The role of lateral and vertical herkogamy in the divergence of the blue- and red-flowered lineages of Lysimachia arvensis

Abstract

Background and Aims Herkogamy, or anther–stigma separation, is known to reduce self-pollen deposition, but little is known about the relative efficacy of different modes or conformations of herkogamy. We assessed the effectiveness of vertical versus lateral herkogamy in preventing or promoting self-pollen deposition in the annual herb Lysimachia arvensis, a plant with lineages that differ in flower colour, and in which flowers first display lateral and then vertical herkogamy. Because mating between the two lineages compromises fitness through the production of low-quality hybrid offspring, we tested the prediction that individuals sampled from sites occupied by both lineages should have flowers that promote autonomous self-pollen deposition and self-fertilization as a result of selection to reduce deleterious reproductive interference. Methods We characterized variation in herkogamy within and among 25 pure and mixed populations of L. arvensis in its European range and assessed the effectiveness of lateral versus vertical herkogamy in avoiding self-pollen deposition. Results Lateral herkogamy was more effective than vertical herkogamy in limiting self-pollen deposition. In the case of vertical herkogamy, only approach herkogamy was effective. Lineages showed consistent differences in herkogamy traits. In general, angles were smaller for blue than red flowers in most populations, and blue flowers showed approach herkogamy, while red flowers showed predominantly reverse herkogamy. In sympatry, the red lineage showed a reduction of both herkogamy traits while for the blue lineage only lateral herkogamy was reduced. Conclusions Our results demonstrate that pollen deposition is affected not only by the degree but also the spatial conformation of herkogamy. They also highlight reduced herkogamy as a potential mechanism for promoting reproductive assurance under pollen limitation, as well as for avoiding reproductive interference between genetically divergent lineages.

Reproductive Assurance Maintains Red-Flowered Plants of Lysimachia arvensis in Mediterranean Populations Despite Inbreeding Depression

“…Genetic differentiation between color morphs strongly suggests that gene flow between them is restricted, being to some extent reproductively isolated. This is also supported by other results found in previous studies and in other previous papers: niche differentiation with the blue-flowered plants more adapted to dry habitats (Arista et al, 2013), differences in flowering phenology found here and in a previous study (Arista et al, 2013) that hinder pollen flow between morphs at least partially, pollinator visitation in polymorphic populations where bees show floral constancy and prefer blue-flowered plants (Ortiz et al, 2015;Jiménez-López et al, 2020a), differences in inbreeding depression and mating system (in this study), and the low frequency of intermediate phenotypes in polymorphic populations (Jiménez-López et al, 2019a;2020b). These facts clearly indicate a history of gene flow limitation between morphs, suggesting they are different lineages.…”

The colourful life of flowers

“…(Figure 4A and B), the blue-flowered form is better adapted to xeric conditions than the red-flowered form, which accounts for its high frequency in the Mediterranean region compared to the red form (Ortiz et al 2015). A difference in herkogamy between these morphs was recently described, blue flowers showing approach herkogamy while red flowers showed reverse herkogamy, with an effect on pollen deposition (Jiménez-López et al 2020). Colour polymorphism is frequent in species with deceptive pollination, and this may be due to disruptive selection caused by inaccurate discrimination by pollinators (Kagawa and Takimono 2016).…”

Changes at a Critical Branchpoint in the Anthocyanin Biosynthetic Pathway Underlie the Blue to Orange Flower Color Transition in Lysimachia arvensis

“…The blue petals of L. arvensis contain malvidin derivatives, whereas orange petals contain pelargonidin derivatives ( Lawrence et al, 1939 ; Harborne, 1968 ; Ishikura, 1981 ). Although both L. arvensis flower colors have long been described as different morphs, recent molecular phylogenetic studies indicate that these flower color phenotypes reflect very closely related, yet distinct, evolutionary lineages ( Jiménez-López, 2019 ; Jiménez-López et al, in review ) with some degree of reproductive isolation ( Jiménez-López et al, 2020 ). Pollinators (mainly Halictus spp.…”