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ABSTRACT Many coastal marine species experienced Pleistocene gene flow between the North Pacific and Atlantic. Understanding historical connectivity between ocean basins should aid in predicting how regional faunas will respond to recent warming that has intensified trans‐Arctic dispersal. Wetland fauna of the Northwestern Atlantic may have survived in estuarine refugia throughout glacial cycles, or recolonised from the southern coast, North Pacific or Northeastern Atlantic. Here, we used multilocus genetic markers and historical climate data to investigate lineage distribution and connectivity among populations of the nominally cosmopolitan sea slugAlderia modesta, sampled from mudflats on both coasts of the North Pacific and North Atlantic. Mitochondrial DNA clades from European and North American populations were deeply divergent and reciprocally monophyletic; differences at seven polymorphic nuclear loci indicated prolonged absence of trans‐Atlantic gene flow. A Pacific ancestor likely first colonised the Atlantic during the marine biotic interchange of the middle Pliocene ~3.5 Ma. Both mtDNA phylogenetics and nuclear genotype assignments support repeated trans‐Arctic colonisation of the Northwestern Atlantic from the Pacific during inter‐glacial cycles; no gene flow was evident since the last glacial maximum, however. Time‐calibrated coalescent phylogenies, Bayesian skyline plots and haplotype networks all indicated recent population expansions in the Pacific and Europe, but not Northwestern Atlantic. In both the Pacific and Northwestern Atlantic, older lineages persisted in patchy refugia north of glacial margins, while a derived clade of Pacific haplotypes indicates northward post‐LGM expansion. The biogeographical history ofAlderiacontrasts with rocky‐shore taxa that were largely extirpated by glacial advance and recolonised from refugia following the last glacial maximum. Based on molecular differences and distinctions in radular and penial stylet morphology, we resurrect the nameAlderia harvardiensisGould 1870 forAlderiafrom the Northwestern Atlantic and North Pacific;A. modestarefers exclusively to European slugs.
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Population genetics of the freshwater red alga Batrachospermum gelatinosum (Rhodophyta) II : Phylogeographic analyses reveal spatial genetic structure among and within five major drainage basins in eastern North America
Abstract The freshwater red algaBatrachospermum gelatinosumhas a well‐documented distribution spanning historically glaciated and unglaciated eastern North America. This alga has no known desiccation‐resistant propagule; thus, long‐distance dispersal events are likely rare. We predicted strong genetic structure among drainage basins and admixture among sites within basins. We predicted greater genetic diversity at lower latitude sites because they likely serve as refugia and the origin of northward, post‐Pleistocene range expansion. We used 10 microsatellite loci to investigate genetic diversity from 311 gametophytes from 18 sites in five major drainage basins: South Atlantic Gulf, Mid‐Atlantic, Ohio River, Great Lakes, and Northeast. Our data showed strong genetic partitioning among drainage basins and among sites within basins, yet no isolation by distance was detected. Genetic diversity varied widely among sites and was not strictly related to latitude as predicted. The results fromB. gelatinosumprovide strong support that each stream site contributes to the unique genetic variation within the species, potentially due to limited dispersal and the prevailing reproductive mode of intragametophytic selfing. Simulations of migration suggested post‐Pleistocene dispersal from the Mid‐Atlantic.Batrachospermum gelatinosumpotentially persisted in refugia that were just south of the ice margins rather than in the southernmost part of its range. Research of other taxa with similar ranges could determine whether these results are generally applicable for freshwater red algae. Nevertheless, these results fromB. gelatinosumadd to the growing literature focused on the patterns and genetic consequences of post‐Pleistocene range expansion by eastern North American biota.
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- Award ID(s):
- 2436117
- PAR ID:
- 10621599
- Publisher / Repository:
- wiley
- Date Published:
- Journal Name:
- Journal of Phycology
- Volume:
- 60
- Issue:
- 6
- ISSN:
- 0022-3646
- Page Range / eLocation ID:
- 1437 to 1455
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/jpy.13512
