Synthesizing the phylogenetic evidence for mutualism-associated diversification.

Mutualisms are associations in which interacting species provide services or resources to each other. It has been suggested that being party to a mutualism can spur the diversification of the interacting species due to several potential hypothesized mechanisms. There is empirical evidence to both support and refute this prediction. However, this evidence comes from a variety of different methodologies, some of which have been found to be unreliable when the phylogenetic model is misspecified, and different data types and it is therefore difficult to weigh together. Here, we synthesize phylogenetic comparative datasets and analyze the data in a consistent manner using both sister-clade comparisons and hidden-trait state-dependent speciation and extinction models. The results are mixed-for the majority of the datasets we find no evidence for an effect on diversification rates in either direction, with several showing significant positive associations and a few showing significant negative associations. In contrast to the generally mixed findings between datasets, we find that qualitative results to be consistent when analyzing taxonomically overlapping datasets using different methods, suggesting that the detected variation in diversification is due to the nature of the mutualism and not due to differences in methodology.