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ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)

peter Offline
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( This post was last modified: 07-29-2015, 05:33 PM by peter )

PLANNING TIGER RECOVERY: UNDERSTANDING INTRASPECIFIC VARIATION FOR EFFECTIVE CONSERVATION - II

2 - TIGER SUBSPECIES


a - Previous studies

In the last two decades, quite many articles on tiger evolution and subspecies have been published. Although each of them is interesting, Wilting and his collegues have a point in that most are based on smallish samples. Furthermore, the two most used approaches (morphological characters and molecular markers) were only combined at a superficial level. For this reason, the result is tentative at best.   

Table 1 - Current tiger subspecies classification:



*This image is copyright of its original author



b1 - Present study

Wilting et al. conducted a molecular analysis of all nine putative tiger subspecies. The conclusion was that 

" ... modern tigers contain substantially lower genetic diversity than other pantherinae or Southeast Asian cats. The demographic reconstruction revealed a population decline around 80 thousand years ago, followed by a late Pleistocene expansion. This suggests that modern tigers succumbed to rapid environmental changes after the Toba super-vulcanic eruption ... in northern Sumatra. The impact of this eruption has been linked to population bottlenecks on other mammals such as humans, orangutans, and clouded leopards. Thus, tigers may have only survived in a single refugium outside the region of ash-cloud fallouts. The ancestral position of haplotype AMO1 suggests the presence of such a refugium in or around southern China ... " (pp. 3).

According to Wilting and his collegues, the presence of tiger fossils dating back 2,55 million years from throughout the the current tiger's range from northern China to Java, Shri Lanka, and Japan (a) as well as the widely accepted view that the tiger's high morphological variation across its wide geographical distribution was an adaption to local habitats (b) prevented a broader discussion of the Late Pleistocene population decline.

There is, however, no question that:

" ... the low molecular as well as morphological variation ... strongly favors the scenario that ancestral Pleistocene tigers became extinct in large parts of their former ... range and were replaced by modern tigers recolonizing large parts of Asia as recently as the Late Pleistocene ... " (pp. 3).


b2 - Conclusions

Molecular analysis, morphological characters (skulls and skins) and ecology enable 3 main conclusions:

1 - Modern tigers evolved after the Toba super eruption about 73 500 years ago (Late Pleistocene). In evolutionary terms, modern tigers are 'younger' than all other roaring cats.
  
2 - Modern tigers evolved from China tigers (Panthera tigris amoyensis), who survived the Toba super eruption. From China, they spread south (Sunda Shelf and Malaysia) first. Western (and central) parts of Asia were occupied later, well before northern parts of Asia were reached. The most recent wave could have been directed at northeast Indochina (Panthera tigris corbetti), and not Manchuria (Panthera tigris altaica).
   
3 - Modern tigers can be divided into 2 groups (or subspecies): island tigers and continental tigers. The last group can be divided into 2 sub-groups: a northern consisting of P.t. virgata, P.t. altaica and P.t. amoyensis and a southern consisting of P.t. tigris, P.t. corbetti and P.t. jacksoni. 

For those interested in details.    

3a - Craniodental morphology. Male (not female!) skulls of northern and eastern tigers (P.t. altaica, P.t. virgata and P.t. amoyensis) are distinct from those of other continental tigers.

3b - Pelage morphology. Skins of northern tigers (P.t. altaica and P.t. virgata) are distinct of those of other continental tigers.

3c - Ecology. Northern tigers (see above) were clearly separated from all other tigers. Southern tigers, except, Malayan tigers, clustered together.

3d - Molecular population structure. Amur and Caspian tigers grouped together, whereas Bengal and Indochinese tigers form distinct groups. Malayan tigers, although genetically separated from other continental tigers, are the only clade with two clear subclades. 


b3 - Can continental tigers be divided into separate subspecies?

" ... None of the six putative continental subspecies could be consistently distinguished by morphological or ecological characters, because they overlapped greatly ... Therefore, our data reject the taxonomic division of continental tigers into six subspecies. Instead, they should be merged into a single subspecies, which shows only minor local ecological adaptation and differentiation by distance ... " (pp. 5 and 7). 


b4 - The difference between Bengal and Javan tigers at a glance

Take notice of the differences in condylobasal skull length between both subspecies. In island tigers, extremes have been removed. In continental tigers, on the other hand, extremes (in both directions) are present. Sizewise, island tigers not only are smaller. They also are much more uniform:
 
   

*This image is copyright of its original author



In words:



*This image is copyright of its original author



b5 - Summary



*This image is copyright of its original author
 


3 - CAPTIVE TIGERS

" ... Our results mostly support current conservation management of captive tigers ... Our results demonstrate that the current breeding programs accridited by the World Association of Zoos and Aquariums (WAZA) could be extended by inclusion of many of these supposed hybryds because southern continental tigers do not need to be managed according to their hitherto conventional subspecific classification ... " (pp. 8).

" ... Our recommendations assist in the maintenance of genetic diversity and are consistent with recent findings, according to which every tiger, both wild and captive, is important as a potential reservoir of genetic diversity of the species. The seperate breeding of Indochinese, South Chinese, and Malayan tigers is likely to be unsustainable because only few founder individuals were available - for instance, only six individuals for South Chionese tigers. In contrast, both the northern continental tiger management units and the Sunda tiger subspecies have been traditionally maintained in seperate breeding programs. Their number of founders were much higher; several hundred individuals are currently part of international breeding programs. For Sumnatran tigers, the international zoo community led by WAZA has even succesfully established a Global Species Management Plan. The seperate conservation breeding and management of these units is supported by our results and should be continued ... " (pp. 9).


4 - CONCLUSIONS

Pocock (1929) saw his proposal on tiger subspecies as a working hypothesis. Over the years, it was refined and extended. In the nineties of the last century, new methods were introduced to get to more insight. Although the attempts to get to a more accurate classification never met with universal approval, it became increasingly clear that Pocock's upgraded proposal had run its course. The question was not if it would be fundamentally changed, but when. And how.      

This year, it was finally replaced by the proposal of Wilting and his collegues. Remarkable, but it wasn't done in a spectaculair way in that their findings are not that different. The difference with most other attempts is Wilting and his collegues combined different factors. More important is that the findings were interpreted in a different way. One could disagree with their conclusions, but not with the methods used. Wilting and his collegues found proof for local types, but concluded the amount of overlap between them is too pronounced to claim the title of subspecies.   

One could use their results to claim the opposite and adjust the decisions regarding conservation. This, as they argued, would backfire in that most of the five remaining subspecies would be doomed because of a lack of tigers. Furthermore, a strict classification would result in the loss of many captive tigers in that they won't be used to rewild or to breed.  

As to those who have a different opinion. I do not doubt that a period of, say, 20 000 years is enough to get to significant differences between local tiger populations, especially if they inhabit isolated regions. The skulls and skins I saw underline there are significant differences between different local populations. Same for body dimensions. It is, on the other hand, also known captive tigers of different subspecies readily breed. They also quickly adjust to new conditions.    

Furthermore, one has to remember that the time of natural conditions affecting morphology is largely past and gone. In the period that tigers recolonized Asia from China, humans had zero influence on the natural world. Animals, therefore, adapted to natural conditions only. The results, skull-, skin- and dimensionwise, really reflected the local conditions. When humans multiplied and fire-arms spread, gene flow was severely restricted. In a very short period of time four subspecies were exterminated. As the other five are close to the edge, Wilting and his collegues developed a classification that could, conservation and managementwise, perhaps help to change the tide.

A gross oversimplification or a life-saver? I thought I saw desperation as well, but the situation is desperate. Wild tigers probably only stand a chance in isolated pockets in India, Malaysia, Thailand and Russia. Maybe pragmatism isn't a bad idea.
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Messages In This Thread
RE: ON THE EDGE OF EXTINCTION - A - TIGERS (Panthera tigris) - peter - 07-28-2015, 02:33 AM
Demythologizing T16 - tigerluver - 04-12-2020, 11:44 AM
Tiger Data Bank - Apollo - 07-28-2014, 09:54 PM
RE: Tiger Data Bank - Apollo - 07-28-2014, 10:02 PM
RE: Tiger Data Bank - Apollo - 07-29-2014, 12:56 AM
RE: Tiger Data Bank - peter - 07-29-2014, 07:05 AM
Tiger recycling bin - Roflcopters - 09-04-2014, 01:36 AM
RE: Tiger recycling bin - Pckts - 09-04-2014, 02:22 AM
RE: Tiger recycling bin - Roflcopters - 09-05-2014, 01:01 AM
RE: Tiger Data Bank - Apollo - 11-15-2014, 10:07 PM
RE: Tiger Data Bank - Apollo - 11-15-2014, 10:57 PM
RE: Tiger Data Bank - Apollo - 11-15-2014, 11:33 PM
RE: Tiger Data Bank - Apollo - 02-19-2015, 11:25 PM
RE: Tiger Data Bank - GuateGojira - 02-23-2015, 11:36 AM
Status of tigers in India - Shardul - 12-20-2015, 03:23 PM
RE: Tiger Directory - Diamir2 - 10-03-2016, 04:27 AM
RE: Tiger Directory - peter - 10-03-2016, 06:22 AM
Genetics of all tiger subspecies - parvez - 07-15-2017, 01:08 PM
RE: Tiger Predation - peter - 11-11-2017, 08:08 AM
RE: Man-eaters - Wolverine - 12-03-2017, 11:30 AM
RE: Man-eaters - peter - 12-04-2017, 09:44 AM
RE: Tigers of Central India - Wolverine - 04-13-2018, 01:17 AM
RE: Tigers of Central India - qstxyz - 04-13-2018, 08:34 PM
RE: Size comparisons - peter - 07-16-2019, 05:28 AM
RE: Amur Tigers - peter - 05-20-2021, 07:13 AM
RE: Amur Tigers - Nyers - 05-21-2021, 08:02 PM
RE: Amur Tigers - peter - 05-22-2021, 08:09 AM
RE: Amur Tigers - GuateGojira - 04-06-2022, 12:59 AM
RE: Amur Tigers - tigerluver - 04-06-2022, 01:08 AM
RE: Amur Tigers - tigerluver - 04-06-2022, 09:08 AM
RE: Amur Tigers - tigerluver - 04-06-2022, 11:30 PM
RE: Amur Tigers - peter - 04-08-2022, 07:27 AM



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