Anne-Marie Labouche

1. Evolutionary transition between nocturnal and diurnal pollination

My main research interest focuses on floral-trait evolution in response to plant-insect interactions (plant-pollinators or/and plant-herbivores). While it is widely understood that the huge diversity of floral traits is an evolutionary response of plants to the selective pressures exerted by both pollinators and enemies, it is important to consider the simultaneous influence of both mutualists and antagonists together. For instance, the combined needs of being attractive and efficient at transferring pollen onto and from the pollinator have favoured the evolution of floral traits such as colour, scent, reward and location of anthers and stigma. But plants also interact with enemies (e.g. florivores, nectar thieves, seed predator) and selection may also favour defensive functions of floral traits (e.g. trichomes, resins, closing bracts, phenology displacement). Some traits selected by mutualists and antagonists may be trade off with one another (e.g. phenology displacement to avoid antagonists may occur at different times of the day or night, and may be traded off between avoiding antagonists and encountering pollinators).

In this project we are studying the role of male and female reproductive success on floral trait and pollination syndrome evolutions of Silene latifolia (Caryophyllaceae).

Silene latifolia displays a typical nocturnal pollination syndrome, which is characterized by deep white flowers that which emit strong scent at dusk and night, and which have a peak of nectar production in the evening and nocturnal flower anthesis. This plant is involved in a particular interaction with the Noctuidae moth, Hadena bicruris, which pollinates the flower (mutualism) and lays egg in the flower, resulting in seed predation by the larva (antagonism).
Hadena bicruris has been recorded in 90% of the European population of S. latifolia surveyed by Lorne Wolfe in 2002, in which 25-70% of the fruits may suffer seed predation.

Considering the large fitness costs this plant incurred through seed predation, the evolution of the nocturnal pollination syndrome favouring the interaction with this seed predator is puzzling. From the plants perspective, it would seem to be better to interact with non-ovipositing pollinators. Although non-ovipositing pollinators may belong to the nocturnal pollinator community, little is known about their overall density and contribution to pollination. Alternatively, interacting with diurnal pollinators may be a better strategy for the female. But what consequences would this have for the male function? We aim to assess male and female fitness of plants exposed to nocturnal and diurnal pollinators to test the hypothesis that sexual conflict over pollination syndrome, played out differently during the day and night, might explain the maintenance of a puzzling pollination strategy. To this end, we are using as a mode F3 hybrids between the nocturnal S. latifolia and its sister species, the diurnal S. dioica.

Ovipositing Hadena bicruris in a female flower of Silene latifolia- Photo credit: AM Labouche

2. Disentangling the effects of pollen limitation vs. pollen competition on offspring quality

Pollen limitation occurs when a plant does not receive enough pollen grains to fertilize all its ovules (flower scale and/or plant scale). While a pollen-limited plant produces fewer seeds, the quality of these seeds may also be affected. First, the absence or the lower intensity of pollen competition, which is viewed as a post-pollination selection mechanism at the flower level, may reduce the genetic quality of the offspring. Alternatively, plants that mature fewer seeds may allocate their resources to their seeds differently, e.g. producing fewer bigger seeds or more variable seed sizes. It is known that seed characteristics may be correlated with offspring quality. We are currently empirically testing these effects of pollen limitation at the plant vs. flower levels using the wind-pollinated dioecious Mercurialis annua. Very little is still known about levels of pollen competition in wind-pollinated plants, nor about the consequences of natural pollination and the resulting pollination for offspring fitness.

Experimental manipulation of pollen limitation using dioecious M. annua - female plants are arranged at increasing distance to the male plants, placed in the centre; photo credit AM Labouche