Evolution of Suites of Traits in Response to Environmental Stress

Abstract

Traits that enable plants to exploit low-resource environments (e.g., slow tissue turnover, low transpiration rate, high root: shoot ratio, and high concentrations of plant defenses against pathogens and herbivores) are physiologically linked to key growth-related traits (low rates of photosynthesis, nutrient uptake, and growth). Similar suites of traits occur as both phenotypically plastic and evolutionary responses to stress. We suggest that a genetic change in a switch or underlying trait that turns on this stress resistance syndrome (SRS), which causes it to be expressed over a wider range of environmental circumstances, would effectively convert a high-resource genotype into one that is more stress-tolerant. Because of physiological linkages between growth-related traits and the SRS, any heritable change in a key growth-related trait will pleiotropically affect the SRS. Therefore, heritable changes in these key growth-related traits could be accompanied by evolution of the entire SRS. Evidence for this hypothesis comes from single-gene mutants that differ in many stress-related traits, rapid evolution of metaltolerant populations that are broadly stress-resistant, and consistent patterns of traits in species along gradients in resource availability. Similar evolutionary patterns occur in many animal taxa, which suggests that it is a general evolutionary phenomenon. We suggest that rapid evolution in response to changing environmental stress may allow many short-lived species to respond to human-induced environmental change and provide opportunities to develop stress-resistant crops. However, the time lag between generations of long-lived species that dominate most natural vegetation may not allow mature individuals of these species to keep pace with rapid global change