Intraspecific Genome Size Variation in Rorippa indica Reveals a Tropical Adaptation by Genomic Enlargement.

Area of Science:

• Plant evolutionary biology
• Genomics
• Ecology

Background:

• Genome size variation is significant across species but less understood within species.
• Interspecific studies suggest selection against large genomes, but intraspecific dynamics are unclear.

Purpose of the Study:

• Investigate genome size diversity within Rorippa indica.
• Determine the causes and ecological consequences of intraspecific genome size variation.
• Explore adaptive strategies related to genome size in different environments.

Main Methods:

• Utilized flow cytometry, plastome phylogeography, genomic repeat profiling, and reciprocal common garden experiments.
• Analyzed 192 accessions from 83 natural populations of Rorippa indica.
• Quantified genome size variation and correlated it with environmental factors and repetitive DNA content.

Main Results:

• Observed a 15.8% genome size range (764–892 Mb) within Rorippa indica, the widest reported for the genus.
• Tropical lineages showed genome size retention or enlargement, while northern lineages exhibited reduction.
• Genome size correlated with tropical environments and was linked to repetitive DNA, particularly 45S rDNA and Ty1-copia retrotransposons.
• Larger genomes conferred higher fitness (32% more fruits) in tropical conditions.

Conclusions:

• Genome size in Rorippa indica is selectively expressed and adaptive, not neutral.
• Genome enlargement driven by repetitive elements is an adaptive strategy for stable tropical climates.
• Implications for ecosystem dynamics and agriculture under global warming, with larger genomes potentially increasing reproductive output.