Phenotypic convergence in Chagas disease vectors: Rhodnius neglectus from Copernicia prunifera palms may express the typical Rhodnius nasutus color phenotype.

BACKGROUND: Selection for camouflage coloration can lead to phenotypic convergence when closely-related taxa adapt to microhabitats with similar substrate color. Such convergence can, in turn, complicate species diagnosis - an issue of practical relevance when human-disease vectors are involved. Here, we present evidence suggesting that the Chagas disease vectors Rhodnius neglectus and R. nasutus may express similar, substrate-matching color phenotypes when they occupy Copernicia prunifera palms - the primary habitat of R. nasutus in northeastern Brazil.

METHODS: We studied triatomines from C. prunifera sampled across the semiarid Caatinga and the Caatinga-Cerrado savanna transition, comparing them with specimens from core-Cerrado Mauritia flexuosa palms. Triatomines were identified by phenotype, then genotyped using mitochondrial cytb and nuclear rDNA ITS2 clone-sequences.

RESULTS: Adult-specimen color patterns distinguished core-Cerrado dark brown (typical) R. neglectus from core-Caatinga light brown (typical) R. nasutus, but were dubious in bugs caught in C. prunifera from the Caatinga-Cerrado transition and parts of the central-western Caatinga. Bayesian cytb genealogies placed dubious-phenotype specimens resembling typical R. nasutus in a sub-clade sister to typical R. neglectus from M. flexuosa - with ~2% mean cytb divergence between sub-clades. ITS2 genealogies recovered R. neglectus and R. nasutus as paraphyletic; however, a multispecies-coalescent analysis suggested that, after accounting for incomplete lineage sorting, dubious-phenotype bugs from C. prunifera cluster with typical R. neglectus.

CONCLUSIONS: Rhodnius neglectus dwelling in C. prunifera palms can be chromatically similar to typical, light brown R. nasutus. Mitochondrial cytb sequence analyses helped address the taxonomic uncertainty brought about by this apparent phenotypic convergence. ITS2 results were less clear-cut, with multispecies-coalescent analysis results suggestive of incomplete lineage sorting. Taken together, our results raise the possibility that the atypical, light brown hue of R. neglectus specimens inhabiting C. prunifera may stem from predator-driven natural selection favoring camouflage phenotypes that better match the palm-crown substrate color. These findings contribute to our understanding of color variation in triatomines and call into question the widespread use of overall body color as a key phenotypic character in the taxonomy of these medically important insects.