Quantitative analysis and mathematical modelling of morphological variation in a calcified red alga Corallina berteroi

Miho Kitazawa, Assistant Professor at the Center for Education in Liberal Arts and Sciences, Osaka University, Japan

Corallina is a genus of marine red algae characterised by a segmented body with repetition of calcified hard parts (intergenicula) and flexible parts (genicula). Despite their importance in marine ecosystems, they are not fully studied, partially because it is difficult to identify species due to high morphological flexibility. To understand the morphological flexibility, we sampled specimens in western Japan and performed quantitative analyses. Shape analysis by Elliptic Fourier transformation revealed that approximately 60 % of variation in intergeniculum shape is explained by an axis between rectangular- and fan-shape. Three dimensional images of internal structure obtained by micro-CT scanning showed that intergenicula are consist of long and narrow cells elongated mostly along with the growth direction of the organ. We modelled intergeniculum development by simplifying cells as proliferating vectors whose angles correspond to the growth direction of each cell, and found that the degree of alignment of cell direction can explain intergeniculum shape change between rectangular- and fan-shape.