Adaptive Developmental Delay in Chagas Disease Vectors: An Evolutionary Ecology Approach

Abstract

BackgroundThe developmental time of vector insects is important in population dynamics, evolutionary biology, epidemiology and in their responses to global climatic change. In the triatomines (Triatominae, Reduviidae), vectors of Chagas disease, evolutionary ecology concepts, which may allow for a better understanding of their biology, have not been applied. Despite delay in the molting in some individuals observed in triatomines, no effort was made to explain this variability.MethodologyWe applied four methods: (1) an e-mail survey sent to 30 researchers with experience in triatomines, (2) a statistical description of the developmental time of eleven triatomine species, (3) a relationship between development time pattern and climatic inter-annual variability, (4) a mathematical optimization model of evolution of developmental delay (diapause).Principal Findings85.6% of responses informed on prolonged developmental times in 5th instar nymphs, with 20 species identified with remarkable developmental delays. The developmental time analysis showed some degree of bi-modal pattern of the development time of the 5th instars in nine out of eleven species but no trend between development time pattern and climatic inter-annual variability was observed. Our optimization model predicts that the developmental delays could be due to an adaptive risk-spreading diapause strategy, only if survival throughout the diapause period and the probability of random occurrence of “bad” environmental conditions are sufficiently high.Conclusions/SignificanceDevelopmental delay may not be a simple non-adaptive phenotypic plasticity in development time, and could be a form of adaptive diapause associated to a physiological mechanism related to the postponement of the initiation of reproduction, as an adaptation to environmental stochasticity through a spreading of risk (bet-hedging) strategy. We identify a series of parameters that can be measured in the field and laboratory to test this hypothesis. The importance of these findings is discussed in terms of global climatic change and epidemiological consequences.

Haematophagy is costly: respiratory patterns and metabolism during feeding inRhodnius prolixus

“…Very little knowledge exists on evolutionary ecology of triatomines (Menu et al, 2010). To fill this gap, we need quantitative estimates of the costs and benefits associated with different activities (e.g.…”

Influence of Vectors’ Risk-Spreading Strategies and Environmental Stochasticity on the Epidemiology and Evolution of Vector-Borne Diseases: The Example of Chagas’ Disease

“…Such risk-spreading strategies exhibited by vector insects in stochastic environments could potentially affect the epidemiology, evolution and control of insect-borne diseases. This has been largely overlooked, except in a recent study suggesting that several species of triatomines, the vectors of Trypanosoma cruzi , the etiological agent of Chagas’ disease, exhibit, even under the same environmental conditions, an inter-individual variability of juvenile development times, and that such variability could have been selected as a response to environmental stochasticity [25]. The consequences of the variability in tick diapause duration on the epidemiology of tick-borne diseases have also been questioned [14].…”

The Quest for Immortality in Triatomines: A Meta-Analysis of the Senescence Process in Hemimetabolous Hematophagous Insects

“…Most studies in triatomines have investigated physiology, population genetics, phylogeny (see Gourbière et al, 2011 for a review) and ecology of a given species (e.g., Dumonteil et al, 2002;Gourbière et al, 2008;Barbu et al, 2011) but very few studies have investigated the evolution of life history traits in the light of evolutionary ecology concepts (Menu et al, 2010). Our study is the first comparative analysis to the senescence pattern and its relationship with life history traits in triatomines.…”

“…Environmental stochasticity and/or density-dependence processes can select bet-hedging dormancy including a development delay in insects (e.g., Menu et al, 2000;Gourbière & Menu, 2009;Rajon et al, 2009). Such a risk spreading strategy has been postulated to exist in triatomines (Menu et al, 2010) and we recommend that this approach be incorporated in future studies for understanding senescence in insects.…”