Abstract
Life history theory predicts that species with shorter lifespan should show higher investments into growth and reproduction at the expense of immune defenses. Labord's chameleon (Furcifer labordi) is the tetrapod with the shortest known life span. To investigate to which extent immunosenescence influences the die-off of these chameleons when they are only about 6 months old, we examined the gastrointestinal-, blood- and ectoparasite burden in F. labordi in Kirindy Forest (western Madagascar) and compared them with sympatric and longer living F. cf. nicosiai. Moreover, we included data from wild F. labordi that were singly housed under ambient conditions with daily food and water supply. Gastrointestinal parasite prevalence of wild F. labordi increased dramatically during the last 3 months of their lives, which include the reproductive period. Furcifer cf. nicosiai was found to have a belated increase in gastrointestinal parasites compared to F. labordi. In F. cf. nicosiai higher prevalence of blood parasites were found, which probably result from the longer exposure to the arthropod intermediate host. Both species showed infestations with ectoparasites, which peaked in the rainy season but disappeared towards the dry season. Male F. labordi showed a significantly higher prevalence of gastrointestinal - and ectoparasites and higher intensities of coccidians and ectoparasites than females. Males of F. cf. nicosiai exhibited higher prevalence of blood- and ectoparasites, as well as higher intensities in ectoparasites. Caged individuals of both sexes showed delayed senescence, reduced parasite burden and lived longer than their wild conspecifics. Overall, the increase in the prevalence in gastrointestinal - and blood parasites towards the disappearance of the wild population of F. labordi indicates that this species invests comparatively less energy in efficient immune system function, supporting the prediction of life history theory.
Highlights
During aging, the accumulation of molecular and cellular damage is thought to lead to functional decline, resulting in compromised health and, death (Kirkwood, 2005)
Our study provides rare information about the age-related patterns of health in the shortest living tetrapod species in the wild and suggest that F. labordi rather relies on nonspecific and inflammatory immune defenses than on acquired immunity
As the prevalence in parasites increased comparatively later in F. cf. nicosiai, we suspect that this species invests more energy in the development of an adaptive immune system until maturation
Summary
The accumulation of molecular and cellular damage is thought to lead to functional decline, resulting in compromised health and, death (Kirkwood, 2005). “fast-living” species are supposed to rely more on low-cost nonspecific and inflammatory immune defenses, whereas “slow-living” species exhibit rather cost-intensive stronger specific and especially antibody-mediated immunity, which is required as defense against parasites, for instance (Lee, 2006). Besides these trade-offs, within vertebrates the functioning of the immune system changes over time, from the development of adaptive immunity at birth to the deterioration of the system at old age (Albright and Albright, 1994; Malaguanera et al 2001; Humphreys and Grencis, 2000; Hayward, 2013). Tissue destruction is often caused by parasites and Th2 cell mediated immunity evolved as an adaptive tissue repair mechanism that quickly heals the wounds they inflict (Allen and Wynn, 2011)
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