Phylogenetic studies of the marine brown algae Cystoseira and Halidrys including coevolution with the associated fungal endophyte Haloguignardia irritans

These collective works are comprised of three overall studies. First, the morphologically based taxonomy for the aforementioned algal genera was compared to the molecular evolution of nuclear ribosome and chloroplast RUBISCO genes belonging to samples collected along the coasts of California and Baja California, Mexico. Second, the morphologically based taxonomy of the obligate endosymbiotic marine ascomycete H. irritans was also tested using sequence data from the nuclear ribosomal small subunit and also via assessment of spore size variation among collection sites. Third, respective phylogenetic analyses for the fungal endophyte and its algal hosts were compared to each other and to geographic locations of sampling sites to illustrate the changing degree of genetic covariation observed between H. irritans and its hosts among sites. Results of the first study strongly suggest that the current taxonomy for Cystoseira and Halidrys does not reflect evolutionary history because Atlantic and Pacific congeners appear to have arrived at similar morphologies independently. Genetic work in the second study was in support of the morphological taxonomy in part, yet lacked resolution below the ordinal level for H. irritans. In a few cases, assessment of spore size ratio variation among collection sites revealed significant, unexpected, differences at a scale within the current morphological definition for H. irritans. Incongruence between fungal and algal host phylogenies observed in the third study indicated a lack of specificity of H. irritans for particular algal host species as well as greater gene-flow among coastal host/endophyte populations compared with an island population. The results from this research support the ideas that morphological characteristics may not always hold evolutionary significance and that conservation efforts toward the maintenance of genetic diversity in marine environments should consider geographic complexity and its effects on the coevolution of symbioses when designing management strategies.