Leptocoma, Cabanis, 1850

Marcaigh, Fionn Ó, Kelly, David J., O’Connell, Darren P., Analuddin, Kangkuso, Karya, Adi, Mccloughan, Jennifer, Tolan, Ellen, Lawless, Naomi, Marples, Nicola M., O, Darren P. & Connell, 2022, Small islands and large biogeographic barriers have driven contrasting speciation patterns in Indo-Pacific sunbirds (Aves: Nectariniidae), Zoological Journal of the Linnean Society 198 (1), pp. 72-92 : 13-14

LEPTOCOMA TAXONOMY

The movement of species between the genera Cinnyris , Leptocoma and Nectarinia has previously caused confusion for taxonomists working with the black sunbird ( LeCroy, 2010). Our analyses suggest that the Leptocoma genus is not monophyletic ( Fig. 2 ). However, the genus-level branches in our tree had lower support than the species- and subspecies-level branches due to our use of mtDNA. We strongly recommend further sequencing of all species within Leptocoma to clarify the genus taxonomy.

Previous research based on plumage differences has not proposed any splits or ‘limbo splits’ within the black sunbird ( Eaton et al., 2021). Nonetheless, we found that the black sunbird exhibited genetic divergence consistent with a species-level split between Wallacea and the Sahul Shelf, with a high genetic distance between Sulawesi and PNG (9.1%). This presents a marked contrast to the ‘Sahul sunbird’, which exhibited minimal divergence between those same populations. Further sequencing of birds from intervening areas (such as the Maluku Islands) would help to clarify the boundaries between these potential species. As several intervening populations are absent from our analysis, we cannot rule out the possibility of clinal variation between the Sulawesi and PNG populations ( Brumfield, 2005; Cros & Rheindt, 2017). However, the genetic divergence we found was so strong (mean p-distance of 9.1%, higher than any observed in the olive-backed sunbird complex) that it seems more likely the two populations represent two species. The patterns we have observed suggest a division along Lydekker’s Line, and so we predict that sampling of the intervening populations would show a Wallacean species occurring from Sulawesi to the Maluku Islands and a separate species on New Guinea. This would involve the elevation of one of the Wallacean subspecies names to species level, as Lesson & Garnot (1828) named the black sunbird initially for a specimen from Manokwari (Doréry) on the New Guinea mainland. The discovery of cryptic species in the black sunbird highlights the importance of comprehensive sampling of species across their range, even in the absence of obvious plumage differences.

The structure within the black sunbird contrasted with the patterns shown by the olive-backed sunbird and ‘Sahul sunbird’ in several ways. The black sunbird exhibited a split between Sulawesi and PNG, where the ‘Sahul sunbird’ had a continuous population. The black sunbird also exhibited structure within both of these regions. Most taxonomic treatments ( Cheke et al., 2001; Billerman et al., 2022) split the black sunbird into distinct subspecies in PNG’s Western Province (L. a. aspasia ), Northern Province (L. a. vicina Mayr 1936) and the Bismarck Islands (L. a. corinna). However, Gill et al. (2022) merged L. a. vicina into L. a. aspasia , following Rand (1967). Our genetic work supports L. a. aspasia and L. a. vicina as distinct subspecies, whereas L. a. corinna appears to warrant species status based on ABGD. However, as this was based on a single sequence, we recommend that the Bismarck populations be examined further before a judgement is made. The Menui black sunbird population was genetically distinct from Sulawesi and the land-bridge islands, with a mean genetic distance (1.72%), a distance greater than that between the two subspecies in PNG (1.48%). This population was also found to be distinct in wing length, bill length, weight and tarsus length (MANOVA, P <0.001 in females). These findings suggest the Menui population of black sunbird may warrant recognition as an endemic subspecies.

Figures

Figure 2. Simplified version of a combined maximum likelihood (ML) and Bayesian phylogenetic tree of Cinnyris and Leptocoma species sampled in Wallacea and the Sahul Shelf. In this figure, the outgroup is omitted and each major clade in the data is collapsed into a single branch. Tips representing focal populations are marked with coloured circles. Nodes are labelled with Bayesian probability/ ML bootstraps. Full versions of the ML and Bayesian trees, including all outgroup taxa, are provided in the Supporting Information (Figs S7, S8).