The expected genetic diversity of Iceland

I was on my way back from Arthropod Genomics Symposium (which was a great conference by the way). The plan was to change planes in Iceland and get home in one go, but my flight to Iceland got delayed and I missed my connection. Fortunately, Iceland is amazing country and even around Reykjavik there is plenty to see. I decided to go to Perlan, a museum of Iceland natural history. I was shocked to hear that the island did not exist more than couple of millions years ago. I did not manage to remember the numbers, so I will take them from this web, where they say that the oldest rock is ~15 ml. Alright, 15 millions is not that little from the perspective of population genetics, enough time to generate some variability. However, we should also consider that the land was fully covered by ice during 30 rounds of glacial periods and the last time whole Iceland was under ice is 13,000 to 10,000 years ago. That means that all (or at least the most of) the macro life have started back then either as:

• tiny population that survived glaciation period (bottleneck).
• or colonization (founder effect).

The last thing that could save genetic diversity of macro species of Iceland is gene flow from the rest of the world. I do admit that I can not possibly know it, but gut feeling is that at least for plants and terrestrial animals it will be quite rare to get to Iceland (although I love stories about polar bears getting there on icebergs).

So lets think of a “native” Icelandic plant, a that I lived there before human era, like Betula pubsescence. How much genetic diversity is going to be in the population? What do you think? I guess that in 10,000 generation there is no way to have more than negligible numbers, I would guess something like human.

The good news is that there actually people who are into Betulas. The bad news is that the Icelandic Betula species hybridize (check this paper. I was not sure about those triploids, but there is a population genomics dataset of Betulas and apparently they can be also tetraploids and admix for more than one generation, it’s in the supplement of this paper. I conclude that a lot of variability in Icelandic population of Betula could have been derived from secondary contact, so it’s not a fair system to check if the heterozygosity/population variability correspond to 10,000 years old founder effect/bottleneck… However, I still think that my thoughts apply to everything without frequent gene flow. It’s the same if the gene flow is due to a secondary contact or a migration from one of the continents around. My problem is that I don’t know enough native Icelandic plants to search for further genomes, so I will stop right here.