Northwest of the striking Golden Gate Bridge and the bustling streets of San Francisco lies Point Reyes National Seashore. Elephant seals sit at the foot of cliffs, barking 100 feet below the steep ridges. Gusty winds whistle through the air as falcons glide through the sky. Hundreds of flowers bloom in unison, painting a picture of serenity.
Over the past two decades, Thomas Givnish, the Henry Allan Gleason Professor of Botany and Environmental Studies, embarked on trips to Oregon, Arizona, Washington and along the West Coast collecting samples of and photographing the diverse Calochortus — a flowering plant in the lily family.
Within the genus, flowering plants appear the same, but their petals can span colors of the rainbow, from a cherry red to a vibrant purple. While the lily has long slender petals, the Calochortus has petite and more rounded petals.
Givnish and his team – including lead author Nisa Karimi, a former post-doc in the Givnish lab – published their findings in Proceedings of the National Academy of Sciences (PNAS). Their research presents a new family tree for the genus Calochortus and explains how the flower migrated across North America (going back millions of years). They found that different lineages occupy diverse regions including the Pacific Northwest, California, Mexico and the Intermountain West. Their findings also explain why some land supports several species in a small region while others support very few.
“My colleagues and I are all really excited to have the results out,” says Givnish. “We have a lot more to publish on this topic, and we’re eager to keep moving forward.”
Givnish and his team analyzed DNA sequences in the cell nucleus for more than 70 species. This helped reconstruct the evolution of chromosome numbers, which assisted them in determining how many local species live in one area. Some species have six, seven, eight or more chromosome pairs, which can prevent certain species from producing offspring with one another.
Givnish says this is important because the greater the range of chromosome numbers, the more mating barriers will be present. Since the species cannot mate, they coexist with one another, allowing more species to live in a region. Then, they harvest different resources, or, in the case of California, they live in different climates, soils and elevations.
Givnish and his team confirmed what few studies before this one have: that mating barriers are as important as diverse environmental conditions for large numbers of closely related species to coexist. Environmental heterogeneity refers to an area that creates livable conditions for species with different ecological requirements. Therefore, a larger number of species can inhabit the area, increasing the species pool.
Amongst the millions of acres in the West and Mexico sits a biodiversity hotspot where a concentration of Calochortus thrive — California Floristic Province. Filled with 3,488 plant species, this land’s environmental heterogeneity serves as the ideal landscape to explain what affects and creates biodiversity.
Ultimately, these factors impact spatial variation across different geographic locations. The natural distribution of Calochortus among an extensive range of climates, elevations, soils and more is a point of interest in the botanical world. The team constructed datasets to document where species were found and environmental conditions.
“We want to account for the remarkable diversity of flowers in Calochortus. We want to see if the same genes are being turned off and on in different lineages that have evolved similar flowers independently,” says Givnish. “We don’t know that yet, but we soon hope to have an answer based on sequencing of whole genomes and studies of floral development by our research team, including colleagues at Cornell.”