Red deer colonised western Norway some time before 8,000 yr BP and skeletal remains indicate that they were well established by the start of the period covered by this analysis (Rosvold et al. unpublished results). While significant Fu’s Fs indicate a population expansion during the early part of our study period (Table
3), the BSP (Figure
4) suggests a relatively stable female effective population size until about 2,000 yr BP. However, as the samples for this early period are widely dispersed in time, the posterior density interval of the BSP is large and the estimate is thus insecure. The Early Iron Age sample (c. 2,500 – 2,000 yr BP) has the highest diversity indices of all periods considered (Table
3), indicating that the population size may have been particularly high during this time.
Historical texts tell of a widespread and large population in Norway until around 500 yr BP, after which there was a dramatic decrease in numbers, allegedly caused by high harvesting rates and increased numbers of predators
[18, 68]. However, as indicated by the diversity indices, the BSP and the ABC analyses, this decrease appears to have been more prolonged, probably starting before medieval times. The estimated effective population sizes should be interpreted with caution
[69, 70], but the relative changes give a reliable picture of the magnitude of the demographic bottleneck. Accordingly, and supported by an earlier study on contemporary microsatellite DNA
, the bottleneck seems not to have been as dramatic as the historic texts may suggest. The mtDNA diversity in the present population is, however, relatively low (Table
2) and especially the nucleotide diversity is low compared to other European populations
. The lowest diversity estimates are found in the northernmost region (N), as expected from a peripheral population loosing diversity during postglacial colonisation
. The current high population density of red deer in Norway is generally believed to be a recent phenomenon
, but our results might indicate that at least the effective female population size, as measured through genetic diversity, was even higher in the past.
Following the spread of agriculture along the coast of western Norway the once dense coastal forests were transformed into the present day heathlands
[73, 74]. A process which was greatly accelerated from around 2,000 yr BP through intensified agricultural activities
, iron, coal, and salt production, and later by mining and timber export
. These changes in the landscape probably facilitated and exacerbated the effects of heavy hunting by increasing habitat fragmentation and possibly reducing migration between areas, thereby isolating populations. The loss of the previously most abundant haplotype (NO4) may indicate extensive genetic drift within these fragmented populations, reducing genetic diversity on a local scale. However, the number of isolated populations were relatively large (at least six) and evenly spread along large parts of its former distribution
. Thus, the overall genetic diversity may have been better maintained by the wide geographic spread of the populations than if they had been reduced to a single but larger population
. Population fragmentation and isolation is expected to cause increased genetic differentiation
, and indeed, there is a high degree of genetic structuring among the present Norwegian female red deer (Figure
1 and Table
2). This indicates that few females have migrated between the areas since the population size reduction, supporting findings that fjords may act as significant dispersal barriers
The ten Norwegian haplotypes observed in the ancient samples are closely related to the rest of the western European clade. The star-like structuring (Figure
3) coupled with low nucleotide diversity (Table
3) is indicative of a population expansion from an ancestral haplotype
 which in this case seems to be NO4. This close relationship, coupled with the observation that all present-day haplotypes except NO3 have been found in samples dating to 2,000 yr BP or older, is an indication of no human translocation of female red deer into Norway during historic times. This conclusion is also supported by ABC analyses, where a scenario of only one post-glacial colonisation of Norway gets highest support. NO3 is first found at low frequency in late medieval samples and has so far only been found in Norway (Figure
5). It is possible that NO3 originated in Norway and became frequent in the Sognefjord area (W, Figure
1) as an effect of genetic drift and subsequent population increase during recent times.
An estimated divergence time of the Norwegian population of around 15,000 yr BP (9,960 – 19,560), as indicated by the ABC analysis (Table
4), coincides with the start of the northward colonisation of Europe after the Last Glacial Maximum
. The haplotype network for the western European red deer (Figure
5) confirms previous findings of a close relationship within the western European clade
[13, 14], with little or no apparent geographic structure and several cross-links indicating uncertain relationships. Out of the ten haplotypes found in the ancient Norwegian dataset five are shared with other countries. Of these, the two central haplotypes NO1 and NO4 are widespread, being present in Scotland and the border forests between Germany and the Czech Republic
[14, 23, 25], with NO4 also found in Spain
, and NO1 being one of the most common types found in the Scottish highlands today
. None of the extant Norwegian haplotypes are shared with other Scandinavian countries; although the ancient NO6 is found in Denmark today
. The Swedish population seems to have experienced a more severe bottleneck than the Norwegian as only one haplotype, closely related to NO1, is found among indigenous animals
[11, 14]. This low diversity makes it hard to postulate the relationship to Swedish animals, but present Scandinavian diversity indicates that some haplotypes never reached Norway and that a large part of those passing through Denmark during the post-glacial colonization (i.e. the Norwegian types) were later lost. Sampling aDNA from both Sweden and Denmark could shed more light on if this was caused by genetic bottlenecks or if they were replaced by later immigrants that never reached Norway.
Two star shaped patterns are apparent among the western European samples, separated by an A-G transition. One of these centres on NO1, which has been described before
, while the other centres on the closely related NO4 and is made more apparent by our ancient samples. This could be an indication of two subgroups within the western European haplogroup, possibly reflecting different refugial areas in France and Iberia
. Most of the European populations have undergone severe population reductions during recent centuries and several translocations which could have distorted any phylogeographic patterns within the haplogroup
[6, 71]. A large-scale sampling of aDNA from other European populations would thus provide valuable insights into the phylogeography of European red deer.