The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Ding Wang - One of the best experts on this subject based on the ideXlab platform.
-
Ex situ options for cetacean conservation : executive summary of the report of the 2018 workshop, Nuremberg, Germany
2020Co-Authors: Barbara L. Taylor, Ding Wang, G. Abel, P. Miller, F. Gomez, L. Von Fersen, Douglas P. Demaster, Randall R. Reeves, Lorenzo Rojas-bracho, Y. HaoAbstract:China’s Yangtze river dolphin (Lipotes vexillifer), was declared likely to be extinct in 2006, due to threats in the wild such as habitat loss, entanglement in fishing gear and ship strikes, which were not effectively dealt with using the management tools available prior to that time. Mexico’s vaquita (Phocoena sinus), a porpoise found only in the Upper Gulf of California, will become extinct in the near future if the illegal fishery to obtain fish swim bladders for illicit international markets is not eliminated very soon. In both of these cases, it took only a short time for the population to decrease from hundreds to tens of animals. This highlights the urgency of gaining information and taking action to anticipate and prevent such rapid declines in other threatened species and populations of small cetaceans. A workshop, “Ex situ Options for Cetacean Conservation” (ESOCC) was held in Nuremberg, Germany, 14-18 December 2018, to start preparing such actions. This report contains the executive summary of the main report of the 2018 workshop in English, French, German, Japanese, Mandarin Chinese, Portuguese and Spanish.
-
Accelerating population decline of Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis)
Biological Conservation, 2012Co-Authors: Zhigang Mei, Samuel T. Turvey, Shiang-lin Huang, Yujiang Hao, Wei-ming Gong, Ding WangAbstract:The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is now the only cetacean species in the Yangtze River following the probable extinction of the baiji (Lipotes vexillifer). However, population abundance estimates and genetic diversity studies both indicate that the porpoise population is declining and may also become extinct in the wild in the near future. We used data from 279 stranded porpoises that were collected along the middle and lower reaches of the Yangtze River since 1978 to construct life tables for the porpoise population before and after 1993. Demographic rate estimates reveal an accelerating decline of the Yangtze porpoise population according to the instantaneous rate of increase ((r) over bar), from (r) over bar = -0.0159 (SD = 0.0135) to (r) over bar = -0.0625 (SD = 0.0169). Using an individual-based Leslie matrix model, there is a high probability of extinction (86.06%) within the next 100 years. Effective conservation measures must be enacted immediately. The pattern of cetacean decline and extinction in the Yangtze provides a startling demonstration of how rapid economic development without adequate environmental control leads to deterioration of natural habitats and threatens native species extremely rapid. This research also emphasizes the need for precautionary conservation action in other riverine systems containing freshwater cetacean species. (C) 2012 Elsevier Ltd. All rights reserved.
-
The conservation of river cetaceans in the Yangtze River
2011 International Symposium on Water Resource and Environmental Protection, 2011Co-Authors: Xiujiang Zhao, Ding Wang, Yongbo ChenAbstract:Baiji, or Yangtze River Dolphin (Lipotes vexillifer) and the Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) are two rare cetacean species endemic to the Yangtze River basin. The threats to both cetaceans include a collection of illegal fishing (electro-fishing and gillnets etc.), transportation, pollution and water constructions. Construction and the operation of the dam would lead to some negative impacts on Yangtze cetaceans by altering its habitats, including alternation of the hydrological feature, fluvial geomorphology, food resources (i.e. fish) and the way of utilization of the river by local communities. The China Three Gorges Corporation funded two conservation projects to remedy the impacts. The first is a monitoring program to investigate the abundance, distribution and trends of porpoises; and the second is to explore the possibility and feasibility of establishing the reservoir above the dam as habitats of the porpoise. As a collection of factors would also contribute a lot to the threats of cetaceans, consequently, the integrated river basin management would be proposed.
-
Distribution pattern of finless porpoises at the junction of the Yangtze River and Poyang Lake observed by towed passive acoustic device
The Journal of the Acoustical Society of America, 2011Co-Authors: Satoko Kimura, Ding Wang, Kexiong Wang, Tomonari Akamatsu, Lijun Dong, Nobuaki AraiAbstract:The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is an endangered freshwater porpoise subspecies unique to the Yangtze River basin. Without immediate conservation measures, it could soon become extinct, just as the Yangtze River dolphin (baiji, Lipotes vexillifer). We report seasonal change in the local distribution of the porpoises living in the conjunction area of the middle reaches of the Yangtze River, side streams, and appended Poyang Lake. A towed stereo acoustic data-logger, A-tag, was used to detect echolocation signals and sound source bearing angles. The independent sound source directions provided the number of animals present, not just the number of sounds. Passive acoustic surveys were performed regularly from May 2007 to August 2010. The water level was highest in August (summer) and lowest in February (winter) and at mid-level in May (spring) and November (autumn). The average number of porpoises detected in 11 surveys conducted in different seasons varied from 0.5...
-
Construction and Characterization of a Lipotes vexillifer Genomic DNA BAC Library
Zoological science, 2007Co-Authors: Xian-feng Zhang, Sheng-guo Fang, Ding WangAbstract:We constructed a genomic DNA library for Lipotes vexillifer (L. vexillifer), the Baiji or Yangtze River dolphin, one of the most endangered mammals in the world. The library consists of 149,000 BAC clones, with an average insert size of 83 kb, representing approximately 3.4 haploid genome equivalents. PCR amplification of four known L. vexillifer genes yielded two to four positive clones each. To demonstrate the utility of this library, we isolated and sequenced the L. vexillifer alpha lactalbumin gene, which is a gene specific to mammals and one which has been widely used as molecular tool in phylogenetic analysis. We also end-sequenced 20 randomly selected clones, resulting in the identification of at least five new L. vexillifer genes, five SSR loci, and one SINE locus. These results suggest that this library is a valuable resource for candidate gene cloning, physical mapping, and genome sequencing of this important and threatened species.
Guang Yang - One of the best experts on this subject based on the ideXlab platform.
-
Considerable MHC diversity suggests that the functional extinction of baiji is not related to population genetic collapse.
PloS one, 2012Co-Authors: Xuming Zhou, Kaiya Zhou, Lian Wang, Guang YangAbstract:To further extend our understanding of the mechanism causing the current nearly extinct status of the baiji (Lipotes vexillifer), one of the most critically endangered species in the world, genetic diversity at the major histocompatibility complex (MHC) class II DRB locus was investigated in the baiji. Nine highly divergent DRB alleles were identified in 17 samples, with an average of 28.4 (13.2%) nucleotide difference and 16.7 (23.5%) amino acid difference between alleles. The unexpectedly high levels of DRB allelic diversity in the baiji may partly be attributable to its evolutionary adaptations to the freshwater environment which is regarded to have a higher parasite diversity compared to the marine environment. In addition, balancing selection was found to be the main mechanisms in generating sequence diversity at baiji DRB gene. Considerable sequence variation at the adaptive MHC genes despite of significant loss of neutral genetic variation in baiji genome might suggest that intense selection has overpowered random genetic drift as the main evolutionary forces, which further suggested that the critically endangered or nearly extinct status of the baiji is not an outcome of genetic collapse.
-
High similarity at three MHC loci between the baiji and finless porpoise: trans-species or convergent evolution?
Molecular phylogenetics and evolution, 2007Co-Authors: Bingyao Chen, Kaiya Zhou, Guang YangAbstract:Two DRA alleles and six MHC-I alleles were identified from a group of 15 baiji (Lipotes vexillifer), the most threatened cetacean in the world. Little sequence variation was detected at the DRA locus but extensive variation at the MHC-I locus. In combination with data at the DQB locus previously reported, three MHC loci exon 2 of the baiji all revealed striking similarity with those of the finless porpoise. Especially, some identical alleles shared by both species at the MHC-I and DQB loci suggested the convergent evolution as a consequence of common adaptive solutions to similar environmental pressures in the Yangtze River. As for DRA locus, the identity alleles were shared not only by baiji and finless porpoise but by some other cetacean species of the families Phocoenidae and Delphinidae, suggesting trans-species evolution on this gene.
-
Molecular phylogenetics of 'river dolphins' and the baiji mitochondrial genome.
Molecular phylogenetics and evolution, 2005Co-Authors: Jie Yan, Kaiya Zhou, Guang YangAbstract:Abstract It is well known that the classical river dolphins are not a natural group, but up to now the phylogenetic relationships among them are not very clear because different views have been referred from different studies. In the present study, we determined the complete nucleotide sequence of the mitochondrial (mt) genome of the baiji ( Lipotes vexillifer ), the most endangered cetacean species, and conducted phylogenetic analyses for the classical river dolphins based on data from cetacean mitochondrial genomes available. In our analyses, the classical river dolphins split into two separate lineages, Platanista and Lipotes + ( Inia + Pontoporia ), having no sister relationship with each other, and the Platanista lineage is always within the odontocete clade instead of having a closer affinity to Mysticeti. The position of the Platanista is more basal, suggesting separate divergence of this lineage well before the other one. The Lipotes has a sister relationship with Inia + pontoporia , and they together formed the sister group to the Delphinoidea. This result strongly supports paraphyly of the classical river dolphins, and the nonplatanistoid river dolphins do represent a monophyletic grouping, with the Lipotidae as the sister taxa to (Iniidae + Pontoporiidae), and is well congruent with the studies based on short interspersed repetitive elements (SINEs).
-
Sequence Variation and Gene Duplication at MHC DQB Loci of Baiji (Lipotes vexillifer), a Chinese River Dolphin
The Journal of heredity, 2005Co-Authors: Guang Yang, K Zhou, J. Yan, F. WeiAbstract:The major histocompatibility complex (MHC) is a fundamental part of the vertebrate immune system, and the high variability in many MHC genes is thought to play an important role in the recognition of parasites. Baiji (Lipotes vexillifer )i s one of the most endangered species in the world. Its wild population has declined to fewer than 100 individuals and has a very high risk of becoming extinct in the near future. In this study we present a first step in the molecular characterization of a DQB-like locus of baiji by nucleotide sequence analysis of the polymorphic exon 2 segments. In the examined 172 bp sequences from a group of 18 incidentally captured or stranded individuals, 48 variable sites were determined and 43 alleles were identified, many of which were represented by only one clone. Three to seven alleles were found in each individual, suggesting gene duplications. No deletion, insertion, or exceptional stop codon was detected, suggesting these alleles function in vivo. Phylogenetic reconstruction using neighbor joining grouped the 43 alleles into two distinct lineages, differing by seven nucleotides and four amino acids. Substitutions of aminoacidstendtobeclusteredaroundsitespostulated toberesponsible for selective peptide recognition.Inthe peptide-binding region (PBR)of theDQBlocus, the average number of nonsynonymous substitutions per site is greater than that of synonymous substitutions per site (0.1962 versus 0.0256, respectively). Nucleotide and amino acid sequences both showed a relatively high level of similarity (nucleotides 90.6%; amino acids 80.6%) to those of beluga whale (Delphinapterus leucas) and narwhal (Monodon monoceros). The high level of baiji MHC polymorphism revealed in the present study has not been reported in other cetaceans and could be a consequence of the small baiji population adapting to freshwater with a relatively high level of pathogens.
-
MOLECULAR SYSTEMATICS OF RIVER DOLPHINS INFERRED FROM COMPLETE MITOCHONDRIAL CYTOCHROME-B GENE SEQUENCES
Marine Mammal Science, 2002Co-Authors: Guang Yang, Kaiya Zhou, Wenhua Ren, Shan Liu, Richardo Bastida, Laura RiveroAbstract:1,140 bp of the complete mitochondrial cytochrome-b gene sequences of baiji (Lipotes vexillifer), franciscana (Pontoporia blainvillei), and Ganges river dolphin (Platanista gangetica gangetica) were determined to address the systematic position and phylogeny of extant river dolphins with combination of homologous sequences of other cetaceans. The neighbor-joining (NJ), maximum parsimony (MP), and maximum likelihood (ML) phylogenetic analyses all identified the river dolphins into three lineages, i.e., Platanista, Lipotes, and Inia + Pontoporia, The Lipotes did not have sister relationship with either Platanista or Inia + Pontoporia, which strongly supported the referral of Lipotes to a separate family, i.e., Lipotidae. There were very high sequence divergences between all river dolphin genera, suggesting a relatively longer period of separation time than those among other odontocete families.
Kexiong Wang - One of the best experts on this subject based on the ideXlab platform.
-
Distribution pattern of finless porpoises at the junction of the Yangtze River and Poyang Lake observed by towed passive acoustic device
The Journal of the Acoustical Society of America, 2011Co-Authors: Satoko Kimura, Ding Wang, Kexiong Wang, Tomonari Akamatsu, Lijun Dong, Nobuaki AraiAbstract:The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is an endangered freshwater porpoise subspecies unique to the Yangtze River basin. Without immediate conservation measures, it could soon become extinct, just as the Yangtze River dolphin (baiji, Lipotes vexillifer). We report seasonal change in the local distribution of the porpoises living in the conjunction area of the middle reaches of the Yangtze River, side streams, and appended Poyang Lake. A towed stereo acoustic data-logger, A-tag, was used to detect echolocation signals and sound source bearing angles. The independent sound source directions provided the number of animals present, not just the number of sounds. Passive acoustic surveys were performed regularly from May 2007 to August 2010. The water level was highest in August (summer) and lowest in February (winter) and at mid-level in May (spring) and November (autumn). The average number of porpoises detected in 11 surveys conducted in different seasons varied from 0.5...
-
first human caused extinction of a cetacean species
Biology Letters, 2007Co-Authors: Samuel T. Turvey, Tomonari Akamatsu, Xiujiang Zhao, Barbara L. Taylor, Randall R. Reeves, Robert L Pitman, Jay Barlow, Leigh A Barrett, Brent S Stewart, Kexiong WangAbstract:The Yangtze River dolphin or baiji ( Lipotes vexillifer), an obligate freshwater odontocete known only from the middle-lower Yangtze River system and neighbouring Qiantang River in eastern China, has long been recognized as one of the world's rarest and most threatened mammal species. The status of the baiji has not been investigated since the late 1990s, when the surviving population was estimated to be as low as 13 individuals. An intensive six-week multivessel visual and acoustic survey carried out in November-December 2006, covering the entire historical range of the baiji in the main Yangtze channel, failed to find any evidence that the species survives. We are forced to conclude that the baiji is now likely to be extinct, probably due to unsustainable by-catch in local fisheries. This represents the first global extinction of a large vertebrate for over 50 years, only the fourth disappearance of an entire mammal family since AD 1500, and the first cetacean species to be driven to extinction by human activity. Immediate and extreme measures may be necessary to prevent the extinction of other endangered cetaceans, including the sympatric Yangtze finless porpoise ( Neophocaena phocaenoides asiaeorientalis).
-
Range-wide Yangtze freshwater dolphin expedition: The last chance to see Baiji?
Environmental science and pollution research international, 2006Co-Authors: Kexiong Wang, Ding Wang, Xian-feng Zhang, August Pfluger, Leigh A BarrettAbstract:Background, Aim and Scope There are two species of fresh water cetaceans surviving in the Yangtze River system in China: Baiji (Lipotes vexillifer) and Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis). As a result of the expansion of human activities on the river, their distribution ranges appear to be decreasing and in the case of the Baiji, are even being restricted to several sections. The Baiji is the world’s most critically endangered cetacean species with a population estimated at only a few tens of individuals. The Yangtze finless porpoise is the world’s only freshwater-adapted population of the species, and it has been estimated that only around 1,000 individuals remain in the river system. In order to prevent the extinction of Baiji and a sharp decline in the abundance of the porpoise, in situ conservation (i.e. in the river) and two ex situ conservation (i.e. in semi-natural reserves and in captivity) strategies were proposed and have been implemented since the early 1990s. In view of both the severely endangered status of the animals and the severely degraded conditions of their habitats, the feasibility and actual status of these two strategies are raised for discussion.
-
echolocation signals of the free ranging yangtze finless porpoise neophocaena phocaenoides asiaeorientialis
Journal of the Acoustical Society of America, 2005Co-Authors: Songhai Li, Ding Wang, Kexiong Wang, Tomonari AkamatsuAbstract:This paper describes the high-frequency echolocation signals from free-ranging Yangtze finless porpoise in the Tian-e-zhou Baiji National Natural Reserve in Hubei Province, China. Signal analysis showed that the Yangtze finless porpoise clicks are typical high-frequency narrow-band (relative width of the frequency spectrum Q=6.6±1.56, N=548) ultrasonic pulses. The peak frequencies of the typical clicks range from 87 to 145 kHz with an average of 125±6.92 kHz. The durations range from 30 to 122 μs with an average of 68±14.12 μs. The characteristics of the signals are similar to those of other members of the Phocoenidae as well as the distantly related delphinids, Cephalorhynchus spp. Comparison of these signals to those of the baiji (Lipotes vexillifer), who occupies habitat similar to that of the Yangtze finless porpoise, showed that the peak frequencies of clicks produced by the Yangtze finless porpoise are remarkably higher than those produced by the baiji. Difference in peak frequency between the two s...
-
Single-hydrophone method for reconstructing dynamic behavior of endangered Chinese river dolphin
Oceans 2003. Celebrating the Past ... Teaming Toward the Future (IEEE Cat. No.03CH37492), 2003Co-Authors: Rajendar Bahl, Ding Wang, Tomonari Akamatsu, M. Yano, Tamaki Ura, Kexiong WangAbstract:Chinese river dolphin (Lipotes vexillifer), usually called 'baiji', is one of the most endangered mammals in the world. The preservation of these mammals directly ensures the health of the ecosystem. However, not much behavioral information on baiji is available so far, that could effectively assist in undertaking their preservation. This research is an attempt to reveal baiji's hitherto unknown underwater dynamic behavior. For this work we have analyzed and extracted motion parameters from clicks of a free-swimming baiji recorded in 1996 at a single hydrophone. The absence of detailed bottom information made it difficult to localize baiji using the multiple reflections and forced us to rely completely on surface reflections only. From measurements of time delay between the direct path and the surface echo, not only large-scale behavior but also fine-scale behavior has been revealed, such as: periods of diving and surfacing, circling behavior underwater and a characteristic nodding motion. These studies have contributed towards a broad understanding of baiji's foraging exercises from the standpoint of formulating an acoustical survey for the search for this endangered marine mammal.
Kaiya Zhou - One of the best experts on this subject based on the ideXlab platform.
-
Considerable MHC diversity suggests that the functional extinction of baiji is not related to population genetic collapse.
PloS one, 2012Co-Authors: Xuming Zhou, Kaiya Zhou, Lian Wang, Guang YangAbstract:To further extend our understanding of the mechanism causing the current nearly extinct status of the baiji (Lipotes vexillifer), one of the most critically endangered species in the world, genetic diversity at the major histocompatibility complex (MHC) class II DRB locus was investigated in the baiji. Nine highly divergent DRB alleles were identified in 17 samples, with an average of 28.4 (13.2%) nucleotide difference and 16.7 (23.5%) amino acid difference between alleles. The unexpectedly high levels of DRB allelic diversity in the baiji may partly be attributable to its evolutionary adaptations to the freshwater environment which is regarded to have a higher parasite diversity compared to the marine environment. In addition, balancing selection was found to be the main mechanisms in generating sequence diversity at baiji DRB gene. Considerable sequence variation at the adaptive MHC genes despite of significant loss of neutral genetic variation in baiji genome might suggest that intense selection has overpowered random genetic drift as the main evolutionary forces, which further suggested that the critically endangered or nearly extinct status of the baiji is not an outcome of genetic collapse.
-
Baiji: Lipotes vexillifer
Encyclopedia of Marine Mammals, 2009Co-Authors: Kaiya ZhouAbstract:Publisher Summary This chapter discusses the baiji or Yangtze River dolphin that is endemic to the middle and lower reaches of the Yangtze River in China. It is a relict species and the only living representative of a whole family of mammals. It was described early in the ancient dictionary, Erh Ya , published as long ago as 200 BC. The baiji is a graceful animal with a very long, narrow, and slightly upturned beak. It can be easily identified by the rounded melon, longitudinally oval blowhole, very small eyes, low triangular dorsal fin, and broad rounded flippers. The color is generally bluish gray or gray above and white or ashy white below. Females are larger than males. The maximum recorded length for females is 253 cm and for males is 229 cm. The baiji probably bred and gave birth in the first half of the year. The peak calving season appeared to be February–April. Body length at birth was estimated to be 91.5 cm for both males and females. Calves were closely accompanied by adults and remained alongside and slightly behind the dorsal fin of their presumed mother. The baiji is classified in the World Conservation Union (IUCN) Red List as Critically Endangered—Possibly Extinct. It is designated in the Chinese National First Category of National Key Protected Wildlife Species and has full legal protection throughout its range.
-
High similarity at three MHC loci between the baiji and finless porpoise: trans-species or convergent evolution?
Molecular phylogenetics and evolution, 2007Co-Authors: Bingyao Chen, Kaiya Zhou, Guang YangAbstract:Two DRA alleles and six MHC-I alleles were identified from a group of 15 baiji (Lipotes vexillifer), the most threatened cetacean in the world. Little sequence variation was detected at the DRA locus but extensive variation at the MHC-I locus. In combination with data at the DQB locus previously reported, three MHC loci exon 2 of the baiji all revealed striking similarity with those of the finless porpoise. Especially, some identical alleles shared by both species at the MHC-I and DQB loci suggested the convergent evolution as a consequence of common adaptive solutions to similar environmental pressures in the Yangtze River. As for DRA locus, the identity alleles were shared not only by baiji and finless porpoise but by some other cetacean species of the families Phocoenidae and Delphinidae, suggesting trans-species evolution on this gene.
-
Molecular phylogenetics of 'river dolphins' and the baiji mitochondrial genome.
Molecular phylogenetics and evolution, 2005Co-Authors: Jie Yan, Kaiya Zhou, Guang YangAbstract:Abstract It is well known that the classical river dolphins are not a natural group, but up to now the phylogenetic relationships among them are not very clear because different views have been referred from different studies. In the present study, we determined the complete nucleotide sequence of the mitochondrial (mt) genome of the baiji ( Lipotes vexillifer ), the most endangered cetacean species, and conducted phylogenetic analyses for the classical river dolphins based on data from cetacean mitochondrial genomes available. In our analyses, the classical river dolphins split into two separate lineages, Platanista and Lipotes + ( Inia + Pontoporia ), having no sister relationship with each other, and the Platanista lineage is always within the odontocete clade instead of having a closer affinity to Mysticeti. The position of the Platanista is more basal, suggesting separate divergence of this lineage well before the other one. The Lipotes has a sister relationship with Inia + pontoporia , and they together formed the sister group to the Delphinoidea. This result strongly supports paraphyly of the classical river dolphins, and the nonplatanistoid river dolphins do represent a monophyletic grouping, with the Lipotidae as the sister taxa to (Iniidae + Pontoporiidae), and is well congruent with the studies based on short interspersed repetitive elements (SINEs).
-
MOLECULAR SYSTEMATICS OF RIVER DOLPHINS INFERRED FROM COMPLETE MITOCHONDRIAL CYTOCHROME-B GENE SEQUENCES
Marine Mammal Science, 2002Co-Authors: Guang Yang, Kaiya Zhou, Wenhua Ren, Shan Liu, Richardo Bastida, Laura RiveroAbstract:1,140 bp of the complete mitochondrial cytochrome-b gene sequences of baiji (Lipotes vexillifer), franciscana (Pontoporia blainvillei), and Ganges river dolphin (Platanista gangetica gangetica) were determined to address the systematic position and phylogeny of extant river dolphins with combination of homologous sequences of other cetaceans. The neighbor-joining (NJ), maximum parsimony (MP), and maximum likelihood (ML) phylogenetic analyses all identified the river dolphins into three lineages, i.e., Platanista, Lipotes, and Inia + Pontoporia, The Lipotes did not have sister relationship with either Platanista or Inia + Pontoporia, which strongly supported the referral of Lipotes to a separate family, i.e., Lipotidae. There were very high sequence divergences between all river dolphin genera, suggesting a relatively longer period of separation time than those among other odontocete families.
Chong Wei - One of the best experts on this subject based on the ideXlab platform.
-
Inducing rostrum interfacial waves by fluid-solid coupling in a Chinese river dolphin (Lipotes vexillifer )
Physical review. E, 2016Co-Authors: Zhongchang Song, Chong Wei, Yu Zhang, Xianyan WangAbstract:Through numerically solving the appropriate wave equations, propagation of biosonar signals in a Chinese river dolphin (baiji) was studied. The interfacial waves along the rostrum-tissue interfaces, including both compressional (longitudinal) and shear (transverse) waves in the solid rostrum through fluid-solid coupling were examined. The baiji's rostrum was found to effect acoustic beam formation not only as an interfacial wave generator but also as a sound reflector. The wave propagation patterns in the solid rostrum were found to significantly change the wave movement through the bone. Vibrations in the rostrum, expressed in solid displacement, initially increased but eventually decreased from posterior to anterior sides, indicating a complex physical process. Furthermore, the comparisons among seven cases, including the combination of (1) the rostrum, melon, and air sacs; (2) rostrum-air sacs; (3) rostrum-melon; (4) only rostrum; (5) air sacs-melon; (6) only air sacs; and (7) only melon revealed that the cases including the rostrum were better able to approach the complete system by inducing rostrum-tissue interfacial waves and reducing the differences in main beam angle and -3 dB beam width. The interfacial waves in the rostrum were considered complementary with reflection to determine the obbligato role of the rostrum in the baiji's biosonar emission. The far-field beams formed from complete fluid-solid models and non-fluid-solid models were compared to reveal the effects brought by the consideration of shear waves of the solid structures of the baiji. The results may provide useful information for further understanding the role of the rostrum in this odontocete species.
-
The role of individual structures within the head of dolphins in formation of biosonar signal and beam
2016Co-Authors: Chong WeiAbstract:New data have significantly increased our understanding of sound propagation within the heads of dolphins. Results of Au et al. (2016) reinforce the notion that source intensity is the primary factor controlling the peak and center frequencies of biosonar clicks which in turn affects the duration and the bandwidth of clicks. Finite element simulation of broadband acoustic signals propagation in the head of the Baiji or Lipotes vexillifer (Wei et al., 2016), and ongoing simulation with Phocoena phocoena and Tursiops truncatus have shown that the air sacs and skull are the major contributor on the shape of the beam and that the melon has a minimum role in the focusing of the signals. The small acoustic impedance gradient in the melon does not allow sufficient ray bending to take place even if the melon is deformed slightly. Comparing the biosonar signals used by free-swimming dolphins to a dolphin in a pen showed a similar tendency of dolphins, like bats, to emit longer duration signals with greater bandwid...
-
Simulation of ultrasound beam formation of baiji (Lipotes vexillifer) with a finite element model
The Journal of the Acoustical Society of America, 2014Co-Authors: Chong Wei, Yu ZhangAbstract:The baiji (Lipotes vexillifer) of the Yangtze River possesses a sophisticated biosonar system. In this study, a finite element approach was used to numerically investigate the propagation of acoustic waves through the head of the Yangtze River dolphin, which possesses an inhomogeneous and complex structure. The acoustic intensity distribution predicted from models with and without the melon and/or skull showed that the emitted sound beam was narrow and formed a highly directed acoustic beam, and the skull and melon significantly enhanced the directional characteristics of the emitted sound. Finally, for a short duration impulsive source, the emitted sound pressure distributions were also simulated at different propagation times. The results provide useful information for better understanding the operation of the biosonar system in this rare and perhaps extinct animal.
-
Enhance beam formation by airsacs and skull in Chinese river dolphin (Lipotes vexillifer)
The Journal of the Acoustical Society of America, 2014Co-Authors: Chong Wei, Zhongchang Song, Yu ZhangAbstract:The melon of dolphins is considered by many as the structure responsible for the focusing of the biosonar beam. However, finite element numerical simulation of the head of the Chinese river dolphin (Lipotes vexillifer) indicates that the biosonar beam is formed by reflections off the airsacs and bony structures in the skull. The finite element approach was applied to numerically simulate the acoustic propagation through dolphin's head in four several situations (complete head, skull only, skull plus melon, and skull plus airsacs). The acoustic intensity distribution and the corresponding polar plots showed that the melon causes the beam to narrow slightly and affects the angle of the main beam. The airsacs kept the sound propagating to the anterior and focused the energy into the main lobe. The bony structure prevented the sound from propagating below the rostrum and contribute to energy in the main beam. The results suggest that the airsacs and the complex bony structure play a dominant role in the formation of the biosonar beam of a dolphin, more so than the melon.