The impacts of invaders: Basal and acute stress glucocorticoid profiles and immune function in native lizards threatened by invasive ants (original) (raw)
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General and comparative endocrinology, 2014
Prolonged elevations of glucocorticoids due to long-duration (chronic) stress can suppress immune function. It is unclear, however, how natural stressors that result in repeated short-duration (acute) stress, such as frequent agonistic social encounters or predator attacks, fit into our current understanding of the immune consequences of stress. Since these types of stressors may activate the immune system due to increased risk of injury, immune suppression may be reduced at sites where individuals are repeatedly exposed to potentially damaging stressors. We tested whether repeated acute elevation of corticosterone (CORT, a glucocorticoid) suppresses immune function in eastern fence lizards (Sceloporus undulatus), and whether this effect varies between lizards from high-stress (high baseline CORT, invaded by predatory fire ants) and low-stress (low baseline CORT, uninvaded) sites. Lizards treated daily with exogenous CORT showed higher hemagglutination of novel proteins by their pla...
Wildlife Research, 2011
Context. Aggressive encounters, including those with venomous species, impose selective pressure on native species. Immediate lethal outcomes of these encounters have been the primary focus of research in this field. However, not all aggressive interactions result in immediate mortality, and indirect consequences of aggressive interactions may be an equally important but under-considered selective force. The red imported fire ant is a globally important venomous invader that imposes novel selective pressure on native communities.
Sublethal effects of invasive fire ant venom on a native lizard
Journal of Experimental Zoology …, 2010
Invasive species can impose novel selection pressures on natives, such as toxins to which native taxa are not adapted. Native species may survive such invasions by evolving mechanisms to avoid toxin exposure or increase toxin tolerance. Red imported fire ants (Solenopsis invicta) employ an alkaloid-based venom to defend their colonies and capture prey. In this study we aim to characterize the sublethal effects of invasive fire ant venom on a native vertebrate, the eastern fence lizard (Sceloporus undulatus), and to determine whether lizard populations that have been exposed to these fire ants for $35 generations have increased physiological resistance to the venom. We documented the sublethal impact of fire ant venom on fence lizard performance by naturally exposing lizards to fire ant stings and recording changes in three fitness-relevant measures: bite force, righting ability, and sprint speed. We also measured blood hemolysis induced by the venom. To test for the development of physiological resistance to fire ant venom we compared whole-body performance and hemolysis for two populations of lizards with different fire ant invasion histories. Fire ant venom showed no dosage-dependent sublethal effects on performance. In addition, there is no evidence that lizards have evolved increased physiological resistance: the impact of fire ant venom on whole-body performance and hemolysis did not differ between the naïve and experienced populations. Lizards may instead rely on adaptive shifts in escape behavior and morphology following invasion to survive fire ant attack.
Invader danger: lizards faced with novel predators exhibit an altered behavioral response to stress
Hormones and behavior, 2011
Animals respond to stressors by producing glucocorticoid stress hormones, such as corticosterone (CORT). CORT acts too slowly to trigger immediate behavioral responses to a threat, but can change longer-term behavior, facilitating an individual's survival to subsequent threats. To be adaptive, the nature of an animal's behavior following elevated CORT levels should be matched to the predominant threats that they face. Seeking refuge following a stressful encounter could be beneficial if the predominant predator is a visual hunter, but may prove detrimental when the predominant predator is able to enter these refuge sites. As a result, an individual's behavior when their CORT levels are high may differ among populations of a single species. Invasive species impose novel pressures on native populations, which may select for a shift in their behavior when CORT levels are high. We tested whether the presence of predatory invasive fire ants (Solenopsis invicta) at a site affects the behavioral response of native eastern fence lizards (Sceloporus undulatus) to elevated CORT levels. Lizards from an uninvaded site were more likely to hide when their CORT levels were experimentally elevated; a response that likely provides a survival advantage for lizards faced with native predatory threats (e.g. birds and snakes). Lizards from a fire ant invaded site showed the opposite response; spending more time moving and up on the basking log when their CORT levels were elevated. Use of the basking log likely reflects a refuge-seeking behavior, rather than thermoregulatory activity, as selected body temperatures were not affected by CORT. Fleeing off the ground may prove more effective than hiding for lizards that regularly encounter small, terrestrially-foraging fire ant predators. This study suggests that invasive species may alter the relationship between the physiological and behavioral stress response of native species.
The urban environment presents new and diVerent challenges to wildlife, but also potential opportunities depending on the species. As urban encroachment onto native habitats continues, understanding the impact of this expansion on native species is vital to conservation. A key physiological indicator of environmental disturbance is the vertebrate stress response, involving increases in circulating glucocorticoids (i.e. corticosterone), which exert inXuence on numerous physiological parameters including energy storage, reproduction, and immunity. We examined how urbanization in Phoenix, Arizona inXuences corticosterone levels, blood parasitism, and innate immunity in populations of tree lizards (Urosaurus ornatus) to determine whether urbanization may be detrimental or beneWcial to this species. Both baseline and stress-induced corticosterone concentrations were signiWcantly lower in urban lizards relative to the rural ones, however, the magnitude of the increase in corticosterone with stress did not diVer across populations. Urban lizards also had a lower ratio of heterophils to lymphocytes, but elevated overall leukocyte count, as compared to lizards from the natural site. Urban and rural lizards did not diVer in their prevalence of the blood parasite, Plasmodium mexicanum. Taken together, these results suggest that urban tree lizards may have suppressed overall corticosterone concentrations possibly from down-regulation as a result of frequent exposure to stressors, or increased access to urban resources. Also, urban lizards may have bolstered immunocompetence possibly from increased immune challenges, such as wounding, in the urban environment, or from greater energetic reserves being available as a result of access to urban resources.
Immune responses vary with parasite burden in an insular lizard
Evolutionary Ecology Research, 2015
Background: Immunological studies are often context-independent. However, an alternative is emerging in the form of eco-immunology, which focuses on the natural variation in immune functions of free-living organisms in relation to their ecological constraints and evolutionary context. Immunological research also tends to study only parasite resistance – that is, mechanisms by which hosts prevent infection or reduce parasite growth. But eco-immunology addresses tolerance as well as resistance. Through tolerance, hosts defend themselves by minimizing the damage caused by parasites instead of reducing parasite infection. Goal: To determine the immune responses of free-living lizards that have varying parasite loads and body conditions. Organism: A wild, insular population of Podarcis lilfordi. Method: Immune response was measured as the bactericidal strength of plasma, and the immune response was examined with respect to parasite load and to body condition. Results: Immune responses we...
Ecology Letters, 1998
Parasites affect the life-histories and fitness of their hosts. It has been demonstrated that the ability of the immune system to cope with parasites partly depends on environmental conditions. In particular, stressful conditions have an immunosuppressive effect and may affect disease resistance. The relationship between environmental stress and parasitism was investigated using a blood parasite of the common lizard Lacerta vivipara. In laboratory cages, density and additional stressors had a significant effect on the intensity of both natural parasitaemia and parasitaemia induced by experimental infection. Four weeks after infection, crowded lizards had three times more parasites than noncrowded lizards. After 1 month of stress treatment, naturally infected lizards had a significantly higher level of plasma corticosterone and a higher parasite load than nonstressed individuals. In seminatural enclosures, stress induced by the habitat quality affected both the natural blood parasite prevalence and the intensity of parasitaemia of the host.
Immune Defense of Ants Is Associated with Changes in Habitat Characteristics
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.
Invasive fire ants alter behavior and morphology of native lizards
Ecology, 2009
Nonnative species introductions are becoming more common, but long-term consequences of the novel pressures imposed by invaders on native species remain poorly known. The red imported fire ant, Solenopsis invicta, is an invasive species with potential global impact. Comparison of lizards across the invasive range within the United States reveals novel antipredator strategies and altered morphologies that mitigate potentially lethal attack by these ants, within 70 years of their introduction. The likelihood that adult lizards will behaviorally respond to fire ant attack increases with time since invasion, but hatchlings exhibit high levels of antipredator behavior irrespective of their site of origin. Adults and hatchlings from sites invaded longer ago also have relatively longer hind limbs. This trait increases the effectiveness of behavioral strategies for removing ants and is likely an adaptive response to minimize envenomation during attack. The observed changes are not correlated with habitat, exposure to fire ants, or latitude, arguing against phenotypic plasticity and learning as causal mechanisms, and museum specimens show that morphological differences were not evident prior to fire ant invasion. These data contribute to our growing awareness that ecological invasions can prompt adaptive responses, altering the nature of interactions between invaders and the natives they contact.