Genetic variation within and among asexual populations of Porphyra umbilicalis Kützing (Bangiales, Rhodophyta) in the Gulf of Maine, USA

Abstract

Abstract:The intertidal marine red alga Porphyra umbilicalis reproduces asexually in the Northwest Atlantic. We looked for population substructure among typical opencoastal and atypical estuarine habitats in seven asexual populations of P. umbilicalis from Maine to New Hampshire using eight expressed sequence tag-simple sequence repeats (EST-SSR) or microsatellite loci. Six genotypes were identified, four of which may represent recombinant genotypes from a recombination event that took place locally, or that took place prior to introduction to the Northwest Atlantic. Genotypic diversity was lowest in a population from Wiscasset, Maine, which inhabits an atypical habitat high in the intertidal zone of a bridge piling in an estuarine tidal rapid. Genotypic diversity was highest in the southernmost populations from New Hampshire; we identified two genotypes that were unique to the southernmost populations, and probably represent the most derived genotypes. We looked at genetic distances among populations in similar habitats, and found that populations were more closely related to their closest neighboring population than to a population in a similar habitat. We show that genotypic diversity within P. umbilicalis populations in the Gulf of Maine is relatively high and thus fits a model of high steady-state variation within asexual populations.

Organism-environment interactions and differential gene expression patterns among open-coastal and estuarine populations of Porphyra umbilicalis Kützing (Rhodophyta) in the Northwest Atlantic

“…We extracted DNA from the small samples set aside for genotyping in a 96-well plate format using a modification of the method by Page (2010) described in Eriksen et al (2016). Species identification was confirmed using restriction fragment length polymorphisms (RFLP) as described by Teasdale et al (2002).…”

“…Tissue from each population was genotyped at three polymorphic microsatellite loci according to Eriksen et al (2016). The thallus samples were then pooled into libraries based on genotype as genotype 3 (g3) or genotype 6 (g6) ( Table 1); no individuals from DP were assayed as g3.…”

“…The number of individuals collected was relatively low due to small population size. The pools of tissue were ground to a fine powder in a mortar and pestle with liquid N. We extracted the total nucleic acids from the tissue as described above and in Eriksen et al (2016). Following extraction, the total nucleic acids were treated with RNase-free DNase (1500 Kunitz units, Qiagen, Germantown, MD, USA) per the manufacturer's instructions at the maximum volume.…”

“…Porphyra umbilicalis typically lives on rocky substrates in the high intertidal zone, but it can also be found in estuarine tidal rapid locations on bridge pilings such as in the mouth of the Great Bay Estuary system in Dover Point, NH, USA. (West et al 2005, Eriksen et al 2016. Estuarine rapids are rare in the Gulf of Maine, and experience high velocity currents and changes in salinity and temperature with tidal changes.…”

“…Estuarine rapids are rare in the Gulf of Maine, and experience high velocity currents and changes in salinity and temperature with tidal changes. Eriksen et al (2016) identified six Porphyra umbilicalis genotypes among populations in the Gulf of Maine based on a limited set of polymorphic microsatellite loci but showed isolation by distance is a more important factor influencing population structure than selection for habitat. This suggests the populations acclimate to different stress conditions in different habitats through physiological adjustments.…”