CACATUINAE (Boles, 1993)

Smith, Brian Tilston, Thom, Gregory & Joseph, Leo, 2024, Revised Evolutionary And Taxonomic Synthesis For Parrots (Order: Psittaciformes) Guided By Phylogenomic Analysis, Bulletin of the American Museum of Natural History 2024 (468), pp. 1-87 : 20-21

CACATUINAE

Callocephalon , Eolophus , Lophochroa , Cacatua , and Licmetis

Callocephalon is a monotypic genus of medium-sized cockatoo, predominantly gray in plumage and having a distinctive, forward-curving crest of filamentous feathers. It is sexually dimorphic in its head plumage, red in males, gray in females. It is endemic to wetter forests and woodlands in southeastern Australia. Eolophus is also a monotypic, medium-sized cockatoo with three recognized subspecies. It is distinctively gray dorsally and pink ventrally with a backward-curving pink to whitish crest having a “split” appearance in some populations. It has bare, carunculated periophthalmic skin varying subspecifically from white to shades of pink. It is one of the most familiar of all Australian birds occurring across the continent in all but the wettest forests and woodlands. Lophochroa comprises one species with two currently recognized subspecies. Resembling in overall morphology the large Cacatua galerita , it differs in having salmon-pink underparts and a similarly pink and yellow crest, and a pale bill. It primarily inhabits arid- and semiarid woodlands. All three of these genera have distinctive vocalizations.

We discuss the taxonomic implications of the phylogenomic data in light of the two phenotypically distinct groups within Cacatua sensu lato that the data in turn mostly affirm. The first of these is Cacatua sensu stricto having mostly forward-curving, yellow or white to orange crests, broad wings, naked white to bluish ocular skin, usually concentric with the eye itself, black bills, and characteristically as well as extraordinarily harsh shrieks. The second is Licmetis , the corellas, having vestigial, backward-curving crests, slender wings, milky to leaden blue ocular skin extending below the eye in an oval shape, white bills and a distinctive yodel or crying vocalizations (see Forshaw, 1973; Schodde et al., 1979; Schodde and Mason, 1997; Forshaw and Knight, 2010).

Relationships within Cacatuinae are the most unstable and taxonomically challenging within Cacatuoidea. This is largely due to lower-quality samples for some taxa (e.g., Cacatua ophthalmica ) and gene tree–species tree discordance reported in Smith et al. (2023). Phylogenetic patterns within Cacatuinae are represented by a series of well-supported and consecutive nodes, then nodes leading to each of the three monotypic genera Callocephalon , Eolophus , and Lophochroa , and a final node subtending a clade comprising white cockatoos long treated within the genus Cacatua (fig. 2). Previous multilocus work found weak evidence of Callocephalon fimbriatum and Eolophus roseicapilla as sister taxa ( White et al., 2011), but we found them diverging on successive branches with 100% bootstrap support. They are each phenotypically unique, and this includes their vocalizations as well as plumage patterns. Generic-level divergences span 9.3–22.6 Mya (fig. 2). We first examine genus-level divergences before discussing species-level issues.

We fully support the retention of Callocephalon , Eolophus , and Lophochroa as monotypic genera. Notably, Lophochroa was sister to a clade comprising Cacatua sensu stricto and the Licmetis corellas, not just the former with which it has long been placed in Cacatua and with some species of which it shares the phenotypic trait of a forward-curving crest. We favor the retention of Lophochroa at generic rank because of its phylogenomic separation from Cacatua and this includes the age of its lineage coupled with its utterly distinct phenotypic traits including bicolored crest and unique vocalizations.

There was topological discordance between the concatenated and species tree topologies for Cacatua . The bulk of the discordance was within the two main clades corresponding to Cacatua sensu stricto and Licmetis , and often involved lower-quality historical samples and nodes with low support, but there are also likely cases of phylogenetic conflict. We find it puzzling that these two groups have for so long been unquestioningly placed in one genus, Cacatua Vieillot, 1817 . This treatment has prevailed in Australian literature at least since RAOU (1926); it is difficult to determine why it was introduced and why it has prevailed despite the obvious phenotypic differences just outlined. Further, it has prevailed despite several demonstrations of substantial genetic divergences ( Adams et al., 1984; Brown and Toft, 1999). We now address in more detail the merit of breaking of Cacatua sensu lato into these two genera. For ease of discussion, we anticipate our recognition of Licmetis at rank of genus.

One source of uncertainty in our analysis is the generic placement of haematuropygia . It is either sister to the remaining Licmetis (concatenated tree) or the clade composed of Cacatua / Licmetis (species tree). Morphologically, haematuropygia would appear to belong in Licmetis in that it is similar in size, shape, and bill color to L. goffiniana , a taxon firmly nested within the corellas (but we note its white ocular skin concentric with the eye). From our additional MAST analysis on Cacatua we found that the concatenated phylogeny, which has a monophyletic Licmetis , was the predominant topology (tree weight: 0.87) across the alignment versus the topology with L. haematuropygia as sister to all other Licmetis and Cacatua as the minor tree (tree weight: 0.13). These results confirm the analyses of this clade by Smith et al. (2023), where there was more signal for the concatenated topology. Given haematuropygia ’s morphological affinities with Licmetis and the overriding phylogenomic signature that indicates it is sister to the other corellas, the best evidence supports the recognition of Cacatua and Licmetis . We do not advocate a new genus for L. haematuropygia .

There were also several cases of gene tree– species tree discordance within both groups. Relationships among the corellas ( L. sanguinea , L. tenuirostris , L. pastinator , and L. goffiniana ) varied among the phylogenomic trees. Similarly, there was such discordance in Cacatua sensu stricto ( C. sulphurea , C. moluccensis , and C. ophthalmica ). Divergence times within Cacatua and Licmetis ranged from 2.3 to 5.8 Mya and 3.4 to 8.2, respectively (fig. 2).

We are confident that the combined weight of our genomic data, uncertainties within the two strongly supported clades notwithstanding, and the phenotypic differentiation in body and wing morphologies generally, crest morphology in particular and vocalizations, all combine to provide strong support for the breakup of Cacatua sensu lato and the reinstatement of Licmetis Wagler, 1832 , for the corellas. Indeed, we argue that this situation strongly parallels the basis for recognition of Calyptorhynchus and Zanda , the separation of which is now accepted and entrenched such that treating them as congeneric is considered little more than bad taxonomic habit. A similarly prevalent generic separation of sister clades is that of Platycercus and Barnardius . We acknowledge the call made by Adams et al. (1984) for detailed comparative study of any social function of crests and bare facial skin in these cockatoos to test whether contrasting combinations of these traits may have arisen through character displacement.

Phylogeographic work in Cacatuinae has been limited to a few species. Engelhard et al. (2015) found that phylogeographic structure in Eolophus roseicapilla broadly corresponds with eastern, western, and northern subspecies recognized by morphological traits. Future work should examine phylogeographic variation in Callocephalon , Cacatua , and Licmetis . In the widely distributed Australian endemic Lophochroa leadbeateri, SNP data identified contains 2–3 genetic groups corresponding with a break across the Eyrean Barrier and in central Queensland ( Ewart et al., 2021). This break corresponds to the subspecies L. l. leadbeateri and L. l. mollis, but interestingly, the genetic structuring among these groups was not observed in mtDNA. Cacatua galerita and the Licmetis sanguinea complex are both of particular interest given their uncertain subspecific taxonomy and their widespread distributions.