Ecological study on the adaptive significance of autumn leaf colouration

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Two hypotheses explaining the adaptive significance of autumn leaf colors (coevolution hypothesis: the color is an honest warning signal of tree defence against herbivores, tritrophic interaction hypothesis: the color attracts myrmecophilous aphids in autumn and in next spring ants attending the aphids defend trees from herbivores) were tested in the field using three tree species of four sites. Neither hypotheses were supported. However, in two tree species, there was significant correlation between autumn leaf colors and resistance against herbivorous insects. The comparison of colors of new spring leaves with those of old autumn leaves in more than 150 plant species revealed that in many species the colors of new leaves were different from those of old leaves, suggesting different natural selection acting on leaf colors between in spring and in autumn.