Artisornis
Bowie, R.C.K., Pasquet, E., McEntee, J.P., Njilima, F., Fjeldså, J., The systematics and biogeography of African tailorbirds (Cisticolidae:
Artisornis) with comment on the choice of Bayesian branch-length prior when analyzing heterogeneous data, Molecular Phylogenetics and Evolution (2017), doi:
http://dx.doi.org/
10.1016/j.ympev.2017.08.011
abstract:
The Long-billed Tailorbird (
Artisornis moreaui), one of Africa’s rarest birds, has a strikingly disjunct distribution, the origin of which has long puzzled biogeographers. One small population (subspecies
moreaui) occurs in montane forest in the East Usambara Mountains, a montane sky island near the coast of northern Tanzania, and another (subspecies
sousae) on Serra Jeci in northwestern Mozambique, 950 km away. At both sites, the Long-billed Tailorbird co-occurs with its putative sister-species the African Tailorbird (
Artisornis metopias). At Serra Jeci, Long-billed Tailorbirds are observed primarily in the mid-canopy and African Tailorbirds in the understorey. This situation contrasts with that in East Usambara Mountains, where both species make extensive use of the understorey (<5 m). The apparent difference in canopy strata occupancy of Long-billed Tailorbird between the East Usambara and Serra Jeci formed the basis for Stuart’s (1981) hypothesis that African Tailorbirds have forced Long-billed Tailorbirds out of the understorey at Serra Jeci through competitive exclusion. We sought to 1) determine that the two species of African Tailorbird are indeed sister-species, and 2) test Stuart’s (1981) competitive exclusion hypothesis. Phylogenetic analyses of our seven gene dataset (3 mtDNA, 4 introns; 4784 bp) places these two species together in the genus Artisornis. We recover deep genetic divergence with geographic structure among populations of both tailorbird species, a result consistent with long-term co-existence of the two species. Thus, our data are consistent with the two species having achieved equilibrium and with successful resource partitioning having taken place over evolutionary time. From a conservation standpoint, our results suggest that extinction of the Long-billed Tailorbird as a function of competition with African Tailorbird is highly unlikely and should not be viewed as imminent. Finally, our empirical results suggest that mis-specification of the branch-length prior in Bayesian analyses of mitochondrial DNA data can have a profound effect on the overall tree-length (sum of branch-lengths), whereas the topology and support values tend to remain more stable. In contrast, mis-specification of the branch-length prior had a lesser impact on all aspects of the nuclear-only DNA analyses. This problem may be exacerbated when mitochondrial and nuclear DNA analyses are combined in a total evidence approach.