Leveraging species invasions to study trait evolution on contemporary timescales
Flowering plants dominate a wide range of terrestrial ecosystems, and display a great variety of shapes, sizes, colours, and appearances. How does such impressive diversity of form arise?
The process of how morphological change happens – trait evolution - is a question which is often explored from a macroevolutionary perspective, using phylogenetic approaches to infer evolutionary history. These are useful because they can reconstruct the past to tell us something about present patterns in trait variation. However, hypotheses about trait shifts that happened in the past can’t be experimentally tested, since the organisms and environments that the shifts took place in no longer exist.
We are increasingly appreciating that evolution doesn’t have to take place gradually over millions of years, but can happen rapidly, on timescales that we can observe. In plants, this is especially apparent in invasive species. When species are introduced to new geographic ranges, more and more research is showing that successful invaders evolve rapidly to adapt to their new habitats.
I am currently working on using invasive species to study trait evolution, specifically, shifts in leaf shape in yellow starthistle (Centaurea solstitialis). Evolving invaders provide great opportunities to learn more about the processes involved in morphological trait shift; by using them as experimental models, we can improve understanding of how the “endless forms” of biodiversity came to be.
Phylogeny, fruit evolution, and diversification rate in Lantaneae
Flowering plants are a remarkably successful lineage of organisms. Darwin famously referred to their rapid diversification and rise to ecological dominance as an “abominable mystery”. Why are there so many different species of flowering plants? One idea is that particular traits (key innovations) which characterize flowering plants have contributed to their evolutionary and ecological success. Fleshy fruits, produced in about half of all flowering plant families to facilitate seed dispersal by animals, has been proposed as one such key innovation.
Using a phylogenetic approach, I have tested whether fleshy fruits are associated with increased diversification rates in a group of Neotropical plants, the tribe Lantaneae in the Verbena family.
About a third of the species in this group have colorful, fleshy fruits, and are classified in the genus Lantana. Most of the rest of the species have dry fruits, and are classified in the genus Lippia. By sampling tissue and comparing DNA sequences from these species, I have found that neither of these genera represent single lineages (monophyletic groups). That is, fleshy fruits have evolved multiple times independently from dry-fruited ancestors.
When the evolutionary history and timing of species divergences are inferred from DNA sequences for species belonging to Lantana and Lippia, they show that the fleshy-fruited species have a faster rate of diversification than the dry-fruited species, supporting the idea that fleshy fruits are a key innovation in this particular group of plants.