Field frequency and pattern of inheritance of the herbivory-defence trait “resistance-by-ducking” in the giant goldenrod (Solidago gigantea, Asteraceae)

Background and aims – For a more complete understanding of the eco-evolutionary dynamics of plant-herbivore interactions, it is important to know the genetic mechanisms that control defence traits, as well as the levels of genetic variation for these traits in plant populations. Here, I present results of a study of the occurrence and pattern of inheritance of the recently discovered trait of ‘resistance-by-ducking’ in the goldenrod Solidago gigantea (Asteraceae).Methods – I grew maternal families of seedlings from fruits collected in a large field population of S. gigantea in southwestern Virginia, USA. I determined stem phenotype (ducking or erect) for 704 plants across 36 maternal families.Key results – Of the 704 plants, 72% had ducking stems and 28% had erect stems. Employing bootstrapping with Hardy-Weinberg principles, I found that the pattern of inheritance was consistent with stem phenotype being controlled by a major gene, with the ducking morph being recessive to the erect morph. The allele frequencies for stem phenotype in the source population were estimated to be 0.85 ducking and 0.15 erect alleles.Conclusions – These findings not only help inform ecological studies of ducking in S. gigantea, but they lay the groundwork for comparative studies of similar goldenrod species whose populations have differing proportions of ducking stems. For example, in all previous studies on populations of S. altissima, ducking stems have been the minority morph, occurring at a frequency of less than 20%. These results suggest that ducking may be costlier in S. altissima, while S. gigantea may face different ecological pressures, or has somehow overcome some of the costs of ducking.