Bears of the Pleistocene

[brotherbear]

palaeo-electronica.org/content/2012-issue-2-articles/263-cave-bears-from-poland

Out of the big mammal species that went extinct during the Pleistocene, the cave bear is probably the most thoroughly genetically studied one. Its fossil material is quite abundant in cave sites across Europe and Asia, and in many cases preserved sufficiently well to allow ancient DNA (aDNA) extraction and analysis (e.g., Hänni et al., 1994; Loreille et al., 2001; Hofreiter et al., 2002, 2004a, 2004b, 2007; Orlando et al., 2002; Noonan et al., 2005; Valdiosera et al., 2006; Bon et al., 2008; Krause et al., 2008; Knapp et al., 2009; Stiller et al., 2010). Cave bears diverged from their sister lineage leading to the brown bear (Ursus arctos), approximately 1.2-1.7 million years ago according to palaeontological (Kurtén, 1968, 1976; Rustioni and Mazza, 1992; Rabeder and Withalm, 2006) and molecular data (Loreille et al., 2001; Bon et al., 2008), although some calculations indicate an earlier split about 2.8 million years ago (Krause et al., 2008). It is usually assumed that Late Pleistocene cave bears (Ursus ex gr. spelaeus) evolved gradually from the Middle Pleistocene cave bears from the deningeri-group still before the Last Interglacial (Mazza and Rustioni, 1994; Rabeder et al., 2000, 2010).
The results of both morphological and genetic studies have shown that during the Late Pleistocene, Europe was inhabited by two main cave bear haplogroups described as separate species, U. spelaeus and U. ingressus (Rabeder, 1995; Hofreiter et al., 2004b; Rabeder and Hofreiter, 2004; Rabeder et al., 2004a, 2004b). They separated between 173,000-414,000 yr BP according to molecular dating (Knapp et al., 2009). Additionally, among U. spelaeus several high-alpine forms with reduced body size, named U. s. eremus and U. s. ladinicus, were discerned whereas the 'classic' Western Europe cave bear was called U. s. spelaeus (Rabeder et al., 2000, 2004a, 2004b, 2008; Hofreiter et al., 2004b; Rabeder and Hofreiter, 2004). For a recent review of most described cave bear taxa and a somewhat different conception of their classification based on craniometrical features see Baryshnikov and Puzachenko (2011). According to this study, the morphological differences between U. spelaeus and U. ingressus do not exceed subspecies level and are too small to consider them as different species.
A large number of radiocarbon dates revealed that cave bears became extinct just before the Last Glacial Maximum (LGM), ca. 24,000 yr BP (27,800 cal. yr BP; Pacher and Stuart, 2009). Comparison of effective female population sizes of cave bears and their sister species, the brown bear, showed that the genetic decline of cave bears preceded their extinction by about 25,000 years, while brown bear population size remained constant (Stiller et al., 2010). The reason(s) for the extinction of cave bears are still unclear but it seems that not only one, but probably several causes played a role in its disappearance, possibly including climatic changes, human impact (Stiller et al., 2010), and predator stress caused by cave lion and cave hyena (Diedrich, 2010).
The phylogeographic picture of cave bears in Eurasia does not offer clear indications of the migration routes of cave bears during the Pleistocene glacials and interglacials. It has been suggested that U. ingressus dominated mainly in Eastern and Central Europe while U. spelaeus did so in Western Europe (Hofreiter et al., 2004a; Knapp et al., 2009). In addition to this picture in Europe, remains of both species were also discovered in Asia (Knapp et al., 2009). Whereas U. spelaeus inhabited mainly low and medium elevation areas, U. ingressus has mostly been found in medium and high elevated regions (Baryshnikov and Puzachenko, 2011). Recent isotopic analyses showed also some dietary differentiation between these cave bear haplogroups (Bocherens et al., 2011; Dotsika et al., 2011). Ursus ingressus was likely better adapted to continental environments and, thus, might have outperformed U. spelaeus during cold and arid climate conditions (Baryshnikov and Puzachenko, 2011). In fact, it was shown that U. ingressus immigrated into the Alps around 50,000 years ago where it replaced two former populations of U. s. eremus and U. s. ladinicus (Rabeder and Hofreiter, 2004; Rabeder et al., 2008). Similarly, the stratigraphically younger U. ingressus replaced quite suddenly the older U. s. spelaeus around 28,000 yr BP (32,000 cal. BP) in three geographically close caves in the Swabian Jura of Germany (Münzel et al., 2011). However, despite the numerous samples that have been genetically analysed so far, there are a number of regions from which no genetic data have been obtained so far and which could contribute to a better understanding of the complex picture of recent cave bear evolution.
Although fossil remains of cave bears are quite common in Poland, i.e., north of the Carpathian and Sudetes Mountain ridges, no DNA analyses were so far performed on cave bear remains from this region of Europe. Such analyses would be an important step towards reconstructing a more complete picture of phylogeographic structure and genetic variation of cave bears sensu lato. In this paper we present the results of the analysis of cave bear specimens discovered in Niedźwiedzia Cave (Wiszniowska, 1976; Wiszniowska et al., 1996; Bieroński et al., 2009) located in the eastern Sudetes Mountains. Phylogenetic analyses were performed with a variety of methods to ensure that the obtained tree topology was not dependent on a specific method. 
 
*From this post: According to this study, the morphological differences between U. spelaeus and U. ingressus do not exceed subspecies level and are too small to consider them as different species. Reply