Only seven percent of plant species in an estimated number of 298,900 total species have separate male and female individuals, experts say. Like animals, male and female plants also exhibit differences, such as growth rates or the production of chemicals used to deter insects.

Researchers from West Virginia University, Cornell University, Texas Tech University and the University of Wisconsin-Madison, as well as the Nanjing Forestry University and Lan Zhou University in China will be studying sex differences in poplars and willows.

Unlike most plants, willows and poplars have male and female varieties. The evolution of separate sexes in plants is a long-standing mystery because outcrossing, sex with different individuals, has distinct disadvantages. For one, each individual has more difficulty finding a mate when compared to hermaphrodite plants, where self-fertilization is an option. Also, hermaphrodites transfer all of their genes to their self-fertilized offspring, effectively doubling their fitness compared to male and female plants, which only transfer half of their genes when they mate.

Plant species with separate sexes actually evolved from hermaphrodite ancestors. Understanding why they evolved and the differences between the two genders can help understand some of the dimensions and significance of biodiversity in ecosystems.

The research team chose to study willows and poplars because of their historical medicinal and cultural roles as well as their importance to the bioenergy and timber industries.

“Willows have been used traditionally for basket-making, and were one of the first sources for aspirin. There are also several projects that are working to develop willows and poplars for bioenergy resources,” said Stephen DiFazio, Professor of Biology and primary investigator for WVU’s efforts on the project.

Researchers on the project, “Dimension U.S.-China: Collaborative Research: Sex Chromosomes and Dioecy in Plants as Drivers of Multi-Level Biodiversity,” will be studying 30 different species in the willow and poplar family, as well as their close relatives. They will be taking samples from each of these species, sequence their genomes and compare the composition and structure of the males and females.

The National Science Foundation program, Dimensions of Biodiversity, focuses on biodiversity itself, as well as its functional consequences.

In addition, they will characterize the insect communities on male and female plants and the chemicals used for defense and pollinator attraction. This will help the researchers understand how, and why, the plants evolved separate sexes.

“One of the really cool things about this family is that willows and poplars have different pollination mechanisms,” DiFazio said. “Willow is insect pollinated, and poplar is wind pollinated. That has really big implications for biodiversity.

“Willows have about 500 species in the world; it’s one of the most diverse genera of trees. Poplars have only 30 species, and we think part of the reason for that is insect pollination versus wind pollination. Furthermore, we think that a big part of the mechanism that generates the diversity is located on the sex chromosomes.”

Dimensions of Biodiversity awarded WVU $540,830 for this project. These funds will help pay for materials, use of facilities, a research assistantship and travel to and from China.

WVU will perform much of the sequencing on the project. DiFazio is the director of the university’s Genomics Core Facility, which houses a sequencer and several robots that will be used to prepare more than 1,500 samples.

DiFazio is considering the use of a drone for the project. Poplars are extremely tall, and a drone will make it a lot easier for DiFazio and his research assistant to collect samples from the trees.

Researchers will also be utilizing Spruce Knob, WVU’s high-performance computing system to run computational analyses.

“That’s one of the biggest challenges we face in this field,” said DiFazio. “The WVU High Performance Computing facility is really critical for us to be able to make any progress. It’s been one of the best infrastructure developments made since I have been faculty here.”



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