Time ticks away at wild bi­son diver­sity

Iso­lated herds mean DNA pool is small. Ef­forts needed to bring buf­falo from other ar­eas

The Peterborough Examiner - - CANADA & WORLD - MOR­GAN LEE

SANTA FE, N.M. — Ev­i­dence is mount­ing that wild North American bi­son are grad­u­ally shed­ding their ge­netic diver­sity across many of the iso­lated herds over­seen by the U.S. gov­ern­ment.

The re­sult is weak­en­ing fu­ture re­silience against dis­ease and cli­mate events in the shadow of hu­man en­croach­ment.

The ex­tent of the creep­ing threat to herds over­seen by the U.S. Depart­ment of In­te­rior — the back­bone of wild bi­son con­ser­va­tion ef­forts for North Amer­ica — is com­ing into sharper fo­cus amid ad­vances in ge­netic stud­ies.

Pre­lim­i­nary results of a ge­netic pop­u­la­tion anal­y­sis com­mis­sioned by the Na­tional Park Ser­vice show three small fed­eral herds would almost cer­tainly die off — extinguish­ing their DNA lin­eage — within 200 years un­der cur­rent man­age­ment prac­tices that limit trans­fers for in­ter­breed­ing among dis­tant herds.

The study is await­ing peer re­view by other sci­en­tists.

It does not in­clude Yel­low­stone Na­tional Park’s herd of some 5,000 un­fenced bi­son, the largest fed­eral con­ser­va­tion herd that’s seen by mil­lions of peo­ple who visit the park an­nu­ally.

“Some of these herds that lost the most ge­netic diver­sity do have a high prob­a­bil­ity of go­ing ex­tinct, due to the ac­cu­mu­la­tion of in­breed­ing,” ex­plained Cyn­thia Hart­way, a con­ser­va­tion sci­en­tist at the bi­son pro­gram with Wildlife Con­ser­va­tion So­ci­ety who led the anal­y­sis.

The pre­lim­i­nary find­ings were pre­sented at a work­shop of the American Bi­son So­ci­ety in the buf­falo-rais­ing Na­tive American com­mu­nity of Po­joaque, amid im­pas­sioned dis­cus­sions about en­sur­ing the iconic mam­mal’s last­ing place in the wild.

Bi­son squeezed through a per­ilously small ge­netic bot­tle­neck in the late 1800s.

Over­hunt­ing of the mas­sive an­i­mals caused near ex­ter­mi­na­tion of a pop­u­la­tion that had num­bered in the tens of mil­lions. At one point, fewer than a 1,000 sur­vived.

Fed­eral wildlife au­thor­i­ties now sup­port about 11,000 ge­net­i­cally pure bi­son with only the slight­est traces of cat­tle in­ter­breed­ing.

The herds rep­re­sent one third of all bi­son main­tained for con­ser­va­tion pur­poses across North Amer­ica.

Many of the con­ser­va­tion herds over­seen di­rectly by the In­te­rior Depart­ment have 400 or fewer an­i­mals — leav­ing them prone to prob­lems of in­breed­ing and ge­netic drift that re­duce en­vi­ron­men­tal adapt­abil­ity.

The new anal­y­sis sug­gests the prob­lem would likely spell doom for small herds wan­der­ing the im­mense Wrangell-St. Elias Na­tional Park and Pre­serve in Alaska, the hemmedin bi­son at the Chick­a­saw Na­tional Recre­ation Area in Ok­la­homa that de­scended from a group of six an­i­mals, and a tiny ed­u­ca­tional dis­play herd at Sullys Hill Na­tional Game Pre­serve in North Dakota.

At the same time, strate­gi­cally ex­chang­ing as few as two bi­son be­tween herds ev­ery 10 years would fore­stall the ge­netic de­te­ri­o­ra­tion of small herds, the re­search found.

Hart­way said trans­fers alone don’t stop that slow ebb of ge­netic diver­sity from the com­bined “metapop­u­la­tion” — the col­lec­tive DNA pro­file of scat­tered fed­eral con­ser­va­tion herds — and that more large herds may be needed in the long run.

“We’re kind of putting a Band-aid on the prob­lem. The prob­lem is we have small, iso­lated herds.”

Others see mod­ern re­pro­duc­tive tech­nol­ogy as a so­lu­tion.

Frozen bi­son em­bryos and in vitro fer­til­iza­tion hold out prom­ise for eas­ing ge­netic iso­la­tion among herds with­out the risks of trans­fer­ring hulk­ing mam­mals or spread­ing dis­eases such as bru­cel­losis that leads to aborted calves, said Gregg Adams, a pro­fes­sor of ve­teri­nary bio­med­i­cal sciences at the Univer­sity of Saskatchew­an who has pi­o­neered the re­pro­duc­tive tech­nolo­gies on bi­son.

But fed­eral wildlife man­agers and some In­dige­nous com­mu­ni­ties are loath to adopt such tech­niques that move away from nat­u­ral se­lec­tion in mat­ing.

Pe­ter Dratch, a se­nior bi­ol­o­gist in Colorado for the Fish and Wildlife Ser­vice’s wildlife in­ven­tory and mon­i­tor­ing pro­gram, cau­tioned against even more sub­tle hu­man in­ter­fer­ence in man­ag­ing wild herds, such as in­oc­u­la­tions or res­cu­ing ailing bi­son for treat­able dis­eases.

He be­lieves do­mes­tic ver­sions of bi­son will emerge from com­mer­cial herds, where bi­son num­ber 400,000 or more.

“You don’t want to go over­board, to play God,” he said.


Rid­ers herd bi­son dur­ing the an­nual bi­son roundup late last month on An­te­lope Is­land in Utah. The loss of ge­netic diver­sity is in­creas­ing the threat of ex­tinc­tion be­cause of an ex­cess of in­breed­ing.

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