Polar bears data collection excluding weight and predation

[tyrannosaurs]

Polar bear data collection excluding weight and predation

[tyrannosaurs]

Kinematic Analysis of the Locomotion of the Polar Bear (Ursus Maritimus, Phipps, 1774) in Natural and Experimental Conditions:

www.researchgate.net/publication/233561675_Kinematic_Analysis_of_the_Locomotion_of_the_Polar_Bear_Ursus_Maritimus_Phipps_1774_in_Natural_and_Experimental_Conditions

The striking ability of the polar bear to travel on ice or frozen snow is tentatively related to different structural features involved in the locomotor behaviour of the animal. A comparison with the brown bear shows the specific features, in gaits, leg movement and in ground contact structures. It is suggested that these specific features constitute a functional complex adapted to locomotion in polar environment. During slow gaits, polar bear hind limbs are maximally extended. The legs are able to resist the transfer of mass during the contralateral limb swing phase. This results in a walk with swaying hips. The polar bear uses transverse gallop to improve stability, whereas the brown bear uses rotary gallop. The polar bear is comfortable on slippery wet substrate, while the brown bear is reluctant to move on it. Proximodistal alternation of pads and large zones with hair constitute the main characteristics of the plantar and palmar soles of the polar bear. These features may constitute a functional specialization for the drainage of water from the feet, the reinforcing of adhesion and an increase in the area of contact (snowshoe). The drainage is produced by two kinds of structures: the superficial network of the epidermis of the pads and the hair between the pads. These hirsute zones absorb the liquid which is drained off the pads by the animal's weight during the stance phase. The hairs are also present in the regions of the soles where thrusts are transmitted to the ground.

[Gorilla king]

ANIMAL TRAINER TREVOR BALE SAYS THE POLAR BEAR IS THE MOST DANGEROUS ANIMAL:

[Gorilla king]

POLAR BEAR SKULL MEASUREMENTS:

[Gorilla king]

THE FRONT AND BACK LEG BONES OF POLAR BEARS ARE DENSER THAN GRIZZLIES.







books.google.com.au/books?dq=the+front+and+back+leg+bones+of+polar+bears+are+denser+than+grizzlies&hl=en&id=aouJPNt1P4gC&lpg=PT34&ots=C9bqEOt9TV&pg=PT34&sa=X&sig=mM5K9chL6f-3368JTO3z9PUixX0&source=bl&ved=0ahUKEwj3i_z0xJHaAhVW9WMKHS7nBn4Q6AEIWjAI#v=onepage&q&f=false

[Gorilla king]

[Gorilla king]

POLAR BEARS (URSUS MARITIMUS), THE MOST EVOLUTIONARY ADVANCED HIBERNATORS, AVOID SIGNIFICANT BONE LOSS DURING HIBERNATION


Abstract

Some hibernating animals are known to reduce muscle and bone loss associated with mechanical unloading during prolonged immobilisation,compared to humans. However, here we show that wild pregnant polar bears (Ursus maritimus) are the first known animals to avoid significant bone loss altogether, despite six months of continuous hibernation. Using serum biochemical markers of bone turnover, we showed that concentrations for bone resorption are not significantly increased as a consequence of hibernation in wild polar bears. This is in sharp contrast to previous studies on other hibernating species, where for example, black bears (Ursus americanus), show a 3-4 fold increase in serum bone resorption concentrations posthibernation,and must compensate for this loss through rapid bone recovery on remobilisation, to avoid the risk of fracture. In further contrast to black bears, serum concentrations of bone formation markers were highly significantly increased in pregnant female polar bears compared to non-pregnant,thus non-hibernating females both prior to and after hibernation. However, bone formation concentrations in new mothers were significantly reduced compared to pre-hibernation concentrations. The de-coupling of bone turnover in favour of bone formation prior to hibernation, suggests that wild polar bears may posses a unique physiological mechanism for building bone in protective preparation against expected osteopenia associated with disuse,starvation, and hormonal drives to mobilise calcium for reproduction, during hibernation. Understanding this physiological mechanism could have profound implications for a natural solution for the prevention of osteoporosis in animals subjected to captivity with inadequate space for exercise,humans subjected to prolonged bed rest while recovering from illness, or astronauts exposed to antigravity during spaceflight.© 2008 Elsevier Inc. All rights reserved.

... The bear gets its energy from stored fats, and muscle mass is not lost, but renewed ( Lohuis et al., 2007). The products of catabolism, such as urea, are not excreted but recycled ( Nelson et al., 1975;Floyd et al., 1990; Barboza et al., 1997) and the bone tissue does not suffer losses but is actively remodelling (Donahue et al., 2006;Lennox and Goodship, 2008;McGee et al., 2008), although at a lower rate than during the active season. During hibernation the synthesis of proteins is made from the ni- trogen compounds produced thanks to the recycling of the reab- sorbed urea. ...

... In conclusion, we provide both in vivo and in vitro evidence supporting the expression of circadian rhythms in bears during winter dormancy. These findings, along with earlier work in grizzly bears [64] and polar bears add to the mounting evidence that these closely related species may exhibit an evolutionarily advanced form of torpid biology [65, 66]. ...


www.researchgate.net/publication/5603402_Polar_bears_Ursus_Maritimus_the_most_evolutionary_advanced_hibernators_avoid_significant_bone_loss_during_hibernation

[tyrannosaurs]

Observations of Cannibalism by Polar Bears (Ursus maritimus) on Summer and Autumn Sea Ice at Svalbard, Norway:

We report three instances of intraspecific killing and cannibalism of young polar bears by adult males on the sea ice in Svalbard in summer and autumn. During breakup and melting in summer, the area of sea ice around the Svalbard Archipelago declines to a fraction of the winter total, and in many areas it disappears completely. As the area of sea ice that polar bears can use for hunting declines, progressively fewer seals are accessible to the bears, and therefore the bears' hunting success likely declines as well. Thus, at this time of year, young polar bears may represent a possible food source for adult males. As the climate continues to warm in the Arctic and the sea ice melts earlier in the summer, the frequency of such intraspecific predation may increase.

www.researchgate.net/publication/285952751_Observations_of_Cannibalism_by_Polar_Bears_Ursus_maritimus_on_Summer_and_Autumn_Sea_Ice_at_Svalbard_Norway

[tyrannosaurs]

Jul 8, 2021 12:30:20 GMT -5 Gorilla king said:

POLAR BEAR SKULL MEASUREMENTS:

Skull shape and morphometry of ~670-800 cal AD +/-25 year-old Alaskan polar bear skull: Evidence for a new polar bear subspecies ?:

www.researchgate.net/publication/313854241_Skull_shape_and_morphometry_of_670-800_cal_AD_-25_year-old_Alaskan_polar_bear_skull_Evidence_for_a_new_polar_bear_subspecies

East Greenland and Barents Sea polar bears (Ursus maritimus): Adaptive variation between two populations using skull morphometrics as an indicator of environmental and genetic differences:

A morphometric study was conducted on four skull traits of 37 male and 18 female adult East Greenland polar bears (Ursus maritimus) collected 18921968, and on 54 male and 44 female adult Barents Sea polar bears collected 19501969. The aim was to compare differences in size and shape of the bear skulls using a multivariate approach, characterizing the variation between the two populations using morphometric traits as an indicator of environmental and genetic differences. Mixture analysis testing for geographic differentiation within each population revealed three clusters for Barents Sea males and three clusters for Barents Sea females. East Greenland consisted of one female and one male cluster. A principal component analysis (PCA) conducted on the clusters defined by the mixture analysis, showed that East Greenland and Barents Sea polar bear populations overlapped to a large degree, especially with regards to females. Multivariate analyses of variance (MANOVA) showed no significant differences in morphometric means between the two populations, but differences were detected between clusters from each respective geographic locality. To estimate the importance of genetics and environment in the morphometric differences between the bears, a PCA was performed on the covariance matrix derived from the skull measurements. Skull trait size (PC1) explained approx. 80% of the morphometric variation, whereas shape (PC2) defined approx. 15%, indicating some genetic differentiation. Hence, both environmental and genetic factors seem to have contributed to the observed skull differences between the two populations. Overall, results indicate that many Barents Sea polar bears are morphometrically similar to the East Greenland ones, suggesting an exchange of individuals between the two populations. Furthermore, a subpopulation structure in the Barents Sea population was also indicated from the present analyses, which should be considered with regards to future management decisions.

www.researchgate.net/publication/229159026_East_Greenland_and_Barents_Sea_polar_bears_Ursus_maritimus_Adaptive_variation_between_two_populations_using_skull_morphometrics_as_an_indicator_of_environmental_and_genetic_differences

[tyrannosaurs]

Polar Bears in Alaska Observed with Patchy Hair Loss and other Skin Lesions:

In the past two weeks, 9 polar bears in the southern Beaufort Sea region near Barrow were observed with alopecia, or loss of fur, and other skin lesions. The animals were otherwise healthy in appearance and behavior. The cause and significance of the observed lesions are unknown. Alopecia has been reported in both wild and captive animals in the past. U.S. Geological Survey scientists have collected blood and tissues samples from afflicted polar bears to investigate the cause of the symptoms and determine whether there is any relationship between the symptoms observed in polar bears and those reported for arctic pinnipeds from the same geographical region earlier this year.

Research scientists with the USGS made the observations at the start of their 2012 field-work season. USGS observes polar bears annually in the southern Beaufort Sea region as part of a long-term research program. This bear population ranges from Barrow in Alaska east to the Tuktoyuktuk region of Canada.

Observations last summer of unusual numbers of ringed seals hauled out on beaches along the Arctic coast of Alaska, and later on, of dead and dying seals with hair loss and skin sores, led to declaration of an Unusual Mortality Event by the National Oceanic and Atmospheric Administration on December 20, 2011. Based on observations of Pacific walruses with similar skin lesions at a coastal haulout in the same region during fall, the U.S. Fish and Wildlife Service joined the UME investigation. Most walruses exhibiting skin lesions appeared to be otherwise healthy, and whether the symptoms observed in the seals and walruses are related is unknown. Since the initial reports from northern Alaska, ice seals with similar symptoms have also been reported in adjacent regions of Canada and Russia and from the Bering Strait region. Despite extensive testing for a wide variety of well known infectious agents, the cause(s) of the observed condition in walruses and ice seals remains unknown. Advanced testing techniques for unidentified infectious agents is continuing as well as further testing for potential causes including man-made and natural biotoxins, radiation, contaminants, auto-immune diseases, nutritional, hormonal and environmental factors.

Upon last week's discovery, USGS immediately informed the wildlife veterinarian and biologists in the North Slope Borough who are responsible for onsite coordination of the Northern Pinniped UME, the USFWS, Alaska Nanuuq Commission and NOAA. The USGS is coordinating closely with the North Slope Borough Department of Wildlife Management, and with the Northern Pinniped UME in developing sampling protocols that will provide information about the cause of alopecia in polar bears, and any possible relationship with the disease observed in seals.

USGS scientists have been operating in the vicinity of Barrow and recently moved eastward to Kaktovik, to continue their studies. They will complete their field-work in early May working from Prudhoe Bay.

Anyone observing or harvesting a polar bear with fur loss or skin sores is encouraged to report their sightings by calling the USGS polar bear hotline at 907-786-7034 or the local numbers established for reporting sightings of affected seals and walruses. These numbers include:

Barrow/North Slope: North Slope Borough Dept. of Wildlife Management • 907-852-0350
Nome/Bering Strait: Eskimo Walrus Commission • 1-877 277-4392
UAF Marine Advisory Program • 1-800-478-2202 or 907-443-2397
NOAA Alaska Marine Mammal Stranding Network • 1-877-925-7773
Alaska Nanuuq Commission • 1-907-443-5044

Both USGS and USFWS are working with the State of Alaska Division of Public Health in their efforts to assess potential risk with respect to food safety and distribute general precautionary guidelines. Hunters are advised to refrain from consumption of any animal that does not look healthy and to thoroughly cook polar bear meat which is the traditional subsistence practice. At present, there is no evidence that consuming animals involved in this disease event has caused any human illness.

The following language is excerpted from a November, 2011 bulletin from the State of Alaska Division of Public Health:

Until more information becomes available, we recommend the following general public health precautions, which also apply when interacting with any animal in the wild:

As a general rule, do not eat any animals that appear sick or diseased. If you find a bear acting abnormally or showing signs of illness, note its location and contact your local wildlife authority;
Do not allow dogs to interact with or eat diseased animals;
Safe handling guidelines for marine mammals should always be followed. These include:
Wearing rubber gloves when you are butchering or handling the animals;
Thoroughly washing your hands and all your equipment after touching/butchering an animal; and;
Although cooking is a personal choice/preference, it can help kill parasites and bacteria that can be present in raw meat;
As always, if you feel sick, contact your local community health care provider immediately.

www.usgs.gov/center-news/polar-bears-alaska-observed-patchy-hair-loss-and-other-skin-lesions

[tyrannosaurs]

Recent Hybridization between a Polar Bear and Grizzly Bears in the Canadian Arctic:

Grizzly bears have recently become more common on the Arctic Islands in the Inuvialuit Settlement Region, concurrently with a period of environmental change. Over the last decade, grizzly bear – polar bear hybrids have been confirmed within this region, triggering extensive discussion and speculation regarding the impact of hybridization on the parent species. Through harvests, sightings, and captures, we document an increase in the presence of grizzly bears and combine field observations of hybrids with genetic analysis and parentage analysis to identify four first-generation (F1) hybrids and four offspring of F1 hybrids and grizzly bears (backcross-to-grizzly-bear individuals). We trace these eight hybrid individuals to a single female polar bear who mated with two grizzly bears. We sampled one of her mates on the sea ice in the High Arctic and deduced the genotype of the other from his five offspring. The two male grizzly bears are sires of both the F1 generation and the backcross-to-grizzly-bear generation. So what initially appeared to be a sudden spate of hybridization in the western Canadian Arctic originated with the unusual mating between three non-hybrid parents. The breakdown of species barriers may start with atypical mating preferences of select individuals; however, the story we present can be traced to a single female polar bear who, along with three of her known F1 offspring, has been killed.

www.researchgate.net/publication/317271906_Recent_Hybridization_between_a_Polar_Bear_and_Grizzly_Bears_in_the_Canadian_Arctic

[tyrannosaurs]

Prevalence and spatio-temporal variation of an alopecia syndrome in polar bears (Ursus maritimus) of the southern Beaufort Sea:

Abstract Alopecia (hair loss) has been observed in several marine mammal species and has potential energetic consequences for sustaining a normal core body temperature, especially for Arctic marine mammals routinely exposed to harsh environmental conditions. Polar bears (Ursus maritimus) rely on a thick layer of adipose tissue and a dense pelage to ameliorate convective heat loss while moving between sea ice and open water. From 1998 to 2012, we observed an alopecia syndrome in polar bears from the southern Beaufort Sea of Alaska that presented as bilaterally asymmetrical loss of guard hairs and thinning of the undercoat around the head, neck, and shoulders, which, in severe cases, was accompanied by exudation and crusted skin lesions. Alopecia was observed in 49 (3.45%) of the bears sampled during 1,421 captures, and the apparent prevalence varied by years with peaks occurring in 1999 (16%) and 2012 (28%). The probability that a bear had alopecia was greatest for subadults and for bears captured in the Prudhoe Bay region, and alopecic individuals had a lower body condition score than unaffected individuals. The cause of the syndrome remains unknown and future work should focus on identifying the causative agent and potential effects on population vital rates.

www.researchgate.net/publication/267871966_Prevalence_and_spatio-temporal_variation_of_an_alopecia_syndrome_in_polar_bears_Ursus_maritimus_of_the_southern_Beaufort_Sea

[tyrannosaurs]

Four Sea Ice Ecoregions
By Dr. Steven Amstrup, Chief Scientist

Most people know that polar bears rely on a platform of sea ice to reach their seal prey, but they may not realize that all sea ice across the Arctic is not created equal. In fact, my work has shown that polar bears roam across four distinct sea ice habitats—or ecoregions—across the Arctic. These ecoregions differ in sea ice freeze-up, break-up, and drift patterns. Also, ice among and within ecoregions may lie over ocean waters that vary greatly in productivity. Ultimately, we will lose sea ice, and the polar bears that depend on it, in all four ecoregions if societies do not stop global warming. The differences in ice character and ocean productivity, however, mean that the impacts of warming on the 19 different polar bear populations living within the four ecoregions are, and will continue to be, very different.

In a 2008 paper, I defined the four Arctic sea ice ecoregions as follows:
Seasonal Ice Ecoregion

The polar bear habitats in much of central and eastern Canada lie within the Seasonal ice Ecoregion (SIE), where, unlike the rest of the Arctic, the sea ice always has melted entirely in summer, forcing bears ashore, where there is little to eat. During the ice-free periods, polar bears must live off their fat reserves until the ice forms in the fall and they can hunt seals again. In the past, polar bears thrived in this seasonal environment because it almost entirely encompasses shallow water over the productive continental shelf. The rich environment allowed polar bears to gain enough weight in spring to survive a long summer fast. The impact of global warming on bears throughout the Seasonal Ice Ecoregion is that the ice is melting earlier in the spring and freezing up later in the fall, and the bears are food deprived for an ever longer period. Much of the Seasonal Ice Ecoregion occurs at the southern extreme of the polar bear's range. Bears in southern Hudson Bay, for example, currently live at the same latitude as Scotland. The number of ice-free days faced by these “southern bears” in Hudson Bay is already impacting the survival of cubs, because mother bears there increasingly can’t gain enough weight in spring to provide sufficient milk.

Divergent Ice Ecoregion

Across the rest of their range, polar bears used to be able to stay on perennial ice (ice that survives the summer melt) year-round. In the Divergent Ice Ecoregion (DIE), which extends around the Arctic from coastal Alaska to Svalbard, ocean currents continually carry the ice offshore as it forms. This movement of ice “diverging from the shoreline” is especially noticeable in summer. As the weather warms, new ice stops forming and the remaining ice drifts toward the center of the polar basin, leaving a gap of ocean water between land and the polar ice pack. Historically, the summer ice retreat was small and these bears were able to hunt on the ice over productive shallow water all summer, reaching peak body weights by fall. As the sea ice retreats farther and farther from shore in a warming Arctic, however, these polar bears are faced with a choice of coming ashore, where there is little to eat, or following the sea ice over the deep polar basin where productivity is very low. Because seals can live a totally pelagic lifestyle, they don’t need to follow the ice and instead remain nearer shore where productivity is high. Polar bears remaining on the ice, like those that come ashore, are food deprived, and end up fasting until autumn freeze-up. Five polar bear populations live in divergent ice areas: Barents Sea, Chukchi Sea, Kara Sea, Laptev Sea, and the Southern Beaufort Sea. Long fasts for these bears which, unlike those in the seasonal ice ecoregion, are accustomed to feeding through the summer, make them among the most vulnerable of all polar bears to warming and sea ice decline.

Convergent Ice Ecoregion

In the Convergent Ice Ecoregion (CIE), ice transported from the Divergent Ice Ecoregion, along with locally formed sea ice, collects along the shore. The collection of ice along coastlines provides polar bears with access to seals over productive waters throughout the summer, and, at least for now, these bears can still remain on the sea ice all year. Three polar bear populations live in these areas: Eastern Greenland, Northern Beaufort Sea, and the Queen Elizabeth Islands.

Archipelago Ecoregion

The ocean channels separating the islands of the far north Canadian Arctic have historically been covered by sea ice all summer, and polar bears living there have been able to remain on ice all year long.

This Archipelago Ecoregion (AE), along with the northernmost portions of the Convergent Ice Ecoregion, is likely to provide a last refuge for polar bears and their sea-ice prey. Six polar bear populations live in the Archipelago Ecoregion: Gulf of Boothia, Kane Basin, Lancaster Sound, M'Clintock Channel, Norwegian Bay, and the Viscount Melville Sound.

Without action to halt global warming, even the farthest north polar bear habitats will lose their ice. Until societies stop global warming, the impact on polar bears, will depend on how many ice-free days polar bears face in different areas, and how much weight polar bears can gain during periods when the ice is present.

polarbearsinternational.org/news/article-polar-bears/four-sea-ice-ecoregions/

[Gorilla king]

The fat % of 10 male polar bears was from 2 to 21%. An 8 year old, 407 kg (897 lbs) polar bear had only 17.8% of body fat, that is just slightly over lions/tigers who weight half of that. 


The anatomy, chemical composition, and metabolism of adipose tissue in wild polar bears (Ursus maritimus)





www.researchgate.net/publication/238026092_The_anatomy_chemical_composition_and_metabolism_of_adipose_tissue_in_wild_polar_bears_Ursus_maritimus

[Gorilla king]

Fur Absorbs Infrared Radiation to Prevent Heat Loss

Guard hairs on the polar bear prevent heat loss by absorbing heat in the form of infrared radiation.

Polar bears living in the Arctic Circle survive in one of the harshest climates in the world. Winter temperatures can fall to -40 °C, but polar bears manage to keep their internal body temperature at a steady 37 °C.

One physical feature that helps the polar bear stay warm is its fur coat. The coat is made up of two distinct layers: a short and dense underfur layer right next to the skin, and an outer layer of longer and coarser guard hairs. The guard hairs are transparent but the polar bear’s coat appears white because the hairs scatter sunlight.

Research on these transparent guard hairs has revealed a key property that helps to prevent heat loss in the cold Arctic air. The guard hairs appear to be very effective at absorbing infrared radiation, which makes up a portion of the electromagnetic spectrum that most mammals (including humans) cannot see but can feel as heat. This means that heat emitted from the polar bear’s warm body could be absorbed by the hairs instead of transmitted through them, where it would be lost to the cold environment. The hairs’ ability to absorb radiation is especially high at the specific part of the infrared spectrum where mammals tend to radiate heat most strongly.

An interesting consequence of this property is that a polar bear appears invisible in the infrared if the temperature at the surface of its coat matches the temperature of the ice and snow around it.

“The high absorptivity of both bear and human hair in this wavelength range is significant because fur, made up of many hairs with this property, will act as a radiatively participating media, almost completely eliminating the radiative losses from a mammalian body in cold environments [6]…[E]volution has resulted in the presence of such an excellent infrared absorber in the coverings of mammals, thus ensuring not only insulation, but also high absorptivity exactly for those wavelengths where it would yield the greatest survival value. The mammalian blackbody radiation peaks near 1000 cm-1 (10 microns) and the high absorptivity in this region minimizes radiative losses during a cold night for any living mammal, polar bear and hominid alike.” (Preciado et al. 2002:58)












asknature.org/strategy/fur-absorbs-infrared-radiation-to-prevent-heat-loss/

[tyrannosaurs]

Is Bone Mineral Composition Disrupted by Organochlorines in East Greenland Polar Bears (Ursus maritimus)?:

We analyzed bone mineral density (BMD) in skulls of polar bears (Ursus maritimus) (n = 139) from East Greenland sampled during 1892-2002. Our primary goal was to detect possible changes in bone mineral content (osteopenia) due to elevated exposure to organochlorine [polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane (DDT) and its metabolites, chlordanes (CHLs), dieldrin, hexacyclohexanes, hexachlorobenzene] and polybrominated diphenyl ether (PBDE) compounds. To ensure that the BMD value in skull represented the mineral status of the skeletal system in general, we compared BMD values in femur and three lumbar vertebrae with skull in a subsample. We detected highly significant correlations between BMD in skull and femur (r = 0.99; p < 0.001; n = 13) and skull and vertebrae (r = 0.97; p < 0.001; n = 8). BMD in skulls sampled in the supposed pre-organochlorine/PBDE period (1892-1932) was significantly higher than that in skulls sampled in the supposed pollution period (1966-2002) for subadult females, subadult males, and adult males (all, p < 0.05) but not adult females (p = 0.94). We found a negative correlation between organochlorines and skull BMD for the sum of PCBs (SigmaPCB; p < 0.04) and SigmaCHL (p < 0.03) in subadults and for dieldrin (p < 0.002) and SigmaDDT (p < 0.02) in adult males; indications for SigmaPBDE in subadults were also found (p = 0.06). In conclusion, the strong correlative relationships suggest that disruption of the bone mineral composition in East Greenland polar bears may have been caused by organochlorine exposure.

www.researchgate.net/publication/8149244_Is_Bone_Mineral_Composition_Disrupted_by_Organochlorines_in_East_Greenland_Polar_Bears_Ursus_maritimus

[tyrannosaurs]

King Kodiak, you got any other sources on the integumentary system of polar bears? Its really cool to see.

[Gorilla king]

Jul 8, 2021 17:57:02 GMT -5 tyrannosaurs said:

King Kodiak, you got any other sources on the integumentary system of polar bears? Its really cool to see.

Not that i could find now, but will see.

[Gorilla king]

SEXUAL DIMORPHISM OF POLAR BEARS


Abstract

Sexual dimorphism in body mass, body length, head width, head length, and foreleg guard hair length of polar bears ( Ursus maritimus ) was examined from live-captured polar bears in Svalbard, Norway. Limited evidence of sexual dimorphism was apparent in cubs shortly after den emergence but was marked after the 1st year of life. Sexual dimorphism in adults resulted from both a higher growth rate and prolonged growth period in males. In mature animals, sexual dimorphism was greatest in mass, followed by foreleg guard hair length, head width, body length, and head length. Foreleg guard hair length was age related and hypothesized to be a form of ornamentation. Geographic variation in sexual dimorphism was evident for mass and body length for seven different populations but there was no evidence of a hyperallometric relationship in sexual dimorphism.

FULL STUDY:

academic.oup.com/jmammal/article/86/5/895/2219068

[Gorilla king]

DOWN TO THE BEAR BONES: HOW POLAR BEARS EVOLVED FROM GRIZZLIES TO HUNT IN THE ARCTIC

Katmai National Park in Alaska holds an annual “Fat Bear Week”, in which Twitter followers are asked to vote for the fattest bear in the park. This year’s winner was Holly, somewhere in the range of 500 to 700 lbs. That’s a big bear. However, in 1960, a male polar bear in Kotzebue Sound, Alaska, weighed in at 2,209 lbs. In fact, on average, polar bears weight up to 60% more than Grizzly bears, their closest animal relative. 


Holly, aka Bear 435, the 2019 winner of the Fat Bear Contest. From Katmai National Park via Twitter.

So just how did Polar Bears get so big? Well, as anyone in the Midwest knows, a harsh winter requires a good winter coat. The advantage of thick skin and fur, as well as a higher capacity to put on weight made heavier polar bears more adept to survive. However, bigger bears that could survive the cold were more likely to fall through the ice, so these adaptations required better foot mechanics.

Consequently, polar bears developed a distinctive gait. A rotary gait is a “double suspension” gait, meaning the animal bounces both off the hind limbs and then the fore limbs . This is contrasted from the grizzly bear’s transverse gallop, which involves only one “bounce,” — this loads each limb for a longer time and more vertically. The rotary gait improves stability, giving the polar bear the ability to travel quickly and smoothly on icy surfaces. 


A series of drawings depicting the gait of a polar bear. Modified from S. Renous, J.P. Gasc, and A. Abourachid, Netherlands Journal of Zoology (1998).

Another significant difference between the species are their skulls, which, while similar in size, vary greatly in bite force and bone strength. The polar bear has a stronger bite, but a weaker skull. Polar bears are one of the most rapid instances of evolution in surviving species of animals, having evolved from the grizzly bear within the last five hundred thousand years. So why are their skulls weaker if their bite is stronger? 

Simply put: seals are easy to chew. Grizzlies are omnivores, as most bear species. Their diet subsists of salmon, elk, and small game, but includes a hefty amount of vegetation. Polar Bears, in the ice and cold, were forced to eat seals (as well as penguins, fish, even belugas). Seals are largely blubber, providing the caloric intake necessary to sustain these large beasts, but offering little resistance in the chewing process. 



Skulls of the polar (left) and grizzly bear (right). Modified from P. Christiansen, Journal of Zoology (2006).

The polar bear’s skull morphed quickly, elongating to allow it to hunt for seals and fish through small holes in the ice. This weakened and lowered the density of the skull; however, because the seal-heavy diet required less effort to chew than vegetation, there was no selective advantage to a skull reinforcing. So, with a more efficient gait and a stronger bite, the polar bear developed into a killing machine in the icy north.

Interested in more of the polar bear’s hunt? Learn about how they can swim for hundreds of miles, or to see these arctic advantages in action, check out this video of a polar bear hunting a seal.





sites.nd.edu/biomechanics-in-the-wild/2019/12/27/down-to-the-bear-bones-how-polar-bears-evolved-from-grizzlies-to-hunt-in-the-arctic/