Gene flow on ice: the role of sea ice and whaling in shaping Holarctic genetic diversity and population differentiation in bowhead whales (Balaena mysticetus)

Abstract

Sea ice is believed to be a major factor shaping gene flow for polar marine organisms, but it remains unclear to what extent it represents a true barrier to dispersal for arctic cetaceans. Bowhead whales are highly adapted to polar sea ice and were targeted by commercial whalers throughout Arctic and subarctic seas for at least four centuries, resulting in severe reductions in most areas. Both changing ice conditions and reductions due to whaling may have affected geographic distribution and genetic diversity throughout their range, but little is known about range-wide genetic structure or whether it differed in the past. This study represents the first examination of genetic diversity and differentiation across all five putative stocks, including Baffin Bay-Davis Strait, Hudson Bay-Foxe Basin, Bering-Beaufort-Chukchi, Okhotsk, and Spitsbergen. We also utilized ancient specimens from Prince Regent Inlet (PRI) in the Canadian Arctic and compared them with modern stocks. Results from analysis of molecular variance and demographic simulations are consistent with recent and high gene flow between Atlantic and Pacific stocks in the recent past. Significant genetic differences between ancient and modern populations suggest PRI harbored unique maternal lineages in the past that have been recently lost, possibly due to loss of habitat during the Little Ice Age and/or whaling. Unexpectedly, samples from this location show a closer genetic relationship with modern Pacific stocks than Atlantic, supporting high gene flow between the central Canadian Arctic and Beaufort Sea over the past millennium despite extremely heavy ice cover over much of this period.

High genetic diversity in a small population: the case of Chilean blue whales

“…However, it is worth noting that only a few studies have directly detected losses in genetic diversity for whale populations in the post-whaling era (e.g. Alter et al 2012 ).…”

“… 2002 ), or have shown that even where diversity remains high, maternal lineages were likely lost from prewhaling populations (e.g. Alter et al 2012 ). Thus, our data support the hypothesis that not enough time has elapsed since the cessation of whaling to show a clear effect of whaling on the genetic diversity in the Corcovado Gulf blue whales.…”

Sea ice loss increases genetic isolation in a high Arctic ungulate metapopulation

“…Such genetic effects can reduce the evolutionary potential, delay population recovery and increase extinction risk (Frankham, 2005). In the Arctic, mammals such as the polar bear (Ursus maritimus), bowhead whale (Balaena mysticetus), walrus (Odobenus rosmarus), Arctic fox (Vulpes lagopus), and caribou and reindeer (Rangifer tarandus) have been extensively harvested in the past (Fay, Kelly, & Sease, 1989;Higdon, 2010;Kruse, 2017), but genetic impact studies have so far been rare (Alter et al, 2012;Petersen, Manseau, & Wilson, 2010;Taylor, Jenkins, & Arcese, 2012). Furthermore, global warming strongly influences the Arctic ecosystem, and is expected to increasingly affect future ecological dynamics (Descamps et al, 2017;Post et al, 2009Post et al, , 2013.…”

Effects of sea ice on Arctic biota: an emerging crisis discipline

“…(e) Overexploitation/overharvesting: many of ASI's effects on Arctic biota, notably on mammals, occur against a background of historical overexploitation that reduced population numbers, genetic variability and distribution ranges, likely establishing legacies on their ability to respond to present changes. For example, Alter et al [53] show much lower present bowhead whales' genetic diversity when compared with historical populations, and current grey whale numbers (approx. 22 000) are estimated to be approximately 3-5 times lower than pre-whaling [54].…”