Spleenworts are evergreen ferns of the genus Asplenium, having undivided to featherlike fronds with oblong to linear sori arranged along the veins. This nearly globally distributed genus is especially suited to study the genome size evolution in ferns.
Ferns are different from other vascular plant lineages as they are the only group to show evidence for a correlation between genome size and chromosome number.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaborators conducted a study to explore whether the evolution of fern genome sizes is not only shaped by chromosome number changes arising from polyploidy but also by constraints on the average amount of DNA per chromosome.
The researchers expanded the existing dataset of fern genome sizes with additional data focused on European accessions of the genus Asplenium (spleenworts). They then analyzed the new data within a phylogenetic framework.
They found that the genome size varied substantially between diploid species, resulting in overlapping genome sizes among diploid and tetraploid spleenworts.
The genome size of polyploid ferns was predictable as long as the genome size of their diploid parents had been reliably deter-mined. The monoploid genome size showed a phylogenetic pattern indicating evolutionary constraints such as chromosome stability, or the influence of ecological factors.
“Our study showed that constraints acting on the average size of chromosomes are one of the main factors which have limited the accumulation of medium to large genomes in many fern lineages”, said Dr. LIU Hongmwei, first author of the study.
The study entitled “Polyploidy does not control all: lineage‐specific average chromosome length constrains genome size evolution in ferns” has been published online in Journal of Systematics and Evolution.
Harald Schneider Ph.D Principal Investigator
Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun, Mengla, Yunnan 666303, China