Morph-ratio variation, population size and female reproductive success in distylous Pulmonaria officinalis (Boraginaceae).
Theory predicts that morph ratios in heterostylous populations are governed by negative frequency-dependent selection typically resulting in equal morph ratios at equilibrium. Previous work on the distylous perennial herb Pulmonaria officinalis, however, showed asymmetric mating between floral morphs and a weak self-incompatibility system, with the long-styled morph (L-morph) producing significantly higher seed set following intramorph crosses and even selfing than the short-styled morph (S-morph), two aspects thought to affect female fecundity and morph-ratio variation. Here, we evaluated morph ratios and population size of all known P. officinalis populations in the northern part of Belgium. Morph ratios deviated significantly from 1:1 (range 0.09-1 L-morph frequency, mean = 0.58). Relative fecundity of the S-morph (i.e. mean seed set of the S-morph/mean seed set of the L-morph) was on average 0.73, was positively related to the frequency of the L-morph, and reached 1 (similar levels of female fecundity) at an average L-morph frequency of 0.66 in the population. As some small populations had the S-morph in majority, our results suggest that local morph ratios are influenced both by the relative fecundity of L- and S-morph individuals and by stochastic processes in small populations.
Brys
R
R
Division of Forest, Nature and Landscape Research, Catholic University of Leuven, Leuven, Belgium. rein.brys@inbo.be
Jacquemyn
H
H
Beeckman
T
T
D028082:Boraginaceae / Q000033:anatomy & histology / Q000502:physiology*; D005298:Fertility; D035264:Flowers / Q000033:anatomy & histology / Q000502:physiology*; D005828:Genetics, Population; D054817:Pollination; D011156:Population Density