Clonal diversity and distance-dependent mate limitation in the self-incompatible understory herb Dicentra canadensis

Background/Question/Methods

Clonality is a common life history that allows plants to produce offspring without sexual recombination and can contribute greatly to population growth. However, extensive clonal reproduction can result in a clumped distribution of ramets and consequently increases the chance of inter-ramet geitonogamy, which can reduce sexual reproduction if outcross pollination is required for zygote formation.  We studied genetic diversity in three Dicentra canadensis populations, one in a well-forested landscape and two in isolated forest remnants.  The frequency of sexual reproduction varied significantly among these populations, with three times more seed being produced in the well-forested site than in the forest remnants, and the variation did not appear correlated with pollinator visitation.  In this study, we evaluated the diversity and spatial structure of genets to test (1) if sexual reproduction was limited by the availability of genetically compatible mates and (2) if spatial aggregation of ramets hindered pollination success.  Leaf tissue of 107 – 187 plants were sampled along four 30-m axes in each population for genetic analysis using ISSR (inter-simple sequence repeat) markers.  

Results/Conclusions

We detected 27, 7 and 2 putative genets in the well-forested population and the two remnant populations, respectively.  The population with only two genets also had the lowest seed set of all, suggesting mate limitation associated with inadequate genet diversity.  In the populations that were genetically more diverse, spatial autocorrelation analysis showed strong similarity of samples up to 6 m.  Considering the average distance of pollen dispersal (2m) estimated for D. canadensis, infrequent pollen transport between genets appeared to be a major limitation on sexual reproduction in these populations.  Prolonged periods of clonal reproduction and inhibition of sex may lead to detrimental consequences in clonal populations.