Evolutionary Patterns in Chemical Composition and Biomechanics of Articulated Coralline Algae

Abstract

Seaweeds inhabiting 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 that avoid drag altogether or as upright branched forms with uncalcified joints (genicula) that confer flexibility to otherwise rigid thalli. Upright corallines have evolved from crustose ancestors independently multiple times, and the repeated evolution of genicula has contributed to the ecological success of articulated corallines worldwide. Structure and development of genicula are significantly different across evolutionary lineages, and yet biomechanical performance is broadly similar. Because chemical composition plays a central role in both calcification and biomechanics, 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, as well as the carbohydrate content of calcified tissues from articulated and crustose species, to search for phylogenetic trends in cell wall chemistry during the repeated evolution of articulated taxa. We also analysed 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 several key differences in carbohydrate content between calcified and uncalcified coralline tissues, though the significance of these differences in relation to the calcification process requires more investigation. Comparisons across a range of articulated and crustose species indicated that carbohydrate chemistry of calcified tissues was generally similar, regardless of morphology or phylogeny; conversely, chemical composition of genicular tissues was different across articulated lineages, suggesting that significantly different biochemical trajectories have led to remarkably similar biomechanical innovations.

Cell wall organic matrix composition and biomineralization across reef‐building coralline algae under global change

“…CMFs are proposed to be the substrate that is crystallized when surrounded by inducing polysaccharides (Lowenstam 1981, Borowitzka and Larkum 1987, however, cellulose abundance alone has not been implicated in biomineralization, and it is well known that cellulose is present in the cell walls of many other species of non-calcifying red algae (Siegel and Siegel 1973). In the articulated coralline, Calliarthron sp., cellulose comprised the same percentage of algal wet weight in genicula as it did in decalcified intergenicula (Martone et al 2019, Janot et al 2022. Thus, biomineralization would likely also depend on the abundance of inducing polysaccharides.…”

“…2019, Janot et al. 2022). Thus, biomineralization would likely also depend on the abundance of inducing polysaccharides.…”

Ecological biomechanics of damage to macroalgae

“…Macroalgae can reduce tissue loss via structural designs that direct where breakage occurs, and tissue properties that determine how cracks propagate across thalli. For example, some species localize where bending occurs by having joints (narrow regions with flexible tissues; Koehl, 1999 ; Martone, 2006 ; Janot and Martone, 2016 ; Janot et al, 2022 ). If breakage occurs at such localized regions of high stress, a macroalga can be pruned by ambient flow ( Figure 1F ) rather than ripped off the shore ( Martone, 2006 ; Martone and Denny, 2008 ).…”

Marine Flora of French Polynesia: An Updated List Using DNA Barcoding and Traditional Approaches

“…A limited number of molecular-assisted alpha-taxonomic studies have been conducted in French Polynesia, encompassing the Rhodophyta (Gelidiales [ 54 ], Gibsmithia [ 55 ], Asparagopsis [ 56 ], Grateloupia filicina [ 57 , 58 ], Corallinophycidae [ 59 , 60 , 61 , 62 ], Laurencieae [ 63 ]), Chlorophyta ( Halimeda [ 64 , 65 , 66 , 67 , 68 ]), Ochrophyta ( Dictyota [ 69 , 70 , 71 , 72 ], Lobophora [ 13 , 73 ], Newhousia [ 21 ], Sargassum [ 74 ], Turbinaria [ 75 ]), and Cyanobacteria [ 20 ], but nothing on seagrasses. These molecular-based studies generated over 500 sequences, but from a limited number of taxa, and a bulk from the genus Lobophora (>350 sequences [ 13 ]), followed by Halimeda (>90 sequences [ 64 , 65 , 66 , 67 , 76 ]), Sargassum (>30 sequences [ 74 ]), and Newhousia (20 sequences [ 21 ]).…”