DETERMINING THE AFFINITIES OF SALT MARSH FUCOIDS USING MICROSATELLITE MARKERS: EVIDENCE OF HYBRIDIZATION AND INTROGRESSION BETWEEN TWO SPECIES OFFUCUS(PHAEOPHYTA) IN A MAINE ESTUARY¹

Abstract

The high degree of morphological plasticity displayed by species of the brown algal genus Fucus L. is well documented. Such variation is especially pronounced for those estuarine taxa lacking holdfasts (termed ecads) that often bear little resemblance to the attached species from which they are derived. To better understand the systematics of salt marsh fucoids, we developed a suite of four microsatellite‐containing loci capable of distinguishing between F. vesiculosus L. and F. spiralis L. The genetic markers were used to determine the relationships of the fucoid ecads F. vesiculosus ecad volubilis (Hudson) Turner and a muscoides‐like Fucus in the Brave Boat Harbor (ME, USA) estuary. Ecad populations had 2‐ to 3‐fold higher levels of heterozygosity than attached populations of F. vesiculosus and F. spiralis. Further, ecads were “intermediate” between F. vesiculosus and F. spiralis in their allele frequencies and genotype composition. Our data indicate that populations of muscoides‐like Fucus in Brave Boat Harbor mainly consist of F1 hybrids between F. vesiculosus and F. spiralis, whereas F. vesiculosus ecad volubilis may arise through backcrosses between F. vesiculosus and other fertile hybrids. Finally, our data support the hypothesis that introgression has occurred between attached populations of F. vesiculosus and F. spiralis.

Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North Atlantic

“…data). The hybridization hypothesis is also supported by our data and several other reports revealing the presence of intermediate genotypes (Wallace et al, 2004;Billard et al, 2005;Engel et al, 2005;Coyer et al, 2006b;Mathieson et al, 2006). Thus, hybridization among F. vesiculosus, Fsp-High, and Fsp-Low is likely to be (or has been) fairly common.…”

“…The contemporary distribution of Fsp-Low appears to be restricted to a few areas in Brittany and only in sympatry with F. vesiculosus, whereas Fsp-High ranges throughout northern Europe, Iceland, and northeastern US-Canadian Maritimes. Hybridization occurs between Fsp-High and F. vesiculosus, but the dwarf hybrids inhabit a much different habitat (salt marsh grass) than either parental species (Wallace et al, 2004;Coyer et al, 2006b;Mathieson et al, 2006).…”

“…From a morphological standpoint, over 125 intraspecific taxa have been described for the nine most common species (Guiry and Guiry, 2010). From a genetic standpoint, several studies using molecular techniques have documented hybridization between the various species based on experimental evidence (Coyer et al, 2002a) or occurrence of intermediate genotypes in nature (Coyer et al, 2002b(Coyer et al, , 2006bWallace et al, 2004;Engel et al, 2005;Mathieson et al, 2006;Billard et al, 2010). Additionally, frequent establishment of successful reproductive hybrids has been noted Coyer et al, 2007).…”

“…Morphological differences exist between the entities and each is subjected to different regimes of desiccation resistance (Billard et al, 2010;Zardi et al, submitted for publication). Although divergence of the habitat-specific ecotypes may have occurred by gradual adaptation of each entity to its respective micro-environment, the possibility of divergence of one entity from the other by hybridization/introgression with a co-occurring species cannot be discounted, especially as inter-specific gene flow is well documented within the genus Fucus (Wallace et al, 2004;Billard et al, 2005Billard et al, , 2010Engel et al, 2005;Coyer et al, 2006b;Mathieson et al, 2006;Perrin et al, 2007).…”

Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

“…The genus Fucus consists of 2 clades, the first containing F. vesiculosus and F. spiralis, and a second that includes F. serratus, which are the dominant Fucus species found on open-coast rocky shores of the European eastern Atlantic. Fucus species are still capable of hybridization (Stomps 1911, Kniep 1925, Coyer et al 2002, Wallace et al 2004, Billard et al 2005, Engel et al 2005 suggesting firstly that their separation is recent and that where they cooccur on the same shores, environmental gradients may play an important role in the maintenance of species. In addition, several morphotypes have been described, of which several varieties are still currently accepted (cf.…”