Blue coloration in young leaves of Moutabea gentryi (Polygalaceae) as a possible antiherbivory defense

Red coloration in young developing leaves is common in tropical plant communities and is generally viewed as an antiherbivory strategy. The red coloration is generally caused by the presence of anthocyanins and the lack of chlorophyll. Red leaves typically expand before building their photosynthetic machinery and by doing so they make their tissue less palatable and reduce the risk of losing valuable proteins to herbivores. Photosynthetic proteins and pigments are incorporated later, once leaves are developed and are mechanically well defended. However, the adaptive value of rare blue coloration in young tropical leaves is virtually unknown. Our objective was to study the physiological ecology of young blue leaves of the liana Moutabea gentryi and to test if leaves delayed their greening until fully developed in order to prevent herbivory damage. We conducted this research on the island of Gorgona, Colombia by following the development of 134 leaves on 9 individuals. The rate of leaf expansion was high and leaves reached their final size after only 17-22 days. Leaf toughness reached a maximum after only 10-20 days when leaf chlorophyll content was still increasing.  The rate of leaf consumption by herbivory was highest when leaves were young but declined significantly as leaves reached their final size. Leaf water content declined gradually as leaves developed (ca. 85% to ca. 70%), which may have contributed to reduce the palatability of older leaves. Our results support the hypothesis that delaying greening in young blue leaves is a possible antiherbivory defense that may prevent the lost of valuable proteins when herbivory rates are highest.