Divergence of tropical pitvipers promoted by independent colonization events of dry montane Andean habitats

Aim: One aspect that is still poorly explored about the origin and maintenance of Neotropical biodiversity is how the evolutionary dynamics of colonization and differentiation in relation to lowland and highland habitats has impacted lineage formation. Most speciation models for this region have focused on vicariant events, and the need to assess the influence of demographic processes has been recognized only recently. We evaluate if the origin of Andean montane lineages of terciopelo pitvipers is explained by either of two historical processes that represent fundamental phylogeographic mechanisms: differentiation by isolation within the highlands or different dispersal events from the lowlands. Location: Western Ecuador. Taxon: Terciopelo pitvipers (Bothrops asper species complex). Methods: We use genomic data and genetic clustering analyses, evaluation of historical migration between genetic clusters, and demographic model selection to investigate recent diversification events in South America using a vertebrate group rarely explored in phylogeographic studies: tropical Andean snakes. Specifically, the origin of two Ecuadorian montane lineages of terciopelo pitvipers was evaluated given ambiguous phylogenetic relationships with the presumably ancestral Pacific lowland lineage. Results: Discrepancies of evolutionary relationships previously obtained with tree-like methods are resolved through the use of modeling approaches. We found strong support for the independent origin of montane lineages based on topologies inferred by maximum-likelihood trees and modeling approaches that take into account possible gene flow. Main conclusions: Recent large-scale studies have found support for identifying dispersal events as important drivers of diversification in the Neotropical region. We contribute to these ideas by identifying a fine-scale case in a rarely explored group of animals -Andean snakes- in which river valleys acted as an entrance for the upward colonization of montane dry habitats and subsequent ecological diversification.

研究目的：新热带生物多样性的起源与维持机制中，仍有诸多维度尚未得到充分探索，其中之一便是沿低地与高地生境的定殖与分化演化动态，如何作用于支系形成过程。该区域既往的物种形成模型多聚焦于异域分化事件，而种群过程对物种分化的影响直至近年才得到学界重视。本研究旨在验证：三色蝰（terciopelo pitvipers）安第斯山地支系的起源，是否符合两类基础系统地理学机制对应的历史演化过程——即高地内部隔离分化，或是源自低地的多次扩散事件。
研究区域：厄瓜多尔西部。
研究类群：三色蝰（terciopelo pitvipers，Bothrops asper物种复合群）。
研究方法：本研究采用基因组数据、遗传聚类分析、遗传类群间历史基因流评估以及种群历史模型选择等手段，针对系统地理学研究中鲜有涉及的脊椎动物类群——热带安第斯蛇类，探究南美洲近期的物种分化事件。具体而言，鉴于该类群的两支厄瓜多尔山地支系，与推测为祖先类群的太平洋低地支系间存在模糊不清的系统发育关系，本研究对其起源展开验证。
研究结果：既往基于类树方法得到的演化关系存在争议，本研究通过模型化分析方法解决了这一问题。基于最大似然树拓扑结构与考虑潜在基因交流的模型分析结果，本研究为山地支系的独立起源提供了强有力的支持证据。
主要结论：近期的大规模研究已证实，扩散事件是新热带区域物种分化的重要驱动因素。本研究通过聚焦一类鲜有研究的动物类群——安第斯蛇类，提供了一个精细尺度的研究案例：河谷作为向上定殖山地旱生生境并伴随后续生态分化的通道，验证了上述观点。