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ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)
ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)
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ON THE EDGE OF EXTINCTION - A - THE TIGER (Panthera tigris)
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 (06-24-2019, 10:02 AM)Greatearth Wrote:(06-24-2019, 05:22 AM)Rishi Wrote: Absolutely! Even if they're considered similar enough to be a single subspecies, Siberian & Caspian tigers lived far enough as well as segregated enough from each other to have significant genetic differences. Firstly, take this into consideration, the reed region of the Panj River on the border of Afghanistan and Tajikistan in Central Asia, where the first tiger was apparently from (http://kavehfarrokh.com/iran-and-central...the-1930s/), is far away from and environmentally different to the hills or mountains of northern Iran in Southwest Asia, where the second tiger was from (http://www.tigers.ca/Foundation%20overview/caspian2.htm), yet nobody questions the idea that they are both Caspian tigers, or members of the same subspecies, right? *This image is copyright of its original author *This image is copyright of its original author Map of distribution of tiger subspecies by Vratislav Mazák, page 3: https://web.archive.org/web/201203091255...1-0001.pdf *This image is copyright of its original author Map by Luo et al.: https://journals.plos.org/plosone/articl...ne.0004125 *This image is copyright of its original author And Luo et al. (https://journals.plos.org/plosone/articl...ne.0004125) used at least one Caspian tiger that was West Asian, a captive tiger in Moscow Zoo that came from Northern Iran in West Asia, and its mtDNA was closer to the mtDNA of Amur tigers than those of some Bengal tigers to others, so just as 'subspecies' is a man-made concept, with one definition being about 2 populations of the same species that are genetically and geographically distinct from each other (https://www.merriam-webster.com/dictionary/subspecies), which wouldn't have applied when Caspian and Siberian tigers were contiguous, or when both were present in the area of Lake Baikal (https://archive.org/stream/mammalsofsov2...rch/Baikal), the names "Caspian tiger" and "Siberian tiger" are man-made names for a race of tigers that are distinguishable from other tigers in that they inhabited temperate or fairly temperate areas, such as northern Iran, the area of Lake Baikal, and the Russian Far East, whereas other tigers, with the exception of the Himalayan Bengal tiger, inhabit hot or warm tropical areas, in the same way that "Bengal tiger" is a man-made name for a tiger that inhabits India or South Asia, whether or not South Asian tigers are closely related in the same way as Korean, Manchurian, Russian, Central Asian and West Asian tigers are. If the great distance between the Amur tigers in Northeast Asia (Korea, Manchuria (Northeast China) and the Russian Far East) and the Caspian tigers in eastern Central Asia is enough to treat them as different subspecies, then why should the latter be treated as the same subspecies as the tigers in Southwest Asia (including Georgia and Iran), such as this Georgian or Iranian tiger (http://kavehfarrokh.com/heritage/the-las...n-georgia/)? *This image is copyright of its original author Luo et al.: https://journals.plos.org/plosone/articl...ne.0004125 "Tigers as a species historically ranged across Eurasia from the Sunda Islands, west through the Indian subcontinent to the Indus river and north along the Pacific seaboard to 60° NL and a wide swath of central Asia from the Russian Far East to eastern Turkey [1], [2]. This wide distribution was primarily influenced by environmental changes associated with Pleistocene glaciation events [3]. Commonly known as the Caspian tiger on the basis of its type locality (N. Persia), the historic range of Panthera tigris virgata also included Trans-Caucasia and Eastern Anatolia, with the greatest population densities in the riverine tugai forest systems of Central Asia [1], [2], [4]. During the Middle Ages Caspian tigers were resident across the steppes of Ukraine and southern Russia [4]. Between 1920 and 1970, tiger populations throughout Central Asia declined and disappeared for reasons common to tigers elsewhere: hunting, conversion of their limited habitat to cultivation with a concomitant decline in prey, and conflict with livestock [1], [4]–[6]. The Caspian tiger became extinct in February of 1970 when the last survivor was shot in Hakkari province, Turkey [1], [7]. In the era before molecular taxonomy tiger subspecies definitions were based on classical criteria: geographical origin, gross size and pelage variation (hair length, color, stripe number and patterning) (Figure 1) [3], [6], [8], [9]. Subspecies so described were often spurious as they were sometimes based on a single, possibly aberrant, individual, or from the unknowing sampling of clinal variation [3]. Such methods led to a lack of consensus, repeated taxonomic revision, and debate [10]. Though debate continues, eight tiger subspecies (three of which are extinct) are widely recognized based on these criteria [1], [2], [6]. However the phylogeny of the five extant recognized tiger taxa (P. t. tigris, P. t. altaica, P. t. amoyensis, P. t. sumatrae, P. t. corbetti) was revisited recently using mitochondrial molecular genetics by Luo et al. [11] who affirmed the validity of subspecies ranking for these groups. Additionally, these authors identified an equivalent sub-specific taxon unique to the Malay peninsula south of the Isthmus of Kra, formerly classified within P. t. corbetti but now designated as the Malay tiger, P. t. jacksoni. Panthera tigris virgata (Illiger, 1815) was the second tiger taxon described following the nominate Panthera tigris tigris (Linnaeus, 1758). However, because no holotype specimen of P. t. virgata exists, the relative scarcity of specimens, and the unreliability of morphological subspecies-diagnostic characters, the taxonomic validity of P. t. virgata has been questioned, its phylogenetic placement relative to other tigers is a matter of speculation, and its biogeographic origin unclear [1], [3], [4], [6]. Here, using well provenanced museum samples and ancient DNA techniques, we explore and interpret the phylogeographic natural history of the Caspian tiger, P. t. virgata in the genetic context of the living tiger subspecies, and explore possible routes taken during tiger colonization of Central Asia. Twenty (of 23) Caspian tiger museum samples (Table S1) were successfully sequenced for at least one segment of five mitochondrial genes – ND5, ND6, CytB, ND2, and COI (1257 bp), amplified as eight short amplicons to facilitate PCR of ancient material (see Methods). The amplification targets include 21 single nucleotide polymorphisms (SNPs), of which 14 are diagnostic (fixed differences) for subspecies affiliation in tigers [11], and include four of the four sites diagnostic for P. t. altaica, five of the seven for P. t. amoyensis, one of the three for P. t. corbetti, two of the three for P. t. tigris and both sites diagnostic for P. t. sumatrae. There are no diagnostic sites for P. t. jacksoni though we survey three signature alleles found uniquely in P.t. jacksoni. Seventeen of twenty P. t. virgata individuals carried a single distinctive mitochondrial haplotype, while three P. t. virgata tigers (Ptv-17, 22, 23) carried autoapomorphic variants (Table 1; Table S2). The amount of mtDNA variability observed in P. t. virgata (4 haplotypes/20 individuals), like P. t. altaica (1 haplotype/32 individuals), is low relative to other tiger subspecies P.t. tigris, (8 haplotypes/19 individuals); P. t. sumatrae, (10 haplotypes/31 individuals); P. t. jacksoni, (5 haplotypes/28 individuals); P. t. corbetti (5 haplotypes/33 individuals) [11]–[13] (Figure 2). Except for Ptv-5, housed in the Moscow Zoo but taken in the wild in Northern Iran, all Caspian tiger specimens are from individuals taken directly from the wild. Because these samples were collected between 1877 and 1951 (i.e., covering ca. 15 tiger generations) from wild tigers in China, Kazakhstan, Afghanistan, and Uzbekistan (see Table S1) it is unlikely they represent the sampling of a single extended family. Moreover, since sample collection took place over the broad geographic range of the subspecies when Central Asian tiger populations were still large, albeit declining, the low endemic mtDNA diversity (relative to other subspecies) indicates that low variability was a natural genetic feature of the 19th century Caspian tiger population and not an anthropogenic effect. To place more accurately the Caspian tiger relative to living tiger subspecies we re-assessed the phylogenetic relationships of tiger subspecies using a previously published dataset [11], but here rooted using clouded leopard (Neofelis nebulosa) [14], leopard (Panthera pardus) [15] and snow leopard (Panthera uncia) [16], with the inclusion of Ptv-2, the Caspian tiger for which the longest combined sequence was available (1.26 kb) (see Methods). The rooting imparted evolutionary polarity to the tiger family tree and showed P. t. amoyensis to be basal and P. t. altaica to be a sister group to P. t. corbetti, while the Caspian tiger haplotype was one step away from that of P. t. altaica (Figure 2). The phylogenetic placement and remarkable similarity observed between P. t. altaica and P. t. virgata indicate that the Amur tiger population is the genetically closest living relative of the extinct Caspian tiger, and strongly implies a very recent common ancestry for the two groups. Russian records from the 19th and early 20th centuries indicate that tigers were sporadically present throughout the region between the core distribution of Caspian and Amur tigers (see Figure 1) and were only hunted out in the modern era [4]. Thus, the actions of industrial-age humans may have been the critical factor in the reciprocal isolation of Caspian and Amur tigers from what was likely a single contiguous population. The origin of the Amur tiger population is estimated at less than 10,000 years ago by molecular genetic analysis: using a rate of mitochondrial evolution calibrated on the tiger-leopard split (estimated at 2 million ya.), Luo et al. [11] inferred that the P. t. altaica population, which showed no mtDNA variation, underwent a genetic reduction less than 20,000 ya, that being the time required for a single mutation to appear. The authors then refined their age estimate of the P. t. altaica subspecies further to around 10,000 ya. using a standard curve of the relationship of microsatellite allele variance in average repeat size to elapsed time [11]. This estimate is supported by biogeographic reconstructions of tiger range covering the last 20,000 years [3]. Furthermore, paleontological evidence suggests that morphologically modern tigers occurred first around two million years ago in eastern China (in the historic range of modern P. t. amoyensis) [8], suggesting that tigers in China may have comprised a stem group that gave rise to modern subspecies. Tigers only recently expanded to the Indian sub-continent (6–12 kya), the Russian Far East (late Pleistocene/Holocene) and Central Asia (Holocene) [1], [3], [4], [10], perhaps impelled by climatic and ecological changes associated with the end of the last glacial period [3]. Therefore, if 19th century Caspian and Amur tigers comprised a single population (as supported by these genetic data), then Caspian tiger diversity (or lack thereof) would likewise date to less than 10,000 years." |
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