Ice, Ice, (Protect My) Baby

One evolutionary misconception is, “because evolution is slow, humans cannot influence it.” In Episode 1 of Blue Planet II Season 1, David Attenborough states that over the past 30 years, the amount of ice in the Arctic Ocean over the summer has reduced by 40%. This drastic decrease in ice is due to sudden warming of the earth, which is likely a result of human activity. This has affected wildlife in the Arctic, specifically walruses, which are highlighted in the documentary. When polar bears threaten land space in the Arctic, mother walruses protect their young by retreating to ice caps and laying with them there. The decreasing amount of floating ice patches nowadays, though, makes it hard for mother walruses to safely protect their young. This unfortunate circumstance also holds true for seals [1].

There is only one species of walrus that exists today: Odobenus rosmarus [2]. This makes protection of this species vital. There is less room for further speciation should this population continue to decline. However, as the climate changes, so does the geographical distribution of walrus populations. While it has been shown that walruses in different areas of the Arctic ocean vary genetically to some degree [3], this geographical analysis mainly serves as a prerequisite to conservation efforts rather than a sign of comfort about the state of conservation of the walrus. Additionally, walruses used to inhabit the Antarctic as well as the arctic, but suffered extirpation from the south due to hunting and no longer live below 55ºN [4]. These southern walruses were morphologically and genetically distinct from the walruses we observe in the arctic today, indicating that they were evolving distinctly from other members of the species, but unfortunately this genetic variation was lost.

What all these facts show is that walruses are vulnerable for many reasons, and that humans have impacted the evolution of walruses. Because hunting and exploitation changed the geographic distribution of the species, they have also influenced the genetic variation within the species, which may limit future adaptation to changing conditions, as genetic variation is needed for evolution.

by Emily Baker and Ana Lee Pokrzywa

Blue Planet II, Season 2 Episode 1, “One Ocean”, starting at 42:10

References

1. BP Kelly. 2001. Climate change and ice breeding pinnipeds. Walther GR., Burga C.A., Edwards P.J. (eds) “Fingerprints” of Climate Change.” Springer, Boston, MA
2. CR Huntington. 2008. The evolution of arctic marine mammals. Ecological Applications 18(2): S23-S40
3. Andersen LW, Jacobsen MW, Lyndersen C, Semenova V, Boltunov A, Born EW, Wiig O, and KM Kovacs. 2017. Walruses (Odobenus rosmarus rosmarus) in the Pechora Sea in the context of contemporary population structure of northeast Atlantic walruses. Biological Journal of the Linnean Society 122(4):897-915.
4. McLeod BA, Frasier TR, and Z Lucas. 2014. Assessment of the extirpated maritimes walrus using morphological and ancient DNA analysis. PLoS One 9(6).