Deadly combination of genes and drought: increased mortality of herbivore‐resistant trees in a foundation species

Abstract

Current climate models predict a shift to warmer, drier conditions in the southwestern US. While major shifts in plant distribution are expected to follow these climate changes, interactions among species and intraspecific genetic variation rarely have been incorporated into models of future plant distributions. We examined the drought-related mortality of pinyon pine (Pinus edulis) in northern Arizona focusing on trees that showed genetically-based resistance or susceptibility to a nonlethal herbivore, the shoot-boring moth, Dioryctria albovittella. Because moth resistant trees have outperformed susceptible trees during 20 years of study, and herbivory has been shown to increase drought related mortality, we expected higher mortality rates in susceptible trees. However, our field observations and greenhouse experiments showed several unexpected patterns relevant to understanding the consequences of climate change: (1) The mortality of adult P. edulis resistant to the moth was three times higher than the mortality of trees susceptible to the moth. (2) Over a few years, differential mortality caused a shift in stand structure from resistant dominated to equality (3 : 1 resistant : -susceptible to 1 : 1). (3) Adult moth resistant trees suffered significantly greater water stress than adult moth susceptible trees, suggesting that variation among the two groups in drought tolerance may be a mechanism for differential mortality. (4) When grown under drought conditions in the greenhouse, seedlings from resistant mothers died sooner than seedlings from susceptible mothers. These data support the hypothesis that drought can act as an agent of balancing selection and that drought resistance is a heritable trait. Taken together, our findings suggest that genetic variation in a population can be an important factor in determining its response to future climate change, and argue for the inclusion of genetics into models developed to understand the consequences of climate change.

Tree growth, cambial phenology, and wood anatomy of limber pine at a Great Basin (USA) mountain observatory

“…Tree growth, and in particular wood formation, is a dynamic process regulated not only by environmental factors, but also by genetic mechanisms (Hertzberg et al 2001;King et al 2013). While the contribution of genotypic plasticity in defining the chances for a given species to withstand new climatic and environmental conditions cannot be overstated (Alfaro et al 2014;Sthultz et al 2009), understanding temporal patterns of tree growth in response to environmental drivers is crucial to improve the interpretation of dendroclimatic records, since environmental parameters affecting wood production may have different effects in different periods of the growing season (Rossi et al 2006b). Trees in general hold a high degree of plasticity to respond to seasonal variations of environmental conditions, in particular water and temperature stress.…”

On underestimation of global vulnerability to tree mortality and forest die‐off from hotter drought in the Anthropocene

“…For example, tree species have optimal climate zones, with populations in colder portions of their distributions expected to have significant genetic capacity for acclimation to warmer temperatures, whereas populations from warmer range-limit portions of the species' distribution are expected to be more vulnerable to stress from warming climate (Rehfeldt et al 2002(Rehfeldt et al , 2004(Rehfeldt et al , 2014. Overall, higher levels of genetic diversity foster adaptive responses to climate change stresses (Jump et al 2009a, Harter et al 2015, including drought and heat stress (Mátyás et al 2009, Sthultz et al 2009). …”

Plant genetic effects on soils under climate change

“…Most importantly, drought was an evolutionary event where differential mortality of moth susceptible (21 % mortality) versus resistant trees (68 % mortality) has altered the genetic structure and function of this ecosystem (Sthultz et al 2009a;Gehring et al unpublished data). Seedlings derived from these same trees show similar drought tolerance as their mothers, suggesting potential heritability of drought tolerance (Sthultz et al 2009a).…”

“…Most importantly, drought was an evolutionary event where differential mortality of moth susceptible (21 % mortality) versus resistant trees (68 % mortality) has altered the genetic structure and function of this ecosystem (Sthultz et al 2009a;Gehring et al unpublished data). Seedlings derived from these same trees show similar drought tolerance as their mothers, suggesting potential heritability of drought tolerance (Sthultz et al 2009a). In addition, the ectomycorrhizal fungal communities of moth resistant and susceptible trees are distinct; susceptible trees are dominated by a single genus of ascomycete fungi while resistant trees have much higher abundance of basidiomycete fungi (Sthultz et al 2009b).…”