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Comparative morphometric and molecular genetic analyses of triatominae (Hemiptera : Reduviidae)
... In general, the elongated heads of northern, primarily palm-dwelling populations (Tsáchilas and Manabí) sharply contrast with the shorter, stouter heads of southern-Andean populations (Figs. 3, 5c, 6a). As discussed below, this may be related to a transition from palm to nest microhabitats [2,89]. ...
... In Loja, wild R. ecuadoriensis often breed inside the nests of the tree-squirrel, Sciurus stramineus/nebouxii [2,30,32,33,91]. Within nest microhabitats, the close physical proximity between the (virtually ectoparasitic) bugs and their hosts would relax selection for long/narrow heads and mouthparts, which may be required for biting free-ranging hosts more safely (at a longer distance) and sucking their blood faster (thanks to larger cibarial-pump muscles) [89,92]. In addition, and as has been also postulated for domestic triatomine populations [4], an overall more predictable food supply within a nest (or human dwelling), with a higher likelihood of repeated smaller blood meals, would relax the need for growing bigger bodies capable of storing larger amounts of blood [89]. ...
... Within nest microhabitats, the close physical proximity between the (virtually ectoparasitic) bugs and their hosts would relax selection for long/narrow heads and mouthparts, which may be required for biting free-ranging hosts more safely (at a longer distance) and sucking their blood faster (thanks to larger cibarial-pump muscles) [89,92]. In addition, and as has been also postulated for domestic triatomine populations [4], an overall more predictable food supply within a nest (or human dwelling), with a higher likelihood of repeated smaller blood meals, would relax the need for growing bigger bodies capable of storing larger amounts of blood [89]. Finally, hostmediated (passive) dispersal is probably more important among nest-dwelling than among palm-dwelling bugs, which might reduce the need for highly efficient flight, hence relaxing selection for elongated wings [27,88]. ...
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"Image missing" .
... Os triatomíneos são encontrados principalmente na região Neotropical, apesar de algumas espécies serem encontradas na Índia, China, Malásia, Indonésia e Austrália (Poinar Jr. 2005, Patterson 2007). Gaunt & Miles (2002) estimaram a divergência entre as duas principais tribos de triatomíneos (Rhodniini e Triatomini) entre 99,7 e 93,6 milhões de anos (Cretáceo) coincidindo com a formação da América do Sul após a fragmentação de Gondwana e com o aparecimento dos primeiros fósseis de palmeiras. ...
... Entretanto, o uso das técnicas de morfometria geométrica em estudos com triatomíneos tem aumentado nos últimos anos. A técnica tem sido aplicada para resolver problemas taxonômicos (Matías et al. 2001, Villegas et al. 2002, Gumiel et al. 2003, Patterson 2007, para estudar a variação morfológica intraespecífica (Jaramillo et al. 2002, Gumiel et al. 2003, Schachter-Broide et al. 2004, Vargas et al. 2006) e para analisar o fenômeno de re-infestação , Feliciangeli et al. 2007). ...
... Patterson (2007) também comparou a morfometria alar e cefálica com os resultados de análises genéticas em triatomíneos; os resultados sugerem que a forma das asas está mais influeciada pelas diferenças genéticas entre as populações do que a forma das cápsulas cefálicas, cuja variação depende de diferenças ecológicas. Assim, as cápsulas cefálicas provavelmente refletem o efeito de pressões seletivas em curto prazo, enquanto a taxa de variação de forma das asas se correlaciona mais fortemente com a taxa de acúmulo de mutações. ...
Tese (doutorado)—Universidade de Brasília, Faculdade de Ciências da Saúde, 2008. Triatomíneos silvestres do gênero Rhodnius freqüentemente invadem casas na América Latina, mantendo o risco de transmissão da doença de Chagas. Nesta tese, foram feitas análises filogeográficas, morfométricas e de distribuição geográfica potencial de populações de Rhodnius no Brasil central, focando Rhodnius neglectus, a principal espécie encontrada em palmeiras no Cerrado. Os triatomíneos foram capturados em palmeiras (Mauritia flexuosa) de quatro bacias hidrográficas (Tocantins, São Francisco, Paraná e Paraguai) e os índices de infestação e infecção por tripanossomatídeos foram analisados. A morfometria geométrica foi aplicada para identificar quais espécies de Rhodnius do grupo R. prolixus são encontradas em palmeiras e casas no Brasil central e para analisar a variação morfológica de populações silvestres de R. neglectus. A distribuição geográfica potencial de R. neglectus foi analisada usando modelagem de nicho ecológico (GARP) baseada na relação entre variáveis ambientais e os registros de ocorrência obtidos durante o estudo. A análise filogeográfica de R. neglectus foi baseada no polimorfismo de seqüências de citocromo b do DNA mitocondrial, testando a hipótese de diferenciação entre populações pelo processo de isolamento por distância. A freqüência de palmeiras infestadas variou de 11 a 100% nas 40 áreas amostradas, sendo coletados 1.581 espécimes em 177 palmeiras, principalmente em ninhos de pássaros; 3,8% dos triatomíneos examinados estavam infectados por tripanossomatídeos (Trypanosoma cruzi e T. rangeli). As análises morfométricas permitiram uma reclassificação quase perfeita dos indivíduos em suas respectivas espécies. Os padrões de forma não revelaram diferenças consistentes entre a maioria dos espécimes coletados nas casas no Brasil central e R. neglectus, mostrando também que R. robustus e R. neglectus ocorrem simpatricamente ao sul da Amazônia. Esses resultados suportam fortemente a idéia que espécimes de R. neglectus, e não de R. prolixus, têm invadido as casas no Brasil central. Os métodos de morfometria geométrica aplicados para explorar a variação fenotípica em R. neglectus mostraram variação significativa de tamanho de asas e, principalmente, cápsulas cefálicas entre as populações analisadas. A temperatura foi a variável ambiental que mais influenciou o tamanho, sendo os menores espécimes encontrados nas áreas mais frias. Entretanto, nenhuma variação significativa de forma foi observada entre populações de diferentes bacias hidrográficas. Os modelos de nicho ecológico foram capazes de predizer, com alta probabilidade, áreas de ocorrência de R. neglectus no bioma Cerrado. Áreas de Caatinga, savanas amazônicas, Pantanal e Chaco boliviano apresentaram menores probabilidades de ocorrência da espécie. Uma grande sobreposição foi observada entre a distribuição de R. neglectus, palmeiras e pássaros. Ao incluir novos registros de R. neglectus, o presente estudo revelou um aumento da distribuição a oeste e nordeste do Brasil na 'diagonal de ecorregiões abertas/secas da América do Sul'. O seqüenciamento da porção 5´ do citocromo b em 144 indivíduos de 33 populações resultou em um fragmento de 567pb, revelando a existência de 13 haplótipos únicos e 22 sítios variáveis. Os haplótipos obtidos formaram um grupo monofilético bem suportado, sendo identificados como R. neglectus e separados claramente das outras espécies de Rhodnius do grupo R. prolixus. Os dois haplótipos mais freqüentes ocorreram em áreas separadas por distâncias maiores que 1.700 km e de três bacias hidrográficas. Haplótipos compartilhados foram observados em áreas de ambas as margens dos principais rios e ambos os lados da Serra Geral de Goiás. As populações de Alto Paraíso-GO e da bacia do Paraguai (Mato Grosso) apresentaram haplótipos únicos e altos níveis de diversidade nucleotídica e divergência entre populações. A rede de haplótipos apresentou dois grupos geograficamente distintos (oeste e leste), mas não houve evidência de isolamento por distância (Mantel, p = 0,446). A dispersão de espécimes de R. neglectus entre no Brasil central poderia ocorrer a partir de um mecanismo passivo de transporte por aves. Finalmente, esses resultados podem auxiliar os programas de vigilância vetorial da doença de Chagas, visto que a invasão das casas por espécimes de Rhodnius mantém o risco de transmissão e limita a eficiência das estratégias de controle. __________________________________________________________________________________________ ABSTRACT Sylvatic triatomines of the genus Rhodnius commonly fly into houses in Latin America, maintaining the risk of Chagas disease transmission. In this thesis, phylogeographical, morphological and potential geographical distribution analyses of Rhodnius populations in central Brazil were carried out, focusing in R. neglectus, the major species found in palm trees in the Brazilian Savannah. Bugs were captured in Mautitia flexuosa palm trees from four hydrogeographic basins (Tocantins, Sao Francisco, Parana and Paraguay); the infestation and trypanosomatid infection indices were analyzed. Geometric morphometric methods were applied to identify the Rhodnius species of the R. prolixus group and to analyze the morphometric variation among R. neglectus populations from these basins. The hypothesis of phenotypic plasticity related to some environment variables was also tested. The potential geographical distribution of R. neglectus was analyzed by using ecological niche modeling (GARP) based on the relation of environmental variables and occurrence records. The phylogeographic analyses of R. neglectus populations were based on polymorphisms of cytochrome b sequences, testing the hypotheses of differentiation and isolation by distance. The frequency of infested palms varied from 11 to 100% in the 40 sampled areas, and 1,581 specimens were collected in 177 palms, mainly in bird nests; 3.8% of the examined bugs were infected by trypanosomatids (Trypanosoma cruzi and T. rangeli). Morphometric analyses of shape variation allowed for an almost perfect reclassification of individuals to their putative species. Shape patterning revealed no consistent differences between most specimens collected inside houses in central Brazil and R. neglectus, and also showed that R. robustus and R. neglectus occur sympatrically in southern Amazonia. These results strongly support the idea that R. neglectus, and not R. prolixus, is the species invading houses in central Brazil. The geometric morphometric methods applied to assess the intraspecific phenotypic variation in R. neglectus showed significant size variation among populations.Wing and head size were influenced by temperature: the smallest specimens were found in the coldest areas. Nevertheless, no significant shape variation was observed among populations of different geographical basins. The ecological niche models were able to predict the occurrence of R. neglectus as a characteristic (although not endemic) species of the Cerrado biome. Meanwhile, Caatinga, Amazonian savannas, Pantanal, and the Bolivian Chaco appear as areas with lower predicted presence probability for the species. A high overlap was observed among the distributions of R. neglectus, some palm trees and birds. By including new records for R. neglectus, the present study has revealed a wider distribution towards the west and northeast areas of Brazil in the ‘diagonal of open/dry ecoregions of South America’. The sequencing of 5´- end of the cytochrome b gene in 144 individuals from 33 populations resulted in a fragment of 567bp, revealing the existence of 13 different haplotypes and 22 variable sites. These haplotypes formed a well-supported monophyletic group identified as R. neglectus and clearly separated for other Rhodnius species of the ‘R. prolixus group’. The two more frequent haplotypes occurred in areas separated by a distance over 1,700 km and from three different hydrogeographic basins. Shared haplotypes were also observed in areas from both sides of large rivers and both sides of ‘Serra Geral de Goias’. The populations from Alto Paraiso-GO and from the Paraguay basin (Mato Grosso) presented unique haplotypes and higher levels of nucleotide diversity and divergence among populations. The haplotype network analysis showed two geographically distinct groups (western and eastern) but there was no evidence of isolation by distance (Mantel, p = 0,446). The dispersal of R. neglectus specimens among the basins may occur through passive carriage by birds. Finally, these results should help the Chagas disease vector surveillance program, given that household invasion by Rhodnius species maintains disease transmission risk and limits the effectivenes of control strategies.
... Previous studies have shown differences in head size between species (Gurgel-- Gonçalves et al., 2011;Oropeza et al., 2017). Patterson (2007) hypothesized that differences in the head may have an evolutionary cause related to feeding strategies, with different morphologies allowing the ingestion of blood from different specific food sources, as well as different growth patterns. If we consider the hypothesis of Patterson (2007), a possible explanation for the fact that there is no difference in the size of the head between haplogroups is that the recent speciation processes that have occurred in the populations of T. pallidipennis may not have led to a segregation of feeding niches. ...
A recent phylogenetic analysis of Triatoma pallidipennis, an important Chagas disease vector in Mexico, based on molecular markers, revealed five monophyletic haplogroups with validity as cryptic species. Here we compare T. pallidipennis haplogroups using head and pronotum features, environmental characteristics of their habitats, and ecological niche modeling. To analyze variation in shape, images of the head and pronotum of the specimens were obtained and analyzed using methods based on landmarks and semi-landmarks. Ecological niche models were obtained from occurrence data, as well as a set of bioclimatic variables that characterized the environmental niche of each analyzed haplogroup. Deformation grids for head showed a slight displacement towards posterior region of pre-ocular landmarks. Greatest change in head shape was observed with strong displacement towards anterior region of antenniferous tubercle. Procrustes ANOVA and pairwise comparisons showed differences in mean head shape in almost all haplogroups. However, pairwise comparisons of mean pronotum shape only showed differences among three haplogroups. Correct classification of all haplogroups was not possible using discriminant analysis. Important differences were found among the environmental niches of the analyzed haplogroups. Ecological niche models of each haplogroup did not predict the climatic suitability areas of the other haplogroups, revealing differences in environmental conditions. Significant differences were found between at least two haplogroups, demonstrating distinct environmental preferences among them. Our results show how the analysis of morphometric variation and the characterization of the environmental conditions that define the climatic niche can be used to improve the delimitation of T. pallidipennis haplogroups that constitute cryptic species.
... Patterson [49] have suggested that the shape of the head may re ect evolutionary mechanisms related to the ability to ingest blood. If the allopatry of the haplogroups populations of T. dimidiata is taken into account and that these must have diverged approximately 0.97 to 0.85 mya, according to results obtained from sequences of the ND4 gene [16], dissimilar feeding strategies may have been established among the haplogroups, which then generated morphological differences. ...
Background Triatoma dimidiata (Reduviidae: Triatominae) is an important vector of Chagas disease in various countries in the Americas. Phylogenetic studies have defined three lineages in Mexico and part of Central America, but methods for identifying them using morphometric analyses with landmarks have not yet been resolved. Elliptical Fourier Descriptors (EFDs), which mathematically describe the shape of any closed two-dimensional contour, could be a potentially useful alternative method. The objective of this work was to validate the use of EFDs for the identification of the three lineages of this species complex.
Method A total of 84 dorsal view photographs of individuals of the three lineages were used. The body contours were described with EFDs using between 5 and 30 harmonics. The number of obtained coefficients was reduced by a Principal Components Analysis and the first axis scores were used as shape variables. A Canonical Variances Analysis, a linear discriminant function analysis and a multilayer perceptron neural networks were then performed using the shape variables, identifying the minimum number of harmonics sufficient to produce efficiently classifications.
Results The first principal component explained 50% of the variability, regardless of the number of harmonics used, but the results of both, Principal Component Analysis and Canonical Variance Analysis get improved by increasing the number of harmonics and components considered. With 25 harmonics and 8 components, the identification of haplogroups was achieved with an overall efficiency greater than 97%. The 30 multilayer perceptron neural networks were also efficient in identification, reaching 91% efficiency with the validation data.
Conclusions The use of EFDs is a simple and useful method for the identification of major lineages of Triatoma dimidiata. This method outperform other novel approaches, therefore could serve as an automated identification method.
... The distance trees cause an equivocal disruption to Triatominae monophyly via the Reduviinae. (Patterson, 2007) and the result is represented in the Fig. 6, the cob phylogeny. The 28S distance tree involves Opisthacidus pertinax and Opisthacidus sp. ...
We previously constructed a single molecular clock to date insect evolution that remains a cornerstone within entomological dating. The insect clock predicts that triatomine bugs, the vectors of South American trypanosomiasis, originated with the formation of South America. We addressed this hypothesis using the insectivorous reduviid bugs and their phylogenetic relationship with the haematophagous reduviid bugs, as well as their biogeographic distribution. Putative paraphyly or monophyly of Triatominae, by non-haematophagous reduviids, have both previously been hypothesized and identified. We sampled a broad range of predatory reduviids, viz. Ectrichodiinae, Emesinae, Hammacerinae, Harpactorinae, Reduviinae, Salyavatinae, Steniopodainae and Vesciinae, including both New World and Old World representatives and sequenced the nuclear 28S ribosomal gene locus and the mitochondrial loci 5' cytochrome oxidase 1 (cox1 [COI]), cox1 3', cytochrome oxidase 2 (cox2 [COII]) and cytochrome oxidase b (cob [cytb]). Robust evidence for the monophyly of Triatominae was observed in 5/5 loci using codon/nucleotide (28S) based maximum likelihood phylogenies, 3/5 loci using codon-based Bayesian phylogenies and in cox2 using amino acid Bayesian phylogenies. Several South American members of the Reduviinae, that are morphologically and phylogenetically a sister group to triatomine bugs, have a modal divergence date with the Triatominae of 109-107 million years ago (MYA). This creates a scenario where the closest (non-haematophagous) ancestor to triatomine bugs evolved immediately prior to the breakup of Gondwanaland whilst the triatomine bugs evolved 95MYA, putatively linking the origin of haematophagous behaviour to the origin of South America and in particular infers a delayed onset to the evolution of haematophagy. The placement of the enigmatic tribe Bolboderini as an ingroup to the Triatominae monophyly, confirms the 95MYA node as the most ancient in the subfamily.
Background. Triatomine bugs, the vectors of Chagas disease, associate with vertebrate hosts in highly diverse ecotopes. When these blood-sucking bugs adapt to new microhabitats, their phenotypes may change. 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/Findings. 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 (SW Ecuador/NW Peru) from house and vertebrate-nest microhabitats are typical, light-colored, small bugs with short heads/wings. Northern-Andean bugs (W Ecuador wet-forest palms) are dark, large bugs with long heads/wings. Finally, northern-lowland bugs (coastal Ecuador dry-forest palms) are light-colored and medium-sized. Wing and (size-free) head shapes are similar across Ecuadorian populations, regardless of habitat or naked-eye 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 structuring/differentiation.
Conclusions. We report sharp naked-eye phenotypic divergence of genetically similar Ecuadorian R. ecuadoriensis (house/nest 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 from house and nest (but not palm) microhabitats (SW Ecuador vs . NW Peru). This remarkable phenotypic diversity within a single nominal species likely stems from microhabitat adaptations possibly involving predator-driven selective pressure (yielding substrate-matching camouflage coloration) and a shift from palm-crown to vertebrate-nest microhabitats (yielding smaller bodies and shorter heads and wings). 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.
Monitoring the changes in the population density of the adult predatory bug, Coranus Africana El-Sebaey (Hemiptera: Reduviidae) was carried out from February 1999 till January 2001 in Kom Oshim district which situated in the Western Desert Agro-ecosystem, Egypt. The highest number of adults was achieved between July and October, while the lowest level of the population was reported between February and March during the two tested successive years. The effect of prevailing physical environmental factors on the population density and life table parameters were also studied by using an artificial population of the predator in field cages. This reduviid completed six overlapping generations in a year. The basic population parameters, expressed as the net reproductive rate(Ro), gross reproductive rate (GRR), instantaneous rate of natural increase (rm), and the mean gemeration time (T) were determined with respect to the date of hatching. The average values of these parameters under natural climatic conditions were 81.16, 902.01, 0.3798, and 12.24 for Ro, GRR, rm and T, respectively.
Rhodnius ecuadoriensis (Hemiptera, Reduviidae) is an important vector of both Trypanosoma hemoflagellates, Trypanosoma cruzi and Trypanosoma rangeli, in Ecuador and Peru. Ecotopes of sylvatic and domestic/peridomestic habitats have been reported in Ecuador. Meanwhile in Peru, to the best of our knowledge, findings of sylvatic populations in their different ecosystem regions have not yet been documented. Could this be the product of a lack of appropriate studies on wild populations of triatominae in Peruvian environments? In order to elucidate this topic, we take advantage of new insights in geometric morphometry as a tool to help differentiate between wild populations and the corresponding domestic/peridomestic ones, collected in their respective environments. When analyzing our results, we confirmed the efficacy of this technique in our study, and furthermore, we believe that it could be a proper tool for rangeliosis and Chagas disease vector control surveillance in Ecuador and Peru.
Keywords: Morphometric geometry, sylvatic, domestic/peridomiestic populations distinction, Rhodnius ecuadoriensis.
RESUMEN
Rhodnius ecuadoriensis (Hemiptera, Reduviidae) es un importante vector de los tripanosomas Trypanosoma cruzi y Trypanosoma rangeli en el Ecuador y Perú. Se han reportado ecotopos de hábitats silvestres y domésticos/peridomésticos en Ecuador. Sin embargo, en Perú, hasta donde sabemos, no se ha documentado hallazgos de dichas poblaciones silvestres. ¿Podría este ser el caso de una falta de estudios focalizados en la búsqueda de poblaciones silvestres de triatominos dentro de los diferentes ecosistemas del Perú? Para elucidar este tema, aplicamos nuevas perspectivas en morfometría geométrica, como una herramienta que podría auxiliar en la diferenciación de poblaciones silvestres de aquellas domésticas/peridomésticas, colectadas en sus respectivos ambientes naturales. Al analizar nuestros resultados, se confirmó la utilidad de esta técnica dentro de nuestro estudio, y esto nos llevó a creer asimismo que serviría como un elemento apropiado en el control vectorial de la enfermedad de Chagas y de la rangeliosis, en Ecuador y Perú.
Palabras claves: Geometría morfométrica, silvestre, diferenciación de poblaciones domesticas/peridomesticas, Rhodnius ecuadoriensis.
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).
An accurately resolved gene tree may not be congruent with the species tree because of lineage sorting of ancestral polymorphisms. DNA sequences from the mitochondrially encoded genes (mtDNA) are attractive sources of characters for estimating the phylogenies of recently evolved taxa because mtDNA evolves rapidly, but its utility is limited because the mitochondrial genes are inherited as a single linkage group (haplotype) and provide only one independent estimate of the species tree. In contrast, a set of nuclear genes can be selected from distinct chromosomes, such that each gene tree provides an independent estimate of the species tree. Another aspect of the gene-tree versus species-tree problem, however, favors the use of mtDNA for inferring species trees. For a three-species segment of a phylogeny, the branching order of a gene tree will correspond to that of the species tree if coalescence of the alleles or haplotypes occurred in the internode between the first and second bifurcation. From neutral theory, it is apparent that the probability of coalescence increases as effective population size decreases. Because the mitochondrial genome is maternally inherited and effectively haploid, its effective population size is one-fourth that of a nuclear-autosomal gene. Thus, the mitochondrial-haplotype tree has a substantially higher probability of accurately tracking a short internode than does a nuclear-autosomal-gene tree. When an internode is sufficiently long that the probability that the mitochondrial-haplotype tree will be congruent with the species tree is 0.95, the probability that a nuclear-autosomalgene tree will be congruent is only 0.62. If each of k independently sampled nuclear-gene trees has a probability of congruence with the species tree of 0.62, then a sample of 16 such trees would be required to be as confident of the inference based on the mitochondrial-haplotype tree. A survey of mtDNA-haplotype diversity in 34 species of birds indicates that coalescence is generally very recent, which suggests that coalescence times are typically much shorter than internodal branch lengths of the species tree, and that sorting of mtDNA lineages is not likely to confound the species tree. Hybridization resulting in transfer of mtDNA haplotypes among branches could also result in a haplotype tree that is incongruent with the species tree; if undetected, this could confound the species tree. However, hybridization is usually easy to detect and should be incorporated in the historical narrative of the group, because reticulation, as well as cladistic events, contributed to the evolution of the group.
Seventeen samples of Rhodnius, representing at least eight different species according to their morphological characteristics, were submitted to multilocus isoenzyme electrophoresis, revealing 17 different loci. A phenetic analysis of the enzyme data not only clustered the species in accordance with their geographical origin but also revealed interspecific relationships that differed from those expected from the morphology.