Cytochromeb gene of marine mammals: Phylogeny and evolution

The DNA sequences of the mitochondrial cytochromeb gene of marine mammals (Cetacea, Pinnipedia, Sirenia) were compared with cytochromeb genes of terrestrial mammals including the semiaquatic hippopotamus. The comparison included 28 sequences, representing 22 families and 10 orders. The dugong (order Sirenia) sequence associated with that of the elephant, supporting the Tethytheria clade. The fin whale and dolphin (order Cetacea) sequences are more closely related to those of the artiodactyls, and the comparison suggests that the hippopotamus may be the extant artiodactyl species that is most closely related to the cetaceans. The seal sequence may be more closely related to those of artiodactyls, cetaceans, and perissodactyls than to tethytheres, rodents, lagomorphs, or primates. The cytochromeb proteins of mammals do not evolve at a uniform rate. Human and elephant cytochromeb amino acid sequences were found to evolve the most rapidly, while those of myomorph rodents evolved slowest. The cytochromeb of marine mammals evolves at an intermediate rate. The pattern of amino acid substitutions in marine mammals is similar to that of terrestrial mammals.     

Olfaction at depth: Cribriform plate size declines with dive depth and duration in aquatic arctoid carnivorans

It is widely accepted that obligate aquatic mammals, specifically toothed whales, rely relatively little on olfaction. There is less agreement about the importance of smell among aquatic mammals with residual ties to land, such as pinnipeds and sea otters. Field observations of marine carnivorans stress their keen use of smell while on land or pack ice. Yet, one dimension of olfactory ecology is often overlooked: while underwater, aquatic carnivorans forage “noseblind,” diving with nares closed, removed from airborne chemical cues. For this reason, we predicted marine carnivorans would have reduced olfactory anatomy relative to closely related terrestrial carnivorans. Moreover, because species that dive deeper and longer forage farther removed from surface scent cues, we predicted further reductions in their olfactory anatomy. To test these hypotheses, we looked to the cribriform plate (CP), a perforated bone in the posterior nasal chamber of mammals that serves as the only passageway for olfactory nerves crossing from the periphery to the olfactory bulb and thus covaries in size with relative olfactory innervation. Using CT scans and digital quantification, we compared CP morphology across Arctoidea, a clade at the interface of terrestrial and aquatic ecologies. We found that aquatic carnivoran species from two lineages that independently reinvaded marine environments (Pinnipedia and Mustelidae), have significantly reduced relative CP than terrestrial species. Furthermore, within these aquatic lineages, diving depth and duration were strongly correlated with CP loss, and the most extreme divers, elephant seals, displayed the greatest reductions. These observations suggest that CP reduction in carnivorans is an adaptive response to shifting selection pressures during secondary invasion of marine environments, particularly to foraging at great depths. Because the CP is fairly well preserved in the fossil record, using methods presented here to quantify CP morphology in extinct species could further clarify evolutionary patterns of olfactory loss across aquatic mammal lineages that have independently committed to life in water.     

The olfactory receptor gene repertoires in secondary-adapted marine vertebrates: evidence for reduction of the functional proportions in cetaceans

An olfactory receptor (OR) multigene family is responsible for the well-developed sense of smell possessed by terrestrial tetrapods. Mammalian OR genes had diverged greatly in the terrestrial environment after the fish-tetrapod split, indicating their importance to land habitation. In this study, we analysed OR genes of marine tetrapods (minke whale Balaenoptera acutorostrata, dwarf sperm whale Kogia sima, Dall's porpoise Phocoenoides dalli, Steller's sea lion Eumetopias jubatus and loggerhead sea turtle Caretta caretta) and revealed that the pseudogene proportions of OR gene repertoires in whales were significantly higher than those in their terrestrial relative cattle and also in sea lion and sea turtle. On the other hand, the pseudogene proportion of OR sequences in sea lion was not significantly higher compared with that in their terrestrial relative (dog). It indicates that secondary perfectly adapted marine vertebrates (cetaceans) have lost large amount of their OR genes, whereas secondary-semi-adapted marine vertebrates (sea lions and sea turtles) still have maintained their OR genes, reflecting the importance of terrestrial environment for these animals.     

The vestigial olfactory receptor subgenome of odontocete whales: phylogenetic congruence between gene-tree reconciliation and supermatrix methods

The macroevolutionary transition of whales (cetaceans) from a terrestrial quadruped to an obligate aquatic form involved major changes in sensory abilities. Compared to terrestrial mammals, the olfactory system of baleen whales is dramatically reduced, and in toothed whales is completely absent. We sampled the olfactory receptor (OR) subgenomes of eight cetacean species from four families. A multigene tree of 115 newly characterized OR sequences from these eight species and published data for Bos taurus revealed a diverse array of class II OR paralogues in Cetacea. Evolution of the OR gene superfamily in toothed whales (Odontoceti) featured a multitude of independent pseudogenization events, supporting anatomical evidence that odontocetes have lost their olfactory sense. We explored the phylogenetic utility of OR pseudogenes in Cetacea, concentrating on delphinids (oceanic dolphins), the product of a rapid evolutionary radiation that has been difficult to resolve in previous studies of mitochondrial DNA sequences. Phylogenetic analyses of OR pseudogenes using both gene-tree reconciliation and supermatrix methods yielded fully resolved, consistently supported relationships among members of four delphinid subfamilies. Alternative minimizations of gene duplications, gene duplications plus gene losses, deep coalescence events, and nucleotide substitutions plus indels returned highly congruent phylogenetic hypotheses. Novel DNA sequence data for six single-copy nuclear loci and three mitochondrial genes (> 5000 aligned nucleotides) provided an independent test of the OR trees. Nucleotide substitutions and indels in OR pseudogenes showed a very low degree of homoplasy in comparison to mitochondrial DNA and, on average, provided more variation than single-copy nuclear DNA. Our results suggest that phylogenetic analysis of the large OR superfamily will be effective for resolving relationships within Cetacea whether supermatrix or gene-tree reconciliation procedures are used.     

Molecular cloning of urea transporters from the kidneys of baleen and toothed whales

Urea transport in the kidney is important for the production of concentrated urine. This process is mediated by urea transporters (UTs) encoded by two genes, UT-A (Slc14a2) and UT-B (Slc14a1). Our previous study demonstrated that cetaceans produce highly concentrated urine than terrestrial mammals, and that baleen whales showed higher concentrations of urinary urea than sperm whales. Therefore, we hypothesized that cetaceans have unique actions of UTs to maintain fluid homeostasis in marine habitat. Kidney samples of common minke (Balaenoptera acutorostrata), sei (B. borealis), Bryde's (B. brydei) and sperm whales (Physeter macrocephalus) were obtained to determine the nucleotide sequences of mRNAs encoding UT. The sequences of 2.5-kb cDNAs encode 397-amino acid proteins, which are 90-94% identical to the mammalian UT-A2s. Two putative glycosylation sites are conserved between the whales and the terrestrial mammals, whereas consensus sites for protein kinases are not completely conserved; only a single protein kinase A consensus site was identified in the whale UT-A2s. Two protein kinase C consensus sites are present in the baleen whale UT-A2s, however, a single protein kinase C consensus site was identified in the sperm whale UT-A2. These different phosphorylation sites of whale UT-A2s may result in the high concentrations of urinary urea in whales, by reflecting their urea permeability.     

The bioelectronic nose and tongue using olfactory and taste receptors: Analytical tools for food quality and safety assessment

Food intake is the primary method for obtaining energy and component materials in the human being. Humans evaluate the quality of food by combining various facets of information, such as an item of food's appearance, smell, taste, and texture in the mouth. Recently, bioelectronic noses and tongues have been reported that use human olfactory and taste receptors as primary recognition elements, and nanoelectronics as secondary signal transducers. Bioelectronic sensors that mimic human olfaction and gustation have sensitively and selectively detected odor and taste molecules from various food samples, and have been applied to food quality assessment. The portable and multiplexed bioelectronic nose and tongue are expected to be used as next-generation analytical tools for rapid on-site monitoring of food quality. In this review, we summarize recent progress in the bioelectronic nose and tongue using olfactory and taste receptors, and discuss the potential applications and future perspectives in the food industry.     

Contributions of Smell and taste to overall intensity

The integration of olfaction and gustation in producing thesensation of flavor was studied using an almond extract stimuluspresented with the Two-Module Delivery System. Almond in themouth was found to influence the scaling of smell. The datasugest that this background effect is due to the diffusion ofairborne molecules from the oral cavity to the olfactory receptorsarea. At least under some stimulation conditons, almond vaporin the nose was shown to afect the scaling of taste. When scalingoverall intensity, subjects apparently added together the sensationsof smell and taste to produce the sensation of overall intensity.However, for all combinations of odorants and tastants, theestimate of overall intensity was less than the sum of the estimateof the smell and the estimate of the taste. The data furthersuggest that when estimating the overall intensity, the magnitudeassigned to the olfactory or gustatory sensations was less thanthat which have been assigned when estimating just smell ortaste.     

The independence and integration of olfaction and taste

To study the influences of smell on the scaling of taste, andvice versa, an unobtrusive device was developed which permitsthe independent varying of the olfactory and gustatory componentsof a flavor compound. With instant coffee and the method ofmagnitude estimation, the slopes of the olfactory, taste, andflavor curves produced by this device were similar to thoseproduced by more traditional delivery systems. To study theinteraction of taste on smell and vice versa, subjects scaledolfactory stimuli against different taste backgrounds and tastestimuli against different odorant backgrounds. Taste backgroundsdid not significantly alter the scaling of olfaction. Similarly,olfactory backgrounds did not significantly alter the scalingof taste. Finally, subjects scaled overall intensity (flavor)when presented with all combinations of four concentrationsof odorants and tastants. Smell and taste were shown to contributeindependently to the estimation of overall intensity.     

Aging Effects on Anatomy and Neurophysiology of Taste and Smell1

Taste and smell have a primary role in food ingestion. Therefore, to understand why eating habits alter in elderly people, age-related differences in the chemical senses should be investigated. In early anatomical studies, substantial decreases in numbers of taste buds in old human and mouse circumvallate papillae were observed. However, recent investigations in humans, monkeys, and rats indicate that there is not a significant loss of taste buds in old age. Neurophysiological recordings from the chorda tympani nerve, innervating taste buds in fungiform papillae, demonstrate significant but small differences in response magnitudes for some chemicals in old rats. Greater age-related differences have been observed in the olfactory sense. Numbers of receptor neurons in the rat olfactory epithelium initially increase in adults and then decline in old animals; this decline is reflected in subsequent changes in the olfactory bulb. However, numbers of synapses in the bulb per receptor neuron are increased in the oldest rats, suggesting some compensatory mechanism. Differences in degree of aging effects in taste and smell might relate to the nature of receptors: a modified epithelial cell in taste versus a neuron in smell. However, in both sensory systems, large numbers of receptors remain even in old age. Since taste bud cells and olfactory receptors turn over and are replaced throughout life, the peripheral taste and smell systems might be relatively resistant to aging effects.     

Degeneration patterns of the olfactory receptor genes in sea snakes

The sense of smell relies on the diversity of olfactory receptor (OR) repertoires in vertebrates. It has been hypothesized that different types of ORs are required in terrestrial and marine environments. Here we show that viviparous sea snakes, which do not rely on a terrestrial environment, have significantly lost ORs compared with their terrestrial relatives, supporting the hypothesis. On the other hand, oviparous sea snakes, which rely on a terrestrial environment for laying eggs, still maintain their ORs, reflecting the importance of the terrestrial environment for them. Furthermore, we found one Colubroidea snake (including sea snakes and their terrestrial relatives)‐specific OR subfamily which had diverged widely during snake evolution after the blind snake–Colubroidea snake split. Interestingly, no pseudogenes are included in this subfamily in sea snakes, and this subfamily seems to have been expanding rapidly even in an underwater environment. These findings suggest that the Colubroidea‐specific ORs detect nonvolatile odorants.     

Genetic Variation at Exon 2 of the MHC Class II DQB Locus in Blue Whale (Balaenoptera musculus) from the Gulf of California

The genes of the Major Histocompatibility Complex (MHC) play an important role in the vertebrate immune response and are among the most polymorphic genes known in vertebrates. In some marine mammals, MHC genes have been shown to be characterized by low levels of polymorphism compared to terrestrial taxa; this reduction in variation is often explained as a result of lower pathogen pressures in marine habitats. To determine if this same reduction in variation applies to the migratory population of blue whales (Balaenoptera musculus) that occurs in the Gulf of California, we genotyped a 172 bp fragment of exon 2 of the MHC Class II DQB locus for 80 members of this population. Twenty-two putatively functional DQB allotypes were identified, all of which were homologous with DQB sequences from other cetacean species. Up to 5 putative alleles per individual were identified, suggesting that gene duplication has occurred at this locus. Rates of non-synonymous to synonymous substitutions (ω) and maximum likelihood analyses of models of nucleotide variation provided potential evidence of ongoing positive selection at this exon. Phylogenetic analyses of DQB alleles from B. musculus and 16 other species of cetaceans revealed trans-specific conservation of MHC variants, suggesting that selection has acted on this locus over prolonged periods of time. Collectively our findings reveal that immunogenic variation in blue whales is comparable to that in terrestrial mammals, thereby providing no evidence that marine taxa are subject to reduced pathogen-induced selective pressures.     

鲸类二次水生生境适应Epac1和Epac2基因的分子进化

心率即心脏跳动的速度,不仅反映了心脏的功能,还与寿命的长短及能量代谢有关。与大多数陆生哺乳动物相比,鲸类心率显著降低。降低的心率有助于鲸类寿命的延长及能量的高效利用,便于其适应极端的海洋环境,而这一适应的分子机制尚不清楚。鉴于此,本研究采用基于最大似然法的枝模型、枝位点模型结合蛋白质功能差异分析等方法,对控制心率的环状腺苷酸结合蛋白（Epac1 和Epac2）基因进行适应性探究。分析结果表明,Epac1在长寿鲸类即须鲸类和抹香鲸（Physeter macrocephalus）组合进化支中检测到加速进化过程,且枝位点模型在须鲸类祖先支中检测到的强烈的正选择位点均位于功能重要的催化区;另外,该蛋白质在鲸类中还发生了显著的功能修饰（θ=0.5296 ± 0.1300;P<0.001）。对Epac2进行相同的分析发现,该基因在寿命长达200年之久的弓头鲸（Balaena mysticetus）中检测到的正选择位点同样位于功能重要的催化区。上述结果提示Epac1和Epac2在鲸类中均产生了适应性进化,这一方面可能有助于鲸类心率降低,另一方面也可能与其较长的寿命及高效的能量利用有关。     

How much does nasal cavity morphology matter? Patterns and rates of olfactory airflow in phyllostomid bats

The morphology of the nasal cavity in mammals with a good sense of smell includes features that are thought to improve olfactory airflow, such as a dorsal conduit that delivers odours quickly to the olfactory mucosa, an enlarged olfactory recess at the back of the airway, and a clear separation of the olfactory and respiratory regions of the nose. The link between these features and having a good sense of smell has been established by functional examinations of a handful of distantly related mammalian species. In this paper, we provide the first detailed examination of olfactory airflow in a group of closely related species that nevertheless vary in their sense of smell. We study six species of phyllostomid bats that have different airway morphologies and foraging ecologies, which have been linked to differences in olfactory ability or reliance. We hypothesize that differences in morphology correlate with differences in the patterns and rates of airflow, which in turn are consistent with dietary differences. To compare species, we make qualitative and quantitative comparisons of the patterns and rates of airflow through the olfactory region during both inhalation and exhalation across the six species. Contrary to our expectations, we find no clear differences among species in either the patterns of airflow through the airway or in rates of flow through the olfactory region. By and large, olfactory airflow seems to be conserved across species, suggesting that morphological differences appear to be driven by other mechanical demands on the snout, such as breathing and feeding. Olfactory ability may depend on other aspects of the system, such as the neurobiological processing of odours that work within the existing morphology imposed by other functional demands on the nasal cavity.     

Olfaction and brain size in the bowhead whale (Balaena mysticetus)

Although there are several isolated references to the olfactory anatomy of mysticetes, it is usually thought that olfaction is rudimentary in this group. We investigated the olfactory anatomy of bowhead whales and found that these whales have a cribriform plate and small, but histologically complex olfactory bulb. The olfactory bulb makes up approximately 0.13% of brain weight, unlike odontocetes where this structure is absent. We also determined that 51% of olfactory receptor genes were intact, unlike odontocetes, where this number is less than 25%. This suggests that bowheads have a sense of smell, and we speculate that they may use this to find aggregations of krill on which they feed.     

From Land to Water: the Origin of Whales, Dolphins, and Porpoises

Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Even though all modern cetaceans are obligate aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial artiodactyls, similar to small deer. The transition from land to water is documented by a series of intermediate fossils, many of which are known from India and Pakistan. We review raoellid artiodactyls, as well as the earliest families of cetaceans: pakicetids, ambulocetids, remingtonocetids, protocetids, and basilosaurids. We focus on the evolution of cetacean organ systems, as these document the transition from land to water in detail.     

Body size and skeletal muscle myoglobin of cetaceans: adaptations for maximizing dive duration

Cetaceans exhibit an exceptionally wide range of body mass that influence both the capacities for oxygen storage and utilization; the balance of these factors is important for defining dive limits. Furthermore, myoglobin content is a key oxygen store in the muscle as it is many times higher in marine mammals than terrestrial mammals. Yet little consideration has been given to the effects of myoglobin content or body mass on cetacean dive capacity. To determine the importance of myoglobin content and body mass on cetacean diving performance, we measured myoglobin content of the longissimus dorsi for ten odontocete (toothed whales) and one mysticete (baleen whales) species ranging in body mass from 70 to 80000 kg. The results showed that myoglobin content in cetaceans ranged from 1.81 to 5.78 g (100 g wet muscle)(-1). Myoglobin content and body mass were both positively and significantly correlated to maximum dive duration in odontocetes; this differed from the relationship for mysticetes. Overall, the combined effects of body mass and myoglobin content accounts for 50% of the variation in cetacean diving performance. While independent analysis of the odontocetes showed that body mass and myoglobin content accounts for 83% of the variation in odontocete dive capacity.     

Molecular evidence of new variant Brucella in North Pacific common minke whales

Brucella, a causative agent of brucellosis, has been isolated recently from a variety of marine mammals. The molecular analysis of marine mammalian Brucella strains, without manifest pathology of brucellosis in the eastern North Atlantic, showed that they are distinct from terrestrial Brucella species. Previously, we reported abnormal gonads in common minke whales (Balaenoptera acutorostrata) in the western North Pacific and suggested the presence of Brucella infection in the whales in pathology and serology studies. In the present study, using polymerase chain reaction (PCR), Brucella was detected in granular testes of the whales showing caseation or calcification. The insertion of an IS711 transposable element specific for marine mammal isolates as well as a seal isolate-specific DNA fragment were also found. Molecular characterization of Brucella based on sequence analysis of the PCR products amplified from the outer membrane protein (omp) 2 gene showed that the Brucella from North Pacific common minke whales was different from terrestrial and North Atlantic marine mammal Brucella strains. The North Pacific Brucella showed the highest similarity to North Atlantic seal strains among the known Brucella strains.     

Effect of Oxidized Arachidonic Acid and Hexanal on the Mouse Taste Perception of Bitterness and Umami

The oxidization of fatty acids generates many volatile compounds forming an aroma, but little is known whether mammals use gustatory sense to detect the oxidized products as a taste or only use olfactory sense to detect as an aroma. We examined in this study the effect of aqueous extracts of the compounds from autoxidized arachidonic acid (AA) ethyl ester or hexanal which is the predominant component generated from oxidized AA by the anosmic mouse licking performance to a tastant. The addition of the water extract from oxidized AA or hexanal to a quinine hydrochloride (QHCl) solution decreased the anosmic mice licking frequency at several concentrations of QHCl. Hexanal also reduced the licking frequency of anosmic mice conditioned to avoid MSG at several concentrations of monosodium glutamate (MSG). These results suggest that hexanal would affect mouse taste perception to QHCl and MSG via the gustatory sensation.     

Avian sebokeratocytes and marine mammal lipokeratinocytes: structural, lipid biochemical, and functional considerations

In terrestrial mammals, stratum corneum lipids derive from two sources: deposition of lamellar body lipids in stratum corneum interstices and excretion of sebaceous lipids onto the skin surface, resulting in a two-compartment ("bricks and mortar") system of lipid-depleted cells surrounded by lipid-enriched intercellular spaces. In contrast, intracellular lipid droplets, normally not present in the epidermis of terrestrial mammals, are prominent in avian and marine mammal epidermis (cetaceans, manatees). We compared the transepidermal water loss, ultrastructure, and lipid biochemistry of the viable epidermis and stratum corneum of pigeon apterium, fledgling (featherless) zebra finches, painted storks, cetaceans, and manatees to those of humans and mice. Marine mammals possess an even more extensive lamellar-body secretory system than do terrestrial mammals; and lamellar-body contents, as in terrestrials, are secreted into the stratum corneum interstices. In cetaceans, however, glycolipids, but not ceramides, persist into the stratum corneum; whereas in manatees, glycolipids are replaced by ceramides, as in terrestrial mammals. Acylglucosylceramides, thought to be critical for lamellar-body deposition and barrier function in terrestrial mammals, are present in manatees but virtually absent in cetaceans, a finding that indicates that they are not obligate constituents of lamellar-body-derived membrane structures. Moreover, cetaceans do not elaborate the very long-chain, saturated N-acyl fatty acids that abound in terrestrial mammalian acylglucosylceramides. Furthermore, cold-water marine mammals generate large, intracellular neutral lipid droplets not found in terrestrial and warm-water marine mammals; these lipid droplets persist into the stratum corneum, suggesting thermogenesis, flotation, and/or cryoprotectant functions. Avians generate distinctive multigranular bodies that may be secreted into the intercellular spaces under xerotic conditions, as in zebra fledglings; ordinarily, however, the internal lamellae and limiting membranes deteriorate, generating intracellular neutral lipid droplets. The sphingolipid composition of avian stratum corneum is intermediate between terrestrials and cetaceans (approximately equal to 50% glycolipids), with triglycerides present in abundance. In the midstratum corneum of avians, neutral lipid droplets are released into the interstices, forming a large extracellular, lipid-enriched compartment, surrounding wafer-thin corneocytes, with a paucity of both lipid and keratin ("plates-and-mortar" rather than the "bricks-and-mortar" of mammals).(ABSTRACT TRUNCATED AT 400 WORDS)