The taxonomic and systematic relationships of several salt marsh <i>Fucus</i> taxa (Heterokontophyta, Phaeophyceae) within the Gulf of Maine and Ireland examined using microsatellite markers
The present thesis utilizes microsatellite markers to examine genetic affinities between several salt marsh Fucus ecads in order to ascertain their relationships with attached parental species. Chapter I provides an introduction to the genus Fucus and discusses morphological plasticity, systematic difficulties, and studies of hybridization between different Fucus species.
Chapter II describes my development of microsatellite markers for Fucus. Four polymorphic microsatellite loci were used to determine the origin of a dwarf muscoides-like Fucus from the Brave Boat Harbor (ME) salt marsh. Similar forms were originally described in Europe, and appear to be derived from F. vesiculosus L. However, my results indicate that dwarf Fucus populations from Brave Boat Harbor are largely comprised of hybrids between F. vesiculosus and F. spiralis L., and differ from morphologically similar European plants.
Chapter III presents the results of a larger Gulf of Maine survey that examined the genetic affinities of several estuarine taxa. My results support the hypothesis that the smallest limicolous muscoides-like forms are generally hybrids of F. vesiculosus and F. spiralis. However, somewhat larger muscoides-like forms that grade into the ecad F. spiralis ecad lutarius (Kützing) Sauvageau are composed of a mixture of hybrid and ‘pure’ genotypes, largely from F. spiralis. The relationships between F. vesiculosus , its variety spiralis Farlow and ecad volubilis (Hudson) Turner are also examined.
Chapter IV examines the affinities of the European dwarf taxon Fucus cottonii Wynne et Magne. Samples were collected from Rosmuc, Ireland, near the type location for this species, and genetic relationships were examined between F. cottonii, F. vesiculosus, F. spiralis, and a putative F. vesiculosus × F. spiralis hybrid. My results suggest that F. cottonii from Rosmuc is not of hybrid origin, but is affiliated with F. vesiculosus . In addition, the putative hybrid was genetically indistinguishable from F. vesiculosus, and may be equivalent to F. vesiculosus var. spiralis from the Gulf of Maine or F. vesiculosus var. volubilis (Hudson) Turner from Europe. Taken together, the work described in this thesis helps shed light on the relationships between several problematic groups of algae and resolves some taxonomic confusions that have plagued the genus Fucus.