Comments on woodpecker classification by Laurent Raty:
- Background -
In recent classifications, the 'pied woodpeckers' have generally been placed in the two genera Picoides and Dendrocopos, but different authors recommended different arrangements. Voous (1973) used a restricted Picoides in which he placed only the three-toed species, P. tridactylus and P. arcticus, while he kept all the other species in a large genus Dendrocopos - a traditional treatment at that time. Short (1971, 1982) argued that the three-toed species are more closely related to the other American representatives of the group than these are to Eurasian species, and he merged the two genera into a still larger Picoides. Ouellet (1977), finally, suggested the same relationships, but chose to retain Dendrocopos for the Eurasian species, while he united the American four-toed species with P. tricactylus and P. arcticus in Picoides. Although Short's classification of the Picidae (1982) is still widely used nowadays, Ouellet's treatment has gained very wide acceptance for the 'pied woodpeckers' (e.g., Sibley & Monroe 1990; AOU 1998; Clements 2000; Winkler & Christie in del Hoyo et al. 2002; Dickinson 2003). However, Short's (1982) taxonomy, in which Dendrocopos is not recognised, is still used in a number of recent publications addressing this group.
- Recent data -
Recent molecular data show Picoides and Dendrocopos to be parts of a clade that also includes three other widely recognised genera : Veniliornis (Moore 1995; Prychitko & Moore 2000; DeFilippis & Moore 2000; Weibel & Moore 2002a; 2002b; Webb & Moore 2005; Moore et al. 2006; Benz et al. 2006; Fuchs et al. 2006; 2007), Dendropicos (Weibel & Moore 2002a; 2002b; Webb & Moore 2005; Benz et al. 2006; Fuchs et al. 2007), and Sapheopipo (Winkler et al. 2005). For relationships in this group, see also Overton & Rhoads (2006), but note the trees in this study were rooted on a Veniliornis, which makes them appear somewhat upside-down as far as the group discussed here is concerned.
The sister group of this clade is composed of Melanerpes, Sphyrapicus and Xiphidiopicus (see Overton & Rhoads 2006 for the latter) - this whole assemblage was recently treated at the tribe level by Webb & Moore (2005) , followed in this by Benz et al. (2006).
Based primarily on plumage and behavioural considerations, Short (1982) regarded Veniliornis as a close relative of Piculus, and Sapheopipo as a close relative of Picus. He indeed placed these two genera and Picoides in three different tribes (Colaptini, Picini and Campetherini, respectively). The molecular results clearly contradict this classification. However, Goodwin (1968) had already argued that Sapheopipo is closely allied to the 'pied woodpeckers', and Goodges (1972) had also suggested a close relationship between the five genera Sapheopipo, Veniliornis, Picoides, Dendrocopos and Dendropicos based on myology, hence these results may not be as unexpected as they may seem at first.
Among the species that have been studied
genetically, several subgroups are likely monophyletic :
(Note - the generic name given in parentheses for each subgroup is the name that (I think) would have priority, should this subgroup ever need such a name; recognition at the generic level is not thereby advocated.)
o Three-toed Picoides (Picoides
Lacépède, 1799, s.s. - type species P.
There are published data for P. tridactylus and P. arcticus (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Winkler et al. 2005, cyt-b; Fuchs et al. 2006 and 2007, nd2, myo-int2 and _-fibint7).
The monophyly of this group is not unambiguously supported by mitochondrial sequence analyses (Weibel & Moore 2002a; 2002b; Winkler et al. 2005), but is strongly indicated in analyses including the nuclear _-fibint7 (Weibel & Moore 2002b), and the group is well characterised morphologically (for a recent analysis, see Browning 2003).
P. dorsalis, if it is considered distinct from P. tridactylus (cf. Zink et al. 2002, nd2, nd3 and cyt-b), is the only other species expected in this group (the specimens used up to now in phylogenetic studies other that Zink's are all from Europe or Russia, hence P. tridactylus s.s.).
o Small white-vented Dendrocopos
(Yungipicus Bonaparte, 1854 - type species Dendrocopos
There are published data for three species, D. canicapillus, D. maculatus and D. kizuki (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Fuchs et al. 2007, nd2, myo-int2 and _-fibint7), and a nd2 sequence of D. moluccensis deposited by Moyle (2005) can be found in GenBank (accession number AY625192).
The mitochondrial and _-fibint7 sequences give a strong support to the monophyly of the first three species (Weibel & Moore 2002a; 2002b), and the nd2 sequence of D. moluccensis links it unambiguously to D. canicapillus, confirming it is part of the group too (own analysis).
These four species have an Asian distribution; they are small and lack any red on the underparts, and their head pattern includes a dark cheek stripe, frequent in species currently placed in Picoides but absent in more typical Dendrocopos.
Together with D. temminckii, they have been separated in the genus Yungipicus in the past. The Afrotropical Dendropicos obsoletus is phenotypically similar and has also been included in this genus (see Dendropicos below for more); it has not been studied genetically. No other species are likely to be part of this group.
o Large red-vented Dendrocopos,
'group 1' (Dendrocopos Koch, 1816, s.s. - type
species Dendrocopos major)
There are published data for D. leucotos, D. major, D. syriacus, D. macei and D. hyperythrus (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Winkler et al. 2005, cyt-b; Fuchs et al. 2006 and 2007, nd2, myo-int2 and _-fibint7; Moore et al. 2006, cyt-b and coi; Benz et al. 2006, cyt-b, nd2 and _-fibint7). Sapheopipo noguchii appears embedded in this group, and would be best treated congeneric with it (Winkler et al. 2005, cyt-b).
Wherever more than one species of this group have been included in a study, they clustered together with high support.
These species are larger than those in the previous group, have some red on the belly and/or vent, and a plain white or pale cheek (but see next group).
It is probably reasonable to assume that at least the other members of the D. major and D. macei superspecies (respectively D. leucopterus, D. assimilis and D. himalayensis, and D. atratus) are also part of this group. D. medius and D. mahrattensis at least are not (see 'group 2' below). Neither is D. minor (see small American four-toed Picoides below).
o Large red-vented Dendrocopos,
'group 2' (possibly Leiopicus Bonaparte, 1854 -
type species Dendrocopos mahrattensis)
There are published data for D. medius and D. mahrattensis (Fuchs et al. 2007, nd2, myo-int2 and _-fibint7).
The nd2 alone did not resolve this part of the tree, but the individual analyses of the two nuclear markers, as well as the combined analysis of the three genes, grouped consistently these two species with high support well away from the previous group and closer to the next one.
There are no obvious consistent morphological differences between the 'group 1' and the 'group 2', however, which makes it largely impossible for now to guess which unsampled species should be ascribed to one or the other. The fact that D. mahrattensis is usually thought to be very closely allied to D. macei (Winkler & Christie in del Hoyo et al. 2002), which Fuchs et al.'s data (2007) place unambiguously in the 'group 1', illustrates the extent of the problem quite well. The absence of known consistent morphological differentiation between them also makes the very existence of two groups, rather than a more complex pattern of radiation, uncertain.
o Afrotropical Dendropicos
(Dendropicos Malherbe, 1849 - type species Dendropicos
There are published data for D. fuscescens, D. pyrrhogaster, D. elliottii, D. goertae and D. griseocephalus (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Webb & Moore 2005, 12s-rRNA, cyt-b and coi; Overton & Rhoads 2006, cyt-b; Benz et al. 2006, cyt-b, nd2 and _-fibint7; Fuchs et al. 2007, nd2, myo-int2 and _-fibint7).
Wherever more then one of these species appeared in a study, they clustered together, often with high support.
D. goertae, D. spodocephalus, D. griseocephalus and, sometimes, D. elliotii are placed by some in the separate genus Mesopicos; D. namaquus, D. pyrrhogaster and D. xantholophus are placed by some in the separate genus Thripias (e.g., Dowsett & Dowsett-Lemaire 1993). Recognising such small genera does not seem necessary, however; the inclusion of D. elliotii in Mesopicos, in any case, is contradicted by Fuchs et al.'s data (2007).
Dendropicos obsoletus is phenotypically similar to the small white-vented Dendrocopos, and is ascribed by some to this genus (most recently : Winkler & Christie in del Hoyo et al. 2002, who suggested a close relationship with D. temminckii) or to Picoides (e.g., Dowsett & Dowsett-Lemaire 1993); this species has not been studied genetically. No other species is expected in this group.
o Small American four-toed Picoides
(Dryobates Boie, 1826, s.s. - type species P.
There are published data for P. nuttallii, P. pubescens and P. scalaris (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Webb & Moore 2005; Moore et al. 2006, cyt-b and coi; Overton & Rhoads 2006, cyt-b; Benz et al. 2006, cyt-b, nd2 and _-fibint7; Fuchs et al. 2006 and 2007, nd2, myo-int2 and _-fibint7). The Eurasian Dendrocopos minor is also part of (basal to) this group (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Moore et al. 2006; Fuchs et al. 2006; 2007), and would be best treated congeneric with it.
Wherever more than one species of this group have been included in a study, they clustered together with high support.
No other species is expected in this group.
o Large American four-toed Picoides
(Leuconotopicus Malherbe, 1845 - type species P.
There are published data for P. albolarvatus, P. stricklandi, P. villosus and P. borealis (Weibel & Moore 2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7; Webb & Moore 2005, 12s-rRNA, cyt-b and coi; Overton & Rhoads 2006, cyt-b; Moore et al. 2006, cyt-b and coi; Fuchs et al. 2007, nd2, myo-int2 and _-fibint7). Veniliornis fumigatus is also part of this group and would be best treated congeneric with it (Moore et al. 2006, cyt-b and coi).
P. albolarvatus, P. stricklandi and P. villosus group with high support wherever they appear together in a study. P. borealis is more basal, and its inclusion in the group more ambiguous (Moore et al. 2006; see also Weibel & Moore 2002a; 2002b) - an alternative possible placement for this species suggested by some of Weibel & Moore's (2002b, _-fibint7) and Moore et al.'s (2006, cyt-b and coi) analyses, although with low support in both cases, would be at the base of the next group. V. fumigatus appears in a position basal to the three first species, with very high support - thus embedded in the group if P. borealis is included (Moore et al. 2006).
The P. stricklandi specimens included up to now in published phylogenetic analyses are from Arizona, hence are actually P. arizonae if this is considered distinct (see Banks et al. 2000); P. stricklandi s.s. is also expected in this group; no other species are likely to be part of it.
o Neotropical Veniliornis (Veniliornis
Bonaparte, 1854 - type species V. sanguineus)
Moore et al. (2006, cyt-b and coi) provided data for V. callonotus, V. cassini, V. chocoensis, V. dignus, V. frontalis, V. kirkii, V. nigriceps, V. passerinus and V. spilogaster; data about some of these species also appear in Weibel & Moore (2002a, cyt-b and coi; 2002b, cyt-b, coi and _-fibint7), Webb & Moore (2005, 12s-rRNA, cyt-b and coi), Overton & Rhoads (2006, cyt-b), Benz et al. (2006, cyt-b, nd2 and _-fibint7) and Fuchs et al. (2007, nd2, myo-int2 and _-fibint7). The two South-American species usually classified as Picoides, P. mixtus and P. lignarius, appear embedded in this group, as the sister taxon of V. spilogaster (Moore et al. 2006, cyt-b and coi; see also Weibel & Moore 2002a; 2002b), and would be best treated congeneric with it.
Wherever more than one species of this group have been included in a study, they clustered together with good to very good support.
P. borealis appeared basal in this group in some of Weibel & Moore's (2002b) and Moore et al.'s (2006) analyses, but with low support. V. fumigatus is not part of this group (see large American four-toed Picoides above); no other non-Veniliornis species is expected to be part of it.
Studies including three-toed Picoides but no small white-vented Dendrocopos showed them basal to the whole assemblage (Winkler et al. 2005; Fuchs et al. 2006). Studies also including small white-vented Dendrocopos clearly showed these and three-toed Picoides to be both highly divergent, but varied somewhat in the topology they suggested. Analyses based on the nuclear _-fibint7 alone suggested that three-toed Picoides form the basal lineage, while small white-vented Dendrocopos are sister to all the other groups, although never with very high support (Weibel & Moore 2002b; Fuchs et al. 2007). Analyses based on mitochondrial markers (when they resolve this part of the tree), as well as analyses including the nuclear myo-int2, and combined analyses having included some of these markers together with the _-fibint7, grouped the small white-vented Dendrocopos with the three-toed Picoides, sometimes with high support (Weibel & Moore 2002a; 2002b; Fuchs et al. 2007). If this second hypothesis is correct, both Picoides and Dendrocopos currently include species that are as distant as two 'pied woodpeckers' could possibly be.
Among the remaining groups, the three American four-toed lineages (large and small American four-toed Picoides - including Dendrocopos minor - and Neotropical Veniliornis) form together a strongly supported subclade (Weibel & Moore 2002a; 2002b; Moore et al. 2006; Fuchs et al. 2007; see also Webb & Moore 2005; Benz et al. 2006; Fuchs et al. 2006). Moore et al. (2006) failed to resolve the between-group relationships within this subclade with their cyt b and coi sequences : depending on the method that was used, their analyses placed Veniliornis either as sister to the small or to the large four-toed Picoides, always with low support. However, the analyses by Fuchs et al. (2007), mainly as a result of the addition of the nd2 marker, grouped V. nigriceps and P. mixtus with P. villosus to the exclusion of D. minor, with high support, providing a strong suggestion that Veniliornis is closer to the large four-toed Picoides group.
Only the most recent study (Fuchs et al. 2007) provided a well-supported picture of the remaining between-group relationships. This study showed the first group of large Dendrocopos to be sister to the American four-toed clade, while the second group appeared as the sister group of Dendropicos.
All in all, this suggests a scenario in which the large red-vented Dendrocopos woodpeckers represent a Eurasian radiation, of which the Afrotropical group and the entire four-toed American clade (including Dendrocopos minor) are two offshoots.
Two possible explanations may be advanced for the relationships of Dendrocopos minor, both of which imply two trans-Beringian colonisation events. One is that it represents the last Eurasian member of a lineage that colonised America twice, giving rise on the first occasion to the large, and on the second occasion to the small four-toed American Picoides while leaving the ancestor of D. minor behind. Under this scenario, the fact that the relationships among the three American four-toed lineages appear as a trichotomy in many analyses would suggest that Veniliornis separated from the first colonisation wave soon after it had entered America, while the second colonisation wave (and its separation from the D. minor lineage) would have occurred significantly later - this is consistent with Veniliornis being closest to the large four-toed Picoides group. The other explanation would be that D. minor derives from an American taxon having retreated to Eurasia, after the three American four-toed groups had differentiated in America. No inference about the relationships between Veniliornis and the two four-toed Picoides groups can be done under this second scenario.
At least two more trans-Beringian crossings are also needed to explain the present distribution of the two basal subgroups.
- Recent proposals of generic rearrangement -
o Dickinson (2003) reinstated the monotypic genus Hypopicus Bonaparte, 1854, for Dendrocopos hyperythrus based on morphological and behavioural distinctness ('in the context of the separation of Dendrocopos from Picoides.')
However, the data of Benz et al. (2006) clearly indicate a close relationship between this species and Dendrocopos major, the type species of Dendrocopos. (An own reanalysis combining the nd2 and _-fibint7 sequences of Benz et al. (2006) with those of Fuchs et al. (2007) suggested hyperythrus is basal to the first large Dendrocopos group.) For the time being, this move seems unnecessary; in any case, a lot of species would have to be removed from Dendrocopos before it could become acceptable.
o Browning (2003) suggested transferring
the American four-toed Picoides to Dryobates, based
primarily on morphological and behavioural considerations, although
he also cited genetic studies.
o Helbig (2005; in Bauer et al. 2005) united Dendrocopos minor and the American four-toed Picoides in Dryobates, based on Weibel & Moore's (2002a; 2002b) molecular data.
However, the monophyly of a so-delimited Dryobates is extremely uncertain in the more recent molecular analyses if it does not include Veniliornis. (Even when the findings of Moore et al. (2006) are accounted by removing P. mixtus and P. lignarius and adding V. fumigatus : the issues of inter-group relationships in the American four-toed clade, and of the poorly-supported position of P. borealis, remain.)
o Winkler et al. (2005) suggested transferring Sapheopipo noguchii to Dendrocopos, based on their own cyt-b sequence analyses.
Although this was based only on a single genetic marker, S. noguchii clearly appeared to be part of the group that includes the type species of Dendrocopos and its closest relatives, with a bootstrap support of 100%. (An own reanalysis combining the cyt-b data of Winkler et al. (2005) with those of Benz et al. (2006) showed S. noguchii to be much closer to D. major than D. hyperythrus.) This move seems legitimate, and would probably result in a stable treatment. (At least as long as nobody merges the entire group in a huge genus Picoides, which would then contain more than one third of the woodpecker species of the world)
o Moore et al. (2006) suggested transferring V. fumigatus to Picoides, and P. mixtus and P. lignarius to Veniliornis.
However, the rationale behind these two
moves takes into account only a very small part of the whole 'pied
When looking at the complete picture, these two moves do not appear compatible with one another : a clade encompassing the type species of Picoides and V. fumigatus would definitely encompass the complete group, so if V. fumigatus is a Picoides, Veniliornis as a whole should cease to exist, and the second move is impossible.
Picoides in this largest sense do not seem very likely ever to become accepted, but the genus-level para/polyphyly in the entire group is such that Veniliornis is actually only a part-of-a-part-of-a-part of what this broad Picoides could be : even if Picoides ends up more restricted, it is not necessarily unlikely that Veniliornis could still to be lumped with something. And both of its two closely related subgroups include the type species of a genus name that would have priority, so any lumping here would result in the name Veniliornis disappearing On the other hand, if Fuchs et al.'s (2007) results suggesting that large American four-toed Picoides are closer to Veniliornis than to small American four-toed Picoides are correct, keeping Veniliornis distinct would force to recognise two separate, very small genera for the two four-toed Picoides subgroups (respectively only 4 and 6 species - assuming P. borealis is not basal in the Veniliornis lineage after all), despite the fact that with P. mixtus and P. lignarius included in Veniliornis and V. fumigatus transferred to the large American four-toed Picoides, the morphological distinctness of the three American four-toed groups tends to vanish. Given all this, it might be worth, at least, to consider the possibility of placing the generic limit on a slightly higher node in the phylogeny, before acting changes that would prove useless if this solution was finally preferred.
Note - There may also be a nomenclatural issue with the transfer of P. mixtus to Veniliornis. P. mixtus comes as the type species of Dyctiopicus Bonaparte, 1854, that was introduced simultaneously with Veniliornis (respectively on p.123 and p.125 of the same work). In such cases and unless one of the names was introduced as a subgenus, the priority among them is undetermined (ICZN 1999 : Article 24) : to have it fixed requires a published First Reviser act ('published' in the sense of the Code - not on a website). If this priority is still undetermined (which it could very well be), acting this change could be a bit risky, because any author publishing a paper in the near future in which he would express a preference for Dyctiopicus, would give priority to this name. The risk seems particularly real : Dyctiopicus appears 2 pages ahead of Veniliornis in Bonaparte's work, and someone might want to 'correct' the situation according to the so-called 'page precedence' rule - there is no such rule in the Code, but such a 'correction' could constitute a First Reviser act.
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