Why do Robust Woodpecker, Lineated Woodpecker and Helmeted Woodpecker look alike?

Could the interspecific social dominance hypothesis explain this plumage convergence?

I recently bought “All the Birds of the World” from Lynx Editions. The title of the book nicely captures its contents, this huge tome contains beautiful drawings of literally all the (known) bird species in the world. Apart from looking up specific species, I enjoy browsing through the pages and admiring the amazing diversity of birds. Skimming the section on woodpeckers (family Picidae), I noticed the striking similarities between distantly related species. For example, several species seem to have converged upon a plumage pattern that consists of a black-and-white body with an eye-catching red crest. Many ornithologists have made this observation (technically known as mimicry complexes) and there are countless hypotheses to explain why certain woodpecker species look alike.

One possible explanation for this plumage convergence is the “interspecific social dominance hypothesis” which states that subordinate species will look like a dominant one to avoid attacks by the dominant species. A recent study in the Journal of Ornithology tested this hypothesis for three South American woodpeckers.

Niche Differentiation

Juan Manuel Fernández and his colleagues studied the ecology of Robust Woodpecker (Campephilus robustus), Lineated Woodpecker (Dryocopus lineatus) and Helmeted Woodpecker (Celeus galeatus) in Argentina. Based on the size of these species, the researchers considered the smaller Lineated Woodpecker and Helmeted Woodpecker as subordinate mimics of the dominant Robust Woodpecker. According to the “interspecific social dominance hypothesis”, the three species should be ecological competitors and thus occupy in the same niches.

However, careful observations revealed clear niche differentiation. It turned out that the three species forage on different parts of the tree. Helmeted Woodpecker collected food on smaller trees and was often seen on dead branches in living trees. Lineated Woodpecker foraged on similar trees compared to Helmeted Woodpecker, but mainly used living healthy trees. And Robust Woodpecker was mainly observed on larger trees and frequently visited dead parts of living and decaying trees. In addition, the researchers did not record any direct interactions between the three species.

From left to right: Robust Woodpecker (Campephilus robustus), Lineated Woodpecker (Dryocopus lineatus) and Helmeted Woodpecker (Celeus galeatus). From: Fernández et al. (2020) Journal of Ornithology.

Deception

These results do not support the “interspecific social dominance hypothesis”. It could be that interspecific interactions in the past have driven these woodpecker species into different niches. But there are alternative explanations. The subordinate species might mimic the dominant species to deceive predators. The larger Robust Woodpecker is not an easy prey for small raptors, such as Sparrowhawks (genus Accipiter). These birds of prey might think twice before attacking a woodpecker that looks like a Robust Woodpecker.

It is also possible that the Lineated Woodpecker and the Helmeted Woodpecker are deceiving members of their own species to avoid direct competition. From a distance, birds might think that a dominant Robust Woodpecker is chiseling away at a tree branch and decide to look for another foraging spot. These explanations remain to be tested with more observations. I won’t mind putting my “All the Birds of the World” book aside and venturing into the Argentine forests.

References

Fernández, J. M., Areta, J. I., & Lammertink, M. (2020). Does foraging competition drive plumage convergence in three look-alike Atlantic Forest woodpecker species?. Journal of Ornithology, 161(4), 1105-1116.

Featured image; Lineated Woodpecker (Dryocopus lineatus) © panza-rayada | Wikimedia Commons

Admixture in Amazonia: Reconstructing the evolutionary history of the Pectoral Sparrow

Genomic data tell the story of how this passerine spread across South America.

Apart from managing the Avian Hybrids Project, I regularly contribute to the blog of the British Ornithologists’ Union (the BOUblog, you can find an overview of my blog posts here). A few weeks ago, I published my 50th story for the BOUblog, which focused on the phylogenetics of the Pectoral Sparrow (Arremon taciturnus). A recent study used mitochondrial DNA to unravel the evolutionary history of this neotropical species. The researchers uncovered six distinct lineages and speculated about the factors responsible for their origins. Here is my summary:

Could it be that the origin of these rivers drove the diversification of the Pectoral Sparrow? Not exactly, because these rivers started crisscrossing the South American landscape between 9 and 2.5 million years ago. The rivers certainly prevent neighboring populations from mixing extensively, but they are not the main cause for the origin of these lineages. Rather, the researchers suspect that ‘past ecological barriers must have played a role in accounting for the observed phylogeographical structure.’ During the glacial cycles of the Pleistocene, forests contracted and expanded. The Pectoral Sparrows became isolated in forest fragments during contraction phases and followed the spreading forests during the expansions. At rivers, however, the birds could not disperse further, giving rise to the geographical boundaries between the six lineages. Amazing what you can deduce from a string of A, T, G and Cs.

Although this scenario seems plausible, it remains largely speculative. Indeed, the authors indicated the uncertainties in their proposed model and wrote that “alternative scenarios could be tested with more powerful genomic datasets.” Luckily, another recent paper did just that. Using genomic data, Nelson Buainain and his colleagues provided a more fine-grained picture of the evolution of the Pectoral Sparrow.

Analyses of mitochondrial DNA indicated six distinct lineages within the Pectoral Sparrow. From: Carneiro de Melo Moura et al. (2020) Ibis.

Genotypes and Phenotypes

In contrast to the six mitochondrial lineages, the genomic data suggested four main genetic clusters. The genetic make-up of these four groups reveals an interesting pattern. Individuals from the Guyana Shield (region A in the figure above), southwestern Amazonia (region F) and the Atlantic Forest (region D) generally have “pure” genotypes. In other words, they do not share genetic variation with other regions. In central Amazonia (regions B, C and E), however, individuals have admixed genotypes.

The genetic patterns are mirrored in the plumage of the birds. In the genetically “pure” populations, pectoral band patterns are mostly homogenous, whereas the admixed populations show a variety of shapes and sizes in the pectoral bands. The most likely scenario is that populations became isolated in different forest patches across central Amazonia and established secondary contact, giving rise to the genetic and morphological variety we see today. This interpretation was further supported by ecological niche modelling.

Genetic and morphological variation across the range of the Pectoral Sparrow. Notice the admixed nature of the populations in central Amazonia. From: Buainain et al. (2020) Molecular Ecology.

North to South

The genetic analyses indicated that the populations north and south of the Amazon separated about 160,000 to 380,000 years ago. The higher genetic diversity in the northern populations of the Guyana Shield suggest that the Pectoral Sparrow started its journey across South America here. As birds spread to the south, they separated into distinct populations, settling in the patches of suitable habitat. These populations were probably separated in at least three regions south of the Amazon River, namely southwestern Amazonia and south‐central Amazonia and the Atlantic Forest. These regions functioned as refugia during harsh climatic periods when forest fragments were isolated. Occasionally, climatic changes would cause these forests to expand, resulting in the secondary contact that I described above. This scenario nicely builds upon the patterns that arose from the mitochondrial study. Step by step, we are unraveling the complex evolutionary history of South American birds.

References

Buainain, N., Canton, R., Zuquim, G., Tuomisto, H., Hrbek, T., Sato, H., & Ribas, C. C. (2020). Paleoclimatic evolution as the main driver of current genomic diversity in the widespread and polymorphic Neotropical songbird Arremon taciturnus. Molecular Ecology, 29(15), 2922-2939.

Featured image: Pectoral Sparrow (Arremon taciturnus) © Caio Brito | eBird

The role of hybridization in the domestication of geese

Gene flow patterns between wild and domestic geese changed during the domestication process.

Geese probably saved the Roman empire. The Gauls were secretly climbing the Capitoline Hill when they woke up a flock of geese. The noise of the honking geese alarmed the Romans that managed to fend off the Gaul attack. This story indicates that geese were already domesticated in Roman times. The earliest reliable reference to domestic geese can be traced back even further, to the 8th century BCE in Homer’s Odyssey. But when did humans domesticate geese?

This question is difficult to answer because different domestic goose breeds are derived from two species: the Greylag Goose (Anser anser) and the Swan Goose (Anser cygnoides). In addition, some breeds are probably the outcome of hybridization between these species, and several breeds are known to hybridize with their wild relatives. Marja Heikkinen and her colleagues tried to solve this complex puzzle of hybridization and domestication with genetic data. Their results recently appeared in the journal G3: Genes | Genomes | Genetics.

Gene Flow

The researchers collected samples from wild and domestic geese across Eurasia. Genomic data revealed a clear separation between wild Greylag Geese, European domestic breeds and Chinese domestic breeds. Demographic analyses suggested that the wild and domestic lineages diverged around 14,000 years BCE (although the authors indicate that this divergence time has wide confidence intervals and will need to be confirmed with more detailed analyses). This divergence was followed by several episodes of hybridization and consequent gene flow.

At the onset of domestication, gene flow was primarily from domestic into wild geese. Probably, geese were not intensively managed at that time, allowing domestic geese to interbreed with their wild relatives. Moreover, goose farmers might occasionally restock their flock by collecting eggs from the wild and raising them in captivity. By Medieval times, goose-keeping was a common phenomenon and the escaped birds would regularly mix with wild flocks. This resulted in gene flow in the opposite direction, from the wild into the domestic population. A patterns that is still visible in present-day goose populations.

A principal component analysis indicates a clear separation between wild Greylag Geese (blue), European domestic breeds (green) and Chinese domestic breeds (red). Some locations, such as Turkey, show admixture from different lineages.

Turkish Hybrids?

Interestingly, the amount of gene flow from wild into domestic goose populations differs between countries. In Finland and Norway – where goose rearing is not so popular – the genetic influence of wild birds is relatively low. In the Netherlands, however, the genetic signs of hybridization is more pronounced. This can be explained by the popularity of waterfowl collections in this country and the fact that many Greylag Geese winter in the Dutch fields (and a large proportion is even present year-round). There is thus ample opportunity for domestic geese to interbreed with wild ones.

Turkish goose populations showed genetic signatures from both European and Chinese domestic breeds. They might thus be a hybrid population between these independently domesticated breeds. Alternatively, the Turkish geese might represent the ancestral genetic variation of Greylag Geese, supplemented with some gene flow from Chinese breeds. More research is needed to solve this mystery and determine whether the domestication of geese started in Turkey.

References

Heikkinen, M. E., et al. (2020). Long-term reciprocal gene flow in wild and domestic geese reveals complex domestication history. G3: Genes, Genomes, Genetics, 10(9), 3061-3070.

Featured image: Domestic geese © Hippopx

This paper has been added to the Anseriformes page.

Convergent evolution of immune proteins in tits, chickadees, and titmice

These small passerines use similar molecular tricks to detect pathogens.

Convergent evolution is a fascinating phenomenon. It concerns the evolution of similar traits in distantly related organisms. Think of the streamlined bodies of fish-eating penguins and auks, birds that diverged more than 60 million years ago. But such similarities are not only limited to morphological traits, evolution can also converge on the same solutions at the molecular level. For example, whales and bats use the same genes for echolocation.

Convergent evolution on the molecular level can be especially important for proteins involved in immunity. These molecular machines need to detect and fight a wide range of pathogens. It is easy to imagine that organisms exposed to the same bacterial or viral species will converge upon similar defense mechanisms. A recent study in the journal Molecular Ecology tested this idea with the bird family Paridae (tits, chickadees, and titmice).

Convergent evolution of body shape in the extinct Great Auk (left) and the Emperor Penguin (right). Credits: Great Auk © Mike Pennington | Emperor Penguin © Samuel Blanc.

 

Toll-like Receptors

Martin Těšický and his colleagues focused on toll-like receptors (TLRs), proteins that recognize signals derived from pathogens and trigger a signaling cascade that starts the innate immune response (first line of defense against all pathogens) and regulates the consequent adaptive immune response (learned response, specific to a particular pathogen). Toll-like receptors have specific structures (called ectodomains, ECD) that contain a ligand-binding region (LBR) which interacts with pathogenic molecules. Because these protein regions have to recognize a wide range of bacteria and viruses, you can expect strong positive selection for successful toll-like receptors.

The study focused on two receptors that are specialized to recognize different signals: TLR4 binds with lipopolysaccharides from gram-negative bacteria, while TLR5 is specific to flagellin (a protein in the bacterial flagellum). The researchers scanned the protein sequences from 29 tit species for sites under positive selection. Next, they investigated whether these positively selected sites altered the structure and binding capacity of the receptors. For instance, a different amino acid in a certain location might have different molecular properties that affect the functioning of the protein. This approach resulted in four positive selected sites in TLR4 and fourteen in TLR5.

Positively selected sites and functionally important sites of the extracellular ectodomain on the great tit TLR4 (a) and TLR5 (b). Positively selected sites are highlighted in blue or orange, and sites under convergent evolution are indicated with red arrows. From: Těšický et al. (2020) Molecular Ecology.

 

Comparing Trees

Now that we have a list of positively selected sites, we can investigate whether they experienced convergent evolution. This can be done by comparing the phylogeny of the Paridae with the evolutionary trajectories of the different sites. These analyses revealed that three positions in
TLR4 and six positions in TLR5 showed signals of molecular convergence. Hence, different tit species independently evolved similar protein structures to fend off invading pathogens. This finding indicates that these species might have experienced similar ecological conditions with shared bacteria or viruses. However, the researchers reported that “the observed evolutionary convergence was not explained by the selected ecological traits, suggesting that more direct evidence on the composition of the microbial communities interacting with TLRs is needed.” Another evolutionary puzzle to solve.

Convergent evolution in Toll‐like receptor 4 (TLR4) in the Paridae family. The species tree on the left does not match the evolutionary history of a particular protein location on the right. Different tit species converged on the same solution independently. From: Těšický et al. (2020) Molecular Ecology.

 

References

Těšický, M., Velová, H., Novotný, M., Kreisinger, J., Beneš, V., & Vinkler, M. (2020). Positive selection and convergent evolution shape molecular phenotypic traits of innate immunity receptors in tits (Paridae). Molecular Ecology, 29(16), 3056-3070.

Featured image: Black-capped Chickadee (Poecile atricapillus) © USFWS | Wikimedia Commons

The constrained evolutionary trajectories of White-eyes on the African mainland and its islands

The patterns of constrained evolution suggest a non-adaptive radiation.

There is more to evolution than adaptation. This message was conveyed by Stephen Jay Gould and Richard Lewontin in their 1979 paper with the wonderful title “The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme.” In this paper, they argued that evolutionary thought has been dominated by the idea that organisms can be broken up into separate traits that are driven to an optimum by natural selection. Researchers would tell an “evolutionary story” to describe the most likely trajectory for a particular adaptation. Gould and Lewontin criticized this approach and proposed an alternative perspective that focuses on non-adaptive processes. Organisms should be analyzed as integrated wholes, with a bauplan that is constrained by phylogenetic history, developmental pathways, and general architecture. Some traits are not the optimal outcome of natural selection, but rather the byproduct of constrained, non-adaptive processes.

 

White-eyes

A similar discussion can be applied to the evolution of species-rich groups, such as island radiations. An often-heard explanation is that an ancestral population arrived on the island and diversified into several species that each adapted to a particular ecological niche. A well-studied case that immediately comes to mind is the Darwin’s Finches, a textbook example of an adaptive radiation. But this reasoning cannot automatically be applied to other radiations on islands on or the mainland. There might also be examples of non-adaptive radiations.

A recent study in the Journal of Biogeography took a closer look at the White-eyes (genus Zosterops). These small songbirds have been called “the Great Speciator” because they have diversified into more than 100 species in the last two million years. But are they also an example of an adaptive radiation? To answer this question, Julia Day and her colleagues performed a morphological analysis of 120 Afrotropical species.

The evolutionary tree of the White-eyes shows an early burst in diversification (warm colors) followed by a slowdown later on (cold colors). From: Day et al. (2020) Journal of Biogeography.

 

Exploring Morphospace

The analyses revealed a striking difference between mainland and island species. On the mainland, morphological evolution seems to be constrained, leading to convergence on certain phenotypes. In particular, White-eyes repeatedly evolve into highland or lowland forms. This pattern suggests that mainland White-eyes are “stuck” in an adaptive landscape with two optima. This constrained evolution can be due to the general morphology of these birds which does not allow for the evolutionary exploration of other phenotypes, or the lack of available niches due to competition with other species.

The situation on islands is slightly different. Here, different White-eye species have evolved novel phenotypes. The authors suspect that the evolution of different morphologies in island species might be due to less interspecific competition, allowing the birds to explore new ecological niches. However, the expansion of morphospace is still limited around the general bauplan of a typical White-eye, indicating that certain phylogenetic or developmental constraints might be at play here. Based on these patterns, the researchers concluded that “Given the apparent lack of ecological diversification, and limited insular diversification in Zosterops, the general pattern observed in this group may be explained by geographical speciation involving non-adaptive radiation.”

Figures a and b: Morphospace occupation of mainland species from the highland (green) and lowland (khaki). Figures c and d: Morphospace occupation of island radiations. Notice the overlap in mainland species and the separation in island species. From: Day et al. (2020) Journal of Biogeography.

 

References

Day, J. J., Martins, F. C., Tobias, J. A., & Murrell, D. J. (2020). Contrasting trajectories of morphological diversification on continents and islands in the Afrotropical white‐eye radiation. Journal of Biogeography, 47(10), 2235-2247.

Featured image: Cape white-eye (Zosterops pallidus) © Lip Kee | Wikimedia Commons

Why the “Red-breasted Meidum Goose” is probably not an extinct species

Convincing evidence to consider it an extinct species is currently lacking.

“Extraordinary claims require extraordinary evidence”, said Carl Sagan in the television program Cosmos. This statement came to mind when I read several news articles with bold titles, such as “4,600-Year-Old Egyptian Painting Depicts Extinct Species of Goose” and  “Ancient art reveals extinct goose.” These headlines refer to a recent study on the Meidum Geese, a 4,600-year-old Egyptian painting that historians described as “one of the great masterpieces of the Egyptian animal genre”. It depicts several goose species, including two Red-breased Geese (Branta ruficollis). However, a closer look at these colorful paintings reveals some striking differences with this well-known species. Could the Meidum Geese represent an extinct taxon?

 

Tobias Criteria

To answer this question, Anthony Romilio applied the Tobias criteria to the artwork. This method scores the characters between closely related taxa on a scale of dissimilarity. Low scores indicate that the taxa are very similar and could be classified as a single taxon (e.g., subspecies ), while high scores point to many dissimilarities and possibly distinct species. The first goose on the artwork showed low scores when compared to Greylag Goose (Anser anser) or Bean Goose (Anser fabalis), while the second painted goose most likely corresponds to a Greater White-fronted Goose (Anser albifrons). The third species of the Meidum Geese, however, did not accurately reflect Red-breasted Goose. Romilio writes that “This raises the possibility that the ‘Medium Geese 3′ may illustrate a distinct, yet now extinct goose population as has been suggested previously.”

The Meidum Geese. The top left and bottom right paintings could correspond to Greylag Goose of Bean Goose. The pair in the top right are most likely Greater White-fronted Geese. But what about the Red-breased Geese?

 

Counterarguments

Stating that there was an extinct goose species in ancient Egypt based on a painting is quite an extraordinary claim. In contrast to the news headlines, the paper provides a very balanced analysis of this claim. And although it is a possibility, I would argue that the extraordinary evidence to back this claim is currently missing. I am not convinced for two main reasons:

1. Unique Artwork. The Meidum Geese are the only depiction of a Red-breased Goose in Egyptian art (to my knowledge). This suggests that they might have been seen as rare vagrants, and were later painted from the artists’ memory which can explain the differences. Moreover, if the painting represented an extinct taxon, you could expect independent artwork depicting this colorful bird.
2. Not Accurate Enough. In the paper, the author argues that other species are realistically painted and hence we can assume that the “Red-breasted Meidum Goose” is also realistic. First, this reasoning is contradicted by the analysis of Meidum Goose 1, which could be either a Greylag Goose or a Bean Goose. If the paintings were accurate, you should be able to tell the difference. And second, the other goose species on the artwork belong to the genus Anser, which is not known for its colorful members. These “grey geese” do not leave much room for artistic freedom, in contrast to the colorful patterns on the Red-breasted Goose.

 

Fossils and Genomes

What could convince me that the “Red-breasted Meidum Goose” does represent an extinct species? Another clue might come from the fossil record or genetic analyses. Recently, a goose skull was discovered on Crete that is similar to the Red-breasted Goose. A morphological analysis of this skull might reveal whether it belonged to an unknown species that is closely related to the Red-breasted Goose. In addition, researchers might be able to extract ancient DNA from the skull and perform a proper phylogenetic analysis.

The genomes of present-day goose species might also hold the key to this mystery. Genomic analyses have uncovered signatures of hybridization events with now extinct species in the genomes of extant species, a phenomenon known as ghost introgression. Given the high levels of hybridization in geese, the extinct Egyptian species might have interbred with the Red-breasted Goose or another goose species. If so, we might be able find genetic traces of these ancient hybridization events. And if we are lucky, the introgressed regions might provide some insights into the phenotype of this extinct species. I am aware that this is very speculative and wishful thinking. But it would certainly be extraordinary evidence!

 

A Hybrid Goose?

In a discussion on Twitter, someone proposed the possibility of a hybrid. Although I like this suggestion, I do not think it is likely. If it was a hybrid, there was clearly a Red-breasted Goose involved. And hybrids with this species tend to be “drab” and lose their bright red markings.

A putative hybrid between Red-breasted Goose and Barnacle Goose. © Dave Appleton | Flickr.

 

References

Romilio, A. (2021). Assessing ‘Meidum Geese’ species identification with the ‘Tobias criteria’, Journal of Archaeological Science: Reports 36:102834.

Splitting the Long-tailed Rosefinch into a Chinese and a Siberian species

Genetic and morphological data support the recognition of two distinct species.

“We echo calls for integrative taxonomy in which genomic and phenotypic data are considered on equal footing when delimiting species.” This concluding remark was stated by Carlos Daniel Cadena and Felipe Zapata in their recent review paper on species delimitation. I wholeheartedly agree with this statement. In fact, I have advocated this integrative approach to taxonomy in other blog posts (see for example here). The rationale behind this approach is quite straightforward: different taxonomic concepts and methods are combined in drawing species limits. Within this context, two general frameworks can be used: integration by congruence and integration by cumulation. The congruence approach entails that different data sets, such as molecular and morphological characters, support the decision to recognize certain taxa as valid and distinct species. In the cumulation approach, evidence from different data sets is gathered, concordances and conflicts are explained within the specific evolutionary context of the taxa under study, and based on the available evidence a decision is made.

 

Five Subspecies

The best way to highlight the importance and usefulness of integrative taxonomy is to see it in action. Luckily, a recent study in the Journal of Ornithology applied this strategy to the Long-tailed Rosefinch (Carpodacus sibiricus). The distribution of this species extends across a large part of eastern Asia. Based on its discontinuous distribution and some subtle differences in plumage, five subspecies have been proposed: the northern sibiricus, ussuriensis and sanguinolentus, and Chinese endemics henrici and lepidus. Simin Liu, Chentao Wei and their colleagues collected samples from all five subspecies and performed detailed genetic, morphological and acoustic analyses to determine how distinct these subspecies are. Perhaps some can be elevated to species rank?

The discontinuous distribution of the Long-tailed Rosefinch. The symbols correspond to different sampling locations for particular subspecies. Colors refer to resident (green) wintering (blue) and breeding (yellow) areas. From: Liu et al. (2020) Journal of Ornithology.

 

Two Clades with Similar Songs

Genetic analyses of the mitochondrial gene COI uncovered two main clades that correspond to the northern and southern grouping of subspecies. The northern clade consists of sibiricus, ussuriensis and sanguinolentus, while the southern clade comprises henrici and lepidus. Interestingly, the subspecies ussuriensis and sanguinolentus form a mixed group, suggesting that they should be considered one subspecies instead of two. The other three subspecies are clearly distinct lineages.

In contrast to the genetic analyses, there were no clear differences in songs. The authors write that “Overall, there was much overlap among the taxa and no clear separation was found, and there was no clear division between the songs of the northern and southern groups.” The lack of song divergence might be due to the recent origin of these groups (ca. 1.36 million years ago) or their allopatric distribution. The birds might not need species-specific songs because they rarely encounter other subspecies. There might thus be no strong selection that could lead to different songs.

The genetic analyses uncovered two main groups (left figure). All subspecies form distinct lineages, except for ussuriensis and sanguinolentus. There were no clear differences in songs between the subspecies (right). From: Liu et al. (2020) Journal of Ornithology.

 

Particular Plumage Patterns

What about morphological differences? Previous studies indicated subtle variation in plumage patterns. Although the authors did not perform a quantitative morphological analysis, they do describe notable differences between the northern and southern groups.

While adult males from the northern group have the entire forehead and crown silvery-pink, in the southern group the feathers of the forehead are silvery-pink, whereas the crown is reddish. The mantle of northern birds is pink to deep red with moderately broad brown streaking, while the mantle of southern birds is more brownish and less reddish. The northern taxa have broader median and greater covert wing bars, while the wing bars of southern birds are relatively narrow. Finally, the three outermost tail feathers are extensively white in northern birds, while in southern birds only the outermost feathers are extensively white, and the white part only covers less than half the length of the second outermost tail feathers.

Based on the gathered evidence, the researchers propose to split the Long-tailed Rosefinch into two species, namely the Siberian Long-tailed Rosefinch (C. sibiricus comprising the subspecies sibiricus and sanguinolentus), and Chinese Long-tailed Rosefinch (C. lepidus comprising the subspecies henrici and epidus). Would you agree?

The different subspecies show some subtle differences in plumage patterns. From: Liu et al. (2020) Journal of Ornithology.

 

Evolutionary History

Regardless of whether the northern and southern group will be recognized as distinct species, it is worthwhile to have a closer look at their evolutionary history. This north-south division between a Siberian-Japanese clade and a Chinese clade has been documented in other bird species and can probably be attributed to the mountains of northern and central China. The combined effects of the geographical isolation of these mountains and the changing vegetation during the Pleistocene turned this area into a formidable barrier for passerines, resulting in genetic divergence between separated populations.  Similarly, these two taxa in the southern group likely diverged in separate mountain ranges: henrici in the Hengduan mountains and lepidus in the Qinling Mountains and Yan Mountains.

Within the northern group, we see a east-west divide between sibiricus and ussuriensis/sanguinolentus. This pattern can be explained by historical glacial isolation in Siberia. It is possible that the eastern and western groups were connected by gene flow in the past. Indeed, one ussuriensis (in yellow) individual is nested within the sibiricus (in blue) group. Whether this concerns a misidentified individual or a signature of gene flow remains to be determined. I am secretly hoping for the latter explanation.

 

References

Liu, S., Wei, C., Leader, P. J., Carey, G. J., Jia, C., Fu, Y., Alström, P & Liu, Y. (2020). Taxonomic revision of the Long-tailed Rosefinch Carpodacus sibiricus complex. Journal of Ornithology, 161(4), 1061-1070.

Featured image: Long-tailed Rosefinch (Carpodacus sibiricus) © Попов Евгений | Wikimedia Commons