Proposal (293) to South American Classification Committee
Recognize Donacobius in its own family, Donacobiidae
The monotypic genus Donacobius has been alternatively regarded as a member of the following oscine passerine families: Turdidae, Troglodytidae, and Mimidae (Bonaparte 1850, Pelzeln 1870, Ridgway 1907, Davis and Miller 1960). More recently, Donacobius was transferred from the Mimidae to the Troglodytidae based on several morphological, behavioral, and ecological similarities shared with species of the latter group (Miller 1964, AOU 1983, Kiltie and Fitzpatrick 1984, Wetmore et al. 1984).
Barker (2004) presented a first phylogenetic hypothesis for the Troglodytidae based on molecular characters, and to investigate the taxonomic affinities of Donacobius under a phylogenetic framework. The phylogenies presented by Barker (2004) were based on both nuclear and mitochondrial DNA sequences, and consistently indicated with very strong statistical support, that Donacobius was neither nested in the Troglodytidae nor grouped anywhere near the sampled genera of Mimidae or Turdidae. In fact, Donacobius could not even be parsimoniously or probabilistically placed as the sister group of the Troglodytidae; instead, it belonged with strong support in a clade with the Old World passerine genera Zosterops (Zosteropidae) and Prinia (Sylviidae). More recently Alström et al. (2006), also based on nuclear and mitochondrial DNA sequences, and with a thorough sampling of the entire superfamily Sylvioidea, confirmed with strong statistical support that Donacobius is indeed nested in the Sylvioidea, even though its phylogenetic affinities within this group could not be fully resolved.
All the phylogenetic evidence available so far is unable to place Donacobius in any of the currently recognized families of Neotropical oscine birds, rather suggesting that it might be a Neotropical relict of the extensive sylvioid passerine radiation that has taken place predominantly in Africa and Eurasia since the Eocene (Barker 2004, Barker et al. 2004, Alström et al. 2006). Giving the apparent evolutionary uniqueness of Donacobius as revealed by two recent and independent studies with adequate and complementary taxon sampling regimes, Aleixo & Pacheco (2007) proposed a new family for this monotypic genus: Donacobiidae.
Aleixo, A. e J. F. Pacheco (2006) A family name for the monotypic oscine passerine genus Donacobius. Rev. Bras. Orn. 14 (2): 172-173.
Alström, P., P. G. P. Ericson, U. Olsson, and P. Sundberg. (2006). Phylogeny and classification of the avian superfamily Sylvioidea. Molecular Phylogenetics and Evolution 38(2): 381-397.
AOU (1983) Check-list of North American birds. 6th ed. Washington, D. C.: American Ornithologists' Union.
Barker, F. K. (2004) Monophyly and relationships of wrens (Aves: Troglodytidae): a congruence analysis of heterogeneous mitochondrial and nuclear DNA sequence data. Molecular Phylogenetics and Evolution 32(2): 486-504.
Barker, F. K., A. Cibois, P. Schikler, J. Feinstein, and J. Cracraft (2004) Phylogeny and diversification of the largest avian radiation. Proc. Natl. Acad. Sci. USA 101(30): 11040-11045.
Bonaparte, C. L. (1850) Conspectus generum avium, Tom. 1. Lugduni Batavorum: E. J. Brill.
Davis, J. and A. H. Miller (1960) Family Mimidae. Pp. 440-458. In: Mayr, E., e J. C Greenway, Jr. (eds.) Check-list of Birds of the World, a continuation of the work of James L. Peters. Vol. IX. Cambridge, Massachusetts: Museum of Comparative Zoology.
Kiltie, R. A. and J. W. Fitzpatrick (1984) Reproduction and social organization of the Black-capped Donacobius (Donacobius atricapillus) in southeastern Peru. Auk 101(4): 804-811.
Miller, A. H. (1964) Mockingbird. Pp. 479-481. In: A. L. Thompson (ed.) A new dictionary of birds. London: Nelson.
Pelzeln, A, v. (1870) Zur Ornithologie Brasiliens: Resultate von J. Natterers Reisen in den Jahren 1817-35. Wien: Druck und Verlag von Pichler's Witwe & Sohn.
Ridgway, R. (1907) The birds of North and Middle America. Part IV, Families Turdidae, Zeledoniidae, Mimidae, Sturnidae, Ploceidae, Alaudidae, Oxyruncidae, Tyrannidae, Pipridae, Cotingidae. Washington, D. C.: Government printing office.
Wetmore, A., R. F. Pasquier and S. L. Olson (1984) The birds of Republic of Panama, part 4. Washington. D. C. Smithsonian Institution (Misc. Coll. 150).
Alexandre Aleixo & J. F. Pacheco, July 2007
Comments from Robbins: "NO. Given that the Alström data set seems to indicate that Donacobius is embedded within the Sylvioidea, I think it might be premature to create a new family for this enigmatic taxon. Why not simply keep it where we have it, i.e., "incertae sedis" between Troglodytidae and Polioptilidae? Hence, I vote "no" on that proposal."
Comments from Thomas Donegan: "Being an old world person with field experience of Donacobius and various of the old world taxa now considered related to it, I have an interest in this proposal and some observations that may be of interest. It should be borne in mind that the status of the family Sylviidae (referred to specifically in both the Donacobiidae paper and above proposal) is a controversial one. The assertion that Prinia is a Sylviidae is far from certain. Various issues arise because the Garden Warbler Sylvia borin (the type species of the genus Sylvia, which is the type genus of the Sylviidae) is more closely related to some babblers (Timaliidae) than to most of the other old world warblers, which were for many decades treated within the Sylviidae. In any event, the genus Prinia, which Barker found possibly to be related to Donacobius based on limited sampling of old world genera, has sometimes been assigned its own family (Priniidae) in the past. On the Barker analysis, ranking Donacobius as a family would have been consistent with those who recognise Zosteropidae and Priniidae. The Alström paper, discussed further below, which includes more extensive taxon sampling, makes this rather a footnote point, however, given that Donacobius is apparently more closely related to other Sylvioidea families.
"Alström et al. (2006) proposed that Sylvia and related warblers, prinias and babblers be subsumed into the greater family Timaliidae (sinking Sylviidae, Priniidae and Zosteropidae). They found Donacobius to be more closely related to the Megaluridae (old world grassbirds and grasshopper warblers) or Acrocephalidae (old world reed warblers and their allies) than to any greater Timaliidae taxon. Acrocephalidae and Megaluridae are both recently resurrected/new families. Donacobius is not embedded within Acrocephalidae or Megaluridae - but may be embedded if an expanded single family is used for all three (i.e. if Acrocephalidae and Megaluridae are merged with Donacobius).
"Turning to matters of what a family "ought" to be, it is of note that prior to the molecular studies referred to above, no-one had dreamed of placing Donacobius with the grasshopper and reed warblers, given morphological differences. There are some interesting parallels between the alarm call of Donacobius and the grating songs of some Acrocephalus (and I have not looked into osteological or nesting data). However, having seen representatives of all three groups in the hand, I find it quite surprising that they could be closely related to each other. Donacobius' plumage colours/patterns and liquid, wren-like territorial song - as well as its large size - are strikingly different to those of its dingy-brown, often migratory, unmusical and skulking apparent relatives. In summary, recognition of Donacobiidae is consistent with my concept of what a family ought to be (assuming it is related to these Sylvioids). For those not familiar with all these old world families, there is a tree available online showing what some of them look like, with a helpful short discussion of where things currently stand on high-level sylvioid systematics:
"The other viable "straw man" option available to SACC, in addition to doing nothing, is to place Donacobius in a greater Acrocephalidae or Megaluridae (whichever is senior or otherwise preferred for the expanded group). I am not aware of Old World committees proposing to merge those two families. The fact that Donacobius is so different from the other two proposed families is itself a good reason to recognise each of them.
"In conclusion, Aleixo & Pacheco's proposal and paper could have discussed the old world taxonomy in more detail and made a more convincing argument. Further, the phylogeny and family limits within Sylvioid birds remain a complex matter that will doubtless be subject to further change. I therefore empathise with Mark Robbins' concerns. However, now that a family has been described for it, the allocation of Donacobius to its own family, rather than to a state of limbo, seems like an inherently sensible idea. Such an approach is consistent with published phylogenies and with subjective considerations of inter-family differences. Finally, I note that the Brazil rarities committee has accepted this change in their checklist, as did Salaman et al. (2007) in a recent Colombia checklist which otherwise followed SACC fairly religiously. A number of other online checklists and resources also recognise the family."
Comments from Cadena: "YES. The phylogeny resulting from combined analysis of mitochondrial (cytb) and nuclear (myoglobin intron 2) in Alström et al. (their figure 3) shows that Donacobius is sister to the family Megaluridae and the clade formed by Megaluridae-Donacobius is sister to the family Acrocephalidae, and these relationships are all well-supported. Although taxon sampling in this study is not great within each of these families, I think the evidence is sufficient to make the proposed change related to Donacobius. As Mark said, Donacobius is indeed nested within Sylvioidea, but I don't see this as something that should prevent us from creating the family Donacobiidae considering that Sylvioidea is already a large assembly of families (including Alaudidae, Pycnonotidae, Hirundinidae, Cettiidae, Aegithalidae, Phylloscopidae, Timaliidae, Acrocephalidae, Megaluridae, and Cisticolidae)."
Comments from Remsen: "NO. I appreciate all the good points made in the proposal and by Thomas and Daniel. Nonetheless, I agree with Mark that this is premature. I suspect that further taxon-sampling is needed before we can make a truly objective decision on this one. What worries me about moving Donacobius to monotypic family rank is that the track record of such New World "families" with Old World sister groups is that they are first placed incorrectly in the New World family that most closely approaches their morphotype, then elevated to family rank once their true affinities are revealed, and finally subsumed in their Old World sister family. Examples of that progression are Chamaea, Psaltriparus, Auriparus, and, likely, Sapayoa. Peucedramus, currently in the monotypic family phase, may be an exception, but one could predict that denser taxon-sampling and broader comparisons might eventually reveal that it is a member of an Old World family. So, until the "dust settles", I prefer Incertae Sedis."
Comments from Stotz: "NO. I don't like incertae sedis, but it does seem to be consistent with what we know about Donacobius - that we don't really know who it is related to. There are still big questions in the group they are part of, and I think that recognizing that uncertainty is the best thing we can do right now."
Comments from Stiles: "YES. I agree with Thomas and Daniel on this one: evidence is sufficient to place Donacobius in its own family. Unlike Chamaea, Sapayoa or Psaltriparus, it is not even remotely "like" any of its putative OW relatives - and looking through what literature I have on possible sylvioid relatives, I can´t see any obvious possibilities there, either, such that I doubt whether better taxon sampling will change things appreciably. This case is not comparable to those of, say, Sapayoa (which looks and acts like a broadbill) or the North American birds that now belong with other OW groups (containing rather similar species) making these Holarctic rather than strictly Palearctic - not particularly surprising. Sampling in the sylvioids has been sufficient to identify the relatives of Donacobius (not all that near, and as mentioned above I fail to see any other obvious candidates); being a sedentary tropical form it has likely been isolated for a pretty long time, to judge by the branch lengths to it. In short, I question whether the "track records" of other NW monotypic families are relevant here."
Comments from Jaramillo: "YES - I don't have anything new to say here other than I am in agreement with the various points made by Stiles, Cadena and Donegan. I don't like incertae sedis in general, and I must admit that I think that we overuse it. There is nothing wrong in my mind with going with the best available data, and adjusting the taxonomy as new and better data arrive. In this case, the data puts Donacobius in the Sylvioidea, various families fit within that group, and none is even remotely similar to Donacobius. Giving Donacobius its own family seems perfectly reasonable given the available data, and I am more comfortable with this arrangement (even if it is to change in the future. maybe), than putting it on hold."
Comments from Nores: "YES. Los análisis genéticos de Barker y Alström et al. muestran que la especie está más relacionada con familias de Sylvioidea del viejo mundo que de América, por lo cual la especie sería un relicto de la expansión de los silvidos como ha sido señalado por Barker y Alström et al. Ante esta situación, y debido al largo tiempo transcurrido de aislación y el sedentarismo de la especie, parece casi imposible que la misma pueda pertenecer a algunas de la familias de "Old world warblers" y por lo tanto debe asignarse a una nueva familia."
Comments from Pacheco: "YES. As co-author of proposal and published note, I reaffirm my favorable vote."
Comments from Zimmer: "YES. Published analyses seem to clearly place Donacobius within Sylvioidea, but don't support a particularly close fit to any of the many families within that broad group. It really seems like a stretch to think of Donacobius as nested within its purported sister groups Acrocephalidae and Megaluridae -- there just isn't a member of those groups that seems even remotely similar vocally or morphologically. Given that, I doubt that denser taxon-sampling is going to break this open. As Thomas Donegan alludes, this becomes partly a philosophical case of what we think a family "ought" to be. In this case, I think that Donacobius is sufficiently distinct, and probably isolated in time from its Old World relatives, to be treated as a separate family. And, as Alvaro asserts, I also see nothing wrong in going with the best available data. I don't have a problem with using incertae sedis in cases where available data don't offer a lot of direction, or where there are truly conflicting data sets. But anything that moves us forward is welcome, even if future tweaking is needed."
Additional Comments from Cadena: "A paper by Johansson et al. recently published online in Molecular Phylogenetics and Evolution (see reference below, I can provide a pdf), adds some more information about the affinities of Donacobius atricapillus within the Sylvioidea. This study is based on sequences of three nuclear introns (total 2315 bp) and although it is still not ideal, its taxon sampling is in some ways more complete than that in the Alström et al. paper that has been discussed in the context of this proposal. Here is the authors' summary of their results regarding Donacobius:
'Megaluridae, Berneridae and the Black-capped Donacobius form a strongly supported clade, but the inter-relationships between the three groups differs with different analytical methods. The Bayesian analysis as well as the MP analysis places the Black-capped Donacobius with the Malagasy Bernieridae (PP = 0.85, MP bootstrap = 56%), whereas the ML analysis places the Donacobius with Megaluridae (ML bootstrap = 45%). Neither of these alternate topologies are strongly support, suggesting that Bernieridae, Megaluridae and the Donacobius form a polytomy.'
U.S., Fjeldså, J., Bowie, R.C.K., Phylogenetic relationships within Passerida
(Aves: Passeriformes): a review and a new molecular phylogeny based on three
nuclear intron markers, Molecular Phylogenetics and Evolution (2008), doi:
"I would add that the Megaluridae-Berneridae-Donacobius clade is sister to the Acrocephalidae, with decent support in the combined analysis.
"In sum, although it does not resolve its relationships definitively, I think this study confirms the close relationship of Donacobius with Old World families and at the same time, it shows that this species is a rather long branch with no obvious close relatives. In my mind, this supports strongly the recognition of the family Donacobiidae. I am convinced we have enough information to avoid using the uncomfortable incertae sedis "rank" for Donacobius."
Comments from Schulenberg: YES. I don't like "incertae sedis," and I don't like dealing the on-going (but fascinating) rearrangement of the Old World warblers, babblers, and other taxa. As Daniel points out, however, I think we actually have a pretty good idea of what the relationships of Donacobius are. The main issue then is whether to recognize a larger number of smaller families (including Donacobiidae) in this radiation, or whether to subsume many of these into fewer, larger families. Ultimately I think that's not really our decision to make. To whatever extent that issue is decided, it will be done by the ornithologists who are the most affected by it (those in the Old World). In the meantime, my sense is that the use of a larger number of smaller families is more current in the literature on these clades, and so the recognition of Donacobiidae is consistent with that.
"On a personal note, it is totally mind-blowing to me that, out of all the many many Old World clades to which Donacobius could be related, it turns out that it might be sister to a group of Malagasy endemics. Who woulda thunk it?"
Additional comments from Remsen: "This proposal has now passed, but I want to go on record in stating that this is, in my opinion, the first mistake in judgment that we have made. [That's not bad, considering we've now acted on something like 350 proposals.]
"Passage of this proposal suggests that any time we cannot resolve relationships among groups of widely separated genera that we should elevate them all to family rank. A rough equivalent would be to re-elevate New World Chamaea to family rank and then elevate all the monophyletic groups of timallid genera within Timaliidae also to their own family rank (assuming that Chamaea is not the sister to all other timaliids). Further, the uncertain position of Donacobius is currently based on limited gene and taxon sampling. Having "watched" groups of genera in the Trochilidae and Furnariidae change their "relationships" with addition of new gene and taxon samples, I have become increasingly conservative about making any major decisions on classification until more thorough analyses are completed.
"Gary questioned whether the track record of North American monotypic families is relevant and noted that Donacobius is "unlike" Old World warblers whereas Chamaea, Auriparus, and Sapayoa are "like" their Old world relatives. I point out that those "like" observations were largely post-hoc. For example, none of us had a clue that Sapayoa was a broadbill, and I still think it is an oddball in that group. By extrapolation, I predict that if we were more familiar with some of the tropical Asian Old World "warblers", we might not be so uncomfortable with Donacobius as "like" them. Just roaming through some of the HBW plates and its accounts of the Megalurinae, and some of the other genera proposed to be in the Megaluridae, I see lots of heterogeneity, lots of long-tailed marsh-dwellers, some fairly large species, some with large and complex voices, some with flank-barring, some with conspicuous white tail-markings, and so on, albeit, obviously, nothing that recalls Donacobius. However, in Johansson et al. (2008), their Timaliidae includes Sylvia, Garrulax, Paradoxornis, and Stachyris, as well as other genera with which I'm not familiar. I defy anyone to see anything phenotypic among that heterogeneous group that would suggest a closer relationship among them than that between Donacobius and the megalurid-acrocephalid warbler group.
"At some point, I may go through the Johansson et al. paper to see if all three of their nuclear genes show the same phylogenetic signal so that we can be sure that we're dealing with more than just a single gene tree in that portion of the tree.
"Finally, that some of the Johansson et al. data show that Donacobius is closest to Malagasy warblers is such a remarkable and unique biogeographic result that additional analyses should be required to confirm this. In fact, their ML analysis places Donacobius with Megaluridae, a more sensible result in terms of biogeographic patterns (in that at least there are others with such a pattern, namely Tropical Asia+New World). I'm not sure why Johansson et al. did not just merge their Megaluridae (which includes Malagasy Dromaeocercus) with Donacobius and their "Bernieridae"; as they noted, the three together form a monophyletic group, but within that group we have a polytomy. Trying to define family-level taxa with just nine species in eight genera sampled from a much richer radiation (e.g. HBW's Megalurinae alone contains 20 species in 8 genera, only 1 of which was sampled!) seems beyond dangerous. Just in terms of branch lengths, such a broader family would be comparable to the even more phenotypically heterogeneous Timaliidae. One could fire back with ... "yeah, but Donacobius is deep in the Neotropics, a long way from the Indomalayan region", but to this I would respond that if distance alone drove classification, then Chamaea and Sapayoa should also be in their own families also. [Note, by the way, that Johansson et al. did not explicitly propose family rank for Donacobius, even though their classification would require them to treat it as a family. They also were evidently unaware of Aleixo and Pacheco (2006), even though it was published in a well-known ornithological journal.] A further point is that unless I've missed the diagnosis, "Bernieridae" does not meet Code requirements as a group name (in contrast to Donacobiidae: Aleixo & Pacheco 2006).
"A redux of the above wordy paragraph is that if Johansson et al. had not declared the Megaluridae and "Bernieridae" separate families, we would be dealing with a proposal to place Donacobius in Megaluridae.
"In sum, I couldn't agree more with Mark's more succinct comment "I think it might be premature to create a new family for this enigmatic taxon." Retention in Incertae Sedis until the phylogeny of this under-sampled group of birds is better resolved would seem wiser than creating a monotypic family that could easily turn out to be embedded with one of two very poorly sampled "families" in Johansson et al."