Friday, July 13, 2018

[Ornithology • 2018] Molecular Phylogenetics and Species Limits in A Cryptically Coloured Radiation of Australo-Papuan Passerine Birds (Pachycephalidae: Colluricincla)



in Marki, Fjeldså, Irestedt & Jønsson, 2018.


Highlights: 
• A time-calibrated molecular phylogeny of all shrikethrushes (Colluricincla).
C. megarhyncha consists of seven unrecognized species.
 • A new taxonomy for C. megarhyncha is proposed.
 • C. megarhyncha melanorhyncha belongs in the genus Pachycephala.

Abstract
Detailed knowledge of species limits is an essential component of the study of biodiversity. Although accurate species delimitation usually requires detailed knowledge of both genetic and phenotypic variation, such variation may be limited or unavailable for some groups. In this study, we reconstruct a molecular phylogeny for all currently recognized species and subspecies of Australasian shrikethrushes (Colluricincla), including the first sequences of the poorly known C. tenebrosa. Using a novel method for species delimitation, the multi-rate Poisson Tree Process (mPTP), in concordance with the phylogenetic data, we estimate species limits in this genetically diverse, but phenotypically subtly differentiated complex of birds. In line with previous studies, we find that one species, the little shrikethrush (C. megarhyncha) is characterized by deep divergences among populations. Delimitation results suggest that these clades represent distinct species and we consequently propose a new classification. Furthermore, our findings suggest that C. megarhyncha melanorhyncha of Biak Island does not belong in this genus, but is nested within the whistlers (Pachycephala) as sister to P. phaionota. This study represents a useful example of species delimitation when phenotypic variation is limited or poorly defined.

Keywords: Passerine birds, Corvides, Australia, New Guinea, Cryptic species, Species delimitation


Fig. 2. A time-calibrated maximum clade credibility tree of Colluricincla shrikethrushes derived from the divergence estimation of the one mitochondrial gene and three nuclear introns in BEAST. Posterior probabilities are shown for major nodes. Error bars show the 95% highest posterior density intervals for the divergence time estimates. Vertical bars indicate the species identified by the mPTP-approach. Species names reflect the new taxonomy proposed in this study. Illustrations are watercolours by Jon Fjeldså and show all eleven delimited species. For species that exhibit significant within-species morphological variation, multiple illustrations are shown.

Fig. 1. Sampling localities for the 129 sequences included in this study. Colours and taxon names refer to the eleven species delimited in this study. 

Conclusion: 
In this study, we present a densely sampled molecular phylogeny for the Australasian shrikethrushes. Our results suggest that species diversity within this complex is underestimated, and we consequently propose a revised classification. Nonetheless, we view our proposed taxonomy as preliminary and hope that this study may stimulate further study of species limits in this group. In particular, we believe that increased study of behaviour, contact zone dynamics and vocalizations coupled with the analysis of genome-wide data are likely to be promising in this respect.


 Petter Z. Marki, Jon Fjeldså, Martin Irestedt and Knud A. Jønsson. 2018. Molecular Phylogenetics and Species Limits in A Cryptically Coloured Radiation of Australo-Papuan Passerine Birds (Pachycephalidae: Colluricincla). Molecular Phylogenetics and Evolution. 124; 100-105. DOI: 10.1016/j.ympev.2018.02.029 


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