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| Mammut americanum (Kerr, 1792) in Karpinski, Hackenberger, Zazula, et al., 2020. |
Abstract
Pleistocene glacial-interglacial cycles are correlated with dramatic temperature oscillations. Examining how species responded to these natural fluctuations can provide valuable insights into the impacts of present-day anthropogenic climate change. Here we present a phylogeographic study of the extinct American mastodon (Mammut americanum), based on 35 complete mitochondrial genomes. These data reveal the presence of multiple lineages within this species, including two distinct clades from eastern Beringia. Our molecular date estimates suggest that these clades arose at different times, supporting a pattern of repeated northern expansion and local extirpation in response to glacial cycling. Consistent with this hypothesis, we also note lower levels of genetic diversity among northern mastodons than in endemic clades south of the continental ice sheets. The results of our study highlight the complex relationships between population dispersals and climate change, and can provide testable hypotheses for extant species expected to experience substantial biogeographic impacts from rising temperatures.
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| Fig. 2: Model of mastodon extirpation and expansion in response to glacial cycles. a Global stack of benthic foraminifera δ18O for the last 1 million years, which tracks changes in deep-water temperature and global ice volume. The y-axis has been inverted so that periods of low ice buildup (and higher temperatures—red) are at the top of the graph, and periods of greater ice buildup (and lower temperatures—blue) are at the bottom. Marine Isotope Stage (MIS) extents are indicated with black bars above (interglacials) or below (glacials) the δ18O record. δ18O values and MIS terminations can be found in Lisiecki and Raymo. One full glacial cycle is represented, showing the change from glacial (b) to interglacial (c) conditions, followed by a fall back into another glaciation (d). North American ice-sheet cover at each stage (c, d) is approximated from recorded δ18O to similar conditions during the transition out of the last glaciation, or from published simulations where available (b). The ecological implications of these transitions are summarised in (e, f), with mastodons being able to occupy most of eastern Beringia and Canada during interglacials (e), but progressively extirpated from these regions as conditions descend into the next glacial period (f). Populations would either need to retract to unglaciated regions south of the ice sheets or north to temporarily unglaciated refugia which would be unlikely to support mastodon populations throughout long glaciations. |
Emil Karpinski, Dirk Hackenberger, Grant Zazula, Chris Widga, Ana T. Duggan, G. Brian Golding, Melanie Kuch, Jennifer Klunk, Christopher N. Jass, Pam Groves, Patrick Druckenmiller, Blaine W. Schubert, Joaquin Arroyo-Cabrales, William F. Simpson, John W. Hoganson, Daniel C. Fisher, Simon Y. W. Ho, Ross D. E. MacPhee and Hendrik N. Poinar. 2020. American Mastodon Mitochondrial Genomes Suggest Multiple Dispersal Events in Response to Pleistocene Climate Oscillations. Nature Communications. 11: 4048. DOI: 10.1038/s41467-020-17893-z
