Low adaptive and neutral genetic diversity in the endangered Antioquia wren (Thryophilus sernai)

Determining the amount and distribution of genetic variation represents a fundamental step for the inference of evolutionary processes acting on populations of endangered species. For these species, adaptive evolutionary potential is highly reduced by the loss of genetic variation due to drift. Here, we examined genetic diversity at the mitochondrial control region (CR), 17 microsatellites, and six Toll-like receptor (TLR) genes, known to play a key role on the innate immune response of vertebrates in the Antioquia wren (AW)Thryophilus sernai, an endangered passerine bird inhabiting the remnant fragments of tropical dry forest in the northernmost part of the Cauca river canyon, Colombia. We found very low variation for the three types of markers. The CR showed scarce variability, while only six of the 17 microsatellites analyzed and two of the six TLRs sequenced were polymorphic. Population structure analyses suggest the occurrence of one single population in the area. Selection tests could not detect signatures of positive selection for the variable sites in the species, and assessment of amino acid changes found within the lineage do not suggest any functional effects that could be associated to selection in either polymorphic TLR loci. Comparisons with species showing widespread and restricted distribution supports a low TLR variability typical of small populations. These results suggest current low evolutionary potential for the species, as its reduced genetic diversity is expected to increase extinction risk by limiting the ability to cope with environmental changes. Our study supports current evidence suggesting drift as the main driver shaping TLR variation.