this hypothesis on hoopoe... more
The ‘energy demand’ hypothesis for short-term adjustments in basal metabolic rate (BMR) posits that birds adjust the size of their internal organs relative to food intake, a correlate of energy demand. We tested this hypothesis on hoopoe larks (Alaemon alaudipes), inhabitants of the Arabian desert, by acclimating birds for 3 weeks at 15 °C and at 36 °C, then measuring their BMR and total evaporative water loss (TEWL). Thereafter, we determined the dry masses of their brain, heart, liver, kidney, stomach, intestine and muscles of the pectoral region. Although mean body mass did not differ initially between the two groups, after 3 weeks, birds in the 15 °C group had gained mass (44.1±6.5 g), whereas larks in the 36 °C group had maintained a constant mass (36.6±3.6 g; means ± S.D., N=6). Birds in the 15 °C group had a mean BMR of 46.8±6.9 kJ day−1, whereas birds in the 36 °C group had a BMR of 32.9±6.3 kJ day−1, values that were significantly different when we controlled for difference...
Research Interests:
Animals exhibit seasonal cycles in a variety of physiological and behavioral traits. Studies of these cycles can potentially offer new insights into the evolution of individual differences. For natural selection to act, a trait must be... more
Animals exhibit seasonal cycles in a variety of physiological and behavioral traits. Studies of these cycles can potentially offer new insights into the evolution of individual differences. For natural selection to act, a trait must be both distinctive within individuals and variable among individuals. The extent to which the amplitude and phase of seasonal cycles fulfill these requirements is not well documented. As a preliminary analysis, we investigated seasonal cycles in the body mass of pigeons, which we weighed quarterly over a period of six years. [Our work with these animals complied with all applicable institutional regulations (University of Groningen Animal Experimentation Committee, license no. 5095) and Dutch and European laws.] We employed several of statistical techniques aimed at 1) quantifying the repeatability of seasonality and 2) comparing within- and among-individual variation in seasonality. Our goal is to take what we have learned from our analyses of mass and...
Research Interests:
Nest survival is critical to breeding in birds and plays an important role in life‐history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal... more
Nest survival is critical to breeding in birds and plays an important role in life‐history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal patterns are biased in favor of temperate regions. Yet, such studies are especially pertinent to the tropics, where nest predation rates are typically high and environmental conditions often allow for year‐round breeding. To tease apart the effects of calendar month and year, population‐level breeding activity and environmental conditions, we studied nest survival over a 64‐month period in equatorial, year‐round breeding red‐capped larks Calandrella cinerea in Kenya. We show that daily nest survival rates varied with time, but not in a predictable seasonal fashion among months or consistently among years. We found negative influences of flying invertebrate biomass and rain on nest survival and higher survival of nests when nests were more abundant, which s...
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Nest survival is critical to breeding in birds and plays an important role in life‐history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal... more
Nest survival is critical to breeding in birds and plays an important role in life‐history evolution and population dynamics. Studies evaluating the proximate factors involved in explaining nest survival and the resulting temporal patterns are biased in favor of temperate regions. Yet, such studies are especially pertinent to the tropics, where nest predation rates are typically high and environmental conditions often allow for year‐round breeding. To tease apart the effects of calendar month and year, population‐level breeding activity and environmental conditions, we studied nest survival over a 64‐month period in equatorial, year‐round breeding red‐capped larks Calandrella cinerea in Kenya. We show that daily nest survival rates varied with time, but not in a predictable seasonal fashion among months or consistently among years. We found negative influences of flying invertebrate biomass and rain on nest survival and higher survival of nests when nests were more abundant, which s...
Research Interests:
Predation risk is thought to modify the physiology of prey mainly through the stress response. However, little is known about its potential effects on the immunity of animals, particularly in young individuals, despite the importance of... more
Predation risk is thought to modify the physiology of prey mainly through the stress response. However, little is known about its potential effects on the immunity of animals, particularly in young individuals, despite the importance of overcoming wounding and pathogen aggression following a predator attack. We investigated the effect of four progressive levels of nest predation risk on several components of the immune system in common blackbird () nestlings by presenting them with four different calls during 1 h: non-predator calls, predator calls, parental alarm calls and conspecific distress calls to induce a null, moderate, high and extreme level of risk, respectively. Nest predation risk induced an increase in ovotransferrin, immunoglobulin and the number of lymphocytes and eosinophils. Thus, the perception of a potential predator per se could stimulate the mobilization of a nestling's immune function and enable the organism to rapidly respond to the immune stimuli imposed ...
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Intercellular and covalently bound lipids within the stratum corneum (SC), the outermost layer of the epidermis, are the primary barrier to cutaneous water loss (CWL) in birds. We compared CWL and intercellular SC lipid composition in 20... more
Intercellular and covalently bound lipids within the stratum corneum (SC), the outermost layer of the epidermis, are the primary barrier to cutaneous water loss (CWL) in birds. We compared CWL and intercellular SC lipid composition in 20 species of birds from desert and mesic environments. Furthermore, we compared covalently bound lipids with CWL and intercellular lipids in the lark family (Alaudidae). We found that CWL increases in birds from more mesic environments, and this increase was related to changes in intercellular SC lipid composition. The most consistent pattern that emerged was a decrease in the relative amount of cerebrosides as CWL increased, a pattern that is counterintuitive based on studies of mammals with Gaucher disease. Although covalently bound lipids in larks did not correlate with CWL, we found that covalently bound cerebrosides correlated positively with intercellular cerebrosides and intercellular cholesterol ester, and intercellular cerebrosides correlated...
Research Interests: Biology, Medicine, Biological Sciences, Lipids, Desert, and 14 moreBirds, Animals, Confidence intervals, Lipid metabolism, Epidermis, Sphingolipids, Laser Scanning Microscopy, Stratum Corneum, Environment, Permeability Barrier, Experimental Biology, Intracellular, Larks, and Medical and Health Sciences
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Summary Birds have adjusted their life-history and physiological traits to the characteristics of the seasonally changing environments they inhabit. Annual cycles in physiology can result from phenotypic flexibility or from variation in... more
Summary Birds have adjusted their life-history and physiological traits to the characteristics of the seasonally changing environments they inhabit. Annual cycles in physiology can result from phenotypic flexibility or from variation in its genetic basis. A key physiological trait that shows seasonal variation is basal metabolic rate (BMR). We studied genetic and phenotypic variation in the annual cycles of body mass, BMR and mass-specific BMR in three stonechat subspecies (Saxicola torquata) originating from environments that differ in seasonality, and in two hybrid lines. Birds were kept in a common garden set-up, under annually variable day length and at constant temperature. We also studied whether stonechats use the proximate environmental factor temperature as a cue for changes in metabolic rate, by keeping birds at two different temperature regimes. We found that the different subspecies kept in a common environment had different annual cycles of body mass, BMR (variance: Kaz...
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Summary Trade-offs between immune function and other physiological and behavioral processes are central in ecoimmunology, but one important problem is how to distinguish a reallocation of resources away from the immune system from a... more
Summary Trade-offs between immune function and other physiological and behavioral processes are central in ecoimmunology, but one important problem is how to distinguish a reallocation of resources away from the immune system from a reallocation or redistribution within the immune system. While variation in baseline values of individual immune parameters is well established, studies in wild animals on multiple parameters during an immune response are lacking. It also remains to be tested if and how immune responses correlate with baseline values that vary e.g. over the course of an annual cycle. We studied immunological responses to an endotoxin challenge in skylarks (Alauda arvensis), a partial migrant bird breeding in temperate zones. We compared birds injected with the endotoxin LPS with un-injected controls, characterizing immunological responses with leukocyte profiles, titres of lytic enzymes and natural antibodies, and concentrations of haptoglobin and heat shock proteins. We...
Research Interests: Immunology, Colorimetry, Biology, Inflammation, Biological Sciences, and 15 moreBirds, Female, Animals, Ecological Immunology, Immune system, Annual Cycle, Heat Shock Proteins, Haptoglobin, Acute Phase Response, Hemagglutination, Leukocytes, Broiler Chickens, Experimental Biology, Hemolysis, and Humoral Immunity
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Summary Animals cope with seasonal variation in environmental factors by adjustments of physiology and life history. When seasonal variation is partly predictable, such adjustments can be based on a genetic component or be phenotypically... more
Summary Animals cope with seasonal variation in environmental factors by adjustments of physiology and life history. When seasonal variation is partly predictable, such adjustments can be based on a genetic component or be phenotypically flexible. Animals have to allocate limited resources over different demands, including immune function. Accordingly, immune traits could change seasonally. Such changes could have a genetic component that differ between environments. We tested this hypothesis in genotypically distinct groups of a widespread songbird, the stonechat (Saxicola torquata). We compared variation in immunity during one year of long-distance migrants, short-distance migrants, tropical residents and hybrids in a common garden environment. Additionally, we investigated phenotypically flexible responses to temperature by applying different temperature regimes to one group. We assessed constitutive immunity by measuring hemagglutination, hemolysis, haptoglobin and bactericidal ...
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SUMMARYOne route to gain insight into the causes and consequences of ecological differentiation is to understand the underlying physiological mechanisms. We explored the relationships between immunological and oxidative status and... more
SUMMARYOne route to gain insight into the causes and consequences of ecological differentiation is to understand the underlying physiological mechanisms. We explored the relationships between immunological and oxidative status and investigated how birds cope physiologically with the effects of immune-derived oxidative damage. We successively implemented two experimental manipulations to alter physiological status in a model bird species: the homing pigeon (Columba livia). The first manipulation, an immune supplementation, was achieved by oral administration of lysozyme, a naturally occurring and non-specific antimicrobial enzyme. The second manipulation, an immune challenge, took the form of an injection with lipopolysaccharide, a bacterial endotoxin. Between groups of lysozyme-treated and control birds, we compared lipopolysaccharide-induced changes in reactive oxygen metabolites, total antioxidant capacity, haptoglobin, oxygen consumption, body mass and cloacal temperature. Lysozy...
Research Interests: Immunology, Life history, Biology, Inflammation, Innate immunity, and 15 moreBiological Sciences, Endotoxin, Antioxidants, Female, Animals, Dietary Supplements, Behavioral Animal Models, Immune system, Barn Swallow, Columbidae, Great Tits, Haptoglobin, Experimental Biology, Columbiformes, and Antioxidant Protection
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SummaryMost birds rely on flight for survival. Yet as an energetically-taxing and physiologically-integrative process, flight has many repercussions. Studying pigeons (Columba livia) and employing physiological and immunological indices... more
SummaryMost birds rely on flight for survival. Yet as an energetically-taxing and physiologically-integrative process, flight has many repercussions. Studying pigeons (Columba livia) and employing physiological and immunological indices that are relevant to ecologists working with wild birds, we determined what, if any, acute immune-like responses result from bouts of intense, non-migratory flight. We compared the effects of flight with the effects of a simulated bacterial infection. We also investigated indices in terms of their post-flight changes within individuals and their relationship with flight speed among individuals. Compared to un-flown controls, flown birds exhibited significant elevations in numbers of heterophils relative to numbers of lymphocytes and significant reductions in numbers eosinophils and monocytes. Furthermore, within-individual changes in concentrations of an acute phase protein were greater in flown birds than in controls. However, none of the flight-aff...
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Despite their central importance for the evolution of physiological variation, the genetic mechanisms that determine energy expenditure in animals have largely remained unstudied. We used quantitative genetics to confirm that both... more
Despite their central importance for the evolution of physiological variation, the genetic mechanisms that determine energy expenditure in animals have largely remained unstudied. We used quantitative genetics to confirm that both mass-specific and whole-organism basal metabolic rate (BMR) were heritable in a captive-bred population of stonechats (Saxicola torquataspp.) founded on birds from three wild populations (Europe, Africa and Asia) that differed in BMR. This argues that BMR is at least partially under genetic control by multiple unknown nuclear loci each with a limited effect on the phenotype. We then tested for a genetic effect on BMR based on mitochondrial–nuclear coadaptation using hybrids between ancestral populations with high and low BMR (Europe–Africa and Asia–Europe), with different parental configurations (femalehigh–malelowor femalelow–malehigh) within each combination of populations. Hybrids with different parental configurations have on average identical mixtures...
Research Interests: Genetics, Biology, Mitochondria, Medicine, Energy Metabolism, and 14 moreBiological Sciences, Mitochondrial DNA, Female, Animals, Male, Research article, Songbirds, Body Size, nuclear DNA, Metabolic rate, Basal metabolic rate (BMR), Genetic variation, Medical and Health Sciences, and Basal Metabolism
Research Interests: Amplification, Biology, Medicine, Energy Metabolism, Mammals, and 15 moreBiological Sciences, Mitochondrial DNA, Birds, Animals, Energy Expenditure, Aridity, Food habits, Arid, Life Histories, Evaporative Water Loss, Alaudidae, Molecular Sequence Data, Larks, Medical and Health Sciences, and Basal Metabolism
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Research Interests: Physiology, Biology, Ecology, Medicine, Energy Metabolism, and 15 moreBirds, Animals, Energy Expenditure, Medical Physiology, Metabolic rate, Doubly Labeled Water, Body water, Ambient Temperature, Arid, Environmental Temperature, Arid Environment, Field Metabolic Rate, Evaporative Water Loss, Phylogenetically independent contrasts, and Basal Metabolism
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Variation in demographic and physiological attributes of life history is thought to fall on one single axis, a phenomenon termed the Pace‐of‐Life. A slow Pace‐of‐Life is characterized by low annual reproduction, long life span and low... more
Variation in demographic and physiological attributes of life history is thought to fall on one single axis, a phenomenon termed the Pace‐of‐Life. A slow Pace‐of‐Life is characterized by low annual reproduction, long life span and low metabolic rate, a fast Pace‐of‐Life by the opposite characteristics. The existence of a single axis has been attributed to constraints among physiological mechanisms that are thought to restrict evolutionary potential. In that case, physiological traits should covary in the same fashion at the levels of individual organisms and species. We examined covariation at the levels of individual and subspecies in three physiological systems (metabolic, endocrine and immune) using four stonechat subspecies with distinct life‐history strategies in a common‐garden set‐up. We measured basal metabolic rate, corticosterone as endocrine measure and six measures of constitutive immunity. Metabolic rate covaried with two indices of immunity at the individual level, and...