Host genetic variation and microenvironment shape an emergent plant–antagonist interaction

Abstract

Geographic mosaics of interspecific interactions can arise as a consequence of intrinsic and extrinsic deterministic factors. In this study, we took advantage of the recent discovery of a specialist leaf-miner (Caloptilia triadicae) on invasive Chinese tallow (Triadica sebifera) in the southeastern United States to examine deterministic drivers of variation in plant–animal antagonistic interactions. We conducted a common garden study to assess the influence of intrinsic host genetic variation and extrinsic microenvironment on Triadica traits as well as Caloptilia infestation and mortality. We found that tree size, branch leaf density, and leaf toughness differed according to multilocus estimates of genetic variation. Host genetic variation also influenced mortality of early instar Caloptilia, but had little effect on peak or late season infestation. Triadica from hyperinvasive populations were larger, exhibited reduced leaf density and tougher leaves, and had the lowest levels of peak season Caloptilia infestation, but also had the lowest levels of early instar mortality. Microhabitat variation associated with edge effects influenced tree size as well as late season infestation. These findings indicate that Caloptilia–Triadica interactions reflect seasonal shifts in the relative influence of intrinsic and extrinsic drivers, where peak season interactions largely reflect genetic variation in hosts, and late–season interactions reflect microenvironmental conditions. Further study of Caloptilia infestations could offer additional understanding of novel interactions that arise following species introductions.