Proposal (417) to South American Classification Committee
Split
Diglossopis from Diglossa
The
recently published analysis of the phylogeny of the flower-piercers by Mauck et
al. (2009) demonstrated a deep division in this group between two monophyletic
clades: one that includes the species caerulescens,
cyanea and glauca (genus Diglossopis of Bock 1985), and a larger
clade containing the remaining species including indigotica. Because this
species was placed in Diglossopis by
Sibley & Monroe (1990), Mauck et al. argued that the genetic data rendered
this genus polyphyletic and that it should not be recognized. The original recommendation for recognition
of Diglossopis was made by Bock
(1985) based upon a morphological study of the bill, skull and especially the
tongue. Bock presented detailed evidence
for differences between Diglossopis and
Diglossa that he considered
sufficiently pronounced to warrant generic separation, and doubted that they
could have derived their adaptations for nectarivory from a recent common
ancestor. (These differences seem to me
to be of the same order of magnitude as those used by Lanyon in a series of
studies to delimit genera in the Tyrannidae).
Bock stated clearly that, while he had not seen anatomical material of indigotica, its bill morphology placed
it in Diglossa, not Diglossopis, which he restricted to
precisely the three species in the aforementioned clade found by Mauck et
al. The inclusion of indigotica in Diglossopis was made by Sibley & Monroe apparently following
the superficial division of Diglossa
into “species-groups” by Vuilleumier (1969), who made a distinction between the
“black” vs. “blue” groups and included indigotica
with caerulescens, cyanea and glauca on the basis of its blue color
and red eye, a feature shared with cyanea
in particular – but evidently he did not examine the morphology in any
detail. Bock argued that the coloration
of indigotica represented a
convergence with his Diglossopis,
perhaps related to social behavior in mixed flocks. Although Sibley & Monroe credited Bock
with recognition of Diglossopis, they
evidently did not read his conclusion regarding indigotica but in effect followed the “black vs. blue” groups of
Vuilleumier – and the same applies to the discussion of Mauck et al. in this
respect, since their genetic data in reality present a strong argument for
recognition of Diglossopis as defined
by Bock. Just how closely related are Diglossopis and Diglossa (specifically, whether or not they are sister groups; Bock
argued on morphological grounds that they are not) is perhaps debatable since
Mauck et al. did not examine in detail the relationships of these two with
respect to a larger set of outgroups within the Thraupidae.
It is worth noting that although
members of Diglossopis as well as Diglossa pierce flowers, they also take
much fruit, which members of Diglossa do
not.
I examined specimens in the ICN collection with data on stomach contents
and found that of 48 specimens of Diglossopis
cyanea, 33 had annotated fruit in stomachs (vs. 38 with insects); stomachs
of 29 of 34 caerulescens contained
fruit, vs.21 with insects; these data contrast with those from Diglossa: for humeralis
58 of 60 contained insects vs. 3 with fruit; for 26 lafresnayi, all contained insects and one, fruit; for albilatera, 49 stomachs all contained
insects vs. two with fruit. An
examination of fecal samples by L. Rosselli produced similar results, as did
detailed observations of foraging behavior by Rojas-Nossa (2005) which also
showed that flower-piercing was also much more frequent in the same Diglossa species vs. those of Diglossopis. This correlates nicely with the depth of the
hook at the tip of the bill: much deeper in Diglossa
(and deeper in Diglossopis cyanea,
which visits flowers more frequently and does not pierce in about half of the
visits, than in caerulescens, which
visits flowers comparatively rarely). By
contrast, 80% or more of the much more frequent visits to flowers by species of
Diglossa involve piercing in the
manner described by Skutch (1954). My
observations of indigotica agree with
its placement in Diglossa – it
pierces flowers as do others of this genus and I never saw it take fruit, nor
was fruit present in the three stomachs I examined. It has a very deeply hooked
bill like that of albilatera, found
by Mauck et al. to be its closest relative in Diglossa.
In conclusion, I submit that the
combination of genetic, morphological and behavioral data strongly support
recognition of Diglossopis as
circumscribed by Bock, and recommend a YES on this proposal. I note that recognition of Diglossopis would not affect the
ordering of species in Proposal 413 (it would merely place the last three in a
different genus).
Gary Stiles, October 2009
Comments
from William Mauck: “The first thing I would like to comment on is the statement
“Mauck et al. did not examine in detail the relationships of these two (clades
of flowerpiercers) with respect to a larger set of outgroups within the
Thraupidae”. Although a phylogeny including outgroups is not presented as a
figure, these analyses were conducted and described in the paper (see Table1,
methods, and results). Twenty-seven species, representing 23 genera, were used
as outgroups to root the phylogeny.
These representatives were chosen specifically to represent major
lineages within Thraupidae (Barker et al. Temporal and phylogenetic patterns of
diversity in New World tanagers, cardinals, sparrows, blackbirds, and warblers
2007 AOU, Wyoming) and taxa thought to be closely related to
flowerpiercers. The latter were chosen
based on molecular and morphological data to test monophyly and elucidate what
taxa are sister to flowerpiercers.
Therefore, a concerted effort was made to test the monophyly of
flowerpiercers and to determine the relationship of flowerpiercers to other
Thraupidae. As described in the results,
support for the monophyly of flowerpiercers was high, with 98% bootstrap
support and 1.0 posterior probability.
Thus, the data reject Bock’s idea that the flowerpiercers are not
monophyletic.
“In regards to the proposal to split flowerpiercers into two genera,
the molecular and relative hook size results are concordant with the internal
cranial morphological and distinctiveness presented by Bock 1985 (as stated in
Mauck & Burns 2009). Despite this,
our paper recommended that all flowerpiercers belong to a single genus, Diglossa. Below is an expanded list of reasons why all
flowerpiercers might be retained in a single genus:
“1. Flowerpiercers represent a monophyletic group of nectarivorous birds
that evolved from a common ancestor (Mauck & Burns 2009) with an overall
bill shape unique from other Thraupidae (Vuilleumier 1969).
“2. Separating flowerpiercers into two genera would emphasize the
uniqueness of a specific (and important difference in) feeding morphology of
this group, but would also obscure the evolution of other morphological
characters and their homoplastic nature, which are currently being investigated
(i.e., evolution of the blue plumage and red eye of D. indigotica as
compared to D. cyanea, D. glauca, and D. caerulescens;
small relative hook size evolving in D. major and D. cyanea, D.
glauca, and D. caerulescens; leapfrog plumage pattern; sexual
dimorphism, etc).
“3. Finally, the emphasis of a ‘deep division’ between D. cyanea, D.
glauca, and D. caerulescens and all other flowerpiercers is a
subjective description and was never described as such in Mauck & Burns
2009. The average uncorrected sequence divergence between D. cyanea,
D. glauca, and D. caerulescens and all other flowerpiercers was
~11.6%, whereas the average uncorrected sequence divergence of the clade
containing D. indigotica and the baritula superspecies complex to
all other flowerpiercers (excluding D. cyanea, D. glauca, and D.
caerulescens) is only ~11.3%. Thus,
the divergence between the proposed species of Diglossopis and all other
flowerpiercers is only slightly larger than that found between other clades of
flowerpiercers. This is also illustrated
by comparing branch lengths on Fig. 2.
Note that the branches involved in the initial split in flowerpiercers
are not any longer than other branches in the phylogeny; there isn’t a ‘deep
division’ here.
“In conclusion, flowerpiercers are a clade of tanagers with a distinct
bill morphology which has evolved into species with different degrees of
specialization for feeding on nectar versus fruit. Despite the degree of specialization of bill
morphology, nectar thieving is a feasible and documented feeding behavior for
many flowerpiercers, even Diglossa cyanea (Moynihan 1963), which is a
member of the proposed Diglossopis genus. Fruit is also a food source for
flowerpiercers, even those with a large relative hook specialized for thieving
nectar (Schondube & Martinez del Rio, 2003). Thus, retaining the genus Diglossa for
all flowerpiercers would preserve the shared evolutionary history found among
these species.
“The
research by Dr. Stiles and colleges explicitly details and quantifies the
behavior, feeding preferences, and food sources of flowerpiercers, which is
invaluable to understand the ecological role and impact flowerpiercers have in
Andean ecosystems. No matter the
decision of the SACC it will bring further attention towards understanding the
evolution and feeding ecology to this interesting group of birds.”
Response
from Stiles:
“I thank
Mauck and Burns for clarifying the outgroup question regarding the evolution of
the flower-piercers: I am willing to accept their argument that they do indeed
constitute a clade. However, this does not
preclude the division of the clade into two monophyletic genera that are well
characterized with respect to morphology, ecology and behavior. In fact,
I feel much more comfortable with this split than I do with the splitting up of
Pheugopedius in this respect. It
seems worth noting that the sampling of the genome with the molecular markers
we have so far is still pretty restricted: one could argue that a considerably
larger part of the genome is involved in producing the series of phenotypic
characters separating the two groups of flowerpiercers. Perhaps this is a
stick-in-the-mud criterion but I do feel that some kind of phenotypic diagnosis
of genera is important (and in the case of Cantorchilus
with song learning, I am a bit leery of using ONLY song as such a criterion.)”
Comments from Zimmer:
“YES,
tentatively. The placement of indigotica is a bit troubling,
considering that bill/cranial morphology points one way, and plumage
pattern/eye color points another, but I am persuaded by the ecological
distinctions that Gary notes.”
Comments from Cadena:
“YES. I tend to be
conservative regarding issues like this one, but since Diglossopis has been in use for some time now by several authors, I
think that a change would not be very traumatic. In addition, recognizing Diglossopis has the added benefit that
it conveys information about phylogeny that is consistent with phenotypic and
ecological data nicely summarized by Gary. The fact that some authors placed indigotica within Diglossopis based on its blue plumage is simply a historical
glitch, considering that Bock explicitly stated that this taxon did not belong
in the group according to the characters that define it (bill and tongue
morphology).”
Comments from Remsen:
“NO, for the reasons outlined by Mauck.
If every genus were to be subdivided into additional genera based on
monophyletic groups within the broad genus …. Well, you can see where this
would lead. So, this is just a matter of
taste, and for my tastes, Diglossopis does not warrant recognition as a genus
because these minor degrees of bill shape, associated with differences in
foraging, are among the most plastic in avian biology – it would be like
subdividing Calidris, Toxostoma, or Loxops based on degree of curvature associated with differences in
foraging behavior.”
Comments
from Pacheco:
“NO. Inevitavelmente, eu levo em consideração
o que foi colocado, em réplica à proposição, por Mauck e Van.”
Comments
from Jaramillo:
“NO. This could go either way and the data would not be violated. I think
that a genus is in the eye of the beholder, and had the division been deeper in
the phylogeny I would have voted yes on this. It was 50-50 for me, and my
choice was whether separating Diglossopis as a separate genus really was
that informative. To me what was more important was to communicate that the
entire group was a distinct, monophyletic group separate from the rest of the
tanagers, and that this group has various unique bill and tongue adaptations
for nectar feeding, and nectar robbing. The fact that the Diglossopis
group does it in a slightly different manner did not sway me from splitting up
this very distinctive group of birds into two genera.”
Comments
from Robbins:
“NO. Obviously there is no wrong course of
action, but I agree with Van in not creating a plethora of genera based on
relatively minor morphological and genetic differences.”
Comments
from Nores:
“NO. Aunque el análisis hecho por Gary resultaba bastante convincente, las
aclaraciones de William Mauck y de Van me hacen inclinar por lo contrario. No
justifica crear nuevos géneros basados en pequeñas diferencias genéticas o
morfológicas, y más aún es este caso en que la creación de un nuevo género
significaría que las especies de “flowerpiercers”
no serian monofiléticas.”