Meeting Abstract
Most biological structures carry out multiple functions. Focusing on only one of these functions to make adaptive inferences overlooks that manifold selection pressures and tradeoffs shape the characteristics of a multitasking structure. Focusing on single functions can only lead to a partial picture of the causes underlying diversity and the evolutionary origin of the structure in question. We illustrate this discussion using bark as a study case. Bark comprises all the tissues surrounding the xylem (wood) in woody plants. Broadly, bark includes an inner and mostly living region and an outer and mostly dead one. Of all plant structures, these two main regions have the most complex anatomical structure and ontogenetic origin involving two (sometimes three) different meristems. Traditionally, the wide morphological, structural and functional diversity of bark has been interpreted as the result of the selective pressures imposed by fire regime. However, recent research has emphasized that in addition to fire protection, bark carries out several other crucial functions for plants including translocation of photosynthates, storage of starch, water, and other compounds, protection from herbivores, pathogens and high temperatures, insulation, mechanical contribution, photosynthesis, and is likely involved in xylem embolism repair. All these functions are crucial for plant performance and are involved in synergistic (e.g., storage of water and insulation) and trade-off relationships (e.g., protection from fire vs photosynthetic activity). Focusing on only one of these functions (e.g. protection from fire) will provide an incomplete picture of the selective forces shaping bark diversity and will severely hinder our incipient understanding of the functional ecology of this crucial region of woody stems.
