Autumn colouration and herbivore resistance in mountain birch (Betula pubescens)

Abstract

We explored Hamilton and Brown's autumn signalling hypothesis in mountain birch (Betula pubescens). As predicted by the hypothesis, early autumn colour change (i.e. high degree of autumn colouration in September) was negatively correlated with insect damage the following season. Furthermore, as expected, indices of physiological stress (i.e. leaf fluctuating asymmetry) and reproductive investment (i.e. catkin production) were positively correlated with insect damage the following season. Indirectly, we also found support for the idea that the proposed handicap signal (i.e. early autumn senescence) might be associated with an honesty ensuring cost in terms of lost primary production. Further work is, however, required to determine whether the link between autumn colours and insect damage observed in this study is causal.

The coevolution theory of autumn colours

“…More importantly, a strong preference of aphids for trees with green leaves was observed. This is in agreement with Hagen et al (2003) and is also the first direct evidence of colour preference (for green) in autumn. Moreover, their observations, compared with previous data gathered on the same species, suggest that aphids colonizing trees with green leaves develop better in spring than aphids colonizing trees with bright autumn colours, which is consistent with a positive correlation between tree quality and defensive commitment.…”

“…Clones of the same species could be grown on different conditions of nutrients or light and the difference in colour could be observed. Alternatively, the condition of different trees could be assessed by indirect measurements, for instance fluctuating asymmetry (see Hagen et al 2003).…”

“…The coevolution theory has been developed by us (Archetti 2000;Hamilton & Brown 2001;Brown 2004) from an idea of W. D. Hamilton, and recently there has been a considerable amount of interest on the subject (e.g. Atkinson 2001;Whitfield 2001;Holopainen & Peltonen 2002;Lev-Yadum et al 2002;Wilkinson et al 2002;Hagen et al 2003).…”

Decoupling vigour and quality in the autumn colours game: Weak individuals can signal, cheating can pay

“…There is no debate on the importance of the first point (colour preference), although it is debated whether insects actually avoid red leaves (the tests performed so far seem to support this claim: Archetti & Leather, 2005;Hagen et al, 2003;Hagen et al, 2004;Karageorgou & Manetas, 2006;Doering et al, 2008; see also Furuta, 1986; contrasting evidence has been reported by ; reviewed by Archetti et al, 2008). This is not the point of this paper.…”

The shared and separate roles of aposematic (warning) coloration and the co-evolution hypothesis in defending autumn leaves

“…It is important to view this definition in the light of the theoretical understanding of the time, since aposematism was not considered to be a handicap at the time. 28 In other studies that favored the co-evolutionary signaling hypothesis, 7,8,[29][30][31] aposematism was not discussed. Interestingly, Lee and Gould, 17 Lee, 32 Gould, 19 Sherratt et al 33 Karageorgou and Manetas, 34 Manetas, 35 Chittka and Döring, 12 Schaefer and Rolshausen 36 and Karageorgou et al 37 interpreted the co-evolutionary hypothesis of autumn coloration presented in the papers by Archetti, 6 Hamilton and Brown 7 and Archetti and Brown 8 as a case of visual aposematism (warning coloration), in spite of the authors' differing view.…”