Triatominae: does the shape change of non-viable eggs compromise species recognition?

Abstract

BackgroundEggs have epidemiological and taxonomic importance in the subfamily Triatominae, which contains Chagas disease vectors. The metric properties (size and shape) of eggs are useful for distinguishing between close species, or different geographical populations of the same species.MethodsWe examined the effects of egg viability on its metric properties, and the possible consequences on species recognition. Four species were considered: Panstrongylus chinai, P. howardi and Triatoma carrioni (tribe Triatomini), and Rhodnius ecuadoriensis (tribe Rhodniini). Digitization was performed on pictures taken when the viability of the egg could not clearly be predicted by visual inspection. We then followed development to separate viable from non-viable eggs, and the metric changes associated with viability status of the eggs were tested for species discrimination (interspecific difference).ResultsThe shape of the complete contour of the egg provided satisfactory species classification (95% of correct assignments, on average), with improved scores (98%) when discarding non-viable eggs from the comparisons. Using only non-viable eggs, the scores dropped to 90%. The morphometric differences between viable and non-viable eggs were also explored (intraspecific comparison). A constant metric change observed was a larger variance of size and shape in non-viable eggs. For all species, larger eggs, or eggs with larger operculum, were more frequently non-viable. However, these differences did not allow for an accurate prediction regarding egg viability.ConclusionsThe strong taxonomic signal present in egg morphology was affected by the level of viability of the eggs. The metric properties as modified in non-viable eggs presented some general trends which could suggest the existence of an optimum phenotype for size and for shape. Globally, viable eggs tended to have intermediate or small sizes, and presented a less globular shape in the Triatomini, or a relatively wider neck in Rhodnius ecuadoriensis.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3104-1) contains supplementary material, which is available to authorized users.

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

“…We used the first harmonic ellipse parameters, to normalize the elliptic Fourier (NEF) coefficients so that they are invariant to size, rotation, and the starting position of the outline trace. NEF were stored in an ASCII file of extension.nef, and the four coefficients (related to the width-on-length ratio of the outline) were used for subsequent multivariate analyses [58].…”

Chagas vectors Panstrongylus chinai (Del Ponte, 1929) and Panstrongylus howardi (Neiva, 1911): chromatic forms or true species?

“…Collected insects from six communities in Loja and one community in Manabí (Additional file 1: Table S1) were maintained under suitable conditions at the CISeAL (Quito, Ecuador). This facility is equipped with a "dual chamber incubator" where the original microhabitat temperature and humidity conditions were the same as those described in Villacís et al [73] and Santillán-Guayasamín et al [74]. Fifth-instar nymphs (NV) of P. chinai and P. howardi were separated because virgin females were needed for crossing.…”

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

“…For that, we used the rst harmonic ellipse parameters, to normalize the elliptic Fourier (NEF) coe cients so that they are invariant to size, rotation, and the starting position of the outline trace. NEF were stored in an ASCII le of extension .nef, and the four coe cients (related to the width-on-length ratio of the outline) were used for subsequent multivariate analyses [58].…”