PARENT SESSION
Poster Session #50: Evolutionary Ecology.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Ecotypic differences and plasticity of developmental hierarchies in a Mediterranean annual.

Zhang, Fengchun¹, Novoplansky, Ariel ¹, ¹

ABSTRACT- Most plants have a hierarchical structure in which small organs depend on the infrastructural support of larger organs. Developmental decisions regarding organ size must take into account the balance between resource-use efficiency and avoidance of risks of losing already invested resources. We hypothesized that plants modify their developmental hierarchies based on both the expected (evolutionary background) and the immediate (environmental conditions) availability and predictability of limiting resources. Seeds of Trifolium purpureum Loisel. plants were collected from Mediterranean (high and more predictable resources) and semi-desert (low and less predictable resources) populations in Israel. The entire growth season was divided into three equal periods in which the plants were grown under all combinations of homogeneous and alternating HIGH and LOW levels of water availability. The results showed that semi-desert plants were more responsive to the changes in water availability when the total amount was low, while Mediterranean plants were more responsive when the total water amount was high. The earlier in the season the plants encountered HIGH water, the greater the effect it had on allocation to large infrastructural branches. Furthermore, Mediterranean plants were more sensitive than semi-desert plants to changes in the timing of water availability. The results indicate that developmental decisions regarding hierarchy and size of organs not only depend on resource availability and the vigor of the plant but also on the evolutionary background of the plant.

KEY WORDS: developmental hierarchies, phenotypic plasticity, ecotype specialization, environmental changes