Morphometric variability among the species of the Sordida subcomplex (Hemiptera: Reduviidae: Triatominae): evidence for differentiation across the distribution range of Triatoma sordida

et al. 2020

Parasites Vectors

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. While there is a marked genetic differentiation, methods for identifying them using morphometric analyses with landmarks have not yet been fully resolutive. Elliptical Fourier descriptors (EFDs), which mathematically describe the shape of any closed two-dimensional contours, could be a potentially useful alternative method. Our objective was to validate the use of EFDs for the identification of three lineages of this species complex. Method: A total of 84 dorsal view images of individuals of the three lineages were used. 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 linear discriminant function analysis and an ordination plot of the discriminant analysis were performed using the shape variables. A confusion matrix of the ordination plot of the discriminant analysis was obtained to estimate the classification errors, the first five PC scores were statistically compared, and a neural network were then performed using the shape variables. Results: The first principal component explained 50% of the variability, regardless the number of harmonics used. The results of discriminant analysis get improved by increasing the number of harmonics and components considered. With 25 harmonics and 30 components, the identification of haplogroups was achieved with an overall efficiency greater than 97%. The ordering diagram showed the correct discrimination of haplogroups, with only one error of discrimination corroborated by the confusion matrix. When comparing the first five PC scores, significant differences were found among at least two haplogroups. The 30 multilayer perceptron neural networks were also efficient in identification, reaching 91% efficiency with the validation data. Conclusions: The use of EFD is a simple and useful method for the identification of the main lineages of Triatoma dimidiata, with high values of correct identification.

Section: Introductionmentioning

confidence: 99%

Identifying Chagas disease vectors using elliptic Fourier descriptors of body contour: a case for the cryptic dimidiata complex

Flores¹,

Arellano²,

et al. 2020

Parasites Vectors

“…This structure has been used in the traditional morphological description of triatomine species [9] and has been used to try to discriminate between species [50]. To our knowledge, only one study has used geometric morphometry techniques on this structure in triatomines [32], in the future a comparative study of the pronotum could evaluate its utility in the discrimination among triatomines.…”

Section: Discussionmentioning

confidence: 99%

“…The identi cation of triatomine species has usually been carried out using traditional morphometry [11,14,22,23]. However, the use of geometric morphometry has led to new techniques for evaluating morphological characters in a taxonomic context; it complements the use of other methods of discrimination [24] and has been used for the recognition of very close species with a long history of controversy among taxonomists [25] and apparently cryptic species, including some of the Triatoma genus [7,26,27,28,29,30,31,32].…”

Section: Introductionmentioning

confidence: 99%

Identifying Chagas disease vectors using Elliptic Fourier Descriptors of body contour: A case for the cryptic dimidiata complex

Flores

Arenas

et al. 2020

Preprint

Abstract 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. While there is a marked genetic differentiation, methods for identifying them using morphometric analyses with landmarks have not yet been fully resolutive. Elliptical Fourier Descriptors (EFDs), which mathematically describe the shape of any closed two-dimensional contours, could be a potentially useful alternative method. Our objective was to validate the use of EFDs for the identification of three lineages of this species complex. Method 84 dorsal view images of individuals of the three lineages were used. 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 linear discriminant function analysis and an Ordination plot of the Discriminant Analysis were performed using the shape variables. A confusion matrix of the Ordination plot of the Discriminant Analysis was obtained to estimate the classification errors, the first five PC scores were statistically compared, and a neural network were then performed using the shape variables. Results The first principal component explained 50% of the variability, regardless the number of harmonics used. The results of Discriminant Analysis get improved by increasing the number of harmonics and components considered. With 25 harmonics and 30 components, the identification of haplogroups was achieved with an overall efficiency greater than 97%. The ordering diagram shown the correct discrimination of haplogroups, with only one error of discrimination corroborated by the confusion matrix. When comparing the first five PC scores, significant differences were found among at least two haplogroups. The 30 multilayer perceptron neural networks were also efficient in identification, reaching 91% efficiency with the validation data. Conclusions The use of EFD is a simple and useful method for the identification of the main lineages of Triatoma dimidiata , with high values of correct identification.

“…In the eld of epidemiological entomology, the delimitation of species of medical importance is vital for the establishment of e cient control strategies [13,18]. Geometric morphometric techniques using landmarks [19,20,21,22] or body contour descriptors [23,24,25,26] have been used for this purpose, mainly because of its superiority over traditional morphometric methods [27] and because it is a cheaper method than, for example, molecular ones.…”

Section: Introductionmentioning

confidence: 99%

Quantitative Imagery Analysis of Spot Patterns for Haplogroup Classification of Triatoma Dimidiata (Latreille, 1811) (Hemiptera: Reduviidae) an Important Vector of Chagas Disease

Flores

Arellano

et al. 2020

Preprint

Background: Spots and coloring patterns evaluated quantitatively can be used to discrimination and identify possible cryptic species. Triatoma dimidiata (Reduviidae: Triatominae) is one of the main complexes of Chagas disease vector species. Phylogenetic studies have defined three haplogroups for Mexico and part of Central America. In this work, we evaluate the possibility of correctly discriminating among these T. dimidiata haplogroups using the pattern of dorsal spots.Results: A distinctive spot pattern was found for each haplogroup. The most differentiated pattern was presented by haplogroup 2, mainly apparent in the notably larger central spots. Haplogroups 1 and 3 were more similar to each other, but there were consistent differences in the shape and orientation of the spots. Significant differences were found among haplogroups in almost all the variables analyzed, these differences being greater in relative spot area, mean relative area of central spots, central spots Feret diameters, lateral spots Feret diameters and aspect ratio. Both the DFA and the neural network had correct discrimination values above 90%. Conclusions: We conclude that the spot pattern can be reliably used to discriminate among haplogroups, and possibly among triatomine species.