Browsing by Author "Maggs, C. A."
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- Evaluating signatures of glacial refugia for North Atlantic benthic marine taxaPublication . Maggs, C. A.; Castilho, Rita; Foltz, D.; Henzler, Christy; Jolly, Marc Taimour; Kelly, J.; Olsen, J. L.; Perez, K. E.; Stam, W. T.; Väinölä, R.; Viard, F.; Wares, J.A goal of phylogeography is to relate patterns of genetic differentiation to potential historical geographic isolating events. Quaternary glaciations, particularly the one culminating in the Last Glacial Maximum ;21 ka (thousands of years ago), greatly affected the distributions and population sizes of temperate marine species as their ranges retreated southward to escape ice sheets. Traditional genetic models of glacial refugia and routes of recolonization include these predictions: low genetic diversity in formerly glaciated areas, with a small number of alleles/ haplotypes dominating disproportionately large areas, and high diversity including ‘‘private’’ alleles in glacial refugia. In the Northern Hemisphere, low diversity in the north and high diversity in the south are expected. This simple model does not account for the possibility of populations surviving in relatively small northern periglacial refugia. If these periglacial populations experienced extreme bottlenecks, they could have the low genetic diversity expected in recolonized areas with no refugia, but should have more endemic diversity (private alleles) than recently recolonized areas. This review examines evidence of putative glacial refugia for eight benthic marine taxa in the temperate North Atlantic. All data sets were reanalyzed to allow direct comparisons between geographic patterns of genetic diversity and distribution of particular clades and haplotypes including private alleles. We contend that for marine organisms the genetic signatures of northern periglacial and southern refugia can be distinguished from one another. There is evidence for several periglacial refugia in northern latitudes, giving credence to recent climatic reconstructions with less extensive glaciation.
- Fucus cottonii (Fucales, Phaeophyceae) is not a single genetic entity but a convergent salt-marsh morphotype with multiple independent originsPublication . Neiva, J.; Hansen, G. I.; Pearson, G. A.; Van De Vliet, M. S.; Maggs, C. A.; Serrão, EsterIn low-energy salt-marsh environments, Fucus spp. frequently exhibit an atypical morphology that is characterized by the absence of an anchoring holdfast and a trend towards reduced size and buoyancy, enhanced vegetative proliferation, and often the loss of sexual reproduction. Such forms, often referred to as ecads, presumably derive from typical attached forms, but their affinities are normally difficult to establish with confidence due to their simplified and largely convergent morphology. Minute salt-marsh forms growing partially embedded in the sediment occur on Atlantic and Pacific coasts and have traditionally been recognized as an independent entity, Fucus cottonii. In this study we analyse with four microsatellite loci two F. cottonii populations from salt-marshes of Oregon (NE Pacific) and Ireland (Europe, near the species type locality), as well as local populations of other Fucus spp. that could be considered potential source populations, either directly or via hybridization. Our results show that the F. cottonii from Oregon derive from F. gardneri whereas the Irish population is closer to F. spiralis. We conclude that F. cottonii is not a coherent genetic entity, but an artificial grouping of evolutionarily independent populations that converged into similar morphologies in different salt-marsh habitats.
- Molecular characterization of the "Cottonii" form of fucus in the North-Eastern Pacific versus the AtlanticPublication . Serrão, Ester; Vliet, M. S.; Hansen, G. I.; Maggs, C. A.; Pearson, G. A.Along the west coast of North America, three species of Fucus are reported to occur: F. gardneri Silva, F. spiralis Linnaeus, and the controversial F. cottonii Wynne & Magne. Our study investigates the identity of F. cottonii in this area and compares it with isolates from the NortheasternAtlantic. The thalli from both areas vegetatively resemble one another, lacking midribs, and they occur in similar salt marsh habitats.