Premise of the study

Distinguishing the contributions of phenotypic plasticity vs. population differentiation to variation in the life history of plants throughout their range is important for predicting their performance after dispersal or their responses to environmental change. In Erysimum capitatum, plants in alpine environments are iteroparous perennials, but those below tree line are semelparous perennials. We tested population differentiation and plasticity of life-history variation and explored the effects of plastic responses at the prereproductive stage on life-history expression.

Methods

Plants from alpine and below tree-line populations were grown in a common greenhouse environment. Soil water content at the prereproductive stage was manipulated to simulate field condition. Because rosette ontogeny of E. capitatum (i.e., production of multiple rosettes, reproductive allocation, and degeneration of rosettes) was highly associated with in situ life-history variation, water effects on rosette ontogeny and life history were assessed.

Key results

Plants from alpine populations showed higher postreproductive survival than those from low-elevation populations in the greenhouse environment, and such difference can be explained by differential rosette ontogeny at both the prereproductive and reproductive stage. In addition, rosette development at the reproductive stage was plastic to water availability at the prereproductive stage, which influences life-history expression as adults.

Conclusions

Because water availability is lower at low-elevation sites, in situ population differentiation is likely caused by plasticity to water availability as well as by genetic differentiation or maternal effects. Plastic or evolutionary changes of prereproductive traits are expected to influence adult life-history expression, which possibly influence population demography.