Question

Q1: Based on your tree, from which living species did polar bears evolve from?

Q2: Using branch lengths, how much total evolution (along both branches) has occurred since these two species diverged from a common ancestor?

Q3: If this mitochondrial gene evolves at a rate of 0.01 substitutions per nucleotide site per million years, how long ago did the American and Asiatic black bears diverge from a common ancestor?

Ailuropoda melanoleuca 0.0494 Helarctos malayanus 0.0494 0.015 Ursus arctos 0.0344 0.015 0.008 0.1037 0.0501 0.015 Ursus maritimus 0.0501 Melursus ursinus 0.0276 0.0581 0.0497 Ursus americanus 0.0084 0.0179 0.0497 0.0858 0.0497 Ursus thibetanus 0.0858 Tremarctos ornatusa 0.02 Giant panda Ailuropoda melanoleuca Sun bear Helarctos malayanus South Asia Asiatic black bear Ursus thibetanu:s Sloth bear Melursus ursinuS South Asia Spectacled bear Tremarctos onatus South American black bear Ursus North America Brown bear Ursus arctos Eurasia 8 North America Polar bear Ursus maritimus Arctic

Answer 1

The bear family (Ursidae, Mammalia) represents an excellent, largely untapped model for investigating complex speciation and rapid evolution of distinct phenotypes. Although polar bears ( PBs; Ursus maritimum) and brown bears (Ursus arctos) are considered separate species, analyse of fossil evidence and mitochondrial sequence data have indicated a recent divergence of PBs from within brown bears. For example, phylogenetic analyses of complete mitochondrial genomes, including from a unique 130,000- to 110,000 year old polar bears jawbone from Norway, confirmed a particularly close relationship between PB and genetically isolated population of brown bears from the Admiralty islands in Alaska's Alexander Archipelago and suggested a split of their maternal linkages ∼150.

The phylogenetic conflict can be caused by incomplete lineage sorting or gene flow, but less likely from lack lack of resolution due to the strong phylogenic signal. Analyses of 8,050 protein coding sequences (10,303,323 bp) from scaffolds previously identified as X chromosomal ( total 74 Mb)^22.