Using text-mined trait data to test for cooperate-and-radiate co-evolution between ants and plants

Mutualisms may be “key innovations” that spur lineage diversification by augmenting niche breadth, geographic range, or population size, thereby increasing speciation rates or decreasing extinction rates. Whether mutualism accelerates diversification in both interacting lineages is an open question. Research suggests that plants that attract ant mutualists have higher diversification rates than non-ant associated lineages. We ask whether the reciprocal is true: does the interaction between ants and plants also accelerate diversification in ants, i.e. do ants and plants cooperate-and-radiate? We used a novel text-mining approach to determine which ant species associate with plants in defensive or seed dispersal mutualisms. We investigated patterns of lineage diversification across a recent ant phylogeny using BiSSE, BAMM, and HiSSE models. Ants that associate mutualistically with plants had elevated diversification rates compared to non-mutualistic ants in the BiSSE model, with a similar trend in BAMM, suggesting ants and plants cooperate-and-radiate. However, the best-fitting model was a HiSSE model with a hidden state, meaning that diversification models that do no account for unmeasured traits are inappropriate to assess the relationship between mutualism and ant diversification. Against a backdrop of diversification rate heterogeneity, the best-fitting HiSSE model found that mutualism actually decreases diversification: mutualism evolved much more frequently in rapidly diversifying ant lineages, but then subsequently slowed diversification. Thus, it appears that ant lineages first radiated, then cooperated with plants.

互利共生可被视为一类“关键创新”，其能够通过拓宽生态位宽度、扩大地理分布范围或提升种群规模，进而提高物种形成速率、降低灭绝速率，以此推动生物谱系的多样化进程。
目前，互利共生是否能够同时加速两个互作双方的谱系多样化，仍是一个悬而未决的科学问题。
已有研究显示，与蚂蚁形成互利共生关系的植物，其物种多样化速率显著高于未与蚂蚁建立关联的植物谱系。
我们由此提出反向设问：蚂蚁与植物的互作是否同样会推动蚂蚁的谱系多样化？换言之，二者是否能够通过互利共生实现协同辐射进化？
我们采用一种新颖的文本挖掘方法，甄别出那些与植物形成防御性或种子传播型互利共生关系的蚂蚁物种。
我们基于最新构建的蚂蚁系统发育树，运用BiSSE、BAMM以及HiSSE三种模型分析其谱系多样化模式。
BiSSE模型结果显示，与植物形成互利共生关系的蚂蚁，其多样化速率显著高于非互利共生蚂蚁；BAMM模型也呈现出类似的趋势，这提示蚂蚁与植物确实存在协同辐射进化的现象。
不过，拟合效果最优的模型为带有隐藏状态的HiSSE模型，这表明未考虑未观测性状的多样化模型，并不适合用于评估互利共生与蚂蚁谱系多样化之间的关联。
在多样化速率存在异质性的研究背景下，拟合效果最佳的HiSSE模型揭示出：互利共生实际上会降低多样化速率——快速多样化的蚂蚁谱系中，互利共生性状的演化频率更高，但该共生关系随后会减缓后续的多样化进程。由此可见，蚂蚁谱系似乎是先发生辐射进化，之后才与植物建立互利共生关系。