Landscape and Climatic Variations Shaped Secondary Contacts amid Barn Owls of the Western Palearctic

Abstract

The combined actions of climatic variations and landscape barriers shape the history of natural populations. When organisms follow their shifting niches, obstacles in the landscape can lead to the splitting of populations, on which evolution will then act independently. When two such populations are reunited, secondary contact occurs in a broad range of admixture patterns, from narrow hybrid zones to the complete dissolution of lineages. A previous study suggested that barn owls colonized the Western Palearctic after the last glaciation in a ring-like fashion around the Mediterranean Sea, and conjectured an admixture zone in the Balkans. Here, we take advantage of whole-genome sequences of 94 individuals across the Western Palearctic to reveal the complex history of the species in the region using observational and modeling approaches. Even though our results confirm that two distinct lineages colonized the region, one in Europe and one in the Levant, they suggest that it predates the last glaciation and identify a secondary contact zone between the two in Anatolia. We also show that barn owls re-colonized Europe after the glaciation from two distinct glacial refugia: a previously identified western one in Iberia and a new eastern one in Italy. Both glacial lineages now communicate via eastern Europe, in a wide and permeable contact zone. This complex history of populations enlightens the taxonomy of Tyto alba in the region, highlights the key role played by mountain ranges and large water bodies as barriers and illustrates the power of population genomics in uncovering intricate demographic patterns.

Genomic bases of insularity and ecological divergence in barn owls (Tyto alba) of the Canary Islands

“…(Siverio 1998). This is consistent with the known limited ability of this bird to live at high altitudes (Machado et al 2018;Cumer et al 2021). However, the observation of individuals up to 1200m a.s.l.…”

“…Notably, the two Canaries insular populations, about 165 km apart, were more distant genetically from each other than either was from Portugal, over 1000 km away. Furthermore, they were more distant from each other even than WC was from any population in continental Europe in a recent genomic study (Cumer et al 2021), as well as in an earlier one with microsatellites (Burri et al 2016). The high private diversity could be partially explained by the small number of samples in north-western Africa, which may be masking any shared polymorphisms between the islands and the nearest mainland as private to the former.…”

“…Whole-genome sequencing, SNP calling and identification of coding regions For this study, 40 individual barn owls were sampled from four populations (Figure 1; Supplementary Table 1): Eastern Canaries (EC, Fuerteventura and Lanzarote), Western Canary (WC, Tenerife), Morocco (MA), Portugal (PT) and Israel (IS). All but the EC and MA populations were published in previous work, including a North American owl that was used as an outgroup for some analyses (Genbank accession JAEUGV000000000 (Cumer et al 2021;. For EC and MA, we followed the same molecular and sequencing protocol as in the aforementioned publications.…”

“…The high private diversity could be partially explained by the small number of samples in north-western Africa, which may be masking any shared polymorphisms between the islands and the nearest mainland as private to the former. However, as we did sample PT and IS, the most diverse populations in the Western Palearctic assumed to meet in northern Africa (Cumer et al 2021), much of this insular diversity is likely indeed private. Therefore, the Canaries appear to have been colonized much earlier than the other studied insular populations and have thus had the time for in situ mutations to accumulate in spite of genetic drift, which is supported by their higher divergence as well.…”

“…It is also found on numerous islands and archipelagos where subspecies have often been described (Uva et al 2018). A recent study of the species' genetic structure in the Western Palearctic (Cumer et al 2021) described two main lineages occupying this region: the eastern lineage in the Levant and the western in Europe. In addition, showed that barn owls from Tenerife (Canary Islands) were very distinct from both lineages.…”