Sources of variation in reciprocal herkogamy in the distyly floral syndrome of Linum tenue (Linaceae)

Abstract

Premise of research. Distyly is a floral polymorphism involving reciprocal herkogamy shaped by selection for pollen transfer efficiency. The variation of the floral organs involved in pollen transfer can be individually affected by environmental and genetic sources of variance, but the organ development will be canalized to minimize reciprocal inaccuracy between anthers and stigmas, as this is the focus of selection. Methodology. We measured floral organ and cell length of both morphs of distylous Linum tenue (Linaceae) at different developmental stages of field- and glasshouse-grown plants. We analyzed the results to measure reciprocal inaccuracy and identify sources of variance. Pivotal results. Flowers from the field were larger than those from the glasshouse owing to both environmental and genetic (population) factors. Pistil and stamen length in adult flowers correlated with flower size, but reciprocal herkogamy was mostly invariant to the size of individual floral organs. The length of short floral organs showed greater maladaptive bias, while the length of tall organs showed greater imprecision. During development, the pistils of pin flowers grew at a faster rate than those of thrum flowers, mostly owing to cell elongation, while cell division was more important for male organ height. Conclusions. Distyly in L. tenue involves the interaction of multiple coordinated developmental and environmental mechanisms, leading to limited but predictable patterns of variance in the expression of reciprocal herkogamy.