Along with a group of researchers from Harvard University, Scott Hodges, professor in the Department of Ecology, Evolution and Marine Biology at UCSB, recently discovered a mechanism of flower petal evolution that contradicts previous scientific theories that have been widely accepted for the past 60 years.
Using Columbine flowers, also known as Aquilegia, the team monitored the evolution of petal spurs. Shaped like long tubes, these spurs hold nectar at their tips and are thought to have evolved to match the tongue length of the Columbine flowers’ pollinators. In fact, certain species of Columbine flowers exhibit spurs up to 16 centimeters in length.
For 60 years, the scientific community has assumed that petal elongation is the result of cell proliferation, or continued cell divisions. However, in his recent publication in the Proceedings of the Royal Society B, Hodges has challenged this hypothesis.
“Previously it was thought that small regions of the developing petal were sites of cell divisions that added cells and made the spur grow out. We found that cell division stops very early in development when the spurs are about eight millimeters in length, even though they can grow to 15 centimeters,” Hodges said.
Upon closer examination, Hodges and his team found that the process of anisotropy may actually be responsible for spur length growth.
“Anisotropy is when a cell grows more in one direction than another, so the shape of the cell changes,” Hodges said. “Isotropy is when a cell grows the same amount in all directions, keeping the same shape. The amazing diversity of petal shape in Aquilegia… is mostly due to differences in cell shape, not cell numbers as had been thought before.”
In light of this new understanding of petal spur growth, Hodges and the research team hope to identify the genes responsible for spur length and determine why different species of Columbine flowers achieve such a diversity of spur lengths. In sum, identifying the genes that promote and control spur cell growth could provide valuable information about the evolution process of flowers, including the evolving relationship between these plants and their pollinators.
“One thing we’d like to understand is what the genes are that control how different species achieve different shapes,” Hodges said. “We now know that we are looking for genes that may affect cell shape and/or how long flowers develop. We know that flowers have evolved to fit the shape of their pollinators and we would like to understand the number and types of genes that have evolved to make this happen.”