Table of Content

    30 November 2018, Volume 38 Issue 6
    The molecular mechanism of visual degradation in cetaceans based on GNAT2 and CNGB3 gene#br#
    NIU Xu, LIANG Yanyan, ZHU Kangli, ZHAO Junpeng, XU Shixia, YANG Guang
    2018, 38(6):  525-534.  DOI: 10.16829/j.slxb.150048
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    Cetaceans are a mysterious group of secondarily-adapted marine mammals that “returned” from the land to the sea approximately 53–56 million years ago (Ma).  In order to adapt to dim aquatic environment, cetaceans have mostly rod photoreceptors and few cone photoreceptors, resulting in a loss of color vision. However, the genetic basis of visual degradation in cetaceans remains poorly explored. The GNAT2 and CNGB3 genes, expressed in cone photoreceptors play the key role in the phototransduction cascade. GNAT2 and CNGB3 genes of eight representative species of cetaceans were obtained by PCR amplified and gene downloaded from NCBI. Protein sequences of GNAT2 and CNGB3 were aligned by MEGA6.0. We found GNAT2 gene might become a pseudogene due to a 1-bp insertions at sites 148 and 1012 in Kogia sima and Physeter catodon, respectively. Similar results were indentified at
    the CNGB3, with 1-bp deletions identified at sites 554 and 1407 of CNGB3 in P. catodon and apremature stop codon at site 1525-1527 in Balaenoptera acutorostrata. We predicted the three-dimensional (3D) structures of GNAT2 and CNGB3 using I-TASSER, and mapped the pseudogenized position onto the 3D structures. 3D structureal analysis showed that the insertion, deletion and premature stop codon were located in an important domain. Furthermore, branch model analysis revealed that relaxed selective pressure acted on cetacean lineages with pseudogenized GNAT2 and CNGB3. The pseudogenized GNAT2 and CNGB3 in cetacean lineages are suggested to be related to its deep diving and visual degradation to adapt completely aquatic environment. In addition, relaxed selection pressure of GNAT2 and CNGB3 was also detected in other cetacean lineages with increased ω values by free-ratio model, consistent with the morphological changes of eye for adapting to aquatic habitats.
    Molecular evolution of Epac1 and Epac2 genes during cetacean secondary aquatic adaptation
    LI Kui, ZHANG Weijing, CHAI Simin, XU Shixia, YANG Guang
    2018, 38(6):  535-542.  DOI: 10.16829/j.slxb.150047
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    Heart rate (HR) is a reflection of cardiac function as well as of the lifespan and energy metabolism among mammals. In comparison with most terrestrial mammals, the extraordinary reduction of cetacean HR rarely has been explored. It has been shown that the decreased HR contributes to an increase of lifespan, and high efficiency of energy utilization which provides many advantages for cetacean adaptation into aquatic habitats. However, the molecular mechanisms leading to the reduced HR in cetaceans remains unresolved until now. Branch models and branch-site models combined with analysis of protein functional differentiation, based on the maximum likelihood method have been used in the present research to test the molecular evolution acting on cetacean exchange proteins directly activated by cAMP (Epac1 and Epac2), two vital molecules in the cAMP signal that controls HR. Our results show an accelerated evolution of Epac1 at the combined branch of Baleen whales and sperm whale (Physeter macrocephalus). Branch-site models have determined remarkable positive selection at the ancestor node of baleen whales with positively selected sites located in the protein catalytic domain. Furthermore, functional modification of Epac1 also has been detected in cetaceans.  In addition, strong positive selection of Epac2 in the bowhead whale (Balaena mysticetus) with a lifespan of up to 200 years has been discovered as was seen for Epac1. These results suggest adaptive evolution of Epac1 and Epac2 in cetaceans, which might not only result in reduced HR, but also may contribute to extended lifespans and high effective energy utilization.
    Navigation noise properties of large vessels in Hechangzhou region of the Yangtze River and their potential effects on the Yangtze finless porpoise
    ZHANG Tianci, JU Tao, LI Songhai, XIE Yan, WANG Ding, WANG Zhitao, WANG Kexiong
    2018, 38(6):  543-550.  DOI: 10.16829/j.slxb.150125
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    The ever-growing number of larger commercial vessels (with length and width over 15m and 5m, respectively) in the Yangtze River is becoming increasingly concerning for the conservation of the local Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis). As such, quantification of the noise emissions of these vessels is greatly in need to better understand the potential impact on the Yangtze finless porpoise. By using a broadband sound recording system, we recorded the noise emissions of a variety of large vessels at Zhenjiang region of the Yangtze River and analyzed their acoustic properties, such as peak-to-peak sound pressure level (SPLp-p) and power spectral density (PSD). The results showed that the vessel noise was featured by broadband (>100kHz) and majority of energy was concentrated in frequencies below 10kHz. The root-mean-square (RMS) sound pressure levels (SPLrms) of all frequency components were higher than 30 dB re 1μPa and raised the ambient noise levels between 3.7 and 66.5 dB across frequency bands ranging from 20Hz to 144kHz. The recorded one-third octave band sound pressure levels (TOL) for all investigated vessels were higher than 70 dB across all frequencies. The RMS levels of vessel noise were higher than the hearing thresholds of the Yangtze finless porpoise at the frequency range from 8kHz to 140kHz. These results indicate that the noise emissions from larger vessels may have negative impacts on the communication and hearing of the Yangtze finless porpoise, such as auditory masking.
    Primary survey of finless porpoise population in the Bohai Sea
    ZUO Tao, SUN Jianqiang, SHI Yongqiang, WANG Jun
    2018, 38(6):  551-561.  DOI: 10.16829/j.slxb.150147
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    The Bohai Sea is an important distribution zone for the temperate population of finless porpoises. However, very few reports has been published on the finless porpoise population in the region. Six surveys were conducted between May to July 2015 and in September and November of 2016. They were based on the line-transect methods in the Bohai Sea. These surveys were meant to explore population status of the finless porpoise in Bohai Sea, which could provide basic data to develop ecological protection strategies for the finless porpoise in the sea. The total effective trackline length of six surveys was 8972 km. A total of 136 individuals and 87 groups of finless porpoises were witnessed. More finless porpoises were observed near the Yellow River estuary, to the northeast of the Qinhuangdao and in the coast of Laizhou Bay. Of the witnessed groups, sightings occurred more at between 14:00–18:00, in the area 15–35 km offshore. Spatially, the finless porpoise can be found in most of the Bohai Sea, including the three bays and central waters. Of the seasons surveyed, the finless porpoise groups were observed frequently in the waters 20–40 km out of the Yellow River estuary in May. The probability values of group sightings on the trackline were 0.399, 0.085 and 1 respectively in Distance 7.0 software, The finless porpoise population number in the whole Bohai Sea was estimated to number 7883(CV=0.21), 3701(CV=0.21), and 3124(CV=0.21) individuals, and its population density was estimated to be 1.441, 0.066, and 0.056 individuals/km2 correspondingly. Compared with those in the southern Yellow Sea and the Inland Sea of Japan, the population density of finless porpoise in the Bohai Sea was relatively smaller. Limited by uncertain effects from the weather, sea conditions and observers’ experience, the estimated values given above need to be confirmed in the future. However, despite the current deficient state of the data, the size of the population of finless porpoise in the Bohai Sea was here estimated for the first time and this work could serve as a reference for future study.
    Identification and Characterizations of Aeromonas salmonicida isolated from Yangtze finless porpoise
    LIU Zhigang, JIANG Huyan, ZHANG Xiaoke, CHEN Minmin, WAN An, YU Daoping
    2018, 38(6):  562-571.  DOI: 10.16829/j.slxb.150093
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    In this study, we have for the first time isolated Aeromonas salmonicida strain XJ-JT from Yangtze finless porpoise which showed clinical symptoms such as ulcers and rotten skin. We found that the strain XJ-JT was a gram-negative bacterium with blunt ends and non-sporulating; 16S rRNA gene fragments of of several strains were amplified and sequenced, and phylogenetic trees were constructed which reveal the similarity with Aeromonas salmonicida isolated from Silver carp. Moreover, we studied its biological characteristics by performing physicochemical characterization, genetic evolution analysis, drug susceptibility assays and a pathogenicity test. 20 common antibiotics were tested in drug susceptibility assays. We showed that XJ-JT is highly sensitive to cefotaxime sodium,  ceftriaxone sodium and kanamycin, moderately sensitive to cefotaxime sodium, ceftriaxone sodium and kanamycin, and not sensitive to amoxicillin, ampicillin, tetracycline, and so on. An in vivo infection assay showed that this new strain, XJ-JT, has a strong pathogenicity in Crucian carp.
    Advances in marine mammal research in China
    YANG Guang, XU Shixia, CHEN Bingyao, SHAN Lei
    2018, 38(6):  572-585.  DOI: 10.16829/j.slxb.150254
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    China is a country with rich marine mammal resources, with a total of 46 species including 38 species of Cetacea, 1 of Dugongidae, 5 of Pinnipedia and 2 of Lutrinae,which provides Chinese scientists with excellent opportunities to study marine mammals. Since 1920s, Chinese scientists have carried out a series of studies on the biology and conservation of marine mammals in Chinese waters through multidisciplinary methods. Especially some important advances were made on the biology and conservation of the baiji (Lipotes vexillifer), finless porpoises (Neophocaena spp.) and Chinese white dolphins (Sousa chinensis), evolutionary history and adaptive mechanism of secondary aquatic adaptation, and population genetic diversity etc, which not only improved our understanding of understandings of marine mammals in China, but promoted their conservation and management. Here we reveiwed the research progresses of marine mammals in China from seven aspects such as diversity, ecology and conservation biology, morphology and anatomy,
    breeding and reproductive biology, acoustic behavior, genetic and evolutionary biology, and genomics etc. In the future, some more attention should be paid to the evolutionary history and adaptive mechanism of secondary aquatic adaptation, whereas it is of great importance to reveal the mechanisms underlying the endangerment of marine mammals and provide adaptive strategies for their conservation and management.
    Mark-recapture technique for demographic studies of Chinese white dolphins - applications and suggestions
    LIN Wenzhi, Stephen C. Y. CHAN, ZENG Chen, Leszek KARCZMARSKI, WU Yuping
    2018, 38(6):  586-596.  DOI: 10.16829/j.slxb.150171
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    Early studies of Chinese white dolphins applied primarily line-transect survey techniques to acquire distribution data and generate abundance estimates, while many recent studies rely on mark-recapture techniques to gain insights into population dynamics and demography. The application of an individual photo-identification approach provides the means to estimate vital population parameters with mark-recapture models which in turn facilitate population viability analysis. Here, we review the application of the photographic mark recapture technique in demographic studies of Chinese white dolphins in China waters; we summarize the quality assessment of individual mark recapture databases; ran simulations to evaluate how survey effort may impact the accuracy and precision of population size estimates; discuss how the survey design, selection of individual-ID marks and data filtering may impact the mark-recapture analysis; and we point out how to minimize the bias associated with data over-dispersion through model selection according to goodness-of-fit testing. We discuss also conceptual challenges that may lead to misinterpretation of data when comparing results from different studies that used different field techniques. With improved understanding of analytical principles behind the data gathering, we hope that demographic studies of Chinese white dolphins in the region will expand and improve in the near future.
    The development of in vitro models and their applications in cetacean research
    YU Xueying, YANG Feng, ZHU Jingmin, MING Yao, LI Ding, LIU Wenhua, WANG Jingzhen
    2018, 38(6):  597-607.  DOI: 10.16829/j.slxb.150225
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    As an alternative and complementary in vitro models, “cell line” provides a new platform for life science research. To a certain extent, it breaks through the limitations of ethics, law, animal welfare and animal protection in scientific research and reveals the biological effects and regulatory mechanisms of complex living organisms from a cellular and molecular perspective. Especially for endangered animals, the establishment of cell lines combined with cryopreservation technology can not only preserve the genetic germplasm of endangered animals with biological expression activity, but also provide a new platform for in vitro conservation research (such as animal toxicology experiments), which is of great significance to animal protection. Cetacean cell culture has so far proven to be a multifunctional tool for cytogenetics, virology and toxicology studies. However, from the perspective of species, tissue sources and cell types, long-term stable continuous cell lines are still relatively few. How to optimize cell culture conditions and use the cell lines to reveal more information about cetacean life mechanism is still a challenge. This paper reviews the development of in vitro models and its application in the study of cetaceans, with a view to promoting the innovation of this technology in the study of cetacean conservation.
    Review on cetacean remote biopsy sampling and its application prospects in China
    LIU Mingzhong, LI Kuan, ZHANG Peijun, LI Songhai
    2018, 38(6):  608-615.  DOI: 10.16829/j.slxb.150133
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    Cetaceans are top predators in the marine food chain; they are of great interest to scientists in studies relating to marine environmental protection worldwide. It is normally very hard for scientists to access wild cetaceans. To conduct research into wild cetaceans without threatening their lives, a remote biopsy sampling (RBS) method was devised. The first RBS system was developed from a cetacean harpoon in 1973. Since then, cetacean RBS systems have been improved in the sequence “Harpoon-Crossbow-Compound bow-Air gun-Pole”. During this course of development, the invasiveness of the RBS system in the animals has been a core issue of concern for scientists. Therefore, many studies have been conducted to evaluate the effect of RBS systems on cetaceans, and RBS was finally concluded to be a non-invasive method. It has thus has become a popular and important method for wild cetacean sample collection in many parts of the world. There are abundant cetacean resources in China. However, the RBS method is seldom used in Chinese wild cetacean research; only one such RBS attempt has been reported, on the Indo-Pacific humpback dolphin (Sousa chinensis) in Hong Kong waters. Therefore, there is great potential for the application and development of RBS tools for use in cetacean studies in China. In the present study, we first briefly introduce the history of RBS development and its application in cetacean research worldwide, and then document the potential value of this method in cetacean research in China. Finally, we assess the future prospects of Chinese cetacean studies for genetics, toxicology, cytology and reproductive endocrinology.
    Morphological measurements of a dead Indo-Pacific humpback dolphin (Sousa chinensis) at Sanya, Hainan Province, China
    LI Kuan, ZHANG Peijun, LIU Mingzhong, LIN Mingli, LI Songhai
    2018, 38(6):  616-623.  DOI: 10.16829/j.slxb.150115
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    On February 2,2015, a dead female Indo-Pacific humpback dolphin (Sousa chinensis) was found in the coastal water of Meilian Village, Yacheng Town, Sanya City, Hainan Province, China. It was the first Indo-Pacific humpback dolphin death case ever found in waters southwest of Hainan Island. In the present study, data about external morphology and skeleton system of the dead dolphin were documented, Body length and body mass of the animal were 235.0 cm and ca. 150 kg, respectively, with completely white body color. The cranium of this dolphin wa 189 mm in zygomatic width, and 415 mm in skull length. Its vertebra formula was C6+T12+L10+Ca20=48. It had 12 pairs of ribs and 11 V-bones. According to previous reports, our skeleton sample may have one cervical vertebra missing, and one or more caudal vertebras and V bones missing. More new skeleton samples from the same population are needed to confirm this presumption.
    A by-caught minke whale’s calf attacked by the shark
    ZHU Qian, YU Shanshan, LIU Yingying, WANG Jing, LIU Wei
    2018, 38(6):  624-626.  DOI: 10.16829/j.slxb.150244
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    A minke whale was by-caught by fishermen in a drift gill net off Shidao, Weihai, Shandong Province on June 15, 2007. The whale, which had been attacked by a shark, was a male with body length 2.43 m, and was suspected to have died soon after the birth. The small size of the whale suggests that a breeding ground for minke whales might exist in the Chinese coastal waters. Evidence of shark attack on this young whale was apparent: half of the fluke was lost and the belly was bitten as well; injuries were not as severe on the caudal peduncle. It was not possible to determine if the shark-related injuries observed occurred prior to the whale being by-caught or were post-mortem. Some conservation measures were proposed in order to better protect the cetaceans in waters off China.