Sri Lanka's laughingthrush: An ecological and phylogenetic assessment of a babbler confused for a laughingthrush

Abstract

The Ashy-headed Laughingthrush (Argya cinereifrons), a species endemic to Sri Lanka, has been historically considered a laughingthrush in the genus Garrulax. However, based on phylogenetic evidence, recent studies have suggested a new classification for the species under the genus Argya (true babblers). Despite the genetic signal showing affinity to true babblers Argya, as its common name suggests, the Ashy-headed Laughingthrush (AHLT) shows remarkable morphological similarities to other laughingthrushes of the Indo-Himalayan region. Here we attempted to address this incongruence in phenotypic and phylogenetic signals in this species by reconstructing the molecular phylogeny of babblers and comparing that with the key morphological, plumage, and vocal features of the two concerned groups. We hypothesized that the convergence of phenotype and vocalization of Garrulax in the wet evergreen forests of the Indian mainland and AHLT in the wet tropical rainforests of southern Sri Lanka has historically confused the taxonomists. The phylogenetic relationships were reconstructed using Bayesian inference using four mitochondrial and seven nuclear gene regions. The molecular phylogenetic tree placed the AHLT with India's Large Grey Babbler (A. malcolmi) as the sister taxon within the genus Argya. The hierarchical clustering based on body size, shape, plumage colour, and vocal properties resulted in the inconsistent placement of ALTH with babblers or laughingthrushes. Therefore, an incongruence in phenotype and genotype is observed. Our findings show that the convergent patterns of phenotypic evolution can confuse both historic and recent taxonomic delimitations in highly divergent groups such as Asian babblers.