How strong is the case for splitting the red panda into a Himalayan and a Chinese species?
On several popular science websites you can read that the red panda actually consists of two species: the Himalayan red panda (A. fulgens) and the Chinese red panda (Ailurus styani). When I checked the original publication in Science Advances, I became skeptical of this conclusion. The title states that there is “genomic evidence for two phylogenetic species”. Do the researchers split the red panda solely based on the phylogenetic species concept? So, this morning, I grabbed a nice cup of coffee and started reading the paper. Let’s have a look at the evidence!
In another blog post, I explained my views on the species problem. There is an important distinction between the theoretical question of what species are (i.e. species concepts) and the ways in which species can be delimited in practice (i.e. species criteria). From a theoretical point of view, we can define species as separately evolving metapopulation lineages. But how do we delineate these lineages in practice? Taxonomy has become pluralistic and combines several lines of evidence from different species criteria (e.g., morphology, behavior, genetics, reproductive isolation, …). In some cases, all criteria agree and it is easy to classify species. In other cases, different criteria result in different taxonomic decisions. For example, taxa might be genetically distinct, but morphologically indistinguishable (i.e. cryptic species).
Three lines of evidence
In this study, the authors mention three species criteria that support a split into two species. First, there are clear morphological differences between the Himalayan and the Chinese red panda (i.e. morphological species criteria):
Morphologically, the Chinese subspecies has much larger zygomatic breadth, the greatest skull length, stronger frontal convexity, more distinct tail rings, and redder face coat color with less white on it.
Second, the genetic data (based on whole genomes, the Y-chromosome and mtDNA) nicely separate the two proposed species (i.e. genetic species criteria):
On the basis of the whole-genome SNPs, the phylogenetic tree, principal components analysis (PCA), and ADMIXTURE results revealed substantial genetic divergence between the two species, providing the first genomic evidence of species differentiation.
Third, demographic analyses reveal that both species experienced drastically different population dynamics (possibly due to differences in geography and climate). This line of evidence correspond to the Evolutionary Species Concept which states that “A species is an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies”. The figure below nicely illustrates that both species have followed an independent evolutionary trajectory.
Combining the three lines of evidence – morphology, genomics and demography – it is safe to say we are indeed dealing with two different species. My initial skepticism was roused by the conservation status of the red panda (endangered). By splitting this species in two, the researchers automatically create two even more endangered species (which could be used to justify funding more research).
In fact, the genomic analyses revealed that the Himalayan red panda has experienced three bottlenecks, resulting in very low genetic diversity and demanding rapid conservation efforts. If the red panda had not been split into two separate species, this reduction in genetic diversity might not have been picked up. This finding thus illustrates the importance of good taxonomic decisions for conservation.
Hu et al. (2020) Genomic evidence for two phylogenetic species and long-term population bottlenecks in red pandas. Science Advances, 6(9):eaax5751.
Ottenburghs, J. (2019). Avian species concepts in the light of genomics. In Avian Genomics in Ecology and Evolution (pp. 211-235). Springer, Cham.