title: Convergent evolution of vascular optimization in kelp (Laminariales).
abstract: Terrestrial plants and mammals, although separated by a great evolutionary distance, have each arrived at a highly conserved body plan in which universal allometric scaling relationships govern the anatomy of vascular networks and key functional metabolic traits. The universality of allometric scaling suggests that these phyla have each evolved an 'optimal' transport strategy that has been overwhelmingly adopted by extant species. To truly evaluate the dominance and universality of vascular optimization, however, it is critical to examine other, lesser-known, vascularized phyla. The brown algae (Phaeophyceae) are one such group--as distantly related to plants as mammals, they have convergently evolved a plant-like body plan and a specialized phloem-like transport network. To evaluate possible scaling and optimization in the kelp vascular system, we developed a model of optimized transport anatomy and tested it with measurements of the giant kelp, Macrocystis pyrifera, which is among the largest and most successful of macroalgae. We also evaluated three classical allometric relationships pertaining to plant vascular tissues with a diverse sampling of kelp species. Macrocystis pyrifera displays strong scaling relationships between all tested vascular parameters and agrees with our model; other species within the Laminariales display weak or inconsistent vascular allometries. The lack of universal scaling in the kelps and the presence of optimized transport anatomy in M. pyrifera raises important questions about the evolution of optimization and the possible competitive advantage conferred by optimized vascular systems to multicellular phyla.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, 1156 High Street, Santa Cruz, CA 95040, USA stepler@ucsc.edu.
authors.forename: Sarah Tepler
authors.initials: ST
authors.lastname: Drobnitch
authors.affiliation: Department of Physics, Technical University of Denmark, Kongens Lyngby 2800, Denmark.
authors.forename: Kaare H
authors.initials: KH
authors.lastname: Jensen
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, 1156 High Street, Santa Cruz, CA 95040, USA.
authors.forename: Paige
authors.initials: P
authors.lastname: Prentice
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, 1156 High Street, Santa Cruz, CA 95040, USA.
authors.forename: Jarmila
authors.initials: J
authors.lastname: Pittermann
mesh_terms: D005075:Biological Evolution; D044662:Macrocystis / Q000254:growth & development / Q000502:physiology*; D008954:Models, Biological
keywords: Laminariales; Macrocystis pyrifera; allometry; kelp; phloem; scaling