Habitat suitability ensembles of genotype and disease resistance for <i>Juglans cinerea</i> to assist restoration efforts

Abstract

The environmental suitability of a particular organism is often a combination of local climatic factors, resource competition intensity, as well as pathogen and predator pressure. Pathogen pressure, or host resistance, is particularly important in host species severely impacted by disease. Variations in heritable pathogen resistance can lead to differences in apparent habitat suitability of resistant or susceptible subpopulations. In the case of the butternut tree (Juglans cinerea), habitat suitability is limited by genetic resistance to the non-native butternut canker disease (BCD) in addition to environmental factors. Further, butternut frequently crosses with the non-native, BCD-resistant, congenic Japanese walnut (Juglans ailantifolia) producing fertile hybrids. We sought to develop models of butternut or hybrid genotype and BCD resistance phenotypes that could inform conservation efforts. We combine two regression-based and three machine-learning based composite models to build a series of ensemble habitat suitability models of butternut and hybrid genotype, as well as butternut BCD resistance phenotype. Our ensembles highlight southern Indiana, western Kentucky, western Michigan, and much of New England as climatically suitable for BCD-resistant butternut. Meanwhile, much of the central Midwest and areas south of the Great Lakes are climatically suitable for hybrids. These ensembles can guide conservation efforts seeking to breed BCD-resistant butternut and hybrids by highlighting areas from which to source breeding stock or locate regeneration orchards.