Genetic, Geographic, and Climate Diversity of a Weedy Species: The Brachypodium distachyon Species Complex

Abstract

The Introduction of novel species into non-native environments can have biodiversity and agricultural effects on landscapes costing billions of dollars in damage each year. Approximately 1.2 million hectares of land are currently deemed unusable globally because of invasive plants. The likelihood of introduced species becoming invasive isn't always understood, nor the effect of introductions immediately apparent. The environment is the primary selection force for screening habitability and is the primary selector for adaptation, but measuring all its components is complex. Therefor climate factors, precipitation and temperature, are the primary variables for determining a species distribution. The three model grasses in the Brachypodium distachyon complex species were used in this study because of their small sequenced genomes, classified as weedy and invasive in some regions, and were once native to the circum-Mediterranean, now global distributed. Genotyping by sequencing was used on 1,573 individuals to determine species identification and genetic diversity of each complex member. A total of 125 unique genotypes of B. distachyon were found from 479 individuals, eight unique genotypes of B. stacei from 50 individuals, and 80 unique genotypes of B. hybridum from 1,015 individuals. MaxEnt distribution modelling was used to find potential area using a training specificity equals sensitivity threshold both natively and globally. B. stacei was the most rare having the smallest potential area in its native range at 2,458,837 square kilometers and 3,207,524 globally. B. distachyon had the largest native potential area at 5,098,573 square kilometers, but rare outside its native range, Australia only. B. hybridum was modelled to have 3,935,266 square kilometers natively, but 6,705,946 square kilometers globally leaving 2,770,680 of potential habitat non-natively. Common genotypes of the polyploid complex member B. hybridum were permutation tested for global abundance across groups of regions, with the genotype NRD-1 being significantly more abundant geographically than random. NRD-1 was also used for global distribution modelling to determine global suitable regions that would be sensitive to NRD-1 introduction. The three complex species were compared for climate breadth where B. hybridum had the widest climate breadth of the three group members. The genotype NRD-1 was also compared to B. hybridum as a whole to see if the NRD-1 genotype had a similar climate breadth as the whole species, possibly defining the species climate breadth. The climate diversity within each species was used to designate climate type identities for sample locations to measure climate range a genotype occupies and the climate diversity of geographic space. The B. hybridum genotype NRD-1 was found in the most climate types through permutation testing and found to have a significantly larger climate breadth than average p-value <0.01. Geographic regions with high climate diversity were also found to have the most genotypes. As B. hybridum was found to be the most widely distributed of the three study species, many specific genotypes occurred in numerous climate types and were sampled on multiple continents, particularly genotype NRD-1, thus were concluded as the most widely adapted B. hybridum and all other B. distachyon complex species genotypes. Show more