Stress-related changes in leukocyte profiles and telomere shortening in the shortest-lived tetrapod, Furcifer labordi.

BACKGROUND: Life history theory predicts that during the lifespan of an organism, resources are allocated to either growth, somatic maintenance or reproduction. Resource allocation trade-offs determine the evolution and ecology of different life history strategies and define an organisms' position along a fast-slow continuum in interspecific comparisons. Labord's chameleon (Furcifer labordi) from the seasonal dry forests of Madagascar is the tetrapod species with the shortest reported lifespan (4-9 months). Previous investigations revealed that their lifespan is to some degree dependent on environmental factors, such as the amount of rainfall and the length of the vegetation period. However, the intrinsic mechanisms shaping such a fast life history remain unknown. Environmental stressors are known to increase the secretion of glucocorticoids in other vertebrates, which, in turn, can shorten telomeres via oxidative stress. To investigate to what extent age-related changes in these molecular and cellular mechanisms contribute to the relatively short lifetime of F. labordi, we assessed the effects of stressors indirectly via leukocyte profiles (H/L ratio) and quantified relative telomere length from blood samples in a wild population in Kirindy Forest. We compared our findings with the sympatric, but longer-lived sister species F. cf. nicosiai, which exhibit the same annual timing of reproductive events, and with wild-caught F. labordi that were singly housed under ambient conditions. RESULTS: We found that H/L ratios were consistently higher in wild F. labordi compared to F. cf. nicosiai. Moreover, F. labordi already exhibited relatively short telomeres during the mating season when they were 3-4 months old, and telomeres further shortened during their post-reproductive lives. At the beginning of their active season, telomere length was relatively longer in F. cf. nicosiai, but undergoing rapid shortening towards the southern winter, when both species gradually die off. Captive F. labordi showed comparatively longer lifespans and lower H/L ratios than their wild counterparts. CONCLUSION: We suggest that environmental stress and the corresponding accelerated telomere attrition have profound effects on the lifespan of F. labordi in the wild, and identify physiological mechanisms potentially driving their relatively early senescence and mortality.

Parasite burden in a short-lived chameleon, Furcifer labordi.

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.

Highly variable lifespan in an annual reptile, Labord's chameleon (Furcifer labordi).

Among tetrapods, the current record holder for shortest lifespan is Labord's chameleon, Furcifer labordi. These reptiles from the arid southwest of Madagascar have a reported lifespan of 4-5 months during the annual rainy season and spend the majority of their life (8-9 months) as a developing embryo. This semelparous, annual life history is unique among tetrapods, but only one population (Ranobe) in the southernmost distribution range has been studied. We therefore investigated the potential for environmentally-dependent variability in lifespan in a population in Kirindy Forest, which has a much longer warm rainy season. While no adults were found after March in Ranobe, the disappearance of adults was delayed by several months in Kirindy. Our data also revealed sex-biased mortality, suggesting that females have a longevity advantage. Furthermore, we found that, after an unusually long previous rainy season, one female was capable of surviving until a second breeding season. Keeping F. labordi in cages under ambient conditions demonstrated that also males can also survive until the next season of activity under these conditions. Our study therefore revealed considerable variability in the extreme life history of this tetrapod that is linked to variation in ecological factors.

Hiding deep in the trees: discovery of divergent mitochondrial lineages in Malagasy chameleons of the Calumma nasutum group.

WE CONDUCTED A COMPREHENSIVE MOLECULAR PHYLOGENETIC STUDY FOR A GROUP OF CHAMELEONS FROM MADAGASCAR (CHAMAELEONIDAE: Calumma nasutum group, comprising seven nominal species) to examine the genetic and species diversity in this widespread genus. Based on DNA sequences of the mitochondrial gene (ND2) from 215 specimens, we reconstructed the phylogeny using a Bayesian approach. Our results show deep divergences among several unnamed mitochondrial lineages that are difficult to identify morphologically. We evaluated lineage diversification using a number of statistical phylogenetic methods (general mixed Yule-coalescent model; SpeciesIdentifier; net p-distances) to objectively delimit lineages that we here consider as operational taxonomic units (OTUs), and for which the taxonomic status remains largely unknown. In addition, we compared molecular and morphological differentiation in detail for one particularly diverse clade (the C. boettgeri complex) from northern Madagascar. To assess the species boundaries within this group we used an integrative taxonomic approach, combining evidence from two independent molecular markers (ND2 and CMOS), together with genital and other external morphological characters, and conclude that some of the newly discovered OTUs are separate species (confirmed candidate species, CCS), while others should best be considered as deep conspecific lineages (DCLs). Our analysis supports a total of 33 OTUs, of which seven correspond to described species, suggesting that the taxonomy of the C. nasutum group is in need of revision.