Hybridization affects seasonal variation of phytochemical phenotypes in an oak hybrid complex (Quercus gambelii x Quercus grisea)

The hybridization of plants can have significant consequences for the structure of consumer communities, and hybridization effects on plant defenses have been suggested to affect the distribution of consumers within hybrid zones. It is currently unknown how hybridization may affect ontogenetic patterns of phenolic biosynthesis. We describe the seasonal variation of absolute and relative concentrations of 18 individual phenolics, total proanthocyanidins, and nitrogen in the Quercus grisea x Quercus gambelii hybrid complex in central New Mexico. Expression patterns of individual compounds were most often equal between hybrid and parental taxonomic categories; nonequal patterns of expression were most often dominant (equal to one parent) toward Q. gambelii. These patterns of phenolic expression contrast with the more common additive patterns reported in hybrid zones of other tree species. Quercus grisea backcrosses displayed significant developmental instability in phenolic biosynthesis relative to other hybrid oaks. Importantly, the composition and structure of phenolic phenotypes were found to vary seasonally. Throughout the growing season, the majority (>93%) of variation between oak phenolic phenotypes was attributed to the relative concentrations of phenolics and nitrogen. The results of this study emphasize the importance of compound-specific evaluations of hybrid plant defense metabolites and metabolic variation in hybrid zones. These considerations are critical for the further empirical study of potential hybridization effects on the complex, dynamic mixtures that make up plant defense chemistry.