Genetic / taxonomic issues for the Cat Specialist Group

[BorneanTiger]

Tiger (Panthera tigris)
 
People would be familiar with the following 9 subspecies or types:
1) The Bengal tiger (Panthera tigris tigris) in South Asia
2) The Caspian tiger (Panthera tigris virgata) in Afghanistan (South Asia), and Central and Southwestern Asia, and possibly Eastern Europe, which is genetically similar to:
3) The Amur tiger (Panthera tigris altaica) in Northeast Asia
4) The Javan tiger (Panthera tigris sondaica) in the Sunda Islands
5) The South Chinese tiger (Panthera tigris amoyensis) in East Asia
6) The Balinese tiger (Panthera tigris balica) in the Sunda Islands
7) The Sumatran tiger (Panthera tigris sumatræ) in the Sunda Islands
8) The (Northern) Indochinese tiger (Panthera tigris corbetti) in Southeast Asia
9) The Malayan or Southern Indochinese tiger (Panthera tigris jacksoni synonym Panthera tigris malayensis) in Southeast Asia
 
The originally described 8 subspecies by Nowell and Jackson, pages 148–149:
   
 
A Malayan tiger, credit: Tigers-World 

*This image is copyright of its original author

 
A map of the distribution of tigers by Vratislav Mazák in 1981:
   
 
Now here is the history between the taxonomic disputes regarding the tiger that I know of:
 
In 2006, Mazák and Groves published a study on the Sumatran, Javan, Balinese and Indochinese tigers of Southeast Asia. They said "The taxonomic affinity of Southeast Asian tigers is re-investigated. Specimens of four traditionally recognized subspecies are examined using various craniological methods, including multivariate craniometric and phenetic analysis. Sumatran tigers differ absolutely (100%) from the geographically neighbouring mainland form P.t.corbetti; the Javanese tiger is also 100% distinguishable from the Sumatran. They are therefore regarded as two distinct species (P.sumatrae, P.sondaica) under the Phylogenetic Species Concept (PSC). The Bali tiger is classified as a subspecies of the Javanese tiger, Panthera sondaica balica."
 
In 2015, Wilting et al. published a study on many sets of data on traits of tigers (morphological (craniodental and pelage), ecological, molecular) that were used to differentiate them into subspecies. They claimed "Our results support recognition of only two subspecies: the Sunda tiger, Panthera tigris sondaica, and the continental tiger, Panthera tigris tigris, which consists of two (northern and southern) management units," with the northern 'unit' of the mainland Asian subspecies being composed of the Amur and Caspian tigers (hence the name "Northern tigers" for them, collectively), and the southern 'unit' being the Bengal, Northern Indochinese, Malayan and South Chinese tigers. Kai Kupferschmidt then published an article in the same year, under the heading "Controversial study claims there are only two types of tiger", in which he mentioned differences in opinion about the study of Wilting et al. For instance, Urs Breitenmoser, a zoologist at the University of Bern, who was not involved in the study, and is a co-chair of the Cat Specialist Group of the International Union for Conservation of Nature (the organization that draws up the red list of threatened species) said that the paper would "surely cause a stir," but that he found "the work quite convincing and in keeping with other findings in recent years,” like a paper that suggested the Caspian and Siberian tigers were the same subspecies, and that the Cat Specialist Group would look at this proposal as well. However, Shu-Jin Luo, a geneticist at Peking University in Beijing who works on endangered species (and whom I will refer to later), was skeptical of the study, arguing that the 9 traditionally recognized subspecies could be distinguished genetically, and that that should be enough, saying "Genetic data is much more reliable and objective than morphology."
 
In 2017, the Cat Classification Taskforce of the Cat Specialist Group, in line with the work of Wilting et al., and what Breitenmoser said, decided to recognize only 2 subspecies of tigers (like with the lion): the Continental or Mainland Asian tiger (Panthera tigris tigris; comprising the Bengal, North Indochinese, Malayan, South Chinese, Amur and Caspian tigers), and the Sunda Island tiger (Panthera tigris sondaica; comprising the Javan, Sumatran and Balinese tigers), while recognizing that the Malayan tiger had a unique mtDNA haplotype, likely because it is close to the ancestral lineage. The border between the ranges of the Continental and Sunda tigers is the Strait of Malacca between the Malayan Peninsula (where the Malayan tiger is present) and the Sunda Island of Sumatra.
   
   
 
The Strait of Malacca between the Malayan Peninsula and Sumatra by Shizhao:

*This image is copyright of its original author

 
However, in 2018, CSG members Driscoll and Luo rebelled against the classification of tigers into only 2 subspecies, by contributing to a study which used the whole-genome sequencing approach for analysis, which was based on 32 tiger specimens. From this, they argued that tigers were divided into 6 monophyletic clades, and hence 6 living subspecies: the Bengal (P. t. tigris), North Indochinese (P. t. corbetti), Malayan (P. t. jacksoni), South Chinese (P. t. amoyensis), Amur (P. t. altaica) and Sumatran tigers (P. t. sumatræ). Reply