Environmental filtering without morphological adaptation: decoupled taxonomic and functional structures in American triatomines.

Species belonging to subfamily Triatominae are vectors of Trypanosoma cruzi, the causative agent of Chagas disease. They have a wide distribution, inhabiting both tropical and temperate regions. We examined the response of triatomine species distributions and morphological traits to environmental conditions at different bioregions, using three matrices: (1) a distribution matrix of 80 triatomine species, (2) a matrix of environmental variables, and (3) a matrix of morphological traits. To determine trait-environment relationships, an RLQ and Fourth Corner analysis were performed. We found environmental filtering of triatomine species across the six bioregions analyzed. In the Temperate North America, Trans-Mexican Volcanic Belt-Sierra Madre del Sur, and Chaco-Southern Andes bioregions, precipitation seasonality (BIO15) and elevation influenced local species assemblages. In contrast, local assemblages of triatomines in the Yucatán-Panama-Northern Andes and Amazon-Central Andes bioregions were governed by vegetation cover and precipitation during the wettest quarter (BIO19). However, in the Caatinga-Cerrado-Pampa bioregion, precipitation seasonality and mean temperature of wettest quarter (BIO8) influenced local species assemblages. No significant association was found between morphological traits and environmental variables. Hence, while climatic and habitat filters dictate species ranges, triatomine morphology follows an unidentified trend.