Núcleo de Medicina Tropical, Faculdade de Medicina, Universidade de Brasília, Brasília, Brazil.
Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, UK.
Parasit Vectors. 2021 Apr 8;14(1):195. doi: 10.1186/s13071-021-04647-z.
Triatomine bugs, the vectors of Chagas disease, associate with vertebrate hosts in highly diverse ecotopes. It has been proposed that occupation of new microhabitats may trigger selection for distinct phenotypic variants in these blood-sucking bugs. Although understanding phenotypic variation is key to the study of adaptive evolution and central to phenotype-based taxonomy, the drivers of phenotypic change and diversity in triatomines remain poorly understood.
METHODS/RESULTS: We combined a detailed phenotypic appraisal (including morphology and morphometrics) with mitochondrial cytb and nuclear ITS2 DNA sequence analyses to study Rhodnius ecuadoriensis populations from across the species' range. We found three major, naked-eye phenotypic variants. Southern-Andean bugs primarily from vertebrate-nest microhabitats (Ecuador/Peru) are typical, light-colored, small bugs with short heads/wings. Northern-Andean bugs from wet-forest palms (Ecuador) are dark, large bugs with long heads/wings. Finally, northern-lowland bugs primarily from dry-forest palms (Ecuador) are light-colored and medium-sized. Wing and (size-free) head shapes are similar across Ecuadorian populations, regardless of habitat or phenotype, but distinct in Peruvian bugs. Bayesian phylogenetic and multispecies-coalescent DNA sequence analyses strongly suggest that Ecuadorian and Peruvian populations are two independently evolving lineages, with little within-lineage phylogeographic structuring or differentiation.
We report sharp naked-eye phenotypic divergence of genetically similar Ecuadorian R. ecuadoriensis (nest-dwelling southern-Andean vs palm-dwelling northern bugs; and palm-dwelling Andean vs lowland), and sharp naked-eye phenotypic similarity of typical, yet genetically distinct, southern-Andean bugs primarily from vertebrate-nest (but not palm) microhabitats. This remarkable phenotypic diversity within a single nominal species likely stems from microhabitat adaptations possibly involving predator-driven selection (yielding substrate-matching camouflage coloration) and a shift from palm-crown to vertebrate-nest microhabitats (yielding smaller bodies and shorter and stouter heads). These findings shed new light on the origins of phenotypic diversity in triatomines, warn against excess reliance on phenotype-based triatomine-bug taxonomy, and confirm the Triatominae as an informative model system for the study of phenotypic change under ecological pressure .
克氏锥虫的传播媒介，即三锥虫，在高度多样化的生态位中与脊椎动物宿主相关联。有人提出，占据新的小生境可能会导致这些吸血昆虫产生不同的表型变异。尽管理解表型变异是研究适应性进化的关键，也是基于表型的分类学的核心，但三锥虫的表型变化和多样性的驱动因素仍知之甚少。
方法/结果：我们结合了详细的表型评估（包括形态和形态测量学）以及线粒体 cytb 和核 ITS2 DNA 序列分析，研究了分布在该物种范围内的厄瓜多尔罗氏锥虫种群。我们发现了三个主要的、肉眼可见的表型变体。主要来自脊椎动物巢穴小生境（厄瓜多尔/秘鲁）的南部安第斯山脉的虫子是典型的、浅色的、小个头/短翅膀的虫子。来自潮湿森林棕榈树（厄瓜多尔）的北部安第斯山脉的虫子是深色的、大个头/长翅膀的虫子。最后，主要来自干燥森林棕榈树（厄瓜多尔）的北部低地虫子是浅色的中型虫子。无论栖息地或表型如何，厄瓜多尔种群的翅膀和（大小无关的）头部形状都相似，但秘鲁种群的翅膀和（大小无关的）头部形状不同。贝叶斯系统发育和多物种合并 DNA 序列分析强烈表明，厄瓜多尔和秘鲁的种群是两个独立进化的谱系，谱系内的地理结构或分化很小。
我们报告了厄瓜多尔罗氏锥虫（巢穴栖息的南部安第斯山脉与棕榈栖息的北部虫子；以及棕榈栖息的安第斯山脉与低地）肉眼可见的显著表型分化，以及主要来自脊椎动物巢穴（而非棕榈）小生境的典型但遗传上不同的南部安第斯山脉虫子的肉眼可见的相似表型。在一个单一的命名物种内出现如此显著的表型多样性，可能源于微生境适应，可能涉及捕食者驱动的选择（产生与基质相匹配的伪装颜色），以及从棕榈树冠到脊椎动物巢穴小生境的转变（产生更小的身体和更短、更结实的头部）。这些发现为三锥虫表型多样性的起源提供了新的线索，提醒人们不要过度依赖基于表型的三锥虫分类学，并证实了三锥虫科是研究生态压力下表型变化的一个有意义的模型系统。
