Head geometric morphometrics of two Chagas disease vectors from Venezuela

Triatominae species are considered the main vectors of Chagas disease or American Trypanosomiasis. In Venezuela, the principal vectors are Rhodnius prolixus （Stal, 1959） and Triatoma maculata （Erichson, 1848）, which are belonged to the tribe Rhodniini and Triatomini, respectively. The head conformation and size development of these species can reflect ontogenetic changes which contribute with the vectors biology studies, as well to support of instars determination. The goal of the paper is to the application of geometric morphometric techniques for describing head conformation and size of instars of these species. We photographed 140 heads in R. prolixus： First instar （I： 16）, second instar （II： 17）, third instar （III： 18）, fourth instar （IV： 21）, fifth instar （V： 21）, adult female （F： 26） and adult males （M： 21）; in T. maculata heads of 136 specimens were photographed,I： 20, II： 17, III： 26, IV： 15, V： 19, F： 20 and M： 19. Landmark coordinate （x, y） configurations were registered and aligned by Generalized Procrustes Analysis. Covariance Analyses were implemented with proportions of re-classified groups and MANOVA. Statistical analyses of variance found not significant differences in head isometric size （Kruskal-Wallis） among IV and V instars in both species. The a posteriori re-classification was almost perfect in R. prolixus （82%） and T. maculata （86%）; the main head differences occurs in antenniferous tubercles, postocular and preocular. Our study using quantitative tools for describing the shape differences contributes to explain the morphology variability and development of Chagas disease vectors.

Shell geometric morphometrics in Biomphalaria glabrata (Mollusca： Planorbidae) uninfected and infected with Schistosoma mansoni

Freshwater planorbid mollusks belonging to the genus Biomphalaria act as intermediate hosts for Schistosoma mansoni, the etiological agent of human intestinal schistosomiasis, in the Neotropical Region. Identification ofBiomphalaria spp. are carried out based on morphological characters, and the Schistosoma infection are determined by the presence of cercariae （verified through microscope preparation and mounting）. Recently, the geometric morphometrics has proven to be a useful tool for determining shape differences in disease vectors arthropods. Due to this, we used geometric morphometrics to determine Biomphalaria glabrata shell differences （shape and size） between uninfected and infected specimens. We digitalized 12 anatomical points over the shell left side （from umbilicus to the last whorl） by combining type I and II landmarks and sliding semilandmarks; the coordinates were aligned by generalized Procrustes analysis. Principal component analyses were implemented for examining main variation axes, and discriminant analysis for testing group membership significance. We found significant separation between infected and uninfected shell conformation. All specimens were 100% correctly classified. The main differences occur in the peristome. The Kruskal-Wallis test finds significant differences in shell isometric size among infected and uninfected specimens. These findings correspond to other studies of traditional morphometrics, that infected snails showed the reduction in shell size in contrast to those uninfected specimens