Modern weights and measurements on wild tigers

[GuateGojira]

(04-22-2022, 03:27 AM)GuateGojira Wrote: On the tiger subspecies:

This is something that I would like to talk some time ago, but for time issue I did not manage to do it.

The subspecies concept is something that is not even quite clear among the experts, and opinions in Biology are divided between "lumpers" which are the ones that want to join innecesary separations between populations, and the "spliters" which are the ones that prefer to separate as much as possible based in morphology or genetic.




Currently, the Cat Specialist Group of the IUCN is following the idea of the lumpers and based in the study of Wilting et al. (2015), which analize morphological and genetic data, they resolve that the current information support the separation of only two subspecies of tigers but also accept the fact that in the mainland tigers there are two different MU (Management units). Kitchener et al. (2017) provide a summary of those conclutions but also accept the fact that there is no complete consensus about this clasification and latter Liu et al. (2018) provided evicence that support the separation of tiger populations in at least 6 subspecies. Now the question is, is genetic-only enough to separate subspecies, or this only reflect an artifitial differenciation between populations made by humans and not by nature?

Originally, the known 8 "subspecies" are based in morphology (size, weight and pelage), but honestly those differences are at some point arbitrary and based in a very small sample of specimens, some of them lost. Kitchener (1999) in the book "Riding the tiger" and copy-pasted with minimal adds in the book of 2010 "Tigers of the World" (this second time together with Yamaguchi) made a full chapter explaining why this clasiffication do not have a real support. Check this table from 2010:

*This image is copyright of its original author

*This image is copyright of its original author

As we can see only the Indochinsese tiger has a good sample, most of them are based in one single specien, which is completelly unreliable. This evidence, togheter with a broader analisys, Kitchener argue that there is no base for differences as even between Bengal tigers there is a difference betwen populations and those from Indochina are indistinguisable from those from India. The next conclution from the late Dr Rabinowitz is interesting in this subject:

*This image is copyright of its original author

*This image is copyright of its original author

I am agree with this information, as the body size and weights reported of the Indochina and Malayan tigers are just slightly shorter than those from India and a little lighter, but they reach aproximatelly the same upper ranges. However the sample from Indochina is very poor in comparison with that of India.

Also in the skulls, I noted that while we can clearly see differences in the skulls of these populations in the images from Mazák (1981), check it:

*This image is copyright of its original author

*This image is copyright of its original author

Upper one from Nepal (Bengal - tigris), lower one from Vietnam (Indochina - corbetti). However in Mazák (2013; reimpression from 1983) the author shows another skull from a Bengal tiger from the Assam and it looks like a transition form between the clasic "Bengal" skull and the classic "Vietnam" skull, check it:

*This image is copyright of its original author

*This image is copyright of its original author

Now compare it with those in Mazák (1981) and you can compare the transitional form. Also the river Irrawaddy (which is normally used to separate the Bengal and Indochina subspecies) is not a significant barrier for tigers, which are know to swim 6-8 kg or even up to 26 km (Mazák, 1981). Here is the river Irrawaddy:

*This image is copyright of its original author

*This image is copyright of its original author

Other problem is with the separation between tigers of Indochina and those of Malaysia. Genetic shows differences which were used by Luo et al. (2004) to suggest them as a different population (followed latter by Liu et al. (2018). However Mazák (2010), Wilting et al. (2015), and Kitchener et al. (2018) do not support this separation and conclude: 

"The taxonomic status of tigers in Indochina and the Malay Peninsula is still unclear; “jacksoni” is diphyletic, based on mtDNA, and must have originated very recently from corbetti. Subspecies corbetti shows further genetic structure which does not appear to have geographical significance (Luo et al. 2004). However, we shouldbe wary of conclusions based only on living tiger populations. Mondolet al. (2013) showed that modern Indian tiger populations show increased population structure compared with historical samples, indicating  a loss of mtDNA and microsatellite diversity, owing to local extirpation and genetic drift."  

*This image is copyright of its original author

*This image is copyright of its original author
And the last nail in the coffin, from Kitchener et al. (2018):

*This image is copyright of its original author

*This image is copyright of its original author

The description of the subspecies was not done correctly and the name can't be accepted and is no a nomen nudum. Evidence suggest that the "differentiation" in body size and genetic was a man-made efect, not a natural separation.

Kitchener & Dugmore (2000) shows that there is no clear geographic separation between Indochina and South China tigers (by a significant gap!), check it:

*This image is copyright of its original author

*This image is copyright of its original author

Also Luo et al. (2004) found that some putative South China tigers has Indochina DNA. Finally Driscoll et al. (2009) found that Amur and Caspian tigers are one and the same and they populations were separated by only about 200 years ago. Contrastingly Singh et al. (2015) found that the Sundarbans tigers are separated of the mainland population by 2,000 years! So, genetically speaking, Caspian are more "Amur" than the Sundarbans been "Bengal".

There is a lot of more information, this is just a very very very breef summary, but here we can see that with this few data those "separations" between populations are/were not as clear as we may think. In fact, that idea of clearle separated "subspecies" provided by Guggisberg and Mazák are not realistic at all, and taking in count that the maximum distance traveled by a tiger, reliabily recorded, is of 1,000 km, this suggest that all mainland tigers could travel between they regions with few to none natural barriers and that morphological differences recorded may be just clinal as suggested by Kitchener. However, I have an hypotesis, that this differences are the efect of a very small sampling, after all check how many Bengal tiger skulls we know and how many South China ones, there is a big difference; check also how many Indochina tiger skulls we had and until resently it was found a new Malayan skull as large as one from Bengal, so in theory maybe the sizes that we normally use and quote could be bigger than we think and similar to those of Bengal. That is the same that happen with Javanese tigers, normally quoted as smaller than Sumatran, when in fact, skull records shows that they were of the same size than South China tigers (Mazák, 2013). By the way, Xue at al. (2015) provided an interesting analysis about the singularity of the Sunda tigers and the idea that while they are a single subspecies, they stoped the gene flow between them years ago.




Knowing all this, I fell that the theory that tigers are separated in only two real subspecies is the correct one, as mainland tigers could travel freele, fromt he map analysis of Ktichener & Yamaguchi (2010) the model HTP (habitat, topography, precipitation) is the best one as it predicted all the tiger populations, in contrast to the model DDP (distribution data prediction) which fail to predict the pupulation of Caspian tigers. Su using the map of 20,000 years ago (late Pleistocene) and the metod HTP, check this:

*This image is copyright of its original author

*This image is copyright of its original author

Here we can see that all the tiger population was interconected with no natural barriers and the separation was probably until the end of the Pleistocene when sea levels rised at 12,000 years ago, but even after that, mainland tigers still were interconected. Mainland tigers were separated only until the humans started to act in they environment, supporting a man-made separation. Now check the modern tiger map:

*This image is copyright of its original author

*This image is copyright of its original author

This map from 2016 shows that the modern tiger populations are very fragmented, we can see a huge gap between the last viable population of tiger in Myanmar/Burma and those from Thailand. There is also no habitat that can be used by tiger to move from Thailand to Malaysia, and Russian together with Sumatran tigers are beyond the reach of any other tiger population. India is like a group of "islands" of tigers and young specimens can barely move between them, and Sundarbans is so separated that Singh et al. (2015) with Barlow et al. (2009) concluded that based in genetic and morphology the Sundarbans tigers "are the most divergent group of Bengal tigers, and ecologically nonexchangeable with other tiger populations, and thus should be managed as a separate “evolutionarily significant unit” (ESU)". Check please that none of the genetic studies from Luo, Liu and Wilting, used ANY Sundarbans tigers in they study.

So, in conclution, we as humans have created 5 artificial populations in mainland: 1- India/Nepal/Buthan/Myanmar; 2 - Sundarbans; 3 - Thailand/Laos; 4 - Malaysia; 5 - Russia. Sumatra is definitelly different and South China tigers exist only in captivity. What we don't know is if the genetic data from Luo at al. (2004 and 2010) and Liu et al. (2018) used old and modern data, or just modern, because that could explain the genetic differences, as these populations are isolated and now relfect speciefic adaptations to they areas, which using the old taxonomical ideas from 19th century could be interpreted as "natural subspecies".




Following Wilting et al. (2015), confirmed by Kitchener et al. (2017) of the CSG of IUCN and adding the study of Singh et al. (2015), there is only two tiger subspecies, divided in conservation units that should not be mixed as they had they own adaptations:

 1 - Continental tiger - Panthera tigris tigris
      1.1 - Mainland tiger - India, Nepal, Bhutan, Myanmar, Thailand, Laos, China (captive amoyensis).
      1.2 - The Sundarbans - India, Bangladesh.
      1.3 - Russian Far East - Russia, China.

2 - Sunda tiger - Panthera tigris sondaica

These will be the modern populations of tigers based in the information. Now, if we follow Luo et al. (2004) and Liu et al. (2018) we should have 6 "subspecies". Interestingly, the artifitial groups created by the human presure match those from the subspecies of Luo and Liu:

1 - Bengal tiger - Panthera tigris tigris - Indian subcontinent.
2 - Indochina tiger - Panthera tigris corbetti - Thailand and Laos.
3 - Malayan tiger - Panthera tigris jacksoni - Malaysia.
4 - South China tiger - Panthera tigris amoyensis - China.
5 - Amur/Caspian tiger - Panthera tigris virgata - Russia and China (altaica is synonimus under this scenario).
6 - Sumatran tiger - Panthera tigris sumatrae - Sumatra (and possible Java and Bali too).

Remember that none of these teams used a single Sundarbans tigers in they analysis.


Which are the implications? Certainly the idea of this person, whoever he or she is, that the tiger subspecies had political implications may be correct, but not in the form that we may think. Subspecies names are tied with countries and some governments will not be happy if they regional or national animal change of scientific name, or if they tigers are no longer "unique". So nationalism may be a problem on the creation o deletion of subspecies. One famous case in the USA is Smilodon, as we know that the real species from North America is Smilodon fatalis, but in California is "officialy" known as Smilodon californicus and they declare it the state fossil! 




What means to have only two subspecies? It means that we can use Indian tigers to repopulate Indochina, Malaysia and South China. Also provides "value" to the mix captive tigers that populate USA and other countries. While the idea will be good, actually it will create a mess if is not correctly used. For example, most of the captive tigers are a mix between Amur and Bengal tigers, and if we remember, these two populations are the most diverged since the Pleistocene and even under the new clasification they belong to two different conservation units, so the large captive tigers of USA are STILL useless for conservation, but I highly doubth that those places that breed tigers for business are going to check and accept these details from the study. Other thing is that there is still a good and viable population of Indochina tigers in Thailand, so there is no point in trying to use Bengal tigers to populated Laos, Vietnam and Cambodia, while the efforts should be focused in increase and care the tigers from Thailand and, with time, used them to repopulate the other Indochina countries. As we can see, the idea of two tiger subspecies could be the correct one, but sadly is the most problematic based in politicar and economic purposes.

What means to have 6 subspecies? It measns to continue with the effrorts to save the tigers like they are in this moment, each country manage thy own populations and keep the "purity" of they specimens. Captive tigers in managed zoos still have they value and the mix tigers from private owners can't be used for breeding which is good! So, the "6 subspecies" scenario could not be realistic in a natural point of view, but is the most realistic in the modern days, based in the current distribution of tigers and will keep the traffic of generic tigers at minimum.

Using all this information, my opinion is that 2 tiger subspecies is the real one, but form management of the modern tiger populations and to avoid traffic and bussines of "paper" tigers, I think that the best is the usage of the 6 subspecies scenario.

Hope this helps, greetings.

Based in this post, about the susbspecies, I made a comparative image in the post No. 869 about what could be the size of the tiger subspecies if we take the idea of only two populations.

However, what happen if we follow the subspecies based in genetic evidence, which is supported by Liu et al. (2018) and others? Well, this is the comparative image of that:

*This image is copyright of its original author

In the image we can see the modern "subspecies" based in DNA, and while the Sundarbans tigers are still not separated, they are already an "ESU" and should be managed separatelly from any other tiger populations.

The figures from the Bengal/Amur/Indochina are only from scientific records. Those from Malaysia and Sumatra include both, scientific and hunting, as the data is very scarse, and the body mass from the Malayan tigers came from captive specimens. South China tigers were completelle remouved as there are no modern weights and measurements reported in litterature.

Finally, the Sundarbans tiger includes only modern records (small sample) and remember that all the specimens were frail and underweight, and I noted that while I use the image of a healthy and very good looking male tiger from that area, his chest is much wider than what suggest the few measurements, suggesting that is possible that Sundarbans tigers could be a little bigger than what we currently believe. Reply