It's my turn to host the lab meeting next week, so I thought I'd continue the trend of picking unusual papers. One that I think sounds interesting came to my attention the other day via the Oikos blog. It's about red colouration in leaves, and whether this functions as a warning signal to herbivorous insects. Anti-herbivory is one theory explaining why we see bright autumn colours, although the paper itself is a study of young plants. Anyway, I thought that the question of why plant leaves can change colour might be a good subject for some discussion and speculation. Usual time and place.
This picture is from Paudash Lake, which is fairly close to where I grew up. I got it from Wikimedia Commons.
Here is the Oikos post, which gives some background on the paper: https://oikosjournal.wordpress.com/2012/11/13/why-red-leaves/
Chen & Huang (2012) Red young leaves have less mechanical defence than green young leaves. Oikos, in press.http://onlinelibrary.wiley.com.ludwig.lub.lu.se/doi/10.1111/j.1600-0706.2012.20852.x/pdf
In many plants, leaves that are young and/or old (senescent) are not green. One adaptive hypothesis proposed that leaf color change could be a warning signal reducing insect attack. If leaf coloration involves less herbivory, it remains unclear why leaves in many species are constantly green. To examine whether green leaves reduce herbivory by physical defense as an alternative to the supposed warning signal of red leaves, we conducted comparative analyses of leaf color and protective tissues of 76 woody species in spring. The protective features (trichomes, enhanced cuticle and multiple epidermis) and the distribution of red pigments within leaves were examined in both young and mature leaves. We observed that redness was more frequent in young leaves than in senescent leaves. Compared to 36 species with red young leaves, 40 species with green young leaves showed a significantly higher incidence of enhanced cuticle and trichomes in both phylogenetic and non-phylogenetic analyses. The phylogenetic analysis indicated that the multiple origins of mechanical protection were generally associated with loss of red coloration. Our finding of relatively poor mechanical protection in red young leaves provides additional evidence for the adaptive explanation of leaf color change.