DOI: 10.5061/dryad.905qfttvd
title: Data from: Oligocene odyssey: Molecular phylogenetic analyses describe the origin and diversification of freshwater Gammarus in eastern North America

description: Aim: Members of the amphipod genus Gammarus have served as an excellent
 model for testing biogeographic hypotheses given the number of species
 within the genus and its unique history, with multiple taxa transitioning
 from marine to freshwater environments independently. However, while
 attention has been placed on Palearctic Gammarus, little is known about
 members in the Nearctic. Given trends observed within the genus, Gammarus
 from eastern North America (ENA) may represent another independent
 lineage, likely reaching the continent using a heretofore unknown pathway.
 We investigate the phylogenetic and evolutionary history of Gammarus spp.
 in this region. Location: eastern North America Taxon: Gammarus Methods:
 Sequence data for two nuclear and two mitochondrial loci were obtained for
 75 individuals, four of which are newly sequenced. Based on a concatenated
 dataset, phylogenetic trees were reconstructed using both Maximum
 likelihood and Bayesian inference. Bayesian trees were time-calibrated
 based on a set of five mixed calibration points. RASP software was used to
 investigate potential ancestral areas. Results: ENA Gammarus spp. were
 recovered as monophyletic, showing affinity to both Palearctic Gammarus
 and G. duebeni. Newly generated sequences solidify the position of
 Gammarus bousfieldi which is found to be related to G. minus.
 Time-calibrated phylogenies place the crown age of the ENA lineage during
 the Eocene/Oligocene. These timings suggest a marine origin for the
 lineage followed by dispersal into freshwaters. Main Conclusions: Members
 of the “ENA Gammarus” are a unique lineage within the genus, originating
 from a marine ancestor during the Eocene/Oligocene and colonizing the
 Nearctic shortly after. The exact route the lineage may have taken is
 unclear, however, three routes are proposed: (I) the Gulf of St. Lawrence
 (II) the Chesapeake Bay (III) and the Mississippi River. Results generated
 here emphasize the lineages’ unique evolutionary history, highlighting
 novel colonization pathways not often considered for invertebrate taxa.
description: # Oligocene odyssey: Molecular phylogenetic analyses describe the origin
 and diversification of freshwater Gammarus in eastern North America
 [https://doi.org/10.5061/dryad.905qfttvd](https://doi.org/10.5061/dryad.905qfttvd) ## Description of the data and file structure Included here are raw tree files in either newick or nexus formats from all tree-building methodologies undertaken (IQTREE, MRBAYES, BEAST), results of the RASP analysis, and a concatenated sequence alignment, generated by SEQUENCEMATRIX. ### Files and variables #### File: Cannizzaro\_and\_Berg\_ENA\_BEAST\_annotated.nexus Description: Annotated BEAST tree. #### File: Cannizzaro\_and\_Berg\_ENA\_Alignment\_Concatenated.nex Description: Concatenated sequence alignment (nexus format) #### File: Cannizzaro\_and\_Berg\_ENA\_ML\_tree.newick Description: Raw Maximum-likelihood tree file from IQTREE #### File: Cannizzaro\_and\_Berg\_ENA\_Mrbayes.newick Description:Raw Bayesian tree file from MRBAYES #### File: Cannizzaro\_and\_Berg\_ENA\_RASP.png Description: Result of RASP analysis