GENETIC ISOLATION BETWEEN THREE CLOSELY RELATED TAXA: FUCUS VESICULOSUS, F. SPIRALIS, AND F. CERANOIDES (PHAOPHYCEAE)¹

Abstract

All traditional markers, both phenotypic and phylogenetic, have failed to discriminate between the taxa composing the Fucus vesiculosus L., F. spiralis L., and F. ceranoides L. species complex, particularly in Brittany (France), so we used five microsatellite markers to compare the allelic frequencies of populations of the three taxa in this region. The aim of this study was to assess whether the different populations were grouped according to their geographical location, their habitat (open coast versus estuary), or their a priori taxonomic assignment. Species-specific alleles were identified at one locus, demonstrating the utility of microsatellite markers for recognizing the three taxa in Brittany. Moreover, our results clearly support the separation of F. vesiculosus, F. spiralis, and F. ceranoides into distinct species, independently of geography. We also identified genetic differentiation between estuarine and coastal populations of F. vesiculosus.

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.…”

“…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).…”

The biogeography of kelps (Laminariales, Phaeophyceae): a global analysis with new insights from recent advances in molecular phylogenetics

“…It is interesting to note the maintenance of the taxonomic rank of species for entities which hybridise in these detailed molecular studies (e.g. Coyer et al 2002a, b;Billard et al 2005), as well of the erection of new species on molecular/ morphological evidence (e.g. Bergstrom et al 2005).…”

Implications of mating system for genetic diversity of sister algal species:Fucus spiralisandFucus vesiculosus(Heterokontophyta, Phaeophyceae)

“…The two species are dominant producers on temperate rocky shores of the northern hemisphere, typically distributed in the mid-upper intertidal zone, with F. spiralis occurring on average higher than F. vesiculosus. The two taxa have broad areas of sympatry across their distribution, and their hybridization has been suggested by laboratory crosses between the two species (Kniep, 1925) as well as the occurrence in natural populations of intermediate phenotypes (Burrows & Lodge, 1951;Scott & Hardy, 1994;Billard et al, 2005a) and genotypes (Wallace et al, 2004(Wallace et al, , 2006Engel et al, 2005, Coyer et al, 2006b. However, at their south-eastern distributional limit (southwest Iberia-Morocco), their distribution is allopatric; the hermaphroditic F. spiralis occurs on the open coast whereas the dioecious F. vesiculosus is present only in isolated protected areas such as estuaries and coastal lagoons.…”