The influence of floral morph ratios and low plant density on mating and fertility in a tristylous colonizing species

Sexual reproduction in heterostylous populations may be vulnerable to demographic conditions because of the small number of mating types in populations. Here, we investigate mating and fertility under natural and experimental conditions in tristylous Lythrum salicaria, an invasive species that exhibits a wide range of floral morph ratios and demographic contexts. We grew 147 open-pollinated seed families from six populations with different morph structures to estimate inter-morph mating (d). In a field experiment, we used progeny ratios from 47 spatially isolated individuals to estimate d, and measured the intensity of pollen limitation experienced by the morphs. The M- and S-morph experienced high rates of d, regardless of population size or morph ratio. Estimates for the L-morph revealed low levels of intra-morph mating in three dimorphic and two trimorphic populations but near complete intra-morph mating in a monomorphic population. Despite high levels of inter-morph mating in the field experiment the morphs experienced significant pollen limitation of fruit and seed set but this did not differ in intensity among the morphs. Our field experiment demonstrates that although plant isolation was associated with pollen limitation of seed set, â long-distanceâ bee-mediated pollen flow served to maintain inter-morph mating. Tristyly in L. salicaria is remarkably robust to demographic variation associated with colonization.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author