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Plant resilience and floral adaptation to pollinator change during a range expansion

Periodic Reporting for period 1 - FLORADAPT (Plant resilience and floral adaptation to pollinator change during a range expansion)

Reporting period: 2016-09-01 to 2018-08-31

FLORADAPT investigated the resilience and potential for evolutionary change of plant populations when faced with changes in pollinator communities. How do plants respond to human-induced changes in their pollinators?

This is currently a very relevant question because evidence is accumulating of pollinator declines and, in consequence, plants are experiencing new “pollinator environments”. Concerns that this can in turn lead to declines in plant populations are growing, and that a negative loop in all interacting species can take place. Alternatively, some plants may be capable of rapid response to changes in their pollinators.

The general aim of FLORADAPT was to explore how plant populations respond to new pollinator environments by comparing native and invasive populations whose exposure to new pollinators has persisted in time for a few generations. For this, a team of students and I used the common foxglove (Digitalis purpurea) as a study system. Foxgloves are herbs native to Europe and pollinated by bumblebees, but have been introduced to all other continents. In tropical mountains, we expect that foxgloves flowers will be visited by a new set of potential pollinators. We used a combination of careful field measurements and genomic tools to study the resilience of the plants to the new pollination conditions. We were also interested in the evolutionary responses by the plant to having new pollinators.
During FLORADAPT we successfully studied wild populations of foxgloves in three countries: England (where foxgloves are native), Colombia and Costa Rica (where they have been naturalised for more than 200 years). We measured reproductive success of plants, the effectiveness of pollinators and how plants have adapted to new pollinators. We also used molecular markers across the genome (discovered using Genotyping-by-Sequencing) to genotype plants from all populations, and are now using this genomic information to estimate the genetic diversity and the potential for evolution of these populations.

Our main discoveries so far are as follows. Foxgloves in naturalised populations in South and Central America have incorporated new pollinators, including hummingbirds and several species of tropical bumblebees. In addition, flowers experience high levels of nectar robbing by specialised nectar robbers (Diglossa birds), bumblebees and hummingbirds. These new conditions allow foxlgoves to successfully repoduce, but lead to new selective pressures. As a consequence, we detect changes in corolla characteristics that are important because they allow or restrict access to the nectar reward offered to pollinators. The molecular analysis will corroborate if these changes we detect are heritable.
We have evidence that flowers are evolving to accommodate the new conditions, an exciting result because it means that, at least in some cases, plants can be resilient to changing pollination conditions. Our findings also shed light on how the amazing diversity of flower form and function evolves: when major changes in pollinators take place, innovative natural selection can occur and lead to new morphological and functional adaptations.

As human change the conditions for wild plants and animals, we are creating new evolutionary pressures. In some cases, like in our study, plants can be resilient. We will continue these studies to understand the genetic basis of this resilience, and to extend these studies to other wild plants.
The tropical bumblebee Bombus hortolanus visting non-native foxgloves in Colombia