The impact of past climate change on genetic variation and population connectivity in the Icelandic arctic fox

Abstract

Previous studies have suggested that the presence of sea ice is an important factor in facilitating migration and determining the degree of genetic isolation among contemporary arctic fox populations. Because the extent of sea ice is dependent upon global temperatures, periods of significant cooling would have had a major impact on fox population connectivity and genetic variation. We tested this hypothesis by extracting and sequencing mitochondrial control region sequences from 17 arctic foxes excavated from two late-ninth-century to twelfth-century AD archaeological sites in northeast Iceland, both of which predate the Little Ice Age (approx. sixteenth to nineteenth century). Despite the fact that five haplotypes have been observed in modern Icelandic foxes, a single haplotype was shared among all of the ancient individuals. Results from simulations within an approximate Bayesian computation framework suggest that the rapid increase in Icelandic arctic fox haplotype diversity can only be explained by sea-ice-mediated fox immigration facilitated by the Little Ice Age.

Figure 1.

A map depicting the approximate current distribution of the Arctic fox in blue [10]. The dashed black line indicates the median sea ice maximum for the period 1979–2000 [16].

Figure 2.

A map of Iceland showing the sample locations and sizes for both the modern and ancient datasets. Pie charts show the proportion of individuals at each locality assigned to each haplotype shown at the bottom of the figure. Median-joining networks to the right of the maps depict the relationships between the ancient and modern haplotypes present on Iceland. Black circles indicate the absence of modern haplotypes in the ancient population. White circles represent inferred haplotypes.

Figure 3.

(a) A joint density graph showing high (yellow) and low (blue) probability regions for the combination of two parameters: a logarithmic scale of effective female population size (N_ef; horizontal axis) and effective number of female immigrants per generation (NM_f; vertical axis). The square and diamond represent median and expected values and the black dashed line shows the borders of the 95% highest density region (HDR). (b) A depiction of the posterior probability distribution of the effective female population size (N_ef) on a logarithmic scale. (c) A depiction of the posterior probability distribution of the effective number of female immigrants per generation (NM_f). In (b,c), vertical lines correspond to the median (left) and expected (right) values, and the lighter blue bars encompass the 95% HDR.