Striking temporal concordance between the new date for divergence of polar bears and persistent freezing of the Arctic Ocean suggests that this may be one of relatively few instances in which a specific paleoclimatological episode can be convincingly linked to a specific evolutionary event, and it provides vivid demonstration of climatic forcing as a determinant of diversification in biological systems

Cook, Joseph A.

Galbreath, Kurt E.

Hoberg, Eric P.

English

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Faculty Publications from the Harold W. Manter
Laboratory of Parasitology Parasitology, Harold W. Manter Laboratory of
6-8-2012
Climate's Role in Polar Bear Past [Letters]
Kurt E. Galbreath
Northern Michigan University, kgalbrea@nmu.edu
Joseph A. Cook
University of New Mexico - Main Campus, cookjose@unm.edu
Eric P. Hoberg
United States Department of Agriculture, Agricultural Research Service, geocolonizer@gmail.com
Follow this and additional works at: http://digitalcommons.unl.edu/parasitologyfacpubs
Part of the Biodiversity Commons, Climate Commons, Terrestrial and Aquatic Ecology
Commons, and the Zoology Commons
This Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University of
Nebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorized
administrator of DigitalCommons@University of Nebraska - Lincoln.
Galbreath, Kurt E.; Cook, Joseph A.; and Hoberg, Eric P., "Climate's Role in Polar Bear Past [Letters]" (2012). Faculty Publications from
the Harold W. Manter Laboratory of Parasitology. 798.
http://digitalcommons.unl.edu/parasitologyfacpubs/798
LETTERS
editedby JenniferSills
Onice. Polar bears' diet ofice-dependent
preyprovides cluesto their past.
Climate's Role in Polar Bear Past
IN THEIR PROVOCATIVE ANALYSIS OF NORTHERN BEARS ("NUCLEAR
genomic sequences reveal that polar bears are an old and distinct
bear lineage," Reports , 20 April , p. 344), F. Hailer et al. use inde-
pendent nuclear loci to show that polar bears originated during the
middle Pleistocene , rather than during the late Pleistocene as previ-
ously inferred from mito-
chondrial data. Although
they discuss the possible
role of climate warm-
ing in creating discord
between nuclear and
mitochondrial genetic
signatures, the authors
do not address climate's
critical role in driving the
evolution ofpolar bears in
the first place . A reliance
on perennial sea ice and a
strongly pagophilic (i.e .,
ice-dependent) prey base,
including seals, suggests that polar bears could not have evolved in
a world in which the Arctic Ocean remained unfrozen for large por-
tions of the year, as it did most recently during the warm period of
the middle Pliocene. Cooling of the Arctic Ocean commenced dur-
ing the late Pliocene , driving a transition from predominantly sea-
sonal to perennial sea ice that was largely complete by the middle
Pleistocene about 700,000 years ago (1, 2). Striking temporal con-
cordance between the new date for divergence of polar bears and
persistent freezing of the Arctic Ocean suggests that this may be one
of relatively few instances in which a specific paleoclimatological
episode can be convincingly linked to a specific evolutionary event,
and it provides vivid demonstration ofclimatic forcing as a determi-
nant of diversification in biological systems .
KURT E. GALBREATH," JOSEPH A. COOK,' ERIC P. HOBERG'
'Department of Biology, Northern Michigan University, Marquette, MI 49855, USA.
' Museum of Southwestern Biology, University of New Mexico, Albuquerque, NM 87131,
USA. ' National Parasite Collection, Agricultural Research Service, U.S. Department of
Agriculture, AnimalParasitic Diseases, Beltsville,MD20705, USA.
*To whom correspondence should beaddressed . E-mail: kgalbrea@nmu.edu
References
1. S. A.Harris, Prog. Phys. Geoqt. 29,218 (2005).
2. Y. Herman, D. M. Hopkins, Science209, 557(1980).
1230 8 JUNE 2012 VOL 336 SCIENCE www.sciencemag.org
Published byAAAS
Galbreath, Cook & Hoberg in Science (June 8, 2012) 336: 1,230. Published by AAAS. 
This is a U.S. government work and is not subject to copyright in the United States.


Climate\u27s Role in Polar Bear Past [Letters]

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnFaculty Publications from the Harold W. ManterLaboratory of Parasitology Parasitology, Harold W. Manter Laboratory of6-8-2012Climate's Role in Polar Bear Past [Letters]Kurt E. GalbreathNorthern Michigan University, kgalbrea@nmu.eduJoseph A. CookUniversity of New Mexico - Main Campus, cookjose@unm.eduEric P. HobergUnited States Department of Agriculture, Agricultural Research Service, geocolonizer@gmail.comFollow this and additional works at: http://digitalcommons.unl.edu/parasitologyfacpubsPart of the Biodiversity Commons, Climate Commons, Terrestrial and Aquatic EcologyCommons, and the Zoology CommonsThis Article is brought to you for free and open access by the Parasitology, Harold W. Manter Laboratory of at DigitalCommons@University ofNebraska - Lincoln. It has been accepted for inclusion in Faculty Publications from the Harold W. Manter Laboratory of Parasitology by an authorizedadministrator of DigitalCommons@University of Nebraska - Lincoln.Galbreath, Kurt E.; Cook, Joseph A.; and Hoberg, Eric P., "Climate's Role in Polar Bear Past [Letters]" (2012). Faculty Publications fromthe Harold W. Manter Laboratory of Parasitology. 798.http://digitalcommons.unl.edu/parasitologyfacpubs/798LETTERSeditedby JenniferSillsOnice. Polar bears' diet ofice-dependentpreyprovides cluesto their past.Climate's Role in Polar Bear PastIN THEIR PROVOCATIVE ANALYSIS OF NORTHERN BEARS ("NUCLEARgenomic sequences reveal that polar bears are an old and distinctbear lineage," Reports , 20 April , p. 344), F. Hailer et al. use inde-pendent nuclear loci to show that polar bears originated during themiddle Pleistocene , rather than during the late Pleistocene as previ-ously inferred from mito-chondrial data. Althoughthey discuss the possiblerole of climate warm-ing in creating discordbetween nuclear andmitochondrial geneticsignatures, the authorsdo not address climate'scritical role in driving theevolution ofpolar bears inthe first place . A relianceon perennial sea ice and astrongly pagophilic (i.e .,ice-dependent) prey base,including seals, suggests that polar bears could not have evolved ina world in which the Arctic Ocean remained unfrozen for large por-tions of the year, as it did most recently during the warm period ofthe middle Pliocene. Cooling of the Arctic Ocean commenced dur-ing the late Pliocene , driving a transition from predominantly sea-sonal to perennial sea ice that was largely complete by the middlePleistocene about 700,000 years ago (1, 2). Striking temporal con-cordance between the new date for divergence of polar bears andpersistent freezing of the Arctic Ocean suggests that this may be oneof relatively few instances in which a specific paleoclimatologicalepisode can be convincingly linked to a specific evolutionary event,and it provides vivid demonstration ofclimatic forcing as a determi-nant of diversification in biological systems .KURT E. GALBREATH," JOSEPH A. COOK,' ERIC P. HOBERG''Department of Biology, Northern Michigan University, Marquette, MI 49855, USA.' Museum of Southwestern Biology, University of New Mexico, Albuquerque, NM 87131,USA. ' National Parasite Collection, Agricultural Research Service, U.S. Department ofAgriculture, AnimalParasitic Diseases, Beltsville,MD20705, USA.*To whom correspondence should beaddressed . E-mail: kgalbrea@nmu.eduReferences1. S. A.Harris, Prog. Phys. Geoqt. 29,218 (2005).2. Y. Herman, D. M. Hopkins, Science209, 557(1980).1230 8 JUNE 2012 VOL 336 SCIENCE www.sciencemag.orgPublished byAAASGalbreath, Cook & Hoberg in Science (June 8, 2012) 336: 1,230. Published by AAAS. This is a U.S. government work and is not subject to copyright in the United States.

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1809&amp;context=parasitologyfacpubs

Climate\u27s Role in Polar Bear Past [Letters]

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