Plant-herbivore coevolution in a fragmented landscape

Interspesific interactions are seldom uniform across a species’ range and very rarely involve only two species. As stated by the geographic mosaic theory of coevolution, variation in species interactions is the raw material for the coevolutionary process, which takes place over a large geographic scale. Understanding the causalities of variation in the outcome of species interactions is fundamental for understanding the evolution of interacting species. We examine spatial variation in the outcome of plant-herbivore interactions focusing on both the herbivores’ and plant’s point of view.

As a model system we use populations of a perennial herb, Vincetoxicum hirundinaria (Asclepiadaceae), and its specialist herbivores. In the study area V. hirundinaria possesses a mixed mating system with varying levels of self-fertilization. We examine spatial variation in plant mating system and whether this variation is related to spatial variation in plant resistance to natural enemies. We aim to find out if self-fertilization leads to reduced resistance (inbreeding depression) to herbivores, thus selecting for outcrossing in populations with high levels of damage.


We also determine the level of genetic variation in resistance to natural enemies, and whether there is spatial variation in the selection imposed by the herbivores for host plant resistance. From the herbivores’ point of view we examine if there is genetic variation in the host use and performance of the herbivores. Moreover, we examine local adaptation of the herbivores and whether the level of adaptation varies depending on the isolation of the populations and the dispersal abilities of the herbivore species in question. Finally, we examine the spatial and temporal variation in the abundance and genetic structure of the herbivore populations in order to understand the meta-population dynamics of these species.


In the archipelago populations levels of herbivory are known to vary extensively among populations and years. These studies are conducted in the southwestern archipelago of Finland where the distribution of the host plant is highly fragmented and forms a geographic mosaic providing an ideal opportunity to examine the coevolutionary dynamics of plant-herbivore interactions at a relatively large spatial scale. The study provides novel information about the spatial structure and variation in plant mating system, plant-herbivore interactions and potential coevolution, as well as about the joint evolution of plant defences against multiple enemies.



 KÄMY project