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Post by grrraaahhh on Jun 11, 2011 5:37:16 GMT -9
Are Bear Subspecies a Thing of the Past?The subspecies concept has had a tortuous history, in part because the definition of a subspecies is rather vague. Before recent genetic advances, subspecies were distinguished only by morphological traits, which are open to varying interpretations. This ambiguity makes it difficult to use subspecies as a definitive unit for conservation. Subspecies have remained controversial because taxonomists have historically cataloged far too many of them to be truly useful entities. Legendary evolutionary biologist Ernst Mayr (1982) concluded that “subspecies fulfilled a most important historical role by undermining the essentialistic species concept and also by contributing to a far better understanding of the geographic variation of species.” Subspecies have aroused much criticism in recent years because molecular phylogenetic findings often do not corroborate historically-identified subspecies (except those on islands; Phillimore and Owens 2006). In an extensive literature review, Haig et al. (1996) “found no universally accepted subspecies definition within or across taxa.” Here’s a definition from Wikipedia: “Organisms that belong to different subspecies of the same species are capable of interbreeding and producing fertile offspring, but they often do not interbreed in nature due to geographic isolation or other factors.” This is a little confusing in that several bear species can interbreed and produce fertile offspring, but they generally do not. For example, brown bears and polar bears may appear to fit this subspecies definition. But with distinct species, we also assume some sort of behavioral separation that deters interbreeding. In order for a subspecies to exist within the range of the broader species, there must be geographical separation sufficient to markedly deter gene flow. Thus bears of truly different subspecies would rarely encounter each other in the wild. Exceptions to this situation may occur with human intervention, as in the case of translocations and reintroductions. For example, in the U.S. during the 1960s, about 160 American black bears from Minnesota were reintroduced into Louisiana, where a small extant population of another (purported) subspecies existed. This sort of reintroduction is not typical today: bear biologists are more cognizant of using stocks for reintroduction that are similar genetically to the local population. But in this day of high-powered genetic testing, have we cast the subspecies concept aside? Most North American bear biologists would not concur with (or even be aware of) the 16 subspecies of American black bear that are still formally accepted by mammalogists (see listing of all currently-recognized subspecies of extant ursids at: www.bucknell.edu/msw3/browse.asp?id=14000939). Genetic isolation is murky even among the three most notable subspecies, Ursus americanus luteolus, U. a. floridanus, and U. a. kermodei (from Louisiana, Florida, and British Columbia, respectively), all of which have been given special legislative protection. The Kermode or “spirit” bear has a single recessive unique nucleotide in white-phased individuals (which is particularly common on islands) but is not genetically isolated from other populations (Marshall and Ritland 2002). In Asia, however, the subspecies concept seems alive and well, and it’s not just that Asian bear biologists are clinging to “old-school” taxonomy. In Asia, there are certain island populations that are sufficiently far from shore, and thus genetically separate, that historical subspecies designations are probably warranted: sloth bears in Sri Lanka (Melursus ursinus inornatus), sun bears on Borneo (Helarctos malayanus euryspilus) [with these two, the generic name is more disputed than the subspecific designation], and Asiatic black bears in Japan (Ursus thibetanus japonicas) and Taiwan (U. t. formosanus). But there are other recognized subspecies on the mainland that also seem fitting of their designation due to long-term isolation: Isabelline (brown) bears (Ursus arctos isabellinus), ranging from northern India to Mongolia (including the “Gobi bear”), and the Baluchistan black bear (U. t. gedrosianus) in southern Iran and Pakistan, are notable examples. But what prompts us to write this piece is the recent genetic investigation of what to most readers will be an unrecognized subspecies – the Ussuri black bear (U. t. ussuricus), so named because it lives near the Ussuri River in the Russian Far East. The northern part of the range of the Asiatic black bear is disjunct: it includes the Russian Far East, the Korean Peninsula, and northeast China. There is a large gap from there to Asiatic black bear populations in central China, caused by a long history of intensive land use by humans (as well as probable heavy exploitation of bears for gall bladders in Chinese population centers). So it makes some sense that this most northern cluster of black bears might be a distinct subspecies. But one might ask how long a period of separation is required for a subspecies to form? The gap between this northern area and other parts of China is not long in evolutionary terms – maybe a few thousand years – and the gap may not have completely blocked gene flow until much more recently (there appear to be a few scattered records of a bears wandering in this area in the past 200 years). Recent genetics work, though, seems to corroborate the northern group as a distinct “evolutionary significant unit (ESU)”, a more precise term that may correspond to subspecies. This recent work shows a clear genetic distinction between the Ussuri bear and bears of central China (Hwang et al. 2008), Japan, and Southeast Asia (Kim et al. 2011). We asked the authors of the later paper to write an article for International Bear News (see following article) because we thought their results were intriguing, and, like a previous genetic investigation of the Isabelline bear (Galbreath et al. 2007), revive the concept of the subspecies. It’s certainly fine for geneticists and conservations to talk about ESUs, but we think that the old subspecies names, if they withstand genetic scrutiny, have a certain natural appeal that can aid conservation. Our view is consistent with that of Kitchener (2010), who recently reviewed the taxonomy of the world’s bears and discussed the potential conservation benefits of distinct taxonomic names. Kitchener thought it was worth recognizing some subspecies, and supported the distinction of U. t. ussuricus, even before publication of the new genetics work. On the other hand, we must guard against naming or retaining existing names of subspecies simply to highlight a group of bears in an area of conservation concern. Identification of genetically-based morphological characteristics that are grouped within a distinct, isolated region (i.e., not just clinical variation) should help sort out the real subspecies from the “imposters”. Genetic work supported the reintroduction of Asiatic black bears from Russia and N. Korea into a small remnant population in southern S. Korea, because this is all a single clade. This work also provided evidence that the Ussuri subspecies may be real. However, more extensive comparisons now ongoing across the range of this species could still challenge that, and redraw the subspecies map. IBN PDF LINK: www.nrccooperative.org/pdfs/IBN%202011%20May.pdf
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Post by grrraaahhh on Jun 11, 2011 5:40:22 GMT -9
Relating material: Analysis of complete mitochondrial genome sequences increases phylogenetic resolution of bears (Ursidae), a mammalian family that experienced rapid speciationBackground Despite the small number of ursid species, bear phylogeny has long been a focus of study due to their conservation value, as all bear genera have been classified as endangered at either the species or subspecies level. The Ursidae family represents a typical example of rapid evolutionary radiation. Previous analyses with a single mitochondrial (mt) gene or a small number of mt genes either provide weak support or a large unresolved polytomy for ursids. We revisit the contentious relationships within Ursidae by analyzing complete mt genome sequences and evaluating the performance of both entire mt genomes and constituent mtDNA genes in recovering a phylogeny of extremely recent speciation events. Results This mitochondrial genome-based phylogeny provides strong evidence that the spectacled bear diverged first, while within the genus Ursus, the sloth bear is the sister taxon of all the other five ursines. The latter group is divided into the brown bear/polar bear and the two black bears/sun bear assemblages. These findings resolve the previous conflicts between trees using partial mt genes. The ability of different categories of mt protein coding genes to recover the correct phylogeny is concordant with previous analyses for taxa with deep divergence times. This study provides a robust Ursidae phylogenetic framework for future validation by additional independent evidence, and also has significant implications for assisting in the resolution of other similarly difficult phylogenetic investigations. Conclusion Identification of base composition bias and utilization of the combined data of whole mitochondrial genome sequences has allowed recovery of a strongly supported phylogeny that is upheld when using multiple alternative outgroups for the Ursidae, a mammalian family that underwent a rapid radiation since the mid- to late Pliocene. It remains to be seen if the reliability of mt genome analysis will hold up in studies of other difficult phylogenetic issues. Although the whole mitochondrial DNA sequence based phylogeny is robust, it remains in conflict with phylogenetic relationships suggested by analysis of limited nuclear-encoded data, a situation that will require gathering more nuclear DNA sequence information. www.biomedcentral.com/content/pdf/1471-2148-7-198.pdfand..... Genetics of the Bears of the WorldOverview Many aspects of bear biology are well studied, but comparatively little is known about bear genetics. Historically, the scarcity of genetic information about bears can be traced to the technical difficulty and high expense of molecular genetic analyses. Due to recent developments in molecular technology, we have moved into a new and exciting age in which genetic analyses of any organism can be performed in a cost-effective manner with relative ease. As an indication of the potential importance of molecular analyses for monitoring the status of the world’s bears, a genetics section has been added to this comprehensive status report. The goals of this section are threefold: 1) to summarize the progress that has been made in bear genetics, 2) to discuss the implications of current genetic research, and most importantly 3) to explore the potential of molecular techniques for providing new perspectives on bear biology and management. Researchers can now routinely utilize genetic information in proteins and DNA to addresses questions about the behavior, ecology, life history, and evolution of bear populations. From a biological perspective, molecular genetic analyses have been utilized to uncover important characteristics of natural populations such patterns of gene flow (Paetkau et al. 1995), reproductive success (Craighead et al. 1995), genetic diversity (Paetkau and Strobeck 1994; Paetkau et al. 1995; Waits et al. 1998a), and evolutionary history (Taberlet and Bouvet 1994; Waits et al. 1998b; Wooding and Ward in press; Talbot and Shields in press a). From a forensic standpoint, researchers have demonstrated the ability to use genetic information to differentiate species (Cronin et al. 1991a; Waits and Ward in press), to trace individuals within a species to a particular geographic area (Waits 1996), and to identify individuals within a population (Paetkau and Strobeck 1994; Paetkau et al. 1995). The molecular methods that are used to analyze DNA and proteins include a wide range of techniques such as protein electrophoresis, immunological assays, chromosome banding, DNA hybridization, restriction enzyme analysis, DNA sequence analysis, and DNA fingerprinting. A detailed description of these techniques is beyond the scope of this manuscript; however, excellent reviews of molecular methods are suggested for further reading (Avise 1994; Lewin 1994). The most important point to convey about the use of different molecular techniques is the fact that each technique provides different information at different levels of resolution. The degree of detectable genetic variation (polymorphism) will vary greatly among markers. Thus, different markers will have different strengths and weaknesses for answering particular questions, and the results may have different implications. One important distinction among DNA markers is the distinction between mitochondrial DNA (mtDNA) markers, Y chromosome markers, and nuclear DNA markers. Mammalian cells contain two distinct types of DNA: nuclear DNA and mtDNA. Nuclear DNA is found in the nucleus of cells, and it is inherited from both parents. Thus, cells have two copies of each nuclear chromosome, one copy from the mother and one copy from the father. MtDNA is a circular DNA molecule residing in the mitochondrion, a cellular organelle of the cytoplasm. Mitochondrial DNA is inherited uniparentally, from mother to offspring (Avise and Lansman 1983). The Y chromosome is also found in the nucleus, but it has a unique property compared to other nuclear DNA chromosomes. It is inherited uniparentally, from father to son. These differences in inheritance patterns have important implications for interpretation of results from DNA studies. MtDNA markers only provide information about maternal evolutionary history, gene flow, and genetic diversity; Y chromosome markers only provide information about paternal evolutionary history, gene flow, and genetic diversity; and nuclear DNA markers provide information about both maternal and paternal evolutionary history, gene flow, and genetic diversity. This status report of bear genetics is organized in five major sections that reflect the five main areas of research: 1) interspecific phylogenetic analyses, 2) intraspecific population structure analyses, 3) genetic diversity within populations, 4) ecological applications, and 5) forensic applications. In section 1, we focus on questions relating to the relative age, evolutionary distinctiveness, and historical evolutionary branching pattern for each species. In section 2, we focus on studies at the species level that answer and raise important questions about historical and current migration patterns, evolutionarily significant genetic groups, and population structure. In section 3, we consider studies of population-specific genetic diversity that are instrumental for determining if threatened populations have suffered a significant loss of genetic diversity, which may lead to inbreeding depression and potentially threaten the survival of the population. In section 4, we explore potential ecological applications of genetic analyses such as DNA-based population census methods and the reconstruction of pedigrees. In the final section, we address the utility of molecular techniques in wildlife forensic identification. wildlife1.wildlifeinformation.org/000ADOBES/Bears/Bears_IUCN_ActionPlan/bearsAP_chapter3.pdf |
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Post by grrraaahhh on Jun 14, 2011 7:33:10 GMT -9
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ktkc
New Member
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Post by ktkc on Jun 22, 2011 23:05:09 GMT -9
Mitochondrial DNA Phylogeographof y the North American Brown Bear and Implications for Conservation
LISETTE P. WAITS,*t SANDRA L. TALBOT,t R. H. WARD,* AND G. F. SHIELDSt
*Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, U.S.A.
tlnstitute of Arctic Biology, University of Alaska, Fairbanks, AK 99775-7000, U.S.A.
Abstract: The historical distribution of the brown bear (Ursus arctos) in North America included Alaska,
western Canada, the western and midwestern states, plus northern Mexico. Currently, the brown bear is limited
to Alaska, the Canadian provinces of the Yukon, Northwest Territories, British Columbia, and Alberta,
and six threatened subpopulations in the lower 48 states. To examine the evolutionary history of U. arctos in
North America and to assess the genetic divergence between individuals from different geographic regions,
we obtained 294 nucleotides of mitochondrial DNA sequence data from the control region for 317 free-ranging
brown bears. Twenty-eight unique sequences, or mitochondrial DNA haplotypes were detected. The average
sequence divergence between haplotypes was high (43 %/), and some haplotypes differed by as many as 23
nucleotides. Phylogenetic analyses using maximum parsimony revealed four major mitochondrial DNA phylogeographic
groups, or clades. The significant phylogeographic structure detected in brown bears strongly
contrasts with results obtainedfor other large carnivores and suggests limitedfemale-mediated gene flow. The
mitochondrial DNA phylogeographic clades do not correlate with taxonomic classifications for U. arctos, and
we hypothesize that the clades were formed prior to migration of this species into North America. We suggest
evolutionarily significant units for conservation in three geographic regions: (1) the Alaskan islands of Admiralty,
Baranof; and Chichagof; (2) mainland Alaska, Kodiak Island, and northern Canada; and (3) southern
British Columbia, southern Alberta, and the states of Idaho, Montana, and Wyoming.
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ktkc
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Post by ktkc on Jun 22, 2011 23:11:27 GMT -9
According this doc., U. a. sitkensis is a separate subspecies.
U. a. gyas = U. a. middendorffi = U a. alascensis; and U. a. horribilis (grizzly bear) should be divided into two subspecies.
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Post by grrraaahhh on Jun 23, 2011 7:02:06 GMT -9
I moved your posts because the discussion was shifting to North America brown bears. In general, a lot of North American brown bear literature describes two types of brown bears, Kodiak bear & Grizzly bear. "Brown and grizzly bears are classified as the same species even though there are notable differences between them. Kodiak bears (brown bears from the Kodiak Archipelago) are classified as a distinct subspecies (U. a. middendorffi) from those on the mainland (U. a. horribilis) because they have been isolated from other bears since the last ice age about 12,000 years ago. “Brown bears” typically live along the southern coast of the state where they have access to seasonally abundant spawning salmon. The coastal areas also provide a rich array of vegetation they can use as food as well as a milder climate. This allows them to grow larger and live in higher densities than their “grizzly” cousins in the northern and interior parts of the state. To minimize confusion, this report uses the term “brown bear” to refer to all members of Ursus arctos. "www.adfg.alaska.gov/index.cfm?adfg=brownbear.mainBrown bear taxonomy revision is an ongoing discussion and only until recent time has there been the benefit of genetic testing. To what extent the earlier dental, cranial, or geographic taxonomic brown bear classification is superseded by genetic mtDNA testing remains to be seen. Although very revealing (it's still a new emerging field of science) genetic testing is not comprehensive. RE: U. a. gyas, conventional thinking associates this longer skull shaped bear with the Alaska Peninsula & not with the broader skull bears of the Kodiak archipelago. Follow up to the Waits, Talbot & Shields material: "The mtDNA phylogeny does not support any of the historic taxonomic classifications (Waits et al. 1998a). There is no support for U. a. middendorffi, U. a. horribilis, or U. a. gyas. The classification by Kurten (1968) and Hall (1984) of bears from the ABC islands and adjacent mainland probably is incorrect. Brown bears from the ABC islands constitute the oldest and most genetically unique mtDNA clade in the New World and are a sister taxa to the polar bear (Talbot and Shields 1996; Shields et al. 2000). However, as stated by Waits et al. (1998a:415), "a revision of the taxonomy of North American brown bears in accordance with the phylogenetic species concept (Cracraft 1983) would result in drastic changes in the current classification. The most frequently recognized subspecies, U a. middendorffi, would be abolished, and 4 new subspecific distributions would be added. But it seems unreasonable to dramatically alter the current taxonomy based on the results from a single mtDNA region." Additional research using additional genes, particularly from the Y chromosome, is needed for taxonomic clarification (Waits et al. 1998a)."
Schwartz, C.C., S.D. Miller, and M.A. Haroldson. 2003. Grizzly bear. Pages 556-586 in G.A. Feldhamer, B.C. Thompson, and J.A. Chapman, editors. Wild Mammals of North America: Biology, Management, and Conservation. Second edition. The Johns Hopkins University Press, Baltimore, Maryland. How this forum classifies brown bear taxonomy is always up for revision. In fact, in the true spirit of real science learning & education, everything is up for revision. How to classify the Caucasus brown bear was not easy. Historical or geographic taxonomic distinctions while often incorrect are also more recognizable to the larger public. In any event, I am flexible to taxonomic modification. |
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ktkc
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Post by ktkc on Jun 23, 2011 13:50:34 GMT -9
Early docment describes two types of Northern America brown bears, Kodiak brown bear and Grizzly bear. But morden mtDNA phylogeny does not support this classifications.
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Post by grrraaahhh on Jun 23, 2011 17:00:37 GMT -9
There are currently no published reports of brown bear nuclear DNA diversity, but preliminary protein allozyme analyses of one locus have suggested substantial genetic divergence between Montana brown bears and Alaskan brown bears (U.S. Fish and Wildlife Service 1987; F. Allendorf, personal communication), and an extensive nuclear DNA micro satellite analysis of North American brown bears is in progress (Paetkau et al., in press).
Until additional nuclear DNA and Y chromosomal data are available, we suggest that three phylogeographic groups of brown bears be defined as ESUs: (1) Clade I, (2) Clades II and III, and (3) Clade IV. Clade I bears from the Admiralty, Baranof, and Chichagof Islands warrant designation based on mtDNA genetic differentiation, antiquity, close phylogenetic relationship to polar bears, and apparent geographic isolation. Special efforts are necessary to preserve this unique group because these islands are suffering increased human pressure from on- going and proposed timber harvests. These harvests should be limited because they lead to habitat fragmentation and increased bear-human conflict, ultimately re- sulting in a decrease in the numbers of bears (Schoen et al., in press). Because the neighbor-joining distance tree grouped haplotypes from Clades II and III, and because a contact zone was detected in the Arctic National Wild- life Refuge, we suggest that the other brown bear populations in Alaska and northern Canada constitute a single ESU. Additional sampling along the contact zone in eastern Alaska and examination of nuclear DNA and Y chromosome loci will be necessary to determine if this single ESU should be divided into two ESUs.
The evolutionary distinctiveness of Clade IV brown bears from the lower 48 states and southern Canada is strongly supported by the mtDNA sequence data and preliminary allozyme analyses.
Waits et al. 1998a.
We need more testing. I am not sure if there has been anything published in recent years but if there has been a new report that's something we can examine.
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Post by grrraaahhh on Jun 24, 2011 19:56:26 GMT -9
David Paetkau (continued)Abstract Understanding the factors that influence the rate at which natural populations lose genetic diversity is a central aspect of conservation genetics because of the importance of genetic diversity in maintaining evolutionary potential and individual fitness. Concerns about loss of genetic diversity are particularly relevant to large carnivores, such as brown bears (Ursus arctos), that are distributed at low densities and are highly susceptible to human-caused population fragmentation. We used eight highly variable nuclear microsatellite markers to study current levels of genetic variation across the North American range of brown bears. The highest levels of within-population genetic diversity (He = 0.76) were found in northern populations in the core of the North American distribution. Diversity was significantly lower in populations at the southern fringe of the distribution, in the Northwest Territories, and in southwest Alaska. Diversity was lower still in the Yellowstone Ecosystem population (He = 0.55), an isolated remnant of the larger distribution that recently extended south from the Canadian border into Mexico. The insular population on the Kodiak Archipelago had very low genetic diversity (He = 0.26). The Yellowstone and Kodiak data suggest that the effective population size for brown bears is much smaller than previously suspected. These results indicate that the levels of diversity in most undisturbed populations can be maintained only through connections to populations on the scale of the current North American distribution. At the same time, the Kodiak data demonstrate that populations well under the size recommended for long-term conservation can persist and thrive for thousands of years, although the probability of such persistence remains unknown. Paetkau, D., Waits, L. P., Clarkson, P. L., Craighead, L., Vyse, E., Ward, R. and Strobeck, C. (1998), Variation in Genetic Diversity across the Range of North American Brown Bears. Conservation Biology, 12: 418–429. onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.1998.96457.x/fullAbstract The brown bears of coastal Alaska have been recently regarded as comprising from one to three distinct genetic groups. We sampled brown bears from each of the regions for which hypotheses of genetic uniqueness have been made, including the bears of the Kodiak Archipelago and the bears of Admiralty, Baranof and Chichagof (ABC) Islands in southeast Alaska. These samples were analysed with a suite of nuclear microsatellite markers. The ‘big brown bears’ of coastal Alaska were found to be part of the continuous continental distribution of brown bears, and not genetically isolated from the physically smaller ‘grizzly bears’ of the interior. By contrast, Kodiak brown bears appear to have experienced little or no genetic exchange with continental populations in recent generations. The bears of the ABC Islands, which have previously been shown to undergo little or no female-mediated gene flow with mainland populations, were found not to be genetically isolated from mainland bears. The data from the four insular populations indicate that female and male dispersal can be reduced or eliminated by water barriers of 2–4 km and 7km in width, respectively. PAETKAU, D., SHIELDS, G. F. and STROBECK, C. (1998), Gene flow between insular, coastal and interior populations of brown bears in Alaska. Molecular Ecology, 7: 1283–1292. PDF LINK: research.amnh.org/~rfr/paetkau98.pdf Abstract Identification of individuals in a free-ranging animal population is potentially hampered by a lack of distinguishing features (e.g., scars, unique color patterns), poor visibility (e.g., densely forested environments), cost and invasiveness of physical capture, and mark loss. Advances in DNA-analysis technology offer alternative methods of individual identification that may overcome several of these problems. We investigated the genetic variability of American black bears (Ursus americanus) and brown (grizzly) bears (Ursus arctos) in the Columbia River basin of British Columbia, Canada, and developed a method to obtain genetic samples from free-ranging bears. We established the background genetic variability using microsatellite genotyping at 9 loci using tissue and blood samples from captured bears. In 3 field trials, we tested methods to obtain hair from free-ranging bears. Although all methods collected hair suitable for DNA analysis, the barbed-wire enclosure hair-trap was superior. We extracted DNA from hair roots and identified sample species with a species-specific mitochondrial DNA (mtDNA) test and sample sex from a Y-chromosome test. Using 6 microsatellite loci from nuclear DNA (nDNA), we screened all hair samples for individual identity and developed match probability functions based on scenarios of random sampling (P sub(random)), the likely presence of parent-offspring groupings in the samples (P sub(par-offs)), and the likely presence of siblings in the samples (P sub(sib)). We applied the P sub(sib) to each hair sample (match criteria at P sub(sib)<0.05) and illustrated how these microsatellite genotypes can be used as genetic tags in mark-recapture bear censuses. The ability to identify species, sex, and individuality of free-ranging bears has numerous potential applications in field studies. Woods, JG | Paetkau, D | Lewis, D | McLellan, BN | Proctor, M | Strobeck, C. Genetic tagging of free-ranging black and brown bears.Wildlife Society Bulletin [Wildl. Soc. Bull.]. Vol. 27, no. 3, pp. 616-627. 1999. PDF LINK: www.wildlifegenetics.ca/media/1999%20Woods.pdfAbstract I present data from 21 population inventory studies — 20 of them on bears — that relied on the noninvasive collection of hair, and review the methods that were used to prevent genetic errors in these studies. These methods were designed to simultaneously minimize errors (which can bias estimates of abundance) and per-sample analysis effort (which can reduce the precision of estimates by limiting sample size). A variety of approaches were used to probe the reliability of the empirical data, producing a mean, per-study estimate of no more than one undetected error in either direction (too few or too many individuals identified in the laboratory). For the type of samples considered here (plucked hair samples), the gain or loss of individuals in the laboratory can be reduced to a level that is inconsequential relative to the more universal sources of bias and imprecision that can affect mark–recapture studies, assuming that marker systems are selected according to stated guidelines, marginal samples are excluded at an early stage, similar pairs of genotypes are scrutinized, and laboratory work is performed with skill and care. D. PAETKAU An empirical exploration of data quality in DNA-based population inventories. Molecular Ecology (2003) 12, 1375–1387. PDF LINK: www.wildlifegenetics.ca/media/2003%20inventory%20errors.pdf
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Post by grrraaahhh on Jul 4, 2011 21:20:40 GMT -9
Early docment describes two types of Northern America brown bears, Kodiak brown bear and Grizzly bear. But morden mtDNA phylogeny does not support this classifications. Brief follow up. Why are North American brown bears called grizzly bears? For the benefit of other readers, the term "grizzly" bear dates back to American expansion into what would later be western USA referring to the bear's coat in its appearance described at the time as 'grizzled' (for better translation & understanding think of a man's beard after not shaving for a day or two & not to confuse it with the word gristly which is associated with horror) with streaks of dark brown, silver, & black fur. |
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Post by grrraaahhh on Jul 9, 2011 20:35:56 GMT -9
Abstract
Variation in size of brown bears, Ursus arctos Linnaeus, indicated by condylobasal length of the skull, has been studied in 357 specimens comprising series from 26 regions in North America. These were selected by criteria defined from a previous study of growth in black bears, U. americanus Pallas, since it was determined that the growth pattern is essentially the same for the two species. Variation in mean condylobasal length in the series studied is clinal; a well-defined gradient exists along the coastal zone from Bella Coola, British Columbia, to the end of the Alaska Peninsula, with mean condylobasal length increasing from south to northwest. A similar gradient was evident along the Arctic Coast, beginning in the region of Coronation Gulf. In the interior, small mean values were obtained for samples from the western Yukon Territory, with mean size increasing toward both the southeast and the northwest. It is concluded that formal recognition of segments of intergrading populations of brown bears at the subspecific level is not justified. Brown bears on Kodiak–Afognak–Shuyak Islands comprise a reproductively isolated population possessing distinctive cranial characteristics, and to them the name U. arctos middendorffi Merriam is applicable. It is proposed that U. a. horribilis Ord be used for brown bears over the greater part of the range of the species in North America. The number of subspecies of U. arctos recognized in Eurasia also may be reduced, with the study of comparable series of skulls.
Rausch, L. Robert. GEOGRAPHIC VARIATION IN SIZE IN NORTH AMERICAN BROWN BEARS, URSUS ARCTOS L., AS INDICATED BY CONDYLOBASAL LENGTH. Canadian Journal of Zoology, 1963, 41:(1) 33-45, 10.1139/z63-005.
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