Barley’s rapid climate-driven adaption revealed in century-old biological experiment

Leveraging one of the world’s oldest biological experiments – which began in 1929 – researchers have uncovered how a major crop, barley, was shaped by both agricultural pressures and its changing natural environment. The results underscore the power of long-term studies in understanding the dynamics of adaptive evolution. The survival of cultivated plants after their dispersal across different environments is a classic example of rapid adaptive evolution. For example, barley, an important neolithic crop, spread widely after domestication over 10,000 years ago to become a staple source of nutrition for humans and livestock throughout Europe, Asia, and Northern Africa over just a few thousand generations. Such rapid expansion and cultivation have subjected the plant to strong selective pressures, including artificial selection for desired traits and natural selection by being forced to adapt to diverse new environments. Although previous research on early barley cultivars has identified some of the plant’s population genetic history and mapped genetic loci that contributed to its spread, the speed and overall dynamics of these processes are difficult to determine without direct observation. Leveraging one of the world’s oldest and most long-term evolutionary experiments, the barley composite cross II (CCII), Jacob Landis and colleagues observed the process of local adaption of barley over nearly a century. CCII is a multigenerational common garden experiment that began in 1929 to adapt a genetically diverse population of 28 barley varieties to the environmental conditions of Davis, California. Although the experiment began with thousands of genotypes many decades ago, Landis et al. show that natural selection has drastically reduced this diversity, wiping out almost all founding genotypes, leading to the dominance of a single clonal lineage constituting most of the population. This shift occurred rapidly, with the clonal line becoming established by generation 50. According to the findings, this successful lineage is primarily composed of alleles originating from Mediterranean-like environments, like that of Davis. Moreover, the authors show that genes targeted by selection indicate a major role for climate during adaptation, including strong selection on reproductive timing. “We found considerable evidence that local adaption dominates evolution in this experiment. However, despite early, rapid gains in yield in CCII, the evolutionary breeding approach failed to keep pace with the gains observed from pedigree-based breeding methods,” write Landis et al. “Understanding why the most competitive genotypes produced during local adaptation are not necessarily the highest yielding will be of great interest in the future.”