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40-423: Arctocephalus Callorhinus † Eotaria Eumetopias Neophoca Otaria Phocarctos † Pithanotaria † Proterozetes † Thalassoleon Zalophus An eared seal , otariid , or otary is any member of the marine mammal family Otariidae , one of three groupings of pinnipeds . They comprise 15 extant species in seven genera (another species became extinct in

80-537: A monophyletic origin of pinnipeds, sharing a common ancestor with Musteloidea , though an earlier hypothesis suggested that Otаriidae are descended from a common ancestor most closely related to modern bears . Debate remains as to whether the phocids diverged from the otariids before or after the walrus. Otariids arose in the Miocene (15–17 million years ago) in the North Pacific, diversifying rapidly into

120-431: A percentage divergence , by dividing the number of substitutions by the number of base pairs analysed: the hope is that this measure will be independent of the location and length of the section of DNA that is sequenced. An older and superseded approach was to determine the divergences between the genotypes of individuals by DNA–DNA hybridization . The advantage claimed for using hybridization rather than gene sequencing

160-524: A constant rate of mutation, provide a molecular clock for dating divergence. Molecular phylogeny uses such data to build a "relationship tree" that shows the probable evolution of various organisms. With the invention of Sanger sequencing in 1977, it became possible to isolate and identify these molecular structures. High-throughput sequencing may also be used to obtain the transcriptome of an organism, allowing inference of phylogenetic relationships using transcriptomic data . The most common approach

200-656: A day or so before giving birth. While considered social animals, no permanent hierarchies or statuses are established on the colonies. The extent to which males control females or territories varies between species. Thus, the northern fur seal and the South American sea lion tend to herd specific harem -associated females, occasionally injuring them, while the Steller sea lion and the New Zealand sea lion control spatial territories, but do not generally interfere with

240-427: A particular species or in a group of related species, it has been found empirically that only a minority of sites show any variation at all, and most of the variations that are found are correlated, so that the number of distinct haplotypes that are found is relatively small. In a molecular systematic analysis, the haplotypes are determined for a defined area of genetic material ; a substantial sample of individuals of

280-547: A phylogenetic tree. The third stage includes different models of DNA and amino acid substitution. Several models of substitution exist. A few examples include Hamming distance , the Jukes and Cantor one-parameter model, and the Kimura two-parameter model (see Models of DNA evolution ). The fourth stage consists of various methods of tree building, including distance-based and character-based methods. The normalized Hamming distance and

320-641: A significant complication to molecular systematics, indicating that different genes within the same organism can have different phylogenies. HGTs can be detected and excluded using a number of phylogenetic methods (see Inferring horizontal gene transfer § Explicit phylogenetic methods ). In addition, molecular phylogenies are sensitive to the assumptions and models that go into making them. Firstly, sequences must be aligned; then, issues such as long-branch attraction , saturation , and taxon sampling problems must be addressed. This means that strikingly different results can be obtained by applying different models to

360-510: A thick underfur, which has historically made them the objects of commercial exploitation . Male otariids range in size from the 70 kg (150 lb) Galápagos fur seal , smallest of all otariids, to the over 1,000-kg (2,200-lb) Steller sea lion . Mature male otariids weigh two to six times as much as females, with proportionately larger heads, necks, and chests, making them the most sexually dimorphic of all mammals. All otariids breed on land during well-defined breeding seasons. Except for

400-575: Is a simple method; however, it is less accurate than the neighbor-joining approach. Finally, the last step comprises evaluating the trees. This assessment of accuracy is composed of consistency, efficiency, and robustness. MEGA (molecular evolutionary genetics analysis) is an analysis software that is user-friendly and free to download and use. This software is capable of analyzing both distance-based and character-based tree methodologies. MEGA also contains several options one may choose to utilize, such as heuristic approaches and bootstrapping. Bootstrapping

440-442: Is an approach that is commonly used to measure the robustness of topology in a phylogenetic tree, which demonstrates the percentage each clade is supported after numerous replicates. In general, a value greater than 70% is considered significant. The flow chart displayed on the right visually demonstrates the order of the five stages of Pevsner's molecular phylogenetic analysis technique that have been described. Molecular systematics

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480-404: Is an essentially cladistic approach: it assumes that classification must correspond to phylogenetic descent, and that all valid taxa must be monophyletic . This is a limitation when attempting to determine the optimal tree(s), which often involves bisecting and reconnecting portions of the phylogenetic tree(s). The recent discovery of extensive horizontal gene transfer among organisms provides

520-415: Is available at Nature Protocol. Another molecular phylogenetic analysis technique has been described by Pevsner and shall be summarized in the sentences to follow (Pevsner, 2015). A phylogenetic analysis typically consists of five major steps. The first stage comprises sequence acquisition. The following step consists of performing a multiple sequence alignment, which is the fundamental basis of constructing

560-482: Is examined in order to see whether the samples cluster in the way that would be expected from current ideas about the taxonomy of the group. Any group of haplotypes that are all more similar to one another than any of them is to any other haplotype may be said to constitute a clade , which may be visually represented as the figure displayed on the right demonstrates. Statistical techniques such as bootstrapping and jackknifing help in providing reliability estimates for

600-482: Is the comparison of homologous sequences for genes using sequence alignment techniques to identify similarity. Another application of molecular phylogeny is in DNA barcoding , wherein the species of an individual organism is identified using small sections of mitochondrial DNA or chloroplast DNA . Another application of the techniques that make this possible can be seen in the very limited field of human genetics, such as

640-534: Is the contrast between the coarse short sea lion hair and the fur seal's fur. Otariids have proportionately much larger foreflippers and pectoral muscles than phocids, and have the ability to turn their hind limbs forward and walk on all fours, making them far more maneuverable on land. They are generally considered to be less adapted to an aquatic lifestyle, since they breed primarily on land and haul out more frequently than true seals. However, they can attain higher bursts of speed and have greater maneuverability in

680-406: Is the process of selective changes (mutations) at a molecular level (genes, proteins, etc.) throughout various branches in the tree of life (evolution). Molecular phylogenetics makes inferences of the evolutionary relationships that arise due to molecular evolution and results in the construction of a phylogenetic tree. The theoretical frameworks for molecular systematics were laid in the 1960s in

720-488: The Australian sea lion , which has an atypical 17.5 month breeding cycle, they form strictly annual aggregations on beaches or rocky substrates, often on islands. All species are polygynous ; i.e. successful males breed with several females. In most species, males arrive at breeding sites first and establish and maintain territories through vocal and visual displays and occasional fighting. Females typically arrive on shore

760-603: The genetic evidence suggests that Callorhinus ursinus is in fact more closely related to several sea lion species. Furthermore, many of the Otariinae appear to be more phylogenetically distinct than previously assumed; for example, the Japanese sea lion ( Zalophus japonicus ) is now considered a separate species, rather than a subspecies of the California sea lion ( Zalophus californius ). In light of this evidence,

800-505: The 1950s) and are commonly known either as sea lions or fur seals , distinct from true seals (phocids) and the walrus ( odobenids ). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans , the southern Indian , and Atlantic Oceans. They are conspicuously absent in

840-529: The Jukes-Cantor correction formulas provide the degree of divergence and the probability that a nucleotide changes to another, respectively. Common tree-building methods include unweighted pair group method using arithmetic mean ( UPGMA ) and Neighbor joining , which are distance-based methods, Maximum parsimony , which is a character-based method, and Maximum likelihood estimation and Bayesian inference , which are character-based/model-based methods. UPGMA

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880-537: The Southern Hemisphere, where most species now live. The earliest known fossil otariid is Eotaria crypta from southern California, while the genus Callorhinus ( northern fur seal ) has the oldest fossil record of any living otariid, extending to the middle Pliocene. It probably arose from the extinct fur seal genus Thalassoleon . Traditionally, otariids had been subdivided into the fur seal (Arctocephalinae) and sea lion (Otariinae) subfamilies, with

920-606: The ever-more-popular use of genetic testing to determine a child's paternity , as well as the emergence of a new branch of criminal forensics focused on evidence known as genetic fingerprinting . There are several methods available for performing a molecular phylogenetic analysis. One method, including a comprehensive step-by-step protocol on constructing a phylogenetic tree, including DNA/Amino Acid contiguous sequence assembly, multiple sequence alignment , model-test (testing best-fitting substitution models), and phylogeny reconstruction using Maximum Likelihood and Bayesian Inference,

960-419: The exact sequences of nucleotides or bases in either DNA or RNA segments extracted using different techniques. In general, these are considered superior for evolutionary studies, since the actions of evolution are ultimately reflected in the genetic sequences. At present, it is still a long and expensive process to sequence the entire DNA of an organism (its genome ). However, it is quite feasible to determine

1000-590: The genus has been questioned, primarily based on limited molecular data. The issue is complicated because some of the species are able to produce fertile hybrids . A recent review recommended the retention of seven species, deprecating the New Zealand fur seals to a subspecies of the South American fur seal, while also questioning the status of the Guadalupe fur seal. Other recent studies have indicated

1040-652: The genus may be paraphyletic , and some taxonomic reshuffling was previously done to account for this; however, more recent studies support it being monophyletic , with the alleged paraphyly being a consequence of incomplete lineage sorting . [REDACTED] 700,000–1,000,000 [REDACTED] [REDACTED] [REDACTED] [REDACTED] 10,000 [REDACTED] [REDACTED] 1,060,000 [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Molecular phylogeny Molecular phylogenetics and molecular evolution correlate. Molecular evolution

1080-418: The major distinction between them being the presence of a thick underfur layer in the former. Under this categorization, the fur seals comprised two genera: Callorhinus in the North Pacific with a single representative, the northern fur seal ( C. ursinus ), and eight species in the Southern Hemisphere under the genus Arctocephalus ; while the sea lions comprise five species under five genera. Recent analyses of

1120-593: The movement of the females. Female New Zealand sea lions are the only otrariids that move up to 2 km (1.2 mi) into forests to protect their pups during the breeding season. Otariids are carnivorous, feeding on fish , squid and krill . Sea lions tend to feed closer to shore in upwelling zones, feeding on larger fish, while the smaller fur seals tend to take longer, offshore foraging trips and can subsist on large numbers of smaller prey items. They are visual feeders. Some females are capable of dives of up to 400 m (1,300 ft). Family Otariidae Although

1160-713: The north Atlantic. The words "otariid" and "otary" come from the Greek otarion meaning "little ear", referring to the small but visible external ear flaps ( pinnae ), which distinguishes them from the phocids . Phocidae Northern fur seal Steller sea lion California sea lion Galápagos sea lion South American sea lion Australian sea lion New Zealand sea lion Brown fur seal Subantarctic fur seal Antarctic fur seal Guadalupe fur seal Juan Fernández fur seal Antipodean fur seal Galápagos fur seal South American fur seal   Walrus Morphological and molecular evidence supports

1200-486: The positions of haplotypes within the evolutionary trees. Every living organism contains deoxyribonucleic acid ( DNA ), ribonucleic acid ( RNA ), and proteins . In general, closely related organisms have a high degree of similarity in the molecular structure of these substances, while the molecules of organisms distantly related often show a pattern of dissimilarity. Conserved sequences, such as mitochondrial DNA, are expected to accumulate mutations over time, and assuming

1240-479: The remaining Southern Hemisphere species. [REDACTED] Arctocephalus Arctocephalus gazella Arctocephalus townsendi Arctocephalus philippii Arctocephalus galapagoensis Arctocephalus pusillus Arctocephalus forsteri Arctocephalus tropicalis Arctocephalus australis The genus Arctocephalus consists of the southern fur seals . Arctocephalus translates to "bear head." The number of species within

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1280-659: The results were not quantitative and did not initially improve on morphological classification, they provided tantalizing hints that long-held notions of the classifications of birds , for example, needed substantial revision. In the period of 1974–1986, DNA–DNA hybridization was the dominant technique used to measure genetic difference. Early attempts at molecular systematics were also termed chemotaxonomy and made use of proteins, enzymes , carbohydrates , and other molecules that were separated and characterized using techniques such as chromatography . These have been replaced in recent times largely by DNA sequencing , which produces

1320-476: The sequence of a defined area of a particular chromosome . Typical molecular systematic analyses require the sequencing of around 1000 base pairs . At any location within such a sequence, the bases found in a given position may vary between organisms. The particular sequence found in a given organism is referred to as its haplotype . In principle, since there are four base types, with 1000 base pairs, we could have 4 distinct haplotypes. However, for organisms within

1360-423: The simplest case, the difference between two haplotypes is assessed by counting the number of locations where they have different bases: this is referred to as the number of substitutions (other kinds of differences between haplotypes can also occur, for example, the insertion of a section of nucleic acid in one haplotype that is not present in another). The difference between organisms is usually re-expressed as

1400-504: The subfamily separation has been removed entirely and the family Otariidae has been organized into seven genera with 16 species and two subspecies. Nonetheless, because of morphological and behavioral similarities among the "fur seals" and "sea lions", these remain useful categories when discussing differences between groups of species. Compared to sea lions, fur seals are generally smaller, exhibit greater sexual dimorphism , eat smaller prey and go on longer foraging trips; and, of course, there

1440-403: The target species or other taxon is used; however, many current studies are based on single individuals. Haplotypes of individuals of closely related, yet different, taxa are also determined. Finally, haplotypes from a smaller number of individuals from a definitely different taxon are determined: these are referred to as an outgroup . The base sequences for the haplotypes are then compared. In

1480-404: The two subfamilies of otariids, the Otariinae (sea lions) and Arctocephalinae (fur seals), are still widely used, recent molecular studies have demonstrated that they may be invalid. Instead, they suggest three clades within the family; one consisting of the northern sea lions ( Eumetopias and Zalophus ), one of the northern fur seal ( Callorhinus ) and its extinct relatives, and the third of all

1520-483: The water. Their swimming power derives from the use of flippers more so than the sinuous whole-body movements typical of phocids and walruses. Otariids are further distinguished by a more dog-like head, sharp, well-developed canines, and the aforementioned visible external pinnae. Their postcanine teeth are generally simple and conical in shape. The dental formula for eared seals is: 3.1.4.1-3 2.1.4.1 . Sea lions are covered with coarse guard hairs, while fur seals have

1560-424: The works of Emile Zuckerkandl , Emanuel Margoliash , Linus Pauling , and Walter M. Fitch . Applications of molecular systematics were pioneered by Charles G. Sibley ( birds ), Herbert C. Dessauer ( herpetology ), and Morris Goodman ( primates ), followed by Allan C. Wilson , Robert K. Selander , and John C. Avise (who studied various groups). Work with protein electrophoresis began around 1956. Although

1600-398: Was that it was based on the entire genotype, rather than on particular sections of DNA. Modern sequence comparison techniques overcome this objection by the use of multiple sequences. Once the divergences between all pairs of samples have been determined, the resulting triangular matrix of differences is submitted to some form of statistical cluster analysis , and the resulting dendrogram

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