Toll-like receptor 5 (TLR5) is a Pattern-recognition receptor responsible for microbial flagellin detection in vertebrates and, hence, recognition of potentially pathogenic bacteria. Herein, we report emergence of TLR5 pseudogene in several phylogenetic lineages of passerine birds (Aves: Passeriformes). Out of 47 species examined in this study 18 possessed a TLR5 pseudogene. Phylogenetic analysis together with the type of mutation responsible for pseudogenization indicate that TLR5 pseudogene emerged at least seven times independently in passerines. Lack of any functional copy of the gene has been verified based on TLR5 mRNA blood expression in four species representing the four main passerine lineages possessing the TLR5 pseudogene. Our results suggest that the non-functional TLR5 variant is fixed in those lineages or, at least, that individuals homozygote in the TLR5 pseudogene are frequent in the investigated species. Further research is needed to assess the impact of the TLR5 loss on immunological performance in birds.

Department of Zoology Faculty of Science Charles University Prague Viničná 7 128 43 Prague Czech Republic

Department of Zoology Faculty of Science Charles University Prague Viničná 7 128 43 Prague Czech Republic; Institute of Vertebrate Biology Academy of Sciences of the Czech Republic v v i Květná 8 603 65 Brno Czech Republic

Institute of Vertebrate Biology Academy of Sciences of the Czech Republic v v i Květná 8 603 65 Brno Czech Republic

Institute of Vertebrate Biology Academy of Sciences of the Czech Republic v v i Květná 8 603 65 Brno Czech Republic; Department of Botany and Zoology Faculty of Science Masaryk University Kotlářská 267 2 611 37 Brno Czech Republic

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