Transmissible spongiform encephalopathies (TSEs) are currently incurable, always fatal, and have the potential to cross species boundaries. The expression of TSEs is thought to be influenced by genetic variation at the prion protein gene (PRNP). Although a wide range of mammals exhibit TSEs, it is currently unclear whether they are evolutionarily clustered or if TSE+ species are randomly distributed phylogenetically. We tested whether mammalian species with TSEs are phylogenetically underdispersed on three phylogenetic trees, one constructed from 20 aligned gene sequences for 102 taxa (a species tree), and PRNP gene trees from nucleotide and from amino acid sequence variation. TSEs were present in a variety of orders excluding Chiroptera, Eulipotyphyla, and Lagomorpha, and cetaceans. The occurrence of TSEs on the PRNP and species trees is non-random (Species tree D-value = 0.291; PRNP tree D-value = 0.273; PRNP amino acid tree D-value = 0.238), and TSEs appears to have arisen independently in the recent history of different mammalian groups. We found no evidence that particular protein motifs segregated between species with or without TSEs. Our findings suggest that the evolution of TSEs develops in groups of species irrespective of PRNP genotype.

传染性海绵状脑病 (TSE) 目前无法治愈，总是致命的，并且有可能跨越物种界限。TSE 的表达被认为受朊病毒蛋白基因 (PRNP) 的遗传变异的影响。尽管范围广泛的哺乳动物都表现出 TSE，但目前尚不清楚它们是进化成簇还是 TSE+ 物种在系统发育上随机分布。我们测试了具有 TSE 的哺乳动物物种是否在三个系统发育树上系统发育不充分，一个是由 102 个分类群的 20 个比对基因序列构建的（物种树），以及来自核苷酸和氨基酸序列变异的 PRNP 基因树。TSE 以多种目存在，不包括手足目、真翅目、兔形目和鲸目类。PRNP 和物种树上 TSE 的出现是非随机的（物种树 D 值 = 0.291；PRNP 树 D 值 = 0.273；PRNP 氨基酸树 D 值 = 0.238），并且 TSE 似乎在不同哺乳动物群的近代史。我们没有发现特定蛋白质基序在有或没有 TSE 的物种之间隔离的证据。我们的研究结果表明，无论 PRNP 基因型如何，TSE 的进化都是在物种组中发展的。