Diversification and species limits in scale-backed antbirds (Willisornis: Thamnophilidae), an Amazonian endemic lineage Author Quaresma, Tânia Fontes Author Cronemberger, Áurea A. Author Batista, Romina Author Aleixo, Alexandre text Zoological Journal of the Linnean Society 2022 2022-04-20 196 4 1408 1430 http://dx.doi.org/10.1093/zoolinnean/zlac011 journal article 10.1093/zoolinnean/zlac011 0024-4082 1719CE06-0D0E-4E8E-94E8-37AC811AED10 WILLISORNIS POECILINOTUS POECILINOTUS ( CABANIS, 1847 ) Taxonomy As discussed below, genetic lineages possessing the plumage attributes described below can be unequivocally assigned to the nominate W. poecilinotus ( type locality: ‘British Guiana’; Peters, 1951 ), distributed in north-eastern Amazonian Brazil , the Guianas and southern Venezuela ( Gill et al. , 2022 ). Plumage attributes Males with overall grey colour and a slightly paler ventral region. Presence of ‘lace’ (see Plumage analyses above). Black tail with white markings and white tips. Females with rufous upperparts overall and underparts mostly grey. ‘Lace’ on the dorsal region similar to that in males, but in black and rufous (instead of white) colours. The tail is black with terminal and intermediate markings also rufous. Genetic differentiation Specimens exhibiting the plumage characteristics above belong to a distinct genetic lineage completely sorted for their mitochondrial DNA, but less so for the nuclear genes, and which is distributed on the eastern part of the Guiana Shield, from Amapá in Brazil and the Guianas westward to the lower east bank of the Rio Negro (Fig. 1). We found significant genetic structure within this group, roughly across the Trombetas River near the Amazonas/Pará border, which prompted us to distinguish them as W. p. poecilinotus A (east of the Trombetas) and W. p. poecilinotus B (west of the Trombetas) (Fig. 1). Our genetic sampling does not allow for a resolution of the relationships in the contact zones between W. p. poecilinotus A and W. p. poecilinotus B, nor between W. p. poecilinotus as a whole and the neighbouring Willisornis lineages. Plumage variation We did not identify noticeable variations in plumage that were consistent with the genetic structure found for this group.