Distribution, morphology, and genetic affinities of dwarf embedded Fucus populations from the Northwest Atlantic Ocean

Abstract

Dwarf embedded Fucus populations in the Northwest Atlantic Ocean are restricted to the upper intertidal zone in sandy salt marsh environments; they lack holdfasts and are from attached parental populations of F. spiralis or F. spiralis = F. vesiculosus hybrids after breakage and entanglement with halophytic marsh grasses. Dwarf forms are dichotomously branched, flat, and have a mean overall length and width of 20.3 and 1.3 mm, respectively. Thus, they are longer than Irish (mean 9.3 mm) and Alaskan (mean 15.0 mm) populations identified as F. cottonii. Reciprocal transplants of different Fucus taxa in a Maine salt marsh confirm that F. spiralis can become transformed into dwarf embedded thalli within the high intertidal zone, while the latter can grow into F. s. ecad lutarius within the mid intertidal zone. Thus, vertical transplantation can modify fucoid morphology and result in varying ecads. Microsatellite markers indicate that attached F. spiralis and F. vesiculosus are genetically distinct, while dwarf forms may arise via hybridization between the two taxa. The ratio of intermediate to species-specific-genotypes decreased with larger thalli. Also, F. s. ecad lutarius consists of a mixture of intermediate and ''pure'' genotypes, while dwarf thalli show a greater frequency of hybrids.

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).…”

Unravelling the complexity of salt marsh ‘Fucus cottonii’ forms (Phaeophyceae, Fucales)

“…Miniaturized salt marsh forms have also been observed in F. distichus from the F. distichus -F. serratus lineage, suggesting that small salt marsh fucoids represent convergent growth forms (Neiva et al, 2012). However, while growth and morphology of small salt marsh F. cottonii was shown to vary with tidal level in a transplant study in a salt marsh locality in Maine (USA) (Mathieson et al, 2006), high stress does not fully explain the habit of these small salt marsh fucoids. For example, Fucus individuals with normal morphology are often found growing side by side with the miniaturized forms ( Fig.…”