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Genetic analysis of Bromus tectorum (Poaceae) in the Mediterranean region: biogeographical pattern of native populations.

ABSTRACT: Genetic diversity within and among 42 native populations of Bromus tectorum (cheatgrass) was characterized within two regions, the eastern Mediterranean and the western Mediterranean. Two hypotheses were tested for the genetic diversity of these populations: (1) populations from the eastern Mediterranean are more genetically diverse compared with populations to the west, a potential consequence of the species' westward dispersal with the spread of agriculture, and (2) populations across the Mediterranean contain comparable genetic diversity but display high genetic differentiation, a potential consequence of both regions having served as refugia during glacial advances in the late Quaternary Period. Populations in the eastern Mediterranean possess 16 polymorphic loci and 37 multilocus genotypes. In contrast, populations from the western Mediterranean include a subset of these polymorphic loci (9) and fewer multilocus genotypes (19), consistent with the dispersal of B. tectorum with the east-west Holocene spread of agriculture. Among the 19 multilocus genotypes identified in populations from the western Mediterranean, 13 are undetected among eastern Mediterranean populations. Average genetic diversity within populations from the eastern Mediterranean is nonetheless comparable to the genetic diversity in populations from the Iberian Peninsula, whereas diversity is the lowest in the populations from southern France. Our results suggest a prominent role for agriculture in the grass's western spread, although glacial history and environmental heterogeneity also could have influenced the grass's genetic diversity. The exceptionally high level of self-pollination (>99%) in B. tectorum has contributed to preserving the genetic signature associated with the species' biogeographical history across the Mediterranean region.

SUBMITTER: Kelly LJ

PROVIDER: S-EPMC7853138 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundGlobal change produces pervasive negative impacts on biodiversity worldwide. Land use change and biological invasions are two of the major drivers of global change that often coexist; however, the effects of their interaction on natural habitats have been little investigated. In particular, we aimed to analyse whether the invasion of an introduced grass (Bromus tectorum; cheatgrass) along roads verges and the disturbance level in the natural surrounding habitat interact to influence the degree of B. tectorum invasion in the latter habitats in north-western Patagonia.MethodsAlong six different roads, totalling approximately 370 km, we set two 50 m × 2 m sampling plots every 5 km (73 plots in total). One plot was placed parallel to the road (on the roadside) and the other one perpendicular to it, towards the interior of the natural surrounding habitat. In each plot, we estimated the B. tectorum plant density in 1 m2 subplots placed every 5 m. In the natural habitat, we registered the vegetation type (grassy steppe, shrub-steppe, shrubland, and wet-meadow) and the disturbance level (low, intermediate, and high). Disturbance level was visually categorized according to different signs of habitat degradation by anthropogenic use.ResultsB. tectorum density showed an exponential decay from roadsides towards the interior of natural habitats. The degree of B. tectorum invasion inside natural habitats was positively related to B. tectorum density on roadsides only when the disturbance level was low. Shrub-steppes, grassy steppes and shrublands showed similar mean density of B. tectorum. Wet-meadows had the lowest densities of B. tectorum. Intermediate and highly disturbed environments presented higher B. tectorum density than those areas with low disturbance.DiscussionOur study highlights the importance of the interaction between road verges and disturbance levels on B. tectorum invasion in natural habitats surrounding roads of north-western Patagonia, particularly evidencing its significance in the invasion onset. The importance of invasion in road verges depends on disturbance level, with better conserved environments being more resistant to invasion at low levels of B. tectorum density along road verges, but more susceptible to road verges invasion at higher levels of disturbance. All the habitats except wet-meadows were invaded at a similar degree by B. tectorum, which reflects its adaptability to multiple habitat conditions. Overall, our work showed that synergies among global change drivers impact native environments favouring the invasion of B. tectorum.

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Genetic analysis of Bromus tectorum (Poaceae) in the Mediterranean region: biogeographical pattern of native populations.

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