title: Genotypic variation in yellow autumn leaf colours explains aphid load in silver birch.
abstract: • It has been suggested that autumn-migrating insects drive the evolution of autumn leaf colours. However, evidence of genetic variation in autumn leaf colours in natural tree populations and the link between the genetic variation and herbivore abundances has been lacking. • Here, we measured the size of the whole aphid community and the development of green-yellow leaf colours in six replicate trees of 19 silver birch (Betula pendula) genotypes at the beginning, in the middle and at the end of autumn colouration. We also calculated the difference between green leaf and leaf litter nitrogen (N) and estimated the changes in phloem sap N loading. • Autumn leaf colouration had significant genetic variation. During the last survey, genotypes that expressed the strongest leaf reflectance 2-4 wk earlier had an abundance of egg-laying Euceraphis betulae females. Surprisingly, the aphid community size during the first surveys explained N loss by the litter of different birch genotypes. • Our results are the first evidence at the tree intrapopulation genotypic level that autumn-migrating pests have the potential to drive the evolution of autumn leaf colours. They also stress the importance of recognizing the role of late-season tree-insect interactions in the evolution of herbivory resistance.
authors.affiliation: University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, FIN-15140 Lahti, Finland.
authors.forename: Aki
authors.initials: A
authors.lastname: Sinkkonen
authors.affiliation: University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, FIN-15140 Lahti, Finland.
authors.forename: Eeva
authors.initials: E
authors.lastname: Somerkoski
authors.affiliation: University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, FIN-15140 Lahti, Finland.
authors.forename: Ulla
authors.initials: U
authors.lastname: Paaso
authors.affiliation: University of Eastern Finland, Department of Environmental Science, PO Box 1627, FI-70211 Kuopio, Finland.
authors.forename: Jarmo K
authors.initials: JK
authors.lastname: Holopainen
authors.affiliation: Finnish Forest Research Institute, Vantaa Research Unit, PO Box 18, FIN-01301 Vantaa, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Rousi
authors.affiliation: University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, FIN-15140 Lahti, Finland.
authors.forename: Juha
authors.initials: J
authors.lastname: Mikola
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001042:Aphids / Q000502:physiology*; D029662:Betula / Q000235:genetics* / Q000469:parasitology*; D005260:Female; D014644:Genetic Variation; D005838:Genotype; D008297:Male; D009584:Nitrogen / Q000378:metabolism; D010641:Phenotype; D010858:Pigmentation / Q000235:genetics*; D018515:Plant Leaves / Q000502:physiology*; D012621:Seasons
chemical_list: D009584:Nitrogen