Genetic diversity and population structure of Gracilaria flabelliformis (Gracilariaceae, Rhodophyta) in the Mexican Atlantic based on the RuBisCo spacer region

Abstract The family Gracilariaceae is the most diverse group in the order Gracilariales, comprising 243 taxonomically accepted agarophyte species. Gracilaria stands out as the most representative genus due to its species richness with the significant overlap of characters. Given its economic potential, a robust set of discriminative characters is essential, as the quality and market value of the phycocolloids they produce vary significantly. Gracilaria flabelliformis , noted for its extensive distribution along the Atlantic and high intraspecific phenotypic plasticity, is prevalent across all Mexican coastal states. This study assessed the genetic diversity of G. flabelliformis populations across the Mexican Atlantic using molecular sequences from the RuBisCo spacer region to investigate potential genetic variation. From the 124 specimens examined, the analysis revealed a genetic structure, statistically supported, reflected in 10 haplotypes divided into two subgroups (R1, like the ancestor, R6 and R7; and R2, R3 and R4) interconnected by haplotypes R8, R9, and R10. Additionally, a bottleneck effect between Veracruz and the Yucatan Peninsula suggested a decrease in haplotypic diversity and genetic isolation. While haplotype R1 was present in all populations, suggesting a historical connectivity between regions, further studies are necessary to fully understand the implications of these findings on the conservation and management of G. flabelliformis .