Proposal (186) to South American Classification Committee

Merge Limnoctites into Cranioleuca

Effect on South American CL: We currently treat Limnoctites as a monotypic genus. This proposal would merge it into Cranioleuca.

Background: Limnoctites rectirostris and Limnornis curvirostris have usually been considered closely related, marsh-dwelling species, but classified in separate monotypic genera; see summary in Olson et al. (2005). Vaurie (1980) and Sibley & Monroe (1990), however, merged Limnoctites into Limnornis based on overall similarity, but see Ridgely & Tudor (1994) and Remsen (2003) for rationale for retaining them as separate genera; Remsen (2003) questioned their close relationship because of differences in tail structure, nest composition, and egg color.

New information: Olson et al. (2005) have shown that Limnornis and Limnoctites are not particularly closely related, with Limnoctites embedded in Cranioleuca, and with Limnornis closely related to Phleocryptes. They analyzed about 2100 bp of 3 genes to produce a phylogenetic hypothesis for the relationships of these two genera with respect to 19 other furnariid genera. Their results show not only that Limnornis and Limnoctites are not sisters but also that they are only distantly related. Limnornis is sister to Phleocryptes (among the genera sampled), whereas Limnoctites is embedded within Cranioleuca (3 species sampled; closest of these three was C. sulphurifera). Bayesian posterior probabilities for these relationships were all 100%.

They also summarized information on nest structure, tail morphology, egg color, and voice that are consistent with the placement of Limnoctites within Cranioleuca. Egg color is also consistent with a relationship between Limnornis and Phleocryptes: these two are the only two genera known to have greenish blue eggs in the Furnariidae.

Analysis: Our linear sequence already has Limnornis and Phleocryptes adjacent, so that part requires no change.

The combination of strongly supported genetic data with phenotypic data consistent with the genetic results means, in my view, that we have only two options with respect to Limnoctites. One would be to move Limnoctites in the linear sequence adjacent to Cranioleuca. The other, which is the one I favor, is to merge Limnoctites into Cranioleuca. To maintain Limnoctites as a monotypic genus would make our Cranioleuca a paraphyletic genus according to the genetic data. Other than minor plumage and morphological characters, Limnoctites has no unique phenotypic characters that I know of; an extra-long bill can hardly be regarded as a feature that diagnoses a genus. Given the phenotypic heterogeneity within the currently defined Cranioleuca, placement of rectirostris within it seems reasonable.

Recommendation: Merger of Limnoctites into Cranioleuca is supported by genetic and phenotypic data, and I see no reason not to recommend a YES on this one.

Lit Cit:

OLSON, S. L., M. IRESTEDT, P. G. P. ERICSON, AND J. FJELDSÅ. 2005. Independent evolution of two Darwinian marsh-dwelling ovenbirds (Furnariidae: Limnornis, Limnoctites). Ornitologia Neotropical 16: 347-359. (see this for other references)

Van Remsen, October 2005

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Comments from Jaramillo: "YES - However, once a more detailed study involving more species of Cranioleuca is done, my guess is that Cranioleuca may need revision. Just a guess, no data."

Comments from Zimmer: "YES". The molecular data are convincing, and consistent with all other data sets, including I might add, vocal considerations. Both song and calls of Limnoctites are consistent with its placement in Cranioleuca, and at odds with an assumption of close relationship with Limnornis. The only fly-in-the-ointment is that long bill, which, as Van points out, is a pretty plastic character with respect to selective pressures on a species in a specialized environment."

Comments from Robbins: "YES. The molecular data of Olson et al. (2005) demonstrate that Limnoctites should be merged into Cranioleuca. It was also good to know (via K. Zimmer) that vocalizations support these conclusions."

Comments from Santiago Claramunt:

"1) The committee should not act precipitously on this decision. As Olson et al. point out, "It would be premature to make any taxonomic or nomenclatural recommendations until the systematics of the entire genus Cranioleuca has been undertaken." Taxon sampling in Olson et al is not good enough to define what are closest relatives of Limnoctites.

"2) More complete molecular phylogenies will be produced soon that will provide a better picture of the relationships within the "Cranioleuca group".

"3) Limnoctites and C. sulphurifera (and may be some other marsh dwelling "cranioleucas") may turn out not to belong to the "core" Cranioleuca (a well-defined group of arboreal species with shared habits and plumage patterns). Therefore, merging Limnoctites into Cranioleuca might aggravate the already suspected paraphyly/polyphyly of Cranioleuca.

"4) Limnoctites is very distinctive phenotypically. It has a plumage pattern and a bill not shown by any other Cranioleuca. Note that the bill is not just longer, is nearly twice (Fig.1*) as long as the bill of any Cranioleuca (otherwise very uniform in this respect). In addition, the cranium of Limnoctites is extremely flat (probably an adaptation for looking for insects between the leaves of Eryngium), whereas the craniums of all Cranioleuca specimen I've examined are "normal". Finally, my morphometric data (Fig. 2**) shows that both Limnornis and C. sulphurifera are well outside the range of variation of the remaining Cranioleuca. Thus, to merge Limnoctites into Cranioleuca will make an already diverse genus, exceedingly (and probably artificially) heterogeneous."

[* -- figure won't display in this program but shows clearly that the bill length of rectirostris is dramatically longer- V. Remsen]

[** -- figure won't display in this program but shows clearly that rectirostris and sulphurifera both lie far outside the cloud of points represented by other Cranioleuca, and that they are about as far apart from each other as either is from the main cloud -- V. Remsen]

Comments from Nores: "NO, aunque con fundamentos menos sólidos que los de Olson et al. "Poner NO en esta propuesta es sobre todo para hacer notar algo que ya viene siendo casi una regla en el Comité: si hay estudios moleculares casi no vale la pena hacer análisis morfológicos, de comportamiento o biogeográficos para contestar una propuesta. Generalmente se acepta el cambio sin mayores comentarios, a tal punto que una posibilidad podría ser que en los casos en que existan estudios moleculares publicados en journals internacionales se incorporen directamente a la lista, sin hacer propuestas. Por ejemplo, nadie mencionó en este caso el trabajo de Zyskowski and Prum (1999) que ponen juntos a Limnornis, Limnoctites y Phleocryptes en base a la estructura del nido, aunque como fue señalado por Olson et al. el nido de Limnoctites no tiene alero. Olson et al. mencionan también que el color verde azulado de los huevos de Phleocryptes y Limnornis, sin excepción, son únicos entre los furnáridos y muestra a estas dos especies como un "sister-group". Sin embargo, Upucerthia certhioides pone también huevos de ese color.

"Olson et al., para apoyar su hipótesis, mencionan que Ricci y Ricci (1984) señalaron la similitud en apariencia de Limnoctites con Cranioleuca sulphurifera. Sin embargo, esta es una información sesgada ya que Ricci y Ricci mencionan que cuando cierra la cola se aparece a Cranioleuca sulphurifera, pero cuando la abre recuerda a Limnornis.

"Siguiendo con esta propuesta, yo no veo que la inclusión de Limnoctites en Cranioleuca esté soportada por datos fenotípicos o de comportamiento. Limnoctites es para mí tan diferente de Cranioleuca, que resulta muy difícil pensar que puedan ser congenéricas. Por ejemplo, el ave abre y cierra la cola alternativamente y muestra una actitud "nerviosa", cosa que no hacen las especies de Cranioleuca, pero si Limnornis. Además, se agrega su largo pico que la asemeja más a Limnornis que a Cranioleuca. También pienso que tienen importancia aspectos biogeográfico. En mi tesis doctoral yo sugerí que Limnornis y Limnoctites se habrían separado durante un ascenso del nivel del mar que cubrió gran parte de la Mesopotamia argentina y dejó un número de penínsulas donde se habrían diferenciado también especies de Sporophila y Pseudoleistes. Note que la zona de superposición de las dos especies es justamente esa área y no hay actualmente algo que explique cómo se podrían haber separado. Por supuesto que también sería posible (o más posible) que haya habido una evolución independiente de las dos especies como sugieren Olson et al. 

"Si nosotros fuéramos a aceptar el árbol presentado por Olson et al. deberíamos poner en nuestra lista base a Geositta y Sclerurus scansor juntos, separados del resto de los furnáridos por los cuatro dendrocoláptidos: Dendrocincla, Sittasomus, Drymornis, Xiphocolaptes.

"Yo sugiero mantener el género Limnoctites y poner la especie adyacente a Cranioleuca sulphurifera. También aparece como posible que Limnoctites y Cranioleuca sulphurifera formen un grupo diferente de las otras especies de Cranioleuca."

Comments from Pacheco: "NO. Considero prematuro acatar tal sugestão, sendo muito oportuna a substanciosa msg de Santiago Claramunt. Minha opinião é a mesma de Giovanni Maurício (in litt. 8 fev 2006): Entre o material considerado no estudo de Olson et al. (2005) não se encontram alguns gêneros supostamente relacionados com Cranioleuca, como Siptornopsis, Siptornis, Hellmayrea e Certhiaxis, o que torna muito prematuro incluir Limnoctites em Cranioleuca.

“Embora haja uma filogenia molecular para boa parte dos Cranioleuca (García-Moreno et al. 1999 em: Mol. Phyl. Evol), a mesma não inclui C. sulphurifera e tampouco Limnoctites ou os gêneros acima citados."

Comments from Remsen: “NO. I think Santiago has a good point: there is a chance that further taxon-sampling will show that Limnoctites is not embedded in Cranioleuca and that Cranioleuca sulphurifera may belong in Limnoctites, so to be conservative, I retract my recommendation on this proposal.”