Fortean Times - - Contents -

White tigers, all known spec­i­mens of which be­long to the Ben­gal tiger sub­species, owe their char­ac­ter­is­ti­cally pal­lid pelage (a con­di­tion called leu­cism, ge­net­i­cally dis­tinct from al­binism) to a sin­gle amino acid change, A477V, in a par­tic­u­lar trans­porter pro­tein known as SLC45A2 (which me­di­ates pig­ment pro­duc­tion). This change in­hibits the syn­the­sis of red and yel­low pig­ment (phæome­lanin), but not black (eu­me­lanin), thereby ex­plain­ing why white tigers still pos­sess dark stripes. Al­though never com­mon, white tigers did oc­cur nat­u­rally in the wild state for cen­turies (as con­firmed by early artis­tic rep­re­sen­ta­tions and hunt­ing records), but their spec­tac­u­lar ap­pear­ance marked them out as sought-af­ter hunt­ing tro­phies, and the strain was even­tu­ally wiped out.

The last known wild spec­i­men, a mag­nif­i­cent male named Mo­han, was cap­tured alive on 27 May 1951, and was housed there­after in the now-dis­used sum­mer palace of the Ma­hara­jah of Rewa. Mo­han was bred with nor­mal tigers, thereby pre­serv­ing and pass­ing on the mu­tant re­ces­sive gene al­lele re­spon­si­ble for the above amino acid change caus­ing leu­cism, and it is there­fore from Mo­han that many of the white tigers ex­ist­ing in cap­tiv­ity to­day ul­ti­mately de­scend (a few have arisen in­de­pen­dently, due to spon­ta­neous mu­ta­tions, or to nor­mal tigers car­ry­ing the re­ces­sive gene al­lele mat­ing with one an­other and thereby en­gen­der­ing the white phe­no­type, i.e. out­ward ap­pear­ance, in off­spring car­ry­ing two copies of this mu­tant al­lele).

So it came as a huge sur­prise to zo­ol­o­gists lately when a white tiger was not only re­ported but also con­clu­sively pho­tographed in the wild, by wildlife pho­tog­ra­pher Ni­lan­jan Ray while on a road trip through a re­serve for­est with a guide dur­ing a re­cent visit to the Nil­giri Bio­sphere Re­serve, sit­u­ated in south­ern In­dia’s Nil­giri Hills and Western Ghats. To en­sure the white tiger’s safety, the pre­cise lo­ca­tion of Ray’s sight­ing has not been made pub­lic, but camera traps are to be sited there in the hope of record­ing fur­ther sight­ings of this re­mark­able an­i­mal, whose ex­is­tence demon­strates that, against all the odds, the mu­tant leu­cism al­lele does still sur­vive within the wild tiger pop­u­la­tion. NB – many on­line re­ports of this in­ci­dent (but not the re­port cited here) are ex­tremely mud­dled, con­flat­ing leu­cism with al­binism, so those should be read with cau­tion. www.the­­tional/ tamil-nadu/white-tiger-in-the-nil­giri­sis-a-first/ar­ti­cle19217223.ece 5 July 2017.

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