Allozyme relationships among ten species of Rhodniini, showing paraphyly of Rhodnius including Psammolestes

New in morphometry: Geometric morphometry of the external female genitalia of Triatominae (Hemiptera: Reduviidae)

The study of geometric morphometry has an impact on Triatominae studies. Currently, several taxonomic and systematic studies use this approach. The Triatominae subfamily comprises three fossil species and 154 extant species potentially capable of transmitting Trypanosoma cruzi, the causative agent of Chagas disease. This study aims to evaluate the external female genitalia of adult triatomines using multivariate geometric morphometric approaches, not only for validation but also for systematic inferences. Specimens belonging to the genera Panstrongylus, Psammolestes, Rhodnius, and Triatoma were evaluated, in addition to two species previously included in Triatoma: T. longipennis and T. phyllosoma. The results show that the external female genitalia have operational morphology and allow characterization of the species and the genera of the Triatominae. In addition, the multivariate technique enabled delimitation of the phylogenetic relationships of the subfamily, presenting results consistent with systematic studies. It can be concluded that the external female genitalia evaluated by geometric morphometry is a useful character for the taxonomy and systematics of Triatominae.

Under pressure: phenotypic divergence and convergence associated with microhabitat adaptations in Triatominae

Background

Triatomine bugs, the vectors of Chagas disease, associate with vertebrate hosts in highly diverse ecotopes. It has been proposed that occupation of new microhabitats may trigger selection for distinct phenotypic variants in these blood-sucking bugs. Although understanding phenotypic variation is key to the study of adaptive evolution and central to phenotype-based taxonomy, the drivers of phenotypic change and diversity in triatomines remain poorly understood.

Methods/results

We combined a detailed phenotypic appraisal (including morphology and morphometrics) with mitochondrial cytb and nuclear ITS2 DNA sequence analyses to study Rhodnius ecuadoriensis populations from across the species’ range. We found three major, naked-eye phenotypic variants. Southern-Andean bugs primarily from vertebrate-nest microhabitats (Ecuador/Peru) are typical, light-colored, small bugs with short heads/wings. Northern-Andean bugs from wet-forest palms (Ecuador) are dark, large bugs with long heads/wings. Finally, northern-lowland bugs primarily from dry-forest palms (Ecuador) are light-colored and medium-sized. Wing and (size-free) head shapes are similar across Ecuadorian populations, regardless of habitat or phenotype, but distinct in Peruvian bugs. Bayesian phylogenetic and multispecies-coalescent DNA sequence analyses strongly suggest that Ecuadorian and Peruvian populations are two independently evolving lineages, with little within-lineage phylogeographic structuring or differentiation.

Conclusions

We report sharp naked-eye phenotypic divergence of genetically similar Ecuadorian R. ecuadoriensis (nest-dwelling southern-Andean vs palm-dwelling northern bugs; and palm-dwelling Andean vs lowland), and sharp naked-eye phenotypic similarity of typical, yet genetically distinct, southern-Andean bugs primarily from vertebrate-nest (but not palm) microhabitats. This remarkable phenotypic diversity within a single nominal species likely stems from microhabitat adaptations possibly involving predator-driven selection (yielding substrate-matching camouflage coloration) and a shift from palm-crown to vertebrate-nest microhabitats (yielding smaller bodies and shorter and stouter heads). These findings shed new light on the origins of phenotypic diversity in triatomines, warn against excess reliance on phenotype-based triatomine-bug taxonomy, and confirm the Triatominae as an informative model system for the study of phenotypic change under ecological pressure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04647-z.

Molecular Characterization of Twenty-Five Marine Cyanobacteria Isolated from Coastal Regions of Ireland

Twenty-five marine cyanobacteria isolated from Irish coasts were characterized based on their morphological characters and 16S rRNA gene sequence analysis. In addition, superoxide dismutase (SOD) and malate dehydrogenase (MDH) isoenzyme banding patterns were used to differentiate two morphologically ambiguous isolates. In this study, six new cyanobacteria-specific primers were designed, and a 16S rRNA gene of twenty-five morphologically diverse cyanobacteria was successfully PCR amplified (1198–1396 bps). Assembled 16S rRNA sequences were used both for a basic local alignment search tool (BLAST) analysis for genus-level identification and to generate a phylogenetic tree, which yielded two major clusters: One with morphologically homogenous cyanobacteria and the other with morphologically very diverse cyanobacteria. Kamptonema okenii and Tychonema decoloratum were isolated from a single field sample of Ballybunion and were originally identified as the same ‘Oscillatoria sp.’ based on preliminary morphological observations. However, an alignment of 16S rRNA gene sequences and SOD and MDH isoenzyme banding pattern analyses helped in differentiating the morphologically-indistinguishable ‘Oscillatoria sp.’. Finally, after a re-evaluation of their morphological characters using modern taxonomic publications, the originally identified ‘Oscillatoria sp.’ were re-identified as Kamptonema okenii and Tychonema decoloratum, thus supporting the polyphasic approach of cyanobacteria characterization.

Evolution, Systematics, and Biogeography of the Triatominae, Vectors of Chagas Disease

In this chapter, we review and update current knowledge about the evolution, systematics, and biogeography of the Triatominae (Hemiptera: Reduviidae)-true bugs that feed primarily on vertebrate blood. In the Americas, triatomines are the vectors of Trypanosoma cruzi, the etiological agent of Chagas disease. Despite declining incidence and prevalence, Chagas disease is still a major public health concern in Latin America. Triatomines occur also in the Old World, where vector-borne T. cruzi transmission has not been recorded. Triatomines evolved from predatory reduviid bugs, most likely in the New World, and diversified extensively across the Americas (including the Caribbean) and in parts of Asia and Oceania. Here, we first discuss our current understanding of how, how many times, and when the blood-feeding habit might have evolved among the Reduviidae. Then we present a summary of recent advances in the systematics of this diverse group of insects, with an emphasis on the contribution of molecular tools to the clarification of taxonomic controversies. Finally, and in the light of both up-to-date phylogenetic hypotheses and a thorough review of distribution records, we propose a global synthesis of the biogeography of the Triatominae. Over 130 triatomine species contribute to maintaining T. cruzi transmission among mammals (sometimes including humans) in almost every terrestrial ecoregion of the Americas. This means that Chagas disease will never be eradicated and underscores the fact that effective disease prevention will perforce require stronger, long-term vector control-surveillance systems.

The Evolutionary Origin of Diversity in Chagas Disease Vectors

Chagas disease is amongst the ten most important neglected tropical diseases but knowledge on the diversification of its vectors, Triatominae (Hemiptera: Reduviidae), is very scarce. Most Triatominae species occur in the Americas, and are all considered potential vectors. Despite its amazing ecological vignette, there are remarkably few evolutionary studies of the whole subfamily, and only one genome sequence has been published. The young age of the subfamily, coupled with the high number of independent lineages, are intriguing, yet the lack of genome-wide data makes it a challenge to infer the phylogenetic relationships within Triatominae. Here we synthesize what is known, and suggest the next steps towards a better understanding of how this important group of disease vectors came to be.

Geological Changes of the Americas and their Influence on the Diversification of the Neotropical Kissing Bugs (Hemiptera: Reduviidae: Triatominae)

BACKGROUND

The family Reduviidae (Hemiptera: Heteroptera), or assassin bugs, is among the most diverse families of the true bugs, with more than 6,000 species. The subfamily Triatominae (kissing bugs) is noteworthy not simply because it is the only subfamily of the Reduviidae whose members feed on vertebrate blood but particularly because all 147 known members of the subfamily are potential Chagas disease vectors. Due to the epidemiological relevance of these species and the lack of an efficient treatment and vaccine for Chagas disease, it is more common to find evolutionary studies focusing on the most relevant vectors than it is to find studies aiming to understand the evolution of the group as a whole. We present the first comprehensive phylogenetic study aiming to understand the events that led to the diversification of the Triatominae.

METHODOLOGY/PRINCIPAL FINDINGS

We gathered the most diverse samples of Reduviidae and Triatominae (a total of 229 Reduviidae samples, including 70 Triatominae species) and reconstructed a robust dated phylogeny with several fossil (Reduviidae and Triatominae) calibrations. Based on this information, the possible role of geological events in several of the major cladogenetic events within Triatominae was tested for the first time. We were able to not only correlate the geological changes in the Neotropics with Triatominae evolution but also add to an old discussion: Triatominae monophyly vs. paraphyly.

CONCLUSIONS/SIGNIFICANCE

We found that most of the diversification events observed within the Rhodniini and Triatomini tribes are closely linked to the climatic and geological changes caused by the Andean uplift in South America and that variations in sea levels in North America also played a role in the diversification of the species of Triatoma in that region.

Rhodnius barretti, a new species of Triatominae (Hemiptera: Reduviidae) from western Amazonia

Rhodnius barretti , a new triatomine species, is described based on adult specimens collected in rainforest environments within the Napo ecoregion of western Amazonia (Colombia and Ecuador). R. barretti resembles Rhodnius robustus s.l. , but mitochondrial cytochrome b gene sequences reveal that it is a strongly divergent member of the “robustus lineage”, i.e., basal to the clade encompassing Rhodnius nasutus , Rhodnius neglectus , Rhodnius prolixus and five members of the R. robustus species complex. Morphometric analyses also reveal consistent divergence from R. robustus s.l. , including head and, as previously shown, wing shape and the length ratios of some anatomical structures. R. barretti occurs, often at high densities, in Attalea butyracea and Oenocarpus bataua palms. It is strikingly aggressive and adults may invade houses flying from peridomestic palms. R. barretti must therefore be regarded as a potential Trypanosoma cruzi vector in the Napo ecoregion, where Chagas disease is endemic.

Chromosomal divergence and evolutionary inferences in Rhodniini based on the chromosomal location of ribosomal genes

In this study, we used fluorescence in situ hybridisation to determine the chromosomal location of 45S rDNA clusters in 10 species of the tribe Rhodniini (Hemiptera: Reduviidae: Triatominae). The results showed striking inter and intraspecific variability, with the location of the rDNA clusters restricted to sex chromosomes with two patterns: either on one (X chromosome) or both sex chromosomes (X and Y chromosomes). This variation occurs within a genus that has an unchanging diploid chromosome number (2n = 22, including 20 autosomes and 2 sex chromosomes) and a similar chromosome size and genomic DNA content, reflecting a genome dynamic not revealed by these chromosome traits. The rDNA variation in closely related species and the intraspecific polymorphism in Rhodnius ecuadoriensis suggested that the chromosomal position of rDNA clusters might be a useful marker to identify recently diverged species or populations. We discuss the ancestral position of ribosomal genes in the tribe Rhodniini and the possible mechanisms involved in the variation of the rDNA clusters, including the loss of rDNA loci on the Y chromosome, transposition and ectopic pairing. The last two processes involve chromosomal exchanges between both sex chromosomes, in contrast to the widely accepted idea that the achiasmatic sex chromosomes of Heteroptera do not interchange sequences.

Genetics and evolution of triatomines: from phylogeny to vector control

Triatomines are hemipteran bugs acting as vectors of the protozoan parasite Trypanosoma cruzi. This parasite causes Chagas disease, one of the major parasitic diseases in the Americas. Studies of triatomine genetics and evolution have been particularly useful in the design of rational vector control strategies, and are reviewed here. The phylogeography of several triatomine species is now slowly emerging, and the struggle to reconcile the phenotypic, phylogenetic, ecological and epidemiological species concepts makes for a very dynamic field. Population genetic studies using different markers indicate a wide range of population structures, depending on the triatomine species, ranging from highly fragmented to mobile, interbreeding populations. Triatomines transmit T. cruzi in the context of complex interactions between the insect vectors, their bacterial symbionts and the parasites; however, an integrated view of the significance of these interactions in triatomine biology, evolution and in disease transmission is still lacking. The development of novel genetic markers, together with the ongoing sequencing of the Rhodnius prolixus genome and more integrative studies, will provide key tools to expanding our understanding of these important insect vectors and allow the design of improved vector control strategies.

2-DE-based proteomic investigation of the saliva of the Amazonian triatomine vectors of Chagas disease: Rhodnius brethesi and Rhodnius robustus

The triatomine bugs are obligatory haematophagous organisms that act as vectors of Chagas disease by transmitting the protozoan Trypanosoma cruzi. Their feeding success is strongly related to salivary proteins that allow these insects to access blood by counteracting host haemostatic mechanisms. Proteomic studies were performed on saliva from the Amazonian triatomine bugs: Rhodnius brethesi and R. robustus, species epidemiologically relevant in the transmission of T. cruzi. Initially, salivary proteins were separated by two-dimensional gel electrophoresis (2-DE). The average number of spots of the R. brethesi and R. robustus saliva samples were 129 and 135, respectively. The 2-DE profiles were very similar between the two species. Identification of spots by peptide mass fingerprinting afforded limited efficiency, since very few species-specific salivary protein sequences are available in public sequence databases. Therefore, peptide fragmentation and de novo sequencing using a MALDI-TOF/TOF mass spectrometer were applied for similarity-driven identifications which generated very positive results. The data revealed mainly lipocalin-like proteins which promote blood feeding of these insects. The redundancy of saliva sequence identification suggested multiple isoforms caused by gene duplication followed by gene modification and/or post-translational modifications. In the first experimental assay, these proteins were predominantly phosphorylated, suggesting functional phosphoregulation of the lipocalins.

Esterase patterns in species of the triatome bug Rhodnius

The aim of the present study was to analyse esterase patterns in three triatomine species of Rhodnius genus. Four loci, Est 1, Est 2, Est 3 and Est 4, were found. The corresponding enzymes were characterized as carboxylesterases (E.C. 3.1.1.1) or cholinesterases (E.C. 3.1.1.8) based on inhibitory experiments, using eserine sulphate, malathion, mercury chloride, p-chloromercuribenzoate (pCMB) and iodoacetamide. Low genetic variability was observed: Est 1, Est 2 and Est 3 were monomorphic in Rhodnius domesticus, Rhodnius robustus and Rhodnius neivai, whereas locus Est 4 was polymorphic in the first two species. The UPGMA analysis based on esterase genotypic frequencies indicated greater similarity between R. domesticus and R. robustus when compared with R. neivai. The present study expands our knowledge about genetic variability among triatomines and accords with the hypothesis that R. domesticus is a species derived from R. robustus.

Deciphering morphology in Triatominae: the evolutionary signals

Many species of Triatominae show evidence for morphological plasticity. Frequent taxonomic questions arose from this variability leading to disputes about describing new subspecies, species or even genera. We suggest this phenotypic flexibility is primarily an intraspecific feature, but with potential for evolutionary changes. We present arguments for a selection regime leading to the separation of species having low developmental canalization into morphologically distinct ecotypes. We suggest that these ecotypes, or morphs, or forms, may have evolutionary importance even if gene flow still exists between them. Thus, although we consider the morphological plasticity of Triatominae as an intraspecific trait, we defend the idea that it might represent a common evolutionary route to new species. Speciation processes in Triatominae could result from disruptive selection regimes combined with weak developmental canalization. Added to this basic pattern, accidental events could hasten evolutionary change. We suggest the heterosis as one of them.

Molecular genetics reveal that silvatic Rhodnius prolixus do colonise rural houses

BACKGROUND

Rhodnius prolixus is the main vector of Chagas disease in Venezuela. Here, domestic infestations of poor quality rural housing have persisted despite four decades of vector control. This is in contrast to the Southern Cone region of South America, where the main vector, Triatoma infestans, has been eliminated over large areas. The repeated colonisation of houses by silvatic populations of R. prolixus potentially explains the control difficulties. However, controversy surrounds the existence of silvatic R. prolixus: it has been suggested that all silvatic populations are in fact Rhodnius robustus, a related species of minor epidemiological importance. Here we investigate, by direct sequencing (mtcytb, D2) and by microsatellite analysis, 1) the identity of silvatic Rhodnius and 2) whether silvatic populations of Rhodnius are isolated from domestic populations.

METHODS AND FINDINGS

Direct sequencing confirmed the presence of R. prolixus in palms and that silvatic bugs can colonise houses, with house and palm specimens sharing seven cytb haplotypes. Additionally, mitochondrial introgression was detected between R. robustus and R. prolixus, indicating a previous hybridisation event. The use of ten polymorphic microsatellite loci revealed a lack of genetic structure between silvatic and domestic ecotopes (non-significant F(ST) values), which is indicative of unrestricted gene flow.

CONCLUSIONS

Our analyses demonstrate that silvatic R. prolixus presents an unquestionable threat to the control of Chagas disease in Venezuela. The design of improved control strategies is essential for successful long term control and could include modified spraying and surveillance practices, together with housing improvements.

Microsatellite markers from the Chagas disease vector, Rhodnius prolixus (Hemiptera, Reduviidae), and their applicability to Rhodnius species

Ten microsatellites were isolated and characterized from a partial genomic library of Rhodnius prolixus, the principal Chagas disease vector in Venezuela, Colombia and Central America. These polymorphic molecular markers could be particularly useful in Chagas disease control initiatives. A wider applicability of the primer-pairs isolated was shown, from 6 to 10 loci being amplifiable in five out of the ten Rhodnius species tested, namely R. domesticus, R. nasutus, R. neglectus, R. neivai and R. robustus. Interestingly, all the loci were amplified in the latter. These markers may be of interest to trace the colonization of human dwellings from triatomine sylvatic populations in order to better define epidemiological risk patterns.

Biogeography and evolution of Amazonian triatomines (Heteroptera: Reduviidae): implications for Chagas disease surveillance in humid forest ecoregions

An ecological-evolutionary classification of Amazonian triatomines is proposed based on a revision of their main contemporary biogeographical patterns. Truly Amazonian triatomines include the Rhodniini, the Cavernicolini, and perhaps Eratyrus and some Bolboderini. The tribe Rhodniini comprises two major lineages (pictipes and robustus). The former gave rise to trans-Andean (pallescens) and Amazonian (pictipes) species groups, while the latter diversified within Amazonia (robustus group) and radiated to neighbouring ecoregions (Orinoco, Cerrado-Caatinga-Chaco, and Atlantic Forest). Three widely distributed Panstrongylus species probably occupied Amazonia secondarily, while a few Triatoma species include Amazonian populations that occur only in the fringes of the region. T. maculata probably represents a vicariant subset isolated from its parental lineage in the Caatinga-Cerrado system when moist forests closed a dry trans-Amazonian corridor. These diverse Amazonian triatomines display different degrees of synanthropism, defining a behavioural gradient from household invasion by adult triatomines to the stable colonisation of artificial structures. Anthropogenic ecological disturbance (driven by deforestation) is probably crucial in the onset of the process, but the fact that only a small fraction of species effectively colonises artificial environments suggests a role for evolution at the end of the gradient. Domestic infestation foci are restricted to drier subregions within Amazonia; thus, populations adapted to extremely humid rainforest microclimates may have limited chances of successfully colonising the slightly drier artificial microenvironments. These observations suggest several research avenues, from the use of climate data to map risk areas to the assessment of the synanthropic potential of individual vector species.

Molecular research and the control of Chagas disease vectors

Chagas disease control initiatives are yielding promising results. Molecular research has helped successful programs by identifying and characterizing introduced vector populations and by defining intervention targets accurately. However, researchers and health officials are facing new challenges throughout Latin America. Native vectors persistently reinfest insecticide-treated households, and sylvatic triatomines maintain disease transmission in humid forest regions (including Amazonia) without colonizing human dwellings. In these scenarios, fine-scale vector studies are essential to define epidemiological risk patterns and clarify the involvement of little-known triatomine taxa in disease transmission. These eco-epidemiological investigations, as well as the planning and monitoring of control interventions, rely by necessity on accurate taxonomic judgments. The problems of cryptic speciation and phenotypic plasticity illustrate this need - and how molecular systematics can provide the fitting answers. Molecular data analyses also illuminate basic aspects of vector evolution and adaptive trends. Here we review the applications of molecular markers (concentrating on allozymes and DNA sequencing) to the study of triatomines. We analyze the suitability, strengths and weaknesses of the various techniques for taxonomic, systematic and evolutionary investigations at different levels (populations, species, and higher taxonomic categories).