Influence of ecological factors on the presence of a triatomine species associated with the arboreal habitat of a host of Trypanosoma cruzi

Abstract

BackgroundThe white-naped squirrel, Simosciurus nebouxii (previously known as Sciurus stramineus), has recently been identified as an important natural host for Trypanosoma cruzi in Ecuador. The nests of this species have been reported as having high infestation rates with the triatomine vector Rhodnius ecuadoriensis. The present study aims to determine the levels of nest infestation with R. ecuadoriensis, the ecological variables that are influencing the nest site selection, and the relationship between R. ecuadoriensis infestation and trypanosome infection.ResultsThe study was carried out in transects in forest patches near two rural communities in southern Ecuador. We recorded ecological information of the trees that harbored squirrel nests and the trees within a 10 m radius. Manual examinations of each nest determined infestation with triatomines. We recorded 498 trees (n = 52 with nests and n = 446 without nests). Rhodnius ecuadoriensis was present in 59.5% of the nests and 60% presented infestation with nymphs (colonization). Moreover, we detected T. cruzi in 46% of the triatomines analyzed.ConclusionsWe observed that tree height influences nest site selection, which is consistent with previous observations of squirrel species. Factors such as the diameter at breast height and the interaction between tree height and tree species were not sufficient to explain squirrel nest presence or absence. However, the nest occupancy and tree richness around the nest were significant predictors of the abundance of triatomines. Nevertheless, the variables of colonization and infection were not significant, and the data observed could be expected because of chance alone (under the null hypothesis). This study ratifies the hypothesis that the ecological features of the forest patches around rural communities in southern Ecuador favor the presence of nesting areas for S. nebouxii and an increase of the chances of having triatomines that maintain T. cruzi populations circulating in areas near human dwellings. Additionally, these results highlight the importance of including ecological studies to understand the dynamics of T. cruzi transmission due to the existence of similar ecological and land use features along the distribution of the dry forest of southern Ecuador and northern Peru, which implies similar challenges for Chagas disease control.Electronic supplementary materialThe online version of this article (10.1186/s13071-018-3138-4) contains supplementary material, which is available to authorized users.

Under pressure: phenotypic divergence and convergence associated with microhabitat adaptations in Triatominae

“…Thus, bug color predicts microhabitat background color, suggesting an adaptive response to selective pressure from sight-guided predators [92]. The small body size of southern-Andean bugs, together with their shorterstouter heads and less elongated wings, predicts that wild populations preferentially exploit nest microhabitats [2,86] -a proposition for which there is some empirical evidence, including abundant squirrel-nest populations [2,30,32,33] and a strong association of domestic bugs with hen nests and guinea-pig pens [1,26,27,35,36,39]. Importantly, we have also shown that populations with extremely divergent phenotypes can share their genetic backgrounds, at least for the two loci we examined; our sequence data indicate that genetic similarity among Ecuadorian bugs is not due to mtDNA introgression [74].…”

“…We conducted a detailed review of external morphological and chromatic characters central to classical triatomine-bug taxonomy [1,41], and placed the results in the broader context of what we know about the systematics, biogeography, and ecology of R. ecuadoriensis [1,2,8,18,[25][26][27][28][29][30][31][32][33][34][35][36]38,39]. In particular, we emphasize that northern populations exploit palm-crown microhabitats just like most Rhodnius species do [2,29], whereas wild southern-Andean populations are associated with vertebrate tree-nests in dry ecoregions where palms are either rare or absent [2,8,[25][26][27][28][29][30][31][32][33][34]. Our sampling thus captures this key ecological difference, with northern Tsáchilas and Manabí bugs representing primarily palm-dwelling populations and southern El Oro, Loja, and Peru bugs representing primarily nest-dwelling populations.…”

“…Rhodnius ecuadoriensis is one such species. In the wild, it seems to be primarily associated with the endemic Phytelephas aequatorialis palm of western Ecuador, but has also been found in vertebrate nests; southern-Andean populations, in particular, occur in dry ecoregions in which palms are rare or absent, and seem to have shifted to squirrel, bird, and opossum nests [1,2,[26][27][28][29][30][31][32][33][34]. In addition, some R. ecuadoriensis populations can infest houses and peridomestic structures -with a preference for hen nests, guinea-pig pens, or dovecotes [1,[24][25][26][27]35,36,38,39].…”

“…This shift likely occurred in the dry Andean environments of southwestern Ecuador-northwestern Peru that overall lack native palm populations [25,26,30,32,39]. In Loja, wild R. ecuadoriensis often breed inside the nests of the tree-squirrel, Sciurus stramineus/nebouxii [2,30,32,33,88]. Within nest microhabitats, the close physical proximity between the (virtually ectoparasitc) bugs and their hosts would relax selection for long/narrow heads and mouthparts, which may be required for biting free-ranging hosts more safely (at a longer distance) and sucking their blood faster (thanks to larger cibarial-pump muscles) [86,89].…”

“…Rhodnius ecuadoriensis is a major domestic vector of T. cruzi in western Ecuador and northwestern Peru [24][25][26]. In Ecuador, northern wild populations are primarily associated with the endemic Phytelephas aequatorialis palm in both Andean wet forests and lowland dry forests; in the dry inter-Andean valleys of southwestern Ecuador, where palms are rare or absent, wild R. ecuadoriensis seem to primarily associate with arboreal squirrel nests [1,2,[27][28][29][30][31][32][33]. The natural habitats of Peruvian populations remain largely unknown, with a few records suggesting association with vertebrate nests/refuges in hollow trees and perhaps cacti [2,26,27,34].…”