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1.
Amor N Halajian A Farjallah S Merella P Said K Ben Slimane B 《Experimental parasitology》2011,128(3):196-204
Fasciolosis caused by Fasciola spp. (Platyhelminthes: Trematoda: Digenea) is considered as the most important helminth infection of ruminants in tropical countries, causing considerable socioeconomic problems. In the endemic regions of the North of Iran, Fasciola hepatica and Fasciola gigantica have been previously characterized on the basis of morphometric differences, but the use of molecular markers is necessary to distinguish exactly between species and intermediate forms. Samples from buffaloes and goats from different localities of northern Iran were identified morphologically and then genetically characterized by sequences of the first (ITS-1) and second (ITS-2) Internal Transcribed Spacers (ITS) of nuclear ribosomal DNA (rDNA). Comparison of the ITS of the northern Iranian samples with sequences of Fasciola spp. from GenBank showed that the examined specimens had sequences identical to those of the most frequent haplotypes of F. hepatica (n = 25, 48.1%) and F. gigantica (n = 20, 38.45%), which differed from each other in different variable nucleotide positions of ITS region sequences, and their intermediate forms (n = 7, 13.45%), which had nucleotides overlapped between the two Fasciola species in all the positions. The ITS sequences from populations of Fasciola isolates in buffaloes and goats had experienced introgression/hybridization as previously reported in isolates from other ruminants and humans. Based on ITS-1 and ITS-2 sequences, flukes are scattered in pure F. hepatica, F. gigantica and intermediate Fasciola clades, revealing that multiple genotypes of Fasciola are able to infect goats and buffaloes in North of Iran. Furthermore, the phylogenetic trees based upon the ITS-1 and ITS-2 sequences showed a close relationship of the Iranian samples with isolates of F. hepatica and F. gigantica from different localities of Africa and Asia. In the present study, the intergenic transcribed spacers ITS-1 and ITS-2 showed to be reliable approaches for the genetic differentiation of Fasciola spp., providing bases for further studies on F. hepatica, F. gigantica and their intermediate forms in the endemic areas in Asia. 相似文献
2.
Chenghui Wang Sifa Li Cuizhang Fu Xiaoling Gong Len Huang Xiao Song Yan Zhao 《Biological invasions》2009,11(2):389-399
Chinese mitten crab (Eriocheir sinensis), a native species in China, has populated Continental Europe and North America since 1912. In this paper, the nucleotide
variation in the fragments of mitochondrial COII (693 bp), Cytb (766 bp), and nucleotide ITS (706 bp) was analyzed in native
(Yantgze, Yellow, and Liaohe Rivers in China) and colonized (Elbe, Rhine, and Thames Rivers in Europe, and San Francisco Bay
in North America) populations of the Chinese mitten crab. The major findings are as follows. First, the genetic variability
in the native populations is higher than that in the colonized European and North American populations, with the exception
of the Elbe River population, which possesses a similar level of variability with the native populations. Second, a remarkable
loss of singletons has been associated with the colonization of Chinese mitten crabs. Third, the AMOVA and F
ST results demonstrate that there are no significant genetic differentiations among the populations from the three continents,
but there is a significant differentiation between pairwise populations within and among continents. Fourth, it is found that
expansion-drift and gene flow pattern are involved in the European populations. The neutrality test and R
2 statistics suggest that a moderate founder population exists in the colonized populations, and only the Yangtze River population
has undergone a recent population expansion. Finally, the results demonstrate that the European populations originate from
multiple rivers in China on multiple occasions. The San Francisco population originates from both the native Chinese populations
and the colonized European populations, most likely the Thames population. 相似文献
3.
Jens Frankowski Sabine Jennerich Thomas Schaarschmidt Claus Ubl Karl Jürss Ralf Bastrop 《Biological invasions》2009,11(6):1301-1309
The screening of 2,735 eels from European waters and aquaculture farms was conducted using mitochondrial Cytochrome b and
16S rRNA gene fragments amplified by polymerase chain reaction. Reaction products were either sequenced directly or subjected
to analysis using restriction fragment length polymorphism which resulted in species-specific restriction patterns. Beside
the expected European eel, Anguilla anguilla (Linnaeus, 1758), the American eel, Anguilla rostrata (Le Sueur, 1817), was also identified in samples from both aquaculture (N = 40 out of 1,025) and from natural waters (N = 44 out of 1,710). The life stages of American eels identified from several German waters draining to either the Baltic
Sea and the North Sea ranged from elver to silver eels. This indicates that stocking with glass eels or elvers must have occurred
several times most likely in the period from 1998 to 2002. The application of a fast and precise method for species identification
and genetic monitoring of eels delivered for stocking is therefore essential for maintaining the autochthonous species composition
in future.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
Peristenus sp. pupae collected from Lygus spp. nymphs in 2001 and 2002 were over-wintered in the laboratory. In both years, more than 30% of adults emerging from over-wintering pupae were identified as ichneumonid hyperparasitoids, Mesochorus curvulus Thomson and Meschorus sp. (Hymenoptera: Ichneumonidae). At the end of the over-wintering period, Peristenus sp. males emerged first followed by Peristenus sp. females and finally Mesochorus spp. The male:female ratio in emerging Peristenus sp. adults was skewed towards males. The Internal Transcribed Spacer (ITS) region and the cytochrome oxidase I (COI) gene from Mesochorus spp. were sequenced. ITS sequences were used to develop PCR primers to detect Mesochorus spp. hyperparasitism in the primary host, Lygus spp. PCR analysis of field-collected Lygus spp. nymphs gave similar estimates of Mesochorus spp. hyperparasitism to the rearing protocols (25–28%). Sequence analysis of COI and ITS regions and subsequent restriction endonuclease analysis of ITS PCR products from Mesochorus spp. indicate the presence of two genotypes in the population. The possibility that these two genotypes represent separate or cyrptic species is discussed. 相似文献
5.
A. Jonathan Shaw 《Plant Systematics and Evolution》1995,197(1-4):43-58
Scopelophila cataractae, one of the so-called copper mosses, has a broad geographic distribution that includes North, Central, and South America, Europe, and Asia, but is rare throughout its range. A genetic analysis of 32 populations from the United States, Europe, and Asia based on 15 putative allozyme loci indicates that levels of genetic diversity vary among geographic regions. Six European populations are fixed for the same alleles at all 15 loci, consistent with the hypothesis thatS. cataractae is a recent immigrant in that region. The species is more diverse in the U.S., where it appears to be native. Five populations collected on copper-enriched soils around shrines and temples in Tokyo are genetically monomorphic, but Asian populations from another Japanese site, India, and Nepal are exceptionally diverse in terms of numbers of alleles and multilocus haplotypes, total gene diversity (HT), and in the degree of differentiation among populations (measured as Nei'sI andD). Long-distance dispersal has probably played an important role in the geographic history ofS. cataractae, but the species appears to be native in both the New and Old Worlds. Gene flow between plants disjunct on different continents is insufficient to explain the lack of geographically correlated morphological and genetic differentiation inS. cataractae. 相似文献
6.
Akihiro Okamura Huan Zhang Naomi Mikawa Aya Kotake Yoshiaki Yamada Tomoko Utoh Noriyuki Horie Satoru Tanaka Hideo P. Oka Katsumi Tsukamoto 《Environmental Biology of Fishes》2008,81(3):347-358
The occurrence, distribution, and biological characteristics of non-native freshwater eels were analyzed using 5524 eels collected
from 16 sites in Japan between 1997 and 2005. Three hundred seventy-four fishes (6.8%) were identified as non-native European
eels, Anguilla anguilla, while the remainder (93.2%) were native Japanese eels, A. japonica. The European eel was found at 7 sites (44%), including 3 rivers, 2 freshwater lakes, one brackish lake, and one sea bay,
suggesting a wide rage of habitat use. This variability of habitat use was also evidenced by the otolith microchemistry, which
showed that they had lived in not only freshwater but also in seawater habitats. The sites with European eel were localized
within the vicinity of southern Japan where a number of these eels were cultivated in the early 1970’s, suggesting that some
had escaped from the culture ponds or were released intentionally into nearby natural waters. The large body size (mean total
length: 803 mm), pigmented skin, enlarged eyes, and relatively matured gonads (mean gonad somatic index: 1.9) found in non-native
European eels indicated that most had metamorphosed into the migratory silver phase, suggesting their ability to initiate
spawning migration. However, the proportion of European eels in Mikawa Bay in 1997 was more than 12%, which decreased markedly
to less than 2% after 2001, corresponding to the recent decline in import of European glass eels for aquaculture. This suggests
that the population of European eels will decrease in Japanese waters in the future. 相似文献
7.
T. K. McCarthy P. Frankiewicz P. Cullen M. Blaszkowski W. O’Connor D. Doherty 《Hydrobiologia》2008,609(1):109-124
The Shannon, Ireland’s largest river, is used for hydroelectricity generation since 1929. Subsequently, the Electricity Supply
Board assumed responsibility for management of its eel stocks, due to the impact of the hydro-dam on recruitment to the commercial
fishery. In order to negate a decline in juvenile recruitment resulting from the installation of hydroelectric facilities,
management was focused on stocking lakes with elvers and fingerling eels. These were trapped at the hydropower facilities
and in estuarine tributaries during their up-stream migrations. Due to the decline of natural recruitment in more recent times,
attempts have also been made to develop an estuarine glass eel fishery. Stock levels are then monitored through annual surveys
of the population trends of juvenile (glass eel, elver), growing phase (yellow eel) and downstream migrating pre-spawners
(silver eels). Survey results and fishery management programmes are reviewed in this article. In addition to the long-term
effects the hydroelectric facilities have had on the stock levels, there is also an annual effect on the migratory patterns
of downstream migratory silver eels. In the lower reaches of the river system flow rates are regulated by the hydroelectric
stations. We review previous work that had highlighted the importance of flow in determining the timing of the silver eels
migrations, and assess the relationship between flow and migration in more detail through the use of hydroacoustic and telemetric
studies. Current research on seaward migrating silver eel populations, suggests that spawner escapement rates can most effectively
be increased by trapping migrating eels at fishing weirs located up-stream of the power station and transporting them towards
the estuary.
Guest editors: R. L. Welcomme & G. Marmulla
Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries 相似文献
8.
Robert W. Pemberton 《Biological Control》1999,14(3):168
Trapa natansis an aquatic plant native to the Old World. In the late 1880s this plant was found to be naturalized in the eastern United States where it has become an important weed. To evaluate the potential of biological control to reduce this weed, surveys for natural enemies ofTrapaspp. were made in Northeast Asia and Europe. In addition, populations ofTrapa japonicain South Korea were monitored for one season to evaluate the occurrence and impact of insect natural enemies. Among the insects found, the leaf beetleGalerucella birmanicawas the most common and damaging species in Asia. It can cause complete defoliation of whole populations of plants. Nymphuline pyralid moths were also common and at times damaging. Both the beetle and the moths feed and develop on unrelated plants and so have no potential as biological control agents ofT. natansin North America. TwoNanophyesweevils were found in Asia which feed in petiole floats of the leaves. They are thought to be specific toTrapabut were not observed to be damaging. Low level populations of polyphagous Homoptera were common. Chironomid midges were also frequently associated with the plants, but for the most part were filter feeders, not herbivores. The greatest impact on the monitored plants in South Korea was by the leaf beetleG. birmanicawhich defoliated most of the plants, causing the mats of plants to sink. In Europe, a similar and related insect fauna was found, but none of the insects was very damaging to the plants. One Italian weevil,Bagous rufimanus,feeds within the fruit stems and might be more damaging at higher than observed population levels. Some diseases were seen on some plants in both regions. European populations ofT. natanshave declined significantly, stimulating conservation efforts. Literature records ofTrapainsects from warm areas are presented. These could be of interest ifT. natansspreads into warmer areas of North America. 相似文献
9.
该研究对我国西南地区钩苞大丁草(Gerbera delavayi)9个居群rDNA ITS序列进行PCR的扩增和检测序列,并以非洲菊(G.jamesonii)的ITS序列作为外类群,比较了序列之间的差异,同时分析了钩苞大丁草不同居群在地理距离与遗传距离之间的关系,构建了NJ系统发育树。结果表明:(1)钩苞大丁草9个居群的ITS序列全长介于600~700 bp之间,平均长度约为657 bp,其中,ITS1长度为243~246 bp,(G+C)含量为45.67%~46.80%之间,5.8S长度191~193 bp,(G+C)含量为58.60%~58.61%之间,ITS2长度为220~221 bp,(G+C)含量为57.00%~57.45%之间;ITS序列共有22个变异位点,ITS1序列(17个)、5.8S序列(2个)以及ITS2序列(3个)上均有变异。(2)地理距离与遗传距离有正相关(r2=0.652),序列间遗传分化距离为0.001 1~0.024 3,其中普洱居群与其他居群间遗传距离最大。(3)钩苞大丁草9个居群分成三个分支,普洱居群单独成支,丽江和洱源居群聚为一支,富源、武定、德昌、石林、新平和开远6个居群聚为一支。rDNA ITS序列可以用于钩苞大丁草群体遗传研究的分析,该研究结果为其保护性开发提供了参考依据。 相似文献
10.
Re-consideration of Peronospora farinosa infecting Spinacia oleracea as distinct species, Peronospora effusa 总被引:3,自引:1,他引:2
Downy mildew is probably the most widespread and potentially destructive global disease of spinach (Spinacia oleracea). The causal agent of downy mildew disease on various plants of Chenopodiaceae, including spinach, is regarded as a single species, Peronospora farinosa. In the present study, the ITS rDNA sequence and morphological data demonstrated that P. farinosa from S. oleracea is distinct from downy mildew of other chenopodiaceous hosts. Fifty-eight spinach specimens were collected or loaned from 17 countries of Asia, Europe, Oceania, North and South America, which all formed a distinct monophyletic group. No intercontinental genetic variation of the ITS rDNA within Peronospora accessions causing spinach downy mildew disease was found. Phylogenetic trees supported recognition of Peronospora from spinach as a separate species. Microscopic examination also revealed morphological differences between Peronospora specimens from Spinacia and P. farinosa s. lat. specimens from Atriplex, Bassia, Beta, and Chenopodium. Consequently, the name Peronospora effusa should be reinstated for the downy mildew fungus found on spinach. Here, a specimen of the original collections of Peronospora effusa is designated as lectotype. 相似文献
11.
Recent studies have shown that anguillid eel populations in habitats spanning the marine–freshwater ecotone can display extreme
plasticity in the range of catadromy expressed by individual fishes. Carbon and nitrogen stable isotope analysis was used
to differentiate between European eels (Anguilla anguilla) collected along a short (2 km) salinity gradient ranging from <1‰ to ~30‰ in Lough Ahalia, a tidal Atlantic lake system.
Significant differences were recorded in mean δ13C, δ15N and C:N values from eels collected from fresh, brackish and marine-dominated basins. A discriminant analysis using these
predictor variables correctly classified ca. 85% of eels to salinity zone, allowing eels to be classified as freshwater (FW),
brackish (BW) or marine (MW) residents. The results of the discriminant analysis also suggested that a significant proportion
of eels moved between habitats (especially between FW and BW). Comparisons of several key population parameters showed significant
variation between eels resident in different salinity zones. Mean condition and estimated age was significantly lower in MW
eels, whilst observed length at age (a correlate of growth) was significantly higher in MW eels, intermediate in BW and lowest
in FW eels. This study has demonstrated that the ecology of eels found along a short salinity gradient can be extremely plastic
and that stable isotope analysis has considerable utility in demonstrating intra-population variation in diadromous fishes. 相似文献
12.
Swimming performance of silver eels is severely impaired by the swim-bladder parasite Anguillicola crassus 总被引:1,自引:0,他引:1
A.P. Palstra D.F.M. Heppener C. Székely 《Journal of experimental marine biology and ecology》2007,352(1):244-256
Infection with the swim-bladder parasite Anguillicola crassus is suggested as one of the principal causes of the collapse of the European eel population. This nematode has been introduced in Europe from Asia in the 80s and parasitized in a short time Anguilla eel species in different geographical regions across the globe. The parasites drain energy due to their sanguivorous feeding and they cause mechanical damage on the swim-bladder wall. These two effects are hypothesized to impair the spawning migration of the European eel. In this study, we have investigated both effects on swimming performance. We hypothesized that parasitic sanguivorous activities - related to parasite weight - reduce swimming endurance, while mechanical damage of the swim-bladder impairs buoyancy control. Eighty eels suffering various degrees of infection were introduced in swim-tunnels and subjected to a swimming fitness test. The relation between A. crassus infection and swimming efficiency was measured for large female silver eels swimming at various speeds. Infected eels had lower cruising speeds and a higher cost of transport. Eels without parasites, but with a damaged swim-bladder showed similar effects. Almost half of the eels that contained damaged swim-bladders (43%) stopped swimming at low aerobic swimming speeds (< 0.7 m/s). Simulated migration trials in a recent related study have confirmed that eels with a high parasite level or with damaged swim-bladder show early migration failure (< 1000-km). Reduced swimming performance appears to be associated with swim-bladder dysfunction. As we found that especially silver eels have much higher infection levels than yellow eels, it is concluded that migrating silver eels with severely infected or damaged swim-bladders are unable to reach the spawning grounds. 相似文献
13.
【目的】芒果象属昆虫是我国禁止进境的植物检疫性有害生物,广泛分布于非洲、北美洲和东南亚,寄主为芒果。其生活隐蔽,羽化孔未出现时看不出危害状,危害率可达30%~80%,严重影响芒果的产量和质量。近年来,我国口岸截获的芒果象甲的数量日益增多,表明该类检疫性有害生物传入我国的风险越来越大。【方法】运用Microsoft Excel工作表对2003—2015年全国口岸截获芒果象属有害生物的疫情进行统计分析。【结果】2003—2015年全国口岸共截获芒果象4156批次,22个直属局有截获记录。其中,截获芒果果核象甲3028批次,数量最多,占截获芒果象总批次的72.86%;芒果果实象甲和芒果果肉象甲相对较少,分别为837和291批次。截获芒果象的来源国主要为非洲和东南亚芒果象疫情分布国家和地区,且主要自进境旅客随身携带物中检出。【结论】我国口岸应加大对芒果象的检疫力度,保护我国农林业生产安全。 相似文献
14.
Uwe Braun Susumu Takamatsu Vasyl Heluta Saranya Limkaisang Rangsi Divarangkoon Roger Cook Herbert Boyle 《Mycological Progress》2006,5(3):139-153
A phylogenetic analysis of the Erysiphe with uncinuloid ascoma appendages (Erysiphe section Uncinula, Erysiphales, Ascomycota) on Carpinus spp. was done using sequences of the rDNA ITS regions and the D1/D2 domains of the 28S rDNA. These results, combined with morphological data, revealed a complex consisting of several distinct taxa. These included the already described Erysiphe
carpinicola on C. japonica distinguishable from the Erysiphe sp. on C. betulus and C. tschonoskii as well as the one on C. laxiflora. Thus, it was shown that Oidium
carpini, described from Europe on Carpinus betulus, the powdery mildew with uncinula-like ascomata, recently found in Europe on this host, as well as an Erysiphe on C. tschonoskii in Japan, described previously as E. carpinicola, all belong to a single new species, named E. arcuata in this paper. As the powdery mildew on C. laxiflora was also distinct from other known species, it is named E. carpini-laxiflorae in this paper. The already described E. pseudocarpinicola and Erysiphe sp. on Carpinus cordata are two additional taxa, which are morphologically and genetically distinguished from the other species of Erysiphe sect. Uncinula on Carpinus spp. 相似文献
15.
Water temperature and upstream migration of glass eels in New Zealand: implications of climate change 总被引:4,自引:0,他引:4
Glass eels migrating upstream in a New Zealand river showed a clear preference for water temperatures between 12 and 20°C,
with an optimum of 16.5°C. Water temperatures <12°C and >22°C almost completely inhibited migration, which implies that warmer
temperatures associated with global climate change might have a detrimental impact on glass eel recruitment in their current
ranges. We established this by trapping glass eels of shortfin, Anguilla australis, and longfin, A. dieffenbachii, eels nightly from September to November. Eels caught in 2001 (50,287) outnumbered those caught in 2002 (19,954); shortfin
glass eels dominated catches in both years, comprising 91–93% of the catch. Longfins were larger than shortfins, and size
and pigmentation in both species increased as the seasons progressed. Temperatures within the migratory season in 2001 showed
∼14-day intervals between maxima that appeared to be associated with the new and full moons. 相似文献
16.
We investigated the environmental factors that affected temporal variability of eel recruitment and upstream migration in
a freshwater coastal river along the southeastern US. Glass eels Anguilla rostrata were collected through ichthyoplankton sampling in the lower Roanoke River, North Carolina. Monthly samples were taken from
fixed stations from May 2001 through June 2003. There was no evidence of consistent seasonal migration patterns for glass
eels in Roanoke River. From May through December in 2001, glass eels were captured only during August. In 2002, glass eels
arrived in February and remained in ichthyoplankton samples through October, with the exception of samples from September.
Peak catch occurred in March at 4.02 ± 1.2 and declined through June to 0.18 ± 0.07 (#/1,000 m3). By August, the mean density increased to 0.96 ± 0.82 and to 3.59 ± 2.77 by October. In 2003 from January through June,
glass eels were captured only during February and March. Glass eels were routinely collected when river discharge rates were
<150 m3 s−1. River discharge rates >650 m−3 s−1 resulted in no glass eels in our samples. Upstream migration during 2002 was not correlated with water temperature or related
to lunar phase. Glass eel freshwater upstream migration was initiated when water temperatures exceeded a threshold range of
10°C to 15°C; however, glass eels continued to migrate when water temperatures approached 30°C. The overall negative effect
of river discharge suggests that changes in the water release schedules of upstream hydroelectric facilities during glass
eel migration could strongly influence their recruitment success. 相似文献
17.
First report of the invasive eel pest Pseudodactylogyrus bini in North America and in wild American eels 总被引:2,自引:0,他引:2
We detected 2 species of monogenean gill worms, Pseudodactylogyrus bini (Kikuchi, 1929) Gusev, 1965 and P. anguillae (Yin & Sproston, 1948) Gusev, 1965 (Monopisthocotylea: Pseudodactylogyridae), on American eel Anguilla rostrata in 2 rivers in South Carolina, USA. One of these, P. anguillae, was reported 5 yr ago from Nova Scotia; as well as in South Carolina, we also discovered it in 2 localities in Chesapeake Bay. Differences in the morphologies of specimens of either species of worm from North America and northeastern Asia were negligible. Similarly, the level of variation in sequences in the ITS2 (internal transcribed spacers) region of ribosomal RNA was minor, and not consistent with geographical origin. These data indicate that these monogeneans invaded North America only recently, possibly in parallel with the nematode Anguillicola crassus (which is known to have been introduced with commercial imports of foreign eels). We map the current global occurrence of these monogeneans, and conclude that their dispersal from northeastern Asia was largely as a result of the eel trade, and has probably been secondarily augmented by longshore migration of infected eels, and possibly also by transport in ballast waters. With present technology, all eel stocks must still be collected from the wild; unless shipments are disinfected at quarantine, these and other eel pathogens (such as A. crassus) are likely to continue to colonise other regions of the world. 相似文献
18.
A phylogenetic analysis was conducted on sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA in 23 species ofAveneae (Poaceae subfam.Pooideaae). These sequences ofHelictotrichon spp.,Arrhenatherum elatius, Avena spp.,Trisetum spp.,Koeleria spp.,Holcus lanatus, Alopecurus vaginatus together with published ITS sequences of furtherAveneae, Poeae, Triticeae, andBromeae were analysed by the neighbor-joining distance method to assess the molecular phylogenetic relationship in perennial and annualAveneae. The results suggest unexpectedly close affinities of the agronomically important genusAvena to comparatively small-flowered taxa ofAveneae. GenusArrhenatherum and small-flowered subgenera ofHelictotrichon are close extant relatives. The large genusHelictotrichon is para- if not polyphyletic, only its subgenera are monophyletic.Trisetum is clearly separated fromHelictotrichon and forms together withKoeleria and perhaps others a monophyletic lineage which is characterised by a conspicuous 9-bp deletion in ITS1. The impact of the ITS data on the delineation of some genera and subtribes ofAveneae and on the recognition of their biogeographical and ecological patterns is outlined. 相似文献
19.
The European eel (Anguilla anguilla Linnaeus 1758) is a species typical for waters of Western Europe. Thanks to early expeditions on the Atlantic Ocean by the
Danish biologist Johannes Schmidt who found small (<10mm) leptocephali larvae in the Sargasso Sea about 100 years ago, we
have now a strong indication where the spawning site for this species is located. The American eel (Anguilla rostrata, LeSueur) also spawns in the Sargasso Sea. The spawning time and location of both species have been supported and refined
in recent analyses of the available historical data. Subsequent ichthyoplankton surveys conducted by McCleave (USA) and Tesch
(Germany) in the 1980s indicated an increase in the number of leptocephali <10 mm , confirming and refining the Sargasso Sea
theory of Johannes Schmidt. Distinctions between the European and American eel are based on morphological characteristics
(number of vertebrae) as well as molecular markers (allozymes, mitochondrial DNA and anonymous genomic-DNA. Although recognised
as two distinct species, it remains unclear which mechanisms play a role in species separation during larval drift, and what
orientation mechanism eels use during migration in the open sea. The current status of knowledge on these issues will be presented.
The hypothesis that all European eel migrate to the Sargasso Sea for reproduction and comprise a single randomly mating population,
the so called panmixia theory, was until recently broadly accepted. However, based on field observations, morphological parameters
and molecular studies there are some indications that Schmidt’s claim of complete homogeneity of the European eel population
and a unique spawning location may be an overstatement. Recent molecular work on European eel indicated a genetic mosaic consisting
of several isolated groups, leading to a rejection of the panmixia theory. Nevertheless, the latest extensive genetic survey
indicated that the geographical component of genetic structure lacked temporal stability, emphasising the need for temporal
replication in the study of highly vagile marine species. Induced spawning of hormone treated eels in the aquarium was collective
and simultaneous. In this work for the first time group spawning behaviour has ever been observed and recorded in eels. Studies
in swim-tunnels indicate that eels can swim four to six times more efficiently than non-anguilliform fish such as trout. After
a laboratory swim trial of eels over 5,500 km, the body composition did not change and fat, protein and carbohydrate were
used in the same proportion. This study demonstrated for the first time that European eel are physiologically able of reaching
the Sargasso Sea without feeding. Based on catches of newly hatched larvae, temperature preference tests and telemetry tracking
of mature hormone treated animals, it can be hypothesised that spawning in the Sargasso Sea is collective and simultaneous,
while presumably taking place in the upper 200 m of the ocean. Successful satellite tracking of longfin female eels in New
Zealand has been performed to monitor migration pathways. Implementation of this new technology is possible in this species
because it is three times larger than the European eel. In the future, miniaturisation of tagging technology may allow European
eels to be tracked in time by satellite. The most interesting potential contribution of telemetry tracking of silver eels
is additional knowledge about migration routes, rates, and depths. In combination with catches of larvae in the Sargasso Sea,
it may elucidate the precise spawning locations of different eel species or groups. Only then, we will be able to define sustainable
management issues by integrating this novel knowledge into spawners escapement and juvenile fishing quota. 相似文献
20.
J. G. Oakeshott J. B. Gibson D. A. Willcocks G. K. Chambers 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1983,65(3):191-196
Summary The octanol dehydrogenase (Odh) and acid phosphatase (Acph) loci of Drosophila melanogaster are each polymorphic for two electrophoretically detectable alleles. The frequencies of the Odh and Acph alleles have been analysed in populations sampled from up to a 40 ° latitudinal range in each of Australasia, North America and Europe/Asia. Odh
S frequency is found to be significantly negatively associated with distance from the equator in all three zones. The relationship of Acph
S frequency to distance from the equator is significant and negative in Australasia but neither significant nor consistent in sign in North America and Europe/Asia. 相似文献