Feeding deterrence of Azolla in relation to deoxyanthocyanin and fatty acid composition.
Higher levels of deoxyanthocyanins in Azolla fronds correlated with feeding deterrence against adult Lymnea [Lymnaea] swinhoei snails and Polypedates leucomystax tadpoles. After 7 days in coculture the growth yield of Azolla filiculoides was almost twice that of Azolla pinnata, which contained approximately 20-fold higher levels of deoxyanthocyanins. Inclusion of snails upon initiating a plant coculture resulted in an A. pinnata growth yield that was 1.5-fold higher than that of A. filiculoides. The two plant species did not differ significantly in fatty acid composition. However, snails incubated for 1 week solely with A. pinnata showed a characteristic starvation-like fatty acid profile, with a two-fold lower proportion of polyunsaturated fatty acids (PUFAs) compared to snails that had access to A. filiculoides, either as a sole food source or in coculture with A. pinnata. A 3-month cultivation of A. pinnata with tadpoles resulted in fronds having a 260% higher concentration of deoxyanthocyanins and a 10-fold lower proportion of PUFAs in comparison to plants unexposed to tadpoles, indicating that prolonged feeding reduces the desirability of the surviving plants as a food source.