Proposal (798) to South American Classification Committee

Split the storm-petrels (Hydrobatidae) into two families

Background: The relationships of the storm-petrels are complicated, and major revisions of this group are warranted. Currently treated as a single family by the AOS Checklist, the storm-petrels have sometimes been divided into two subfamilies, the northern (Hydrobatinae) and southern storm-petrels (Oceanitinae), with most Oceanitinae breeding in the Southern Hemisphere, and many Hydrobatinae breeding in the Northern Hemisphere (Dickinson and Remsen 2013).

New Information: Recently, the monophyly of the storm-petrels has come into question. Although the exact relationships of the storm-petrels, both with respect to each other and the other Procellariiformes, has not been fully resolved, the two storm-petrel subfamilies have nonetheless been consistently been found to not be sister taxa (Kennedy and Page 2002, Hackett et al. 2008, Prum et al. 2015, Reddy et al. 2017). An early supertree analysis from Kennedy and Page (2002) was the first to suggest that the storm-petrels did not represent a monophyletic group. Their supertree, largely based on mtDNA sequence data, found that the northern storm-petrels (Hydrobatinae) were sister to the rest of the tubenoses, including the southern storm-petrels (Oceanitinae). The Oceanitinae were found to be sister to the petrels and shearwaters (Procellariidae) (Kennedy and Page 2002).

In more recent studies that investigate the deeper relationships of the avian tree of life, the storm-petrels have again been found to be paraphyletic. Although the different studies that have included the two groups of storm-petrels have not agreed on the exact placement within the Procellariiformes, they have consistently been found to be paraphyletic. Hackett et al. (2008) found a relationship opposite the findings of Kennedy and Page (2002), with Oceanites of Oceanitinae sister to the rest of Procellariiformes, and Oceanodroma of Hydrobatinae sister to the petrels and shearwaters (Procellariidae). A third hypothesis for relationships among Procellariiformes was proposed by both Prum et al. (2015) and Reddy et al. (2017), who found Hydrobatinae to be sister to Procellariidae, and Oceanitinae sister to the clade of Hydrobatinae + Procellariidae.

Recommendation: Despite the conflicting hypotheses for relationships of the main groups of tubenoses, all recent analyses that include representatives of both northern and southern storm-petrels consistently find that they are not monophyletic. Therefore, I recommend that they be treated as separate families. The northern storm-petrels should retain the name Hydrobatidae, and the southern storm-petrels should be named Oceanitidae, based on the existing subfamily name. Although there has been no consensus of the exact placement of the storm-petrel groups, I recommend adopting a linear sequence following the relationships in Prum et al. (2015) and Reddy et al. (2017). Many others have taken the approach of splitting the two storm-petrel families, including the Howard and Moore Checklist (Dickinson and Remsen 2013) and the HBW/Birdlife Checklist (del Hoyo and Collar 2014). The linear sequence adopted by other authorities has differed. For example, Dickinson and Remsen (2013) followed the relationships in Hackett et al. (2008) and placing Oceanitidae first in the linear sequence, followed by Diomedeidae, Hydrobatidae, and Procellariidae. Del Hoyo and Collar (2014), in contrast, placed Oceanitidae first in the linear sequence, followed by Hydrobatidae, Diomedeidae, and finally Procellariidae.

Proposed Linear Sequence (family-level):

PROCELLARIIFORMES

Diomedeidae (Albatrosses)

Oceanitidae (Southern Storm-Petrels)

Hydrobatidae (Northern Storm-Petrels)

Procellariidae (Petrels and Shearwaters)

Literature Cited:

Del Hoyo, J. and N. J. Collar (2014). Illustrated Checklist of the Birds of the World, Volume 1: Non-Passerines. Lynx Edicions and Birdlife International.

Dickinson, E. C. and J. V. Remsen Jr. (eds.) (2013). The Howard and Moore Complete Checklist of the Birds of the World. 4^th Edition, Volume 1. Aves Press, Eastbourne, U. K.

Hackett, S. J., R. T. Kimball, S. Reddy, R. C. K. Bowie, E. L. Braun, M. J. Braun, J. L. Chojnowski, W. A. Cox, K. Han, J. Harshman, C. J. Huddleston, B. D. Marks, K. J. Miglia, W. S. Moore, F. H. Sheldon, D. W. Steadman, C. C. Witt, and T. Yuri (2008). A phylogenetic study of birds reveals their evolutionary history. Science. 320 1763-1768.

Kennedy, M. and R. D. M. Page (2002). Seabird supertrees: combining partial estimates of Procellariiform phylogeny. The Auk. 119(1) 88-108.

Prum, R. O., J. S. Berv, A. Dornburg, D. J. Field, J. P. Townsend, E. M. Lemmon, and A. R. Lemmon (2015). A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature. 526 569-573.

Reddy, S., R. T. Kimball, A. Pandey, P. A. Hosner, M. J. Braun, S. J. Hackett, K. Han, J. Harshman, C. J. Huddleston, S. Kingston, B. D. Marks, K. J. Miglia, W. S. Moore, F. H. Sheldon, D. W. Steadman, C. C. Witt, T. Yuri, and E. J. Braun (2017). Why do phylogenomic data sets yield conflicting trees? Data type influences the avian tree of life more than taxon sampling. Systematic Biology. 66(4) 857-879.

Shawn M. Billerman, June 2018

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Comments from NACC members (provided by Remsen):

Yes. Studies using either dense taxonomic sampling or dense character sampling consistently show lack of monophyly.

YES (tentative). The fact that multiple independent data sets corroborate the lack of a sister relationship between northern and southern storm-petrels suggests to me that this split is warranted. I may change my mind but would like to talk with Rauri about this to see if he has any relevant data from the VertLife project.

NO. I agree with Van about being cautious here, given the morphological similarity between the northern and southern storm-petrels and the dissimilarity between these two taxa and other tubenoses. I think it would be best to first recognize the two subfamilies (we do not do so) and add in Notes that these may not be sister taxa.

YES, for reasons stated in the proposal. Again, we might wait a long time for further studies that may or may not help resolve the uncertain placement, and the fact that all these studies at least show the two groups to be highly divergent has got to count for something.

Remsen: NO. I'd like to hear what those familiar with problems with deep branches in tree topology say about this before voting yes. I appreciate the excellent point that there are no current genetic data that support the two taxa as sisters. I also recognize that the two groups ought to be treated as subfamilies, as they have been in other classifications based on morphology alone. Nonetheless, given the dramatic conflict among current data sets, is it not possible that additional, better data might also show that they indeed are sisters? Because of the remarkable phenotypic similarity of the two storm-petrel taxa compared to Procellariidae (with genera as dramatically different as Macronectes, Bulweria, and Pelecanoides, for example), I think we should be extra cautious on this one.

NO.I am concerned that the genetic studies seem to be all over the map in terms of what the relationships between the major groups are. I would favor as other have suggested, splitting the two groups into subfamilies to await more clarity.

YES. I have a feeling that eventually more data may show that the two Storm-Petrel families are sisters, but who knows when that will be. So I vote yes to keep up with other current taxonomies.

YES. A split here seems warranted, even if the lineages remain incertae sedis.

Comments solicited from Carl Oliveros by Remsen:

“On deep branches: They are indeed deep branches. However, what concerns me more in general are really short interbranches between deep branches which causes gene tree discordance as a result of incomplete lineage sorting. Interbranches in the clade containing Diomedea, Oceanites, Oceanodroma, and Puffinus + Pelecanoides in our ML tree are kinda short. (These short interbranches are usually longer than they should be in dated trees, unfortunately). Coalescent-based species tree methods take into consideration gene tree discordance resulting from short-interbranch scenarios. I have run only one coalescent-based method so far on our dataset and it still recovers the storm-petrels paraphyletic. So in my opinion, it is very unlikely that Oceanitinae and Hydrobatinae are sister taxa.  

“On having better data to tease these relationships apart: I consider Prum et al., which uses hundreds of genes, superior to the supertrees and single gene studies that derive most of the signal from mtDNA. Prum and our unpublished data provide independent evidence from genome-wide loci of the non-sister relationship between Oceanitinae and Hydrobatinae.

“By the way, the Kennedy & Page sister relationship between Oceanitinae and Procellariidae and Hackett topology of Oceanites being sister to the rest of Procellariiformes were not well-supported. So these two supposed alternative relationships should not be taken as conflicts. If considered as polytomies (as they should), they actually do not conflict with the Prum topology.”

Comments from Remsen: “YES. (Carl, by the way, is the post-doc working in Brant Faircloth’s lab here at LSU and working on a new phylogeny of birds of the world). Carl’s comments alleviate my concerns expressed in my NACC comments above.”

Comments from Jaramillo: “YES – Although peculiar, it is about as surprising as the diving-petrels being Procellarids. Seabirds have some color patterns that recur, such as “M” markings on the back, and these come up in various unrelated forms. Being small and dark, or small and dark with white rump and pale wing panel could all be elements of a restricted palette of patterns and colors, as well as convergence. The foraging styles and long legs of Oceanitidae are quite distinct and odd in some species, and quite unlike Hydrobatidae.

“Note that this division goes farther back to Nunn and Stanley 1998 (Body size effects and rates of cytochrome b evolution in tube-nosed seabirds. Molecular Biology and Evolution 15: 1360–1371).”

Comments from Claramunt: “YES. I think we have to surrender to the molecular evidence… for now.”

Comments from Pacheco: “YES. From the well-supported view of Carl Oliveros.”

Comments from Robbins: “YES, particularly based on Carl Oliveros’s comments.”

Comments from Stotz: “YES. I was not completely convinced by this when we considered it for North America, but the comments from Oliveros make me more confident of this change.”