Immune defence, dispersal and local adaptation

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Proceedings of the Royal Society B: Biological Sciences, 2004

Because parasite faunas typically show considerable spatio-temporal variation, and because parasites can have important f itness consequences, host defence mechanisms, including the immune system, can be expected to coevolve with natal dispersal, i.e. the movement of a newborn individual from its site of birth to its f irst site of reproduction. We demonstrate that immigrant individuals show a signif icantly higher humoral immune response towards a novel antigen than do local recruits in two independent populations of the great tit (Parus major). There was no effect of age, sex, tarsus length or body mass on immune responsiveness. Our results are consistent with the idea that phenotypedependent dispersal and/or dispersal-by-phenotypedependent selection establish a relation between immune responsiveness and natal dispersal.

2008

Immunity is an important biological property of organisms that protects them from parasites. Similarly, body size is one of the most important biological traits because almost all biological processes, from the cellular to the ecosystem level, scale with body size. Our goal was to determine the correlation between body size and immune function in different populations of the eastern lubber grasshopper (Romalea microptera) which differ in body size. Field data was collected on grasshopper location, size (thorax and femur lengths), and immune function (measured by melanization response). In accordance with previous work, we found a significant body size cline among populations of south Florida grasshoppers: on average, small adult grasshoppers are found in western populations whereas large grasshoppers are found in eastern populations. However, we did not find a significant relationship between body size and one measure of immune function, either within or across these populations. Fu...

2004

Ecological immunology attempts to elucidate the causes of the large variation in immunity and resistance observed in natural populations. Here we report on a novel experiment that investigated how the risks of parasitism and predation altered investment in immunity and condition in insects during larval development. The study organism is the damselfly Coenagrion puella, the parasite is a water mite and the predators are encaged Aeshna cyanea dragonflies. Our experiments show that females increase their investment in a cellular as well as a humoral component of the immune system in the presence of natural enemies. By contrast, males do not show such alteration. However, males show altered condition under the risks of parasitism and predation. Our results highlight the importance of species interactions for the plasticity of immune function.

Philosophical Transactions of the Royal Society B: Biological Sciences, 2009

An organism's fitness is critically reliant on its immune system to provide protection against parasites and pathogens. The structure of even simple immune systems is surprisingly complex and clearly will have been moulded by the organism's ecology. The aim of this review and the theme issue is to examine the role of different ecological factors on the evolution of immunity. Here, we will provide a general framework of the field by contextualizing the main ecological factors, including interactions with parasites, other types of biotic as well as abiotic interactions, intraspecific selective constraints (life-history trade-offs, sexual selection) and population genetic processes. We then elaborate the resulting immunological consequences such as the diversity of defence mechanisms (e.g. avoidance behaviour, resistance, tolerance), redundancy and protection against immunopathology, life-history integration of the immune response and shared immunity within a community (e.g. social immunity and microbiota-mediated protection). Our review summarizes the concepts of current importance and directs the reader to promising future research avenues that will deepen our understanding of the defence against parasites and pathogens.

Environmental Entomology, 2008

Although the immune functions of insects are known to correlate with body condition and food resources, the association between habitat structure and immune function is still largely unknown. We studied the effects of forest clear-cutting on encapsulation rate in gynes and workers in the forestdwelling ant Formica aquilonia. Forest logging resulted in disturbed immunity in workers and gynes. Logging enhanced encapsulation reaction in gynes, whereas decreased that of workers. In gynes, there was a likely trade-off between growth and immune function that was apparent in terms of different investment in size and immune function in different habitats. In workers, however, such associations were not found.

Functional …, 2011

1. Ecoimmunologists aim to understand the costs, benefits, and net fitness consequences of different strategies for immune defense. 2. Measuring the fitness consequences of immune responses is difficult, partly because of complex relationships between host fitness and the within-host density of parasites and immunological cells or molecules. In particular, neither the strongest immune responses nor the lowest parasite densities necessarily maximize host fitness. 3. Here, we propose that ecoimmunologists should routinely endeavour to measure three intertwined parameters: host fitness, parasite density, and relevant immune responses. We further propose that analyses of relationships among these traits would benefit from the statistical machinery used for analyses of phenotypic plasticity and/or methods that are robust to the bi-directional causation inherent in host-parasite relationships. For example, analyses of how host fitness depends upon parasite density, which is an evolutionary ecological definition of tolerance, would benefit from these more robust methods. 4. Together, these steps promote rigorous quantification of the fitness consequences of immune responses. Such quantification is essential if ecoimmunologists are to decipher causes of immune polymorphism in nature and predict trajectories of natural selection on immune defense.

Organisms in the wild are constantly faced with a wide range of environmental variability, such as fluctuation in food availability. Poor nutritional conditions influence life-histories via individual resource allocation patterns, and trade-offs between competing traits. In this study, we assessed the influence of food restriction during development on the energetically expensive traits flight metabolic rate (proxy of dispersal ability), encapsulation rate (proxy of immune defence), and lifespan using the Glanville fritillary butterfly, Melitaea cinxia, as a model organism. Additionally, we examined the direct costs of flight on individual immune function, and whether those costs increase under restricted environmental conditions. We found that nutritional restriction during development enhanced adult encapsulations rate, but reduced both resting and flight metabolic rates. However, at the individual level metabolic rates were not associated with encapsulation rate. Interestingly, individuals that were forced to fly prior to the immune assays had higher encapsulation rates than individuals that had not flown, suggesting that flying itself enhances immune response. Finally, in the control group encapsulation rate correlated positively with lifespan, whereas in the nutritional restriction group there was no relationship between these traits, suggesting that the association between encapsulation rate on adult lifespan was condition-dependent. Thus stressful events during both larval development (food limitation) and adulthood (forced flight) induce increased immune response in the adult butterflies, which may allow individuals to cope with stressful events later on in life.

Biological Journal of the Linnean Society, 2005

Ecological and evolutionary consequences of host-parasite interactions have attracted considerable attention from evolutionary biologists. Previous studies have suggested that immune responsiveness may be genetically or developmentally linked with colour pattern, such that the evolution of animal colour patterns may be influenced by correlated responses to selection for parasite resistance. We studied interactions between the endoparasitic fly Leiophora innoxia (Meigen) (Diptera: Tachinidae) and its colour polymorphic pygmy grasshopper host Tetrix undulata (Sow.) (Orthoptera: Tetrigidae) to test for morph-specific differences in parasitization and immune defence, and hostinduced variation in parasite phenotypes. Our results revealed that c. 2 and 30% of adult grasshoppers collected from the same natural population in two subsequent years, respectively were parasitized. Parasite prevalence was independent of host sex and colour morph. Pupae were larger if the parasite had developed in a female than in a male host, possibly reflecting host resource value or a physical constraint on larval growth imposed by host body size. Pupal size was also associated with host colour morph, with individuals that had developed in dark morphs being smaller at pupation compared to those that developed in paler morphs. However, immune defence, measured as the encapsulation response to a novel antigen, did not differ among individuals belonging to alternative colour morphs or sexes. Darker morphs warm up more quickly and prefer higher body temperatures than paler ones. Encapsulation was not influenced by maintenance temperature (15 vs. 30 ∞ C), however, suggesting that indirect effects of coloration on parasite resistance mediated via differential body temperature are unlikely. The dependence of parasite body size on host colour morph may thus reflect plasticity of growth and development of the larvae in response to differential host body temperature, rather than variable host immune defence.

Functional Ecology, 2011