Abstract
Polyploidization and the shift to apomictic reproduction are connected to changes in DNA cytosine-methylation. Cytosine-methylation is further sensitive to environmental conditions. We, therefore, hypothesize that DNA methylation patterns would differentiate within species with geographical parthenogenesis, i.e., when diploid sexual and polyploid apomictic populations exhibit different spatial distributions. On natural populations of the alpine plant Ranunculus kuepferi, we tested differences in methylation patterns across two cytotypes (diploid, tetraploid) and three reproduction modes (sexual, mixed, apomictic), and their correlation to environmental data and geographical distributions. We used methylation-sensitive amplified fragment-length polymorphism (methylation-sensitive AFLPs) and scored three types of epiloci. Methylation patterns differed independently between cytotypes versus modes of reproduction and separated three distinct combined groups (2x sexual + mixed, 4x mixed, and 4x apomictic), with differentiation of 4x apomicts in all epiloci. We found no global spatial autocorrelation, but instead correlations to elevation and temperature gradients in 22 and 36 epiloci, respectively. Results suggest that methylation patterns in R. kuepferi were altered by cold conditions during postglacial recolonization of the Alps, and by the concomitant shift to facultative apomixis, and by polyploidization. Obligate apomictic tetraploids at the highest elevations established a distinct methylation profile. Methylation patterns reflect an ecological gradient rather than the geographical differentiation.
Highlights
Epigenetic processes are regulatory mechanisms that may affect phenotypes without altering DNA sequences [1,2,3]
Our study explored cytosine methylation patterns in di- and tetraploid cytotypes and in different reproduction modes of R. kuepferi
Previous AFLPs studies indicated that genetic divergence of diploid and tetraploid cytotypes is in this species extremely low, and genetic variation within and among populations in the two cytotypes is on a similar level [59,63]
Summary
Epigenetic processes are regulatory mechanisms that may affect phenotypes without altering DNA sequences [1,2,3] They undergo constant transformation [4] and may cause high phenotypic plasticity and potentially heritable variation [5,6,7]. Temperature seems to trigger certain methylation conversions [23,24,25] Such sensitivity might be associated with high plasticity in response to extreme environments [20], especially if induced methylation changes are heritable [19,26]
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