Geometric morphometrics and ecological niche modelling for delimitation of Triatoma pallidipennis (Hemiptera: Reduviidae: Triatominae) haplogroups

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.

Morphological and ecological data confirm Reithrodontomys cherrii as a distinct species from Reithrodontomys mexicanus

The integrative taxonomy approach has recently been widely suggested in systematic studies.  Lines of evidence such as the geometric morphometrics and ecological analyses have been useful for discriminating between genetically well-differentiated species.  Within the genus Reithrodontomys, R. mexicanus is one of the more taxonomically complex species, being considered a cryptic species complex.  R. cherrii was considered a subspecies of R. mexicanus, until molecular evidence raised it to the species-level.  Herein, we evaluate these two forms using morphological and ecological data based on the premise that they constitute genetically differentiated species.  We carried out geometric morphometric analyses on dorsal and ventral views of the skull.  Landmark and semi-landmark configurations for both views of the skull were selected based on previous studies of cricetid rodents.  We tested the presence of sexual dimorphism, and the skull shape and size differences between species on both cranial views.  Additionally, we characterized the environmental space of each species habitat using bioclimatic variables, elevation, and the Normalized Difference Vegetation Index (NDVI).  Females and males of R. mexicanus and R. cherrii did not show sexual dimorphism in shape or size of both skull views.  We found significant differences between the two species in both shape and size of the skull.  Cranial structures of the ventral view were more useful to differentiate both species.  R. mexicanus exhibited a broader environmental space than R. cherrii, with relatively similar values of temperature and elevation, but not of precipitation.  The pairwise comparison showed significant differences in the majority of the environmental variables analyzed.  Although for each view, we found statistical differences in the skull shape of R. cherrii and R. mexicanus, the ventral side showed major resolutive power differentiating both species. Our findings suggest that R. cherrii tends to have a larger skull than R. mexicanus.  However, the morphological and pelage coloration similarity between these species reported in the past, could explain the previous inclusion of R. cherrii as a subspecies of R. mexicanus.  R. mexicanus occurs in a variety of vegetation-types coinciding with the broader environmental space that it occupies compared to that of R. cherrii. The natural areas where both species are distributed were associated with high NDVI values.  Our results complement the molecular evidence and, under an integrative taxonomy approach, support R. cherrii as a different species from R. mexicanus.

An improved and low-cost protocol for high-quality DNA isolation for the Chagas disease vectors

An improved protocol for DNA extraction for the Chagas disease vectors is proposed based on modification to a low cost method described twenty years ago. Quality DNA and high molecular weight were obtained from all samples. NADH-4 gene was successfully amplified by PCR using the isolated DNA. The extraction protocol presented in this technical note is a fast, low-cost, and non-aggressive method to human health for obtaining genetic data from this group of epidemiological importance and potentially other insects.

Species Identity Supersedes the Dilution Effect Concerning Hantavirus Prevalence at Sites across Texas and México

Recent models suggest a relationship exists between community diversity and pathogen prevalence, the proportion of individuals in a population that are infected by a pathogen, with most inferences tied to assemblage structure. Two contrasting outcomes of this relationship have been proposed: the "dilution effect" and the "amplification effect." Small mammal assemblage structure in disturbed habitats often differs from assemblages in sylvan environments, and hantavirus prevalence is often negatively correlated with habitats containing high species diversity via dilution effect dynamics. As species richness increases, prevalence of infection often is decreased. However, anthropogenic changes to sylvan landscapes have been shown to decrease species richness and/or increase phylogenetic similarities within assemblages. Between January 2011 and January 2016, we captured and tested 2406 individual small mammals for hantavirus antibodies at 20 sites across Texas and México and compared differences in hantavirus seroprevalence, species composition, and assemblage structure between sylvan and disturbed habitats. We found 313 small mammals positive for antibodies against hantaviruses, evincing an overall prevalence of 9.7% across all sites. In total, 40 species of small mammals were identified comprising 2 taxonomic orders (Rodentia and Eulipotyphla). By sampling both habitat types concurrently, we were able to make real-world inferences into the efficacy of dilution effect theory in terms of hantavirus ecology. Our hypothesis predicting greater species richness higher in sylvan habitats compared to disturbed areas was not supported, suggesting the characteristics of assemblage structure do not adhere to current conceptions of species richness negatively influencing prevalence via a dilution effect.