Belongs within: Platycercini.
Platycercus includes the rosellas, medium-sized long-tailed parrots native to Australia. Members of the genus have mottled backs, with lighter edges around the dark feathers, and contrasting blue, yellow or white cheek patches. Examples include the crimson rosella P. elegans of eastern Australia, which is predominantly red with blue cheeks, wings, tail and mottling on the back. The green rosella P. caledonicus has similar blue cheeks to the crimson rosella but is green above and greenish yellow below (Morcombe 2003).
Parrots in the early days of molecular analysis
Published 21 November 2007
Rosellas (Platycercus) are a genus of five or more species of smallish parakeet found in more coastal areas of Australia, particularly the eastern states. Significant differences in opinion exist about just how many species there are in the genus. A number of subspecies are recognised that may be raised as separate species depending on author (I’m going to take a neutral position and treat all taxa as if they were species—see Wikipedia for a more detailed taxonomy). At least one taxon in the genus, the variable Platycercus adelaidae (the Adelaide rosella), is claimed by some to be a hybrid swarm derived from cross-breeding between two other subspecies and therefore not a valid taxon at all*. Rosellas are also possibly the most familiar parrot in New Zealand, at least in the north, due to abundant populations of introduced Platycercus eximius (the eastern rosella, shown at the top of the page in a photo from Wikipedia).
*The ICZN (in contrast to the ICBN) does not permit the recognition of taxa based on hybrids. This rule works fine when dealing with singleton hybrid specimens, which were doubtless what the ICZN had in mind when they drafted it, but is somewhat problematic when dealing with populations that have a hybrid origin, some of which may become established as new species.
The species of Platycercus can be readily divided into two groups, referred to as the “P. elegans” and “P. eximius” groups (though the latter should probably be called the P. adscitus group as that species has priority). Platycercus elegans and P. caledonicus are the blue-cheeked rosellas. Platycercus adscitus, P. eximius and P. venustus are the white-cheeked rosellas. The geographically isolated P. icterotis (the western rosella) from the south-west of Western Australia has white or yellow cheeks and was once included in the P. eximius group, but is now generally excluded from either group.
At the time Ovenden et al. (1987) was published, molecular phylogenetics were still very much in their infancy. PCR, the technique that revolutionised molecular studies, was not to appear until the following year (Saiki et al. 1998). Before the advent of PCR, most molecular techniques were expensive, time-consuming, delicate and often unreliable (after the advent of PCR, they became expensive, delicate, often unreliable, and able to be done much more readily*). As such, most molecular studies in the 1980s used methods that by modern standards appear decidedly rough and ready. In the case of the one I’m looking at today, the method of choice was mitochondrial restriction fragment polymorphisms.
*It’s a bit like the joke about the soldiers in the desert camp being to told by their general that there was bad news and good news. The bad news was that supplies had run so low that all they had left to eat was horseshit. The good news was that there was plenty of it.
Restriction endonucleases are enzymes that cut DNA into bits. There are a huge number of endonucleases in use at the present, and each one works by attaching to a specific sequence of bases in a DNA strand and dividing it at that point. Depending on need, there are enzymes that require relatively long sequences of bases and so would cut a given DNA strand rarely if at all, or there are enzymes that only require short sequences and so would be expected to cut strands far more readily. Probably the most familiar use of endonucleases to the general public is in DNA fingerprinting, where the resulting fragments from the endonuclease treatment of DNA samples are compared to see whether or not the samples contain the same fragment. The use of RFLPs (restriction fragment length polymorphisms) in phylogenetics is essentially a distance method—it proceeds by the assumption that samples that are most similar to each other in the resulting restriction fragment pattern are the most closely related phylogenetically. As for the use of mitochondrial DNA, there were a number of reasons why mitochondrial DNA was preferred to nuclear DNA for molecular studies at the time, but not least of them was that there is usually a lot more of it about and it is much easier to extract from a specimen than nuclear DNA. It should not be forgotten that prior to PCR, researchers only had as much sample to work with as they could directly draw out of the specimen.
There are a great many reasons why the use of RFLP for phylogenetics should not work. The assumption that genetic distance is equivalent to phylogenetic distance is simply not reliable, because evolution does not always occur at the same rate in separate lineages. Add to that the fact that in an ideal phylogenetic data set changes in one character state should not affect the state of other characters—a requirement blatantly violated by RFLP data, as the loss of a restriction site causes the resulting data set to “lose” two fragments and gain a whole “new” fragment. Fortunately for this case, the results actually make a certain degree of sense. Ovenden et al. recovered the same two species groups that had already been identified on the basis of morphological data. The only exception was that Platycercus icterotis, rather than clustering with the P. eximius group, came out as the most divergent species of all. However, this, too, had already been suggested on morphological grounds.
Unfortunately, the phylogeny of Platycercus does not appear to have been re-examined since the advent of more reliable analytical methods. There are no obvious reasons not to believe Ovenden et al.‘s results, but considering the methodology they can hardly be said to not be worth a further look.
Systematics of Platycercus
<==Platycercus Vigors 1825CC10
| i. s.: P. flaviventrisS13
| P. splendens [=Pyrrhulopsis splendens]S66
| P. spuriusSJ85
| P. variusSJ85
| P. zonariusSJ85
| |--P. z. zonariusSJ85
| `--P. z. semitorquatusSJ85
|--+--P. elegans (Gmelin 1788)BKB15, CC10 [=Psittacus elegansCC10; incl. Ps. pennantii Latham 1790CC10, *Platycercus pennantiiCC10]
| | |--P. e. elegansCC10
| | |--P. e. melanoptera North 1906CC10
| | |--P. e. nigrescens Ramsay 1888CC10 [=P. pennanti var. nigrescensC38]
| | `--P. e. victoriae Mathews 1912C38
| `--P. caledonicus (Gmelin 1788)BKB15, C38 [=Psittacus caledonicusC38]
| |--P. c. caledonicusC38
| |--P. c. flindersi Mathews 1917C38
| `--P. c. henriettae Mathews 1915C38
`--+--P. icterotis (Kuhl 1820)BKB15, WS48 [=Psittacus icterotisWS48]
| |--P. i. icterotis [incl. P. icterotis salvadori Mathews 1912, P. stanleyii Vigors 1830]WS48
| `--P. i. xanthogenys Salvadori 1891 [incl. P. icterotis whitlocki Mathews 1912]WS48
`--+--P. adelaidae Gould 1840BKB15, C38 [=P. elegans adelaidaeOMC87; incl. P. fleurieuensisM03]
`--+--P. flaveolus Gould 1837BKB15, C38 [=P. elegans flaveolusOMC87]
| |--P. f. flaveolusC38
| `--P. f. subadelaidae Mathews 1912 [incl. P. flaveolus innominatus]C38
`--+--Psephotus Gould 1845BKB15, C38
| `--*P. haematonotus (Gould 1837) [=Platycercus haematonotus]C38
| |--P. h. haematonotusRN72
| `--P. h. caeruleus Condon 1941RN72
`--+--P. venustus (Kuhl 1820)BKB15, WS48 (see below for synonymy)
`--+--P. adscitus (Latham 1790)BKB15, WS48 [=Psittacus adscitusWS48]
| |--P. a. adscitusOMC87
| |--P. a. amathusiaeOMC87
| |--P. a. elseyi Mathews 1912C38
| |--P. a. mackaiensisOMC87
| `--P. a. palliceps Lear 1832C38
`--P. eximius (Shaw 1792)BKB15, CC10 [=Psittacus eximiusCC10]
|--P. e. eximiusC38
|--P. e. ceciliae Mathews 1911C38 [incl. P. eximius splendidusRN72]
|--P. e. colei Mathews 1917C38
|--P. e. diemenensis North 1911C38
`--P. e. elecicaM03
Hybrid: P. mastersianus [P. adscitus × P. elegans]C38
Platycercus venustus (Kuhl 1820)BKB15, WS48 [=Psittacus venustusWS48, Pl. adscitus venustusWS48; incl. Pl. caledonicus browniiM03, C38, Pl. venustus hillia Mathews 1910WS48]
*Type species of generic name indicated
References
[BKB15] Burleigh, J. G., R. T. Kimball & E. L. Braun. 2015. Building the avian tree of life using a large-scale, sparse supermatrix. Molecular Phylogenetics and Evolution 84: 53–63.
[C38] Cayley, N. W. 1938. Australian Parrots: Their Habits in the Field and Aviary. Angus & Robertson Limited.
[CC10] Checklist Committee (OSNZ). 2010. Checklist of the Birds of New Zealand, Norfolk and Macquarie Islands, and the Ross Dependency, Antarctica 4th ed. Ornithological Society of New Zealand and Te Papa Press: Wellington.
[M03] Morcombe, M. 2003. Field Guide to Australian Birds 2nd ed. Steve Parish Publishing.
[OMC87] Ovenden, J. R., A. G. Mackinlay & R. H. Crozier. 1987. Systematics and mitochondrial genome evolution of Australian rosellas (Aves: Platycercidae). Molecular Biology and Evolution 4 (5): 526–543.
[RN72] Rutgers, A., & K. A. Norris (eds.) 1972. Encyclopaedia of Aviculture vol. 2. Blandford Press: London.
Saiki, R. K., D. H. Gelfand, S. Stoffel, S. J. Scharf, R. Higuchi, G. T. Horm, K. B. Mullis & H. A. Ehrlich. 1988. Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science 239: 487–491.
[S13] Sarasin, F. 1913. Die Vögel Neu-Caledoniens und der Loyalty-Inseln. In: Sarasin, F., & J. Roux (eds) Nova Caledonia: Forschungen in Neu-Caledonian und auf den Loyalty-Inseln. A. Zoologie vol. 1 pt 1 pp. 1–78, pls 1–3. C. W. Kreidels Verlag: Wiesbaden.
[S66] Sclater, P. L. 1866. Remarks on recent additions to the Society’s menagerie. Proceedings of the Zoological Society of London 1866: 203.
[SJ85] Storr, G. M., & R. E. Johnstone. 1985. Field Guide to the Birds of Western Australia 2nd ed. Western Australian Museum: Perth (Australia).
[WS48] Whittell, H. M., & D. L. Serventy. 1948. A systematic list of the birds of Western Australia. Public Library, Museum and Art Gallery of Western Australia, Special Publication 1: 1–126.