Herbivory influences the relative fitness of three native Lythrum salicaria populations, but no evidence of local adaptation along a latitudinal gradient

• Local adaptation along environmental gradients has been documented in many plant species, but the extent to which biotic interactions influence the relative fitness of local and non-local genotypes has rarely been examined experimentally. Previous common-garden experiments detected clinal variation in life history, phenology and resistance to herbivory in the perennial herb Lythrum salicaria along a latitudinal gradient in Sweden, which coincides with a decrease in the length of the growing season and intensity of herbivory from south to north. Here, we included a herbivore-removal treatment in a reciprocal transplant experiment to test whether three populations sampled along the latitudinal gradient are locally adapted, whether differences in resistance and tolerance are consistent across sites and whether herbivory influences the relative performance of the study populations. The results did not reveal any evidence of local adaptation. Instead the southernmost population had the highest relative fitness at all three sites and was consistently less damaged by herbivores than were the other populations. The intensity of herbivory was greatest at the southern site and very low at the northernmost site. The removal of insect herbivores positively affected plant growth and fecundity at the southern and central sites. Herbivore removal also affected the relative fitness of the study populations at the southern site, and tended to do so at the central site. However, the relative ranking of the three populations did not change, indicating that herbivores influenced the strength but not the direction of selection. Genetic drift, recent climatic warming and intermittent strong selection against southern genotypes at northern latitudes may all contribute to the documented patterns of among-population variation in fitness, while similarity in the behaviour and preferences of herbivore populations along the studied gradient may explain the consistent differences in resistance.

Nyckelord

Female reproductive success

Galerucella calmariensis

Galerucella pusilla

Nanophyes marmoratus

Plant-herbivore interactions

Reciprocal transplant

Plant resistance

Tolerance to herbivory

Biology with specialization in Ecological Botany

Biologi med inriktning mot ekologisk botanik

Publikations- och innehållstyp

vet (ämneskategori)

ovr (ämneskategori)