Meeting Abstract

S10-6    Evolutionary patterns in chemical composition and biomechanics of joints in wave-swept, segmented seaweeds. Martone, PT*; Janot, K; University of British Columbia, Vancouver, BC Canada; University of British Columbia, Vancouver, BC Canada pmartone@mail.ubc.ca http://www3.botany.ubc.ca/martone/

Seaweeds living along wave-battered coastlines are generally flexible, bending with the waves to adopt more streamlined shapes and reduce drag. Coralline algae, however, are firmly calcified, existing largely as crusts, which avoid drag altogether, or as erect, branched forms with uncalcified joints (genicula), which confer flexibility to otherwise rigid thalli. Upright corallines have evolved from crustose ancestors independently multiple times, and the repeated evolution of genicula has clearly contributed to the ecological success of articulated corallines worldwide. Across evolutionary lineages, structure and development of genicula are significantly different and yet some biomechanical properties are surprisingly similar. Because the chemical composition of cell walls plays a central role in both decalcification and biomechanical properties, we explored evolutionary trends in cell wall chemistry across crustose and articulated taxa. We compared the carbohydrate content of genicula across convergently-evolved articulated species, and we compared the carbohydrate content of calcified tissues from articulated and crustose species to search for phylogenetic trends in cell wall chemistry during the evolution of articulated taxa. We also analyzed the carbohydrate content of one crustose coralline species that evolved from articulated ancestors, allowing us to examine trends in chemistry during this evolutionary reversal and loss of genicula. We found chemical similarity between calcified tissues across articulated and crustose species, likely reflecting a common structural role for polysaccharides across coralline algae. Conversely, the cell wall chemistry of genicula was variable across evolutionary lineages, suggesting that significantly different biochemical trajectories have led to remarkably similar biomechanical innovations.