Postglacial Colonization of Northern Coastal Habitat by Bottlenose Dolphins: A Marine Leading-Edge Expansion?

Milaja Nykänen,Kristin Kaschner,Rod Penrose,Andrew D Foote,M Thomas P Gilbert,Emer Rogan,Kathleen Kesner-Reyes,Simon N Ingram,Valentina Islas-Villanueva,Marie Louis,Andrew Brownlow,Nathan Wales,Nicholas J Davison,Cristina Garilao,Rob Deaville,Willy Dabin,Kim Andrews

doi:10.1093/jhered/esz039

Abstract

Oscillations in the Earth's temperature and the subsequent retreating and advancing of ice-sheets around the polar regions are thought to have played an important role in shaping the distribution and genetic structuring of contemporary high-latitude populations. After the Last Glacial Maximum (LGM), retreating of the ice-sheets would have enabled early colonizers to rapidly occupy suitable niches to the exclusion of other conspecifics, thereby reducing genetic diversity at the leading-edge. Bottlenose dolphins (genus Tursiops) form distinct coastal and pelagic ecotypes, with finer-scale genetic structuring observed within each ecotype. We reconstruct the postglacial colonization of the Northeast Atlantic (NEA) by bottlenose dolphins using habitat modeling and phylogenetics. The AquaMaps model hindcasted suitable habitat for the LGM in the Atlantic lower latitude waters and parts of the Mediterranean Sea. The time-calibrated phylogeny, constructed with 86 complete mitochondrial genomes including 30 generated for this study and created using a multispecies coalescent model, suggests that the expansion to the available coastal habitat in the NEA happened via founder events starting ~15 000 years ago (95% highest posterior density interval: 4 900-26 400). The founders of the 2 distinct coastal NEA populations comprised as few as 2 maternal lineages that originated from the pelagic population. The low effective population size and genetic diversity estimated for the shared ancestral coastal population subsequent to divergence from the pelagic source population are consistent with leading-edge expansion. These findings highlight the legacy of the Late Pleistocene glacial cycles on the genetic structuring and diversity of contemporary populations.

Highlights

During the Late Quaternary period (1 Ma to present) the Earth’s climate was governed by a series of glacial and interglacial events and temperature fluctuations that occurred at approximately 100,000-year intervals (Shackleton, 2000)
Models of suitable habitat t According to the AquaMaps model, the core suitable habitat for common bottlenose dolphins rip during the Last Glacial Maximum (LGM) ranged from ~42°N c in the Northwest Atlantic southwards along the coast to lower latitudes (Fig. 2, Appendix s S3)
In the Northeast Atlantic, their coastal range was restricted to approximately 40°N, u corresponding to the south of the Iberian Peninsula, and to an area around the Alboran Sea in n the Mediterranean

Summary

Introduction

During the Late Quaternary period (1 Ma to present) the Earth’s climate was governed by a series of glacial and interglacial events and temperature fluctuations that occurred at approximately 100,000-year intervals (Shackleton, 2000). These glacial cycles are thought to have played an important role in shaping the current distribution and genetic structuring of species and populations. M Hewitt (1999, 2000) proposed that colonization of terrestrial species during the warm interglacial periods typically occurred via long-range dispersal events, or ‘leading-edge range d expansions’. The refugial distribution during the Last Glacial Maximum (LGM) of the source populations for these re-colonizing temperate marine species is largely unknown

Methods

Results

Conclusion