Trait Matching: What does it tell us?

Bruce Anderson (April 5, 2011)

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Recently, several studies have used the geographic matching of morphological traits (e.g. proboscis versus corolla length) to infer that coevolution has taken place between two interacting organisms. However, geographic trait matching alone is not sound evidence for coevolution because it is not a mandatory end point for coevolutionary relationships, and nor is coevolution the only selective mechanism capable of giving rise to geographic trait matching. Here I demonstrate how both coevolved and non-coevolved relationships result in patterns of trait matching but that through selection studies and by a process of elimination, it is possible to determine what the mechanism is behind trait matching patterns. In addition, using data from several published studies, I suggest how the steepness of the slope and intercept may yield important information about the relative strength of selection acting on the morphological traits of interacting species. For example in plant-insect relationships, plants seem to consistently have more exaggerated morphological traits than insects at high trait magnitudes. This suggests that selection to exaggerate the magnitude of the plant trait is stronger than for insects to exaggerate the magnitude of their corresponding traits. Thus, when plant and insect morphological traits are coevolved, insects are the most likely to be the losers of the coevolutionary race.