Small genome size ensures adaptive flexibility for an alpine ginger.

Abstract

Understanding the proximate and ultimate causes of genome size (GS) variation has been the focus of considerable research. However, the extent and cause of intraspecific variation in GS are debated and poorly understood. This study aimed to test the role of genome size in adaptation through variations in intraspecific GS. GS was measured in 53 Roscoea tibetica populations from the Hengduan Mountains using flow cytometry. Stomatal size and density data were collected from wild and common garden populations. Associations among GS, environmental factors, and stomatal traits were explored. We found that high GS variability was positively correlated with most environmental factors, but negatively correlated with solar radiation during the growing season. The environment, rather than geography, significantly influenced variations in GS. Stomatal traits measured in the wild were significantly correlated with GS, but no such correlations were detected in the common garden. Populations in the common garden had larger stomatal sizes and lower stomatal densities. Populations with smaller GS presented a larger degree of stomatal trait variation from the wild to the common garden. Our findings suggest that intraspecific GS has undergone adaptive evolution driven by environmental stress. A smaller GS is more advantageous for the alpine ginger to adapt to and thrive in changing alpine habitats.