Data from: Diversification and phylogeographic structure in widespread Azteca plant-ants from the northern Neotropics

The Neotropical myrmecophytic tree Cordia alliodora hosts symbiotic Azteca ants in most of its widespread range. The taxonomy of the genus Azteca is notoriously difficult, which has frequently obscured species identity in ecological studies. We used sequence data from one mitochondrial and four nuclear loci to infer phylogenetic relationships, patterns of geographic distribution, and timing of diversification for 181 colonies of Azteca from Mexico to Colombia. We identified at least eight lineages of C. alliodora-dwelling Azteca, including at least five lineages within the most abundant and specialized species, Azteca pittieri. Mitochondrial and nuclear data were concordant at the species level, but not within species; comparison of the two datasets suggested that both introgression and incomplete lineage sorting contributed to these inconsistencies. Divergence time analyses estimated that C. alliodora-dwelling Azteca shared a common ancestor approximately 9-18 million years ago, coinciding with arid climatic conditions that favored their primary habitat, seasonally dry tropical forests. Significant differentiation not correlated with geographic distance was found among the five lineages of A. pittieri, which suggests limited historical gene flow among geographically restricted populations. This contrasts with the previously reported lack of phylogeographic structure in the host tree. Climatic niches, and particularly precipitation-related variables, did not overlap between the sites occupied by northern and southern lineages of A. pittieri. Together, these results suggest that restricted gene flow among ant populations may facilitate local adaptation to environmental heterogeneity. Differences in evolvability between the ants and their host trees may affect the evolutionary stability of this widespread ant-plant mutualism.

新热带区蚁栖树种破布木（Cordia alliodora）在其广泛分布的大部分区域中，均与共生的阿兹特克蚁属（Azteca）蚂蚁形成互利共生关系。阿兹特克蚁属的分类学研究历来极具挑战性，这一难题常常导致生态学研究中无法准确界定其物种身份。本研究利用1个线粒体位点与4个核位点的序列数据，对采集自墨西哥至哥伦比亚区域的181个阿兹特克蚁属蚁群开展了系统发育关系、地理分布格局以及分化时间的推断分析。本研究共鉴定出至少8个寄生于破布木的阿兹特克蚁属支系，其中在丰度最高、特化程度最强的物种——皮特丽阿兹特克蚁（Azteca pittieri）——内部，还可区分出至少5个支系。线粒体与核基因数据在物种水平上表现出一致性，但在种内水平上却存在冲突；对两类数据集的比较分析显示，基因渐渗与不完全谱系分选均是导致这些不一致现象的原因。分化时间分析估算结果表明，寄生于破布木的阿兹特克蚁属类群拥有共同祖先的时间约为900万至1800万年前，这一时间与有利于其主要栖息地——季节性干燥热带森林——形成的干旱气候时期相吻合。在皮特丽阿兹特克蚁的5个支系之间，研究发现了与地理距离无显著相关性的遗传分化，这表明受地理隔离的种群间历史基因流较为有限。这一结果与此前报道的寄主树缺乏系统地理结构的结论形成鲜明对比。皮特丽阿兹特克蚁南北支系所占据的生境的气候生态位，尤其是与降水相关的环境变量，并未出现重叠。综合以上研究结果，我们认为蚁群种群间受限的基因流可能促进了其对环境异质性的局部适应。蚂蚁与其寄主破布木之间的演化能力差异，或会影响这一广泛分布的蚁植互利共生关系的进化稳定性。