Recent research has unveiled significant insights into the evolutionary history of the Solanum genus, renowned for its vast diversity of fleshy fruits. This genus includes economically and agriculturally important plants such as tomatoes, potatoes, and eggplants. By analyzing genetic data from 247 species, researchers have provided a clearer picture of how Solanum fruits evolved, focusing on their size and color.
The study reconstructs the evolutionary timeline of Solanum, indicating that the genus likely originated around 53.1 million years ago. Major diversification events occurred between 35 and 27 million years ago, a period predating many modern frugivores (fruit-eating animals). This extensive timeline highlights the long-standing evolutionary processes that have shaped the genus.
One of the key discoveries is the strong conservatism in fruit traits across the Solanum lineage. The analysis shows that both fruit color and size are highly conserved, meaning these traits have remained relatively unchanged throughout the genus's evolutionary history. It appears that the ancestral Solanum fruit was medium-sized and green when ripe. This conservative pattern suggests that once certain fruit characteristics evolved, they tended to persist across different Solanum species, rather than frequently changing to adapt to new ecological conditions.
Another important finding is the correlation between fruit size and color. Larger Solanum fruits tend to have duller colors, such as green or brown, while smaller fruits are more likely to be brightly colored, including hues like black, purple, or red. This relationship implies that fruit size and color evolved in tandem, possibly influenced by the feeding behaviors and preferences of various frugivores. For example, dull-colored, larger fruits might be more suited for consumption by mammals, while brightly colored, smaller fruits could attract birds, which have better color vision.
The study's findings suggest that evolutionary constraints play a more significant role in shaping Solanum fruit traits than direct adaptation to frugivore preferences. Instead of continually evolving new fruit characteristics to match the needs of different fruit-eating animals, Solanum species appear to have retained their ancestral traits. These traits then found their fit in diverse ecological niches over time, a process known as ecological fitting. This highlights how evolutionary history can influence the current diversity of fruit traits in a genus and underscores the complex interaction between phylogenetic conservatism and ecological adaptation.
For a comprehensive view of this research, see the full study
Messeder, J. V. S., et al. (2024). A highly resolved nuclear phylogeny uncovers strong phylogenetic conservatism and correlated evolution of fruit color and size in Solanum L. New Phytologist..