首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
    
  1. Mammalian herbivores that consume both aquatic and terrestrial vegetation may have important but little understood effects on freshwater ecosystems. We assessed the effects of North American moose (Alces americanus) and/or beaver (Castor canadensis) on aquatic vegetation and abiotic conditions of three types of waterbodies.
  2. We established year‐round aquatic exclosures and reference plots in glacial lakes, dammed lakes and riverine ponds (n = 3 in each case). Within plots, we monitored parameters including dissolved oxygen, light, plant diversity and species‐specific plant biomass.
  3. The effects of herbivory by beaver and moose appear to be contingent upon abiotic and plant community characteristics. Exposure to herbivory decreased biomass in riverine ponds and dammed lakes but not in glacial lakes and decreased species richness in riverine ponds and glacial lakes but not in dammed lakes. Changes in macrophyte species diversity correlated with exposure to herbivory only in glacial lakes. Disaggregating the effects of herbivory according to abiotic conditions and plant community characteristics revealed outcomes that are not detectable when results are aggregated.
  4. In some catchments, the response of the aquatic plant community to beaver and moose herbivory may substantially differ from the response of the surrounding terrestrial plant community. Five of the six waterbodies created by beavers (dammed lakes and riverine ponds) maintained >80% macrophyte cover, despite seasonal reduction in biomass by both moose and beaver. Herbivores appear to cause a short‐term reduction in plant biomass in dammed lakes, resulting in greater light availability, without depleting biomass over a number of years.
  相似文献   

2.
    
  1. Patterns of coexistence and exclusion among resident and invading species in freshwaters may be generated by direct biotic interactions well as by indirect interactions with the broader abiotic and biotic environments. The North American ‘shrimp’ Crangonyx pseudogracilis (Crustacea: Amphipoda) is invasive in Europe where it forms complex patterns of apparent exclusion and coexistence with resident Gammarus spp. amphipods. Using a comprehensive integrated approach, we investigated the potential biotic and interacting abiotic factors driving these distribution patterns.
  2. A 2009 survey of 69 sites on a small British Island, The Isle of Man, revealed that of 56 river sites containing amphipods, only six contained C. pseudogracilis and these always co‐occurred with Gammarus spp. In contrast, C. pseudogracilis was the only species present in the 12 ponds/reservoirs containing amphipods.
  3. Field transplant experiments in ponds and laboratory oxygen tolerance experiments revealed that C. pseudogracilis tolerates physicochemical regimes which Gammarus spp. are incapable of surviving.
  4. River microhabitat sampling showed C. pseudogracilis dominating in slower, more pooled and macrophyte‐dense patches, while Gammarus spp. were dominant in faster, more riffled areas.
  5. Field bioassays indicated that predation of C. pseudogracilis by Gammarus spp. may be frequent in patches of rivers if/when the species meet.
  6. River drift sampling revealed that C. pseudogracilis was greatly underrepresented in night/day drift relative to the Gammarus spp. Laboratory studies showed C. pseudogracilis to be more photophobic and less active than Gammarus spp., both behaviours potentially contributing to low drift prevalence and consequent reduced exposure to shared drift predators.
  7. These interacting factors may ultimately contribute to the coexistence, exclusion and relative distributions of C. pseudogracilis and Gammarus spp. The former is potentially subject to intense predation from the latter if they encounter one another in the same microhabitat. However, with C. pseudogracilis being more physicochemically tolerant and displaying different habitat utilisation patterns than the Gammarus spp. in respect of the benthos and drift, such encounters are probably minimised. Hence C. pseudogracilis can persist in the same sites with the Gammarus spp., albeit in different microhabitats.
  相似文献   

3.
    
An experimental decay methodology is developed for a cnidarian model organism to serve as a comparison to the many previous such studies on bilaterians. This allows an examination of inherent bias against the fossilisation of cnidarian tissue and their diagnostic characters, under what conditions these occur, and in what way. The decay sequence of Actinia equina was examined under a series of controlled conditions. These experiments show that cnidarian decay begins with an initial rupturing of the epidermis, followed by rapid loss of recognisable internal morphological characters. This suggests that bacteria work quicker on the epidermis than autolysis does on the internal anatomy. The data also show that diploblastic tissue is not universally decayed more slowly under anoxic or reducing conditions than under oxic conditions. Indeed, some cnidarian characters decay more rapidly under anoxic conditions than they do under oxic conditions. This suggests the decay pathways acting may be different to those affecting soft bilaterian tissue such as soft epidermis and internal organs. What is most important in the decay of soft polyp anatomy is the microbial community, which can be dominated by oxic or anoxic bacteria. Different Lagerstätte, even of the same type, will inevitably have subtle difference in their bacterial communities, which among other factors, could be a control on soft polyp preservation leading to either an absence of compelling soft anthozoans (Burgess Shale) or an astonishing abundance (Qingjiang biota).  相似文献   

4.
    
The affinity of Tullimonstrum gregarium, a pincer‐mouthed, soft bodied bilaterian, has been subject to debate since its recovery from Carboniferous coal deposits at Mazon Creek, Illinois. After decades of impasse focused on mollusc, arthropod and annelid attributes, two recent, yet conflicting, high‐profile studies concluded that the ‘Tully Monster’ is a vertebrate, a relative of lampreys or jawed fishes. Here, we find that structures described as supporting vertebrate, and particularly crown vertebrate, affinity face significant challenges from biological, functional and taphonomic perspectives. Problems with comparator choice, interpretation of taphonomic processes at Mazon Creek and estimation of convergence within the bilaterian tree may have misled these recent studies, leading to conclusions which do not accommodate current understanding of the vertebrate record. For example, the absence of taphonomically‐expected synapomorphies in Tullimonstrum (e.g. otic capsules, body pigment) calls into question vertebrate identity and implies that convergence or deeper origins are responsible for vertebrate‐like traits. Further, phylogenetic placement within vertebrates is only made possible by the constraints of a chordate‐only dataset with limited outgroups and use of selective characters. Long‐discussed alternative placements among molluscs (e.g. heteropod gastropods), arthropods (e.g. anomalocarids) or elsewhere within non‐vertebrate deuterostomes are more congruent. Indeed, many of these lineages independently evolved vertebrate‐like traits, including complex eyes and ‘teeth’. Thus, given the totality of evidence, Tullimonstrum should be excluded from the vertebrate crown. Potential assignments for aberrant bilaterians, common throughout the Palaeozoic fossil record, need to be considered in light of the number and likelihood of required exceptions to established schemes.  相似文献   

5.
    
The freshwater red algal order Thoreales has triphasic life history composed of a diminutive diploid “Chantransia” stage, a distinctive macroscopic gametophyte with multi‐axial growth and carposporophytes that develop on the gametophyte thallus. This order is comprised of two genera, Thorea and Nemalionopsis. Thorea has been widely reported with numerous species, whereas Nemalionopsis has been more rarely observed with only a few species described. DNA sequences from three loci (rbcL, cox1, and LSU) were used to examine the phylogenetic affinity of specimens collected from geographically distant locations including North America, South America, Europe, Pacific Islands, Southeast Asia, China, and India. Sixteen species of Thorea and two species of Nemalionopsis were recognized. Morphological observations confirmed the distinctness of the two genera and also provided some characters to distinguish species. However, many of the collections were in “Chantransia” stage rather than gametophyte stage, meaning that key diagnostic morphological characters were unavailable. Three new species are proposed primarily based on the DNA sequence data generated in this study, Thorea kokosinga‐pueschelii, T. mauitukitukii, and T. quisqueyana. In addition to these newly described species, one DNA sequence from GenBank was not closely associated with other Thorea clades and may represent further diversity in the genus. Two species in Nemalionopsis are recognized, N. shawii and N. parkeri nom. et stat. nov. Thorea harbors more diversity than had been recognized by morphological data alone. Distribution data indicated that Nemalionopsis is common in the Pacific region, whereas Thorea is more globally distributed. Most species of Thorea have a regional distribution, but Thorea hispida appears to be cosmopolitan.  相似文献   

6.
    
Abstract: Middle Miocene tests of Clypeaster from L’Arrabassada (Tarragona, north‐east Spain) show evidence of intense endoskeletozoan colonization, preserved as borings and associated carbonate secretions that allow gastrochaenid bivalves to be identified as the colonizers. Two modes of occurrence have been recognized for these bivalve dwelling cavities; ‘intrastereom clavate borings’ which are restricted to the echinoid stereom, and ‘semi‐endoskeletal dwellings’, which penetrate across the test wall and extend as carbonate crypts into the sediment fill of the internal test cavity. Their size, density and position rule out a syn‐vivo relationship with the echinoids and demonstrate that colonization was post mortem. Because of the endurance of clypeasteroid skeleton and the pronounced bell‐shaped morphology of Clypeaster, the tests of these echinoids provided the most suitable substrates for hard‐bottom colonizers on an otherwise sandy seafloor. The scenario described from Tarragona can be extended to other Neogene and Quaternary strata elsewhere; there is ample evidence for the long‐term utilization of tests of Clypeaster by gastrochaenid bivalves in shoreface palaeoenvironments.  相似文献   

7.
    
Exceptionally preserved specimens of Ernietta in a shallow‐marine gutter cast from southern Namibia reveal that all previously figured specimens of this iconic Ediacaran megafossil are incomplete, representing only the base of a larger and more complex organism. The complete organism is interpreted as comprising a buried, sand‐filled anchor exhibiting the classical Ernietta morphology that passes distally into a trunk that is crowned by two facing fans that extended into the overlying water column. All parts of Ernietta, from the base of its buried anchor to the tip of its fans, appear to have been composed of a palisade of tubular elements that have been variably preserved. Similarity of tubule morphology despite the inherent difference in function between these constructions supports the view that these tubes were integral to all anatomical parts and functions of Ernietta. This style of architecture, construction and function is unique to the Erniettomorpha, supporting the view that it represents an extinct Ediacaran clade in the early evolution of multi‐cellular life.  相似文献   

8.
    
Macroscopic impression fossils from the Xingmincun Formation of the Jinxian Group, Liaoning Province of northeastern China, are identified as members of the Aspidella plexus of Ediacaran age. This is the first recognition of the taxon in the Liaoning Province, although such fossils have been previously recorded in the succession, but were referred to as new species and relegated to an earlier Neoproterozoic age. A revision of the taxonomic interpretation and relative age estimation of the previous record is provided, as well as an evaluation of abiotic vs. biotic processes that could produce similar structures to studied impressions. The mode of preservation of the fossils is considered from a biochemical point of view and along with the properties of organic matter in the integument of soft‐bodied metazoans. The selective preservation of the Ediacaran organisms, including metazoans, as impressions (moulds and casts) against the organically preserved contemporaneous cyanobacterial and algal microfossils, and an exceptionally small number of terminal Ediacaran metazoan fossils (Sabellidites, Conotubus and Shaanxilithes), demonstrates the non‐resistant characteristics and the very different biochemical constitution of the Ediacaran metazoans compared with those that evolved in the Cambrian and after. The refractory biomacromolecules in cell walls of photosynthesizing microbiota (bacterans, cutans, algaenan and sporopollenin groups) and in the chitinous body walls of Sabellidites contrast sharply with the labile biopolymers in Ediacaran metazoans known only from impressions. The newly emerging biosynthesis of resistant biopolymers in metazoans (chitin and collagen groups) initiated by the annelids at the end of Ediacaran and fully evolved in Cambrian metazoans, considered with the ability to biomineralize, made their body preservation possible. The Chengjiang and Burgess Shale metazoans show evidence of this new biochemistry in body walls and cuticles, and not only because of the specific taphonomic window that enhanced their preservation.  相似文献   

9.
  相似文献   

10.
    
Little is known about the genetic basis differentiating resident and anadromous forms found in many salmonid species. Using a medium‐density SNP array, we documented genomic diversity and divergence at 2336 genetically mapped loci among three pairs of North American anadromous and freshwater Atlantic salmon populations. Our results show that across the genome, freshwater populations have lower diversity and a smaller proportion of private polymorphism relative to anadromous populations. Moreover, differentiation was more pronounced among freshwater than among anadromous populations at multiple spatial scales, suggesting a large effect of genetic drift in these isolated freshwater populations. Using nonhierarchical and hierarchical genome scans, we identified hundreds of markers spread across the genome that are potentially under divergent selection between anadromous and freshwater populations, but few outlier loci were repeatedly found in all three freshwater–anadromous comparisons. Similarly, a sliding window analysis revealed numerous regions of high divergence that were nonparallel among the three comparisons. These last results show little evidence for the parallel evolution of alleles selected for in freshwater populations, but suggest nonparallel adaptive divergence at many loci of small effects distributed through the genome. Overall, this study emphasizes the important role of genetic drift in driving genome‐wide reduction in diversity and divergence in freshwater Atlantic salmon populations and suggests a complex multigenic basis of adaptation to resident and anadromous strategies with little parallelism.  相似文献   

11.
    
The morphology and phylogeny of Loxodes vorax and L. striatus orientalis subsp. n. were investigated based on infraciliature and small subunit (SSU) rRNA gene sequence data. Loxodes striatus orientalis subsp. n. was separated from L. striatus striatus stat. n. by having fewer dikinetids in the intrabuccal kinety (35–55 vs. 50–70) and a variable number of macronuclei (2–4 vs. 2). In addition, the SSU rRNA gene sequence of the new subspecies differs in 13 and 11 nucleotides from that of two populations of the nominotypic subspecies. We also summarized the morphological differences between Loxodes and Remanella based on the data available. Phylogenetic analyses revealed that the genus Loxodes was monophyletic and nested within Remanella species. This study might, therefore, support the hypothesis that the freshwater genus Loxodes evolved from the marine genus Remanella.  相似文献   

12.
    
While the mechanisms by which adult terrestrial plants deploy constitutive and induced responses to grazing pressure are well known, the means by which young aquatic plants defend themselves from herbivory are little studied. This study addresses nitrogen transport in the aquatic angiosperm Myriophyllum spicatum in response to herbivore exposure. Nitrogen tracers were used to monitor nitrogen uptake and reallocation in young plants in response to grazing by the generalist insect herbivore Acentria ephemerella. Total nitrogen content (N%) and patterns of nitrogen uptake and allocation (δ15N) were assessed in various plant tissues after 24 and 48 h. Following 24 h exposure to herbivore damage (Experiment 1), nitrogen content of plant apices was significantly elevated. This rapid early reaction may be an adaptation allowing the grazer to be sated as fast as possible, or indicate the accumulation of nitrogenous defense chemicals. After 48 h (Experiment 2), plants' tips showed depletion in nitrogen levels of ca. 60‰ in stem sections vulnerable to grazing. In addition, nitrogen uptake by grazed and grazing‐prone upper plant parts was reduced and nutrient allocation into the relatively secure lower parts increased. The results point to three conclusions: (1) exposure to an insect herbivore induces a similar response in immature M. spicatum as previously observed in mature terrestrial species, namely a rapid (within 48 h) reduction in the nutritional value (N%) of vulnerable tissues, (2) high grazing intensity (100% of growing tips affected) did not limit the ability of young plants to induce resistance; and (3) young plants exposed to herbivory exhibit different patterns of nutrient allocation in vulnerable and secure tissues. These results provide evidence of induced defense and resource reallocation in immature aquatic macrophytes which is in line with the responses shown for mature aquatic macrophytes and terrestrial plants.  相似文献   

13.
    
  1. Freshwater mussels are large, long‐lived and can be important contributors to benthic biomass and processes. They are currently one of the most endangered groups of organisms and it is urgent to develop tools to predict their distribution and the potential effect of their decline or disappearance on these ecosystems. Cyr ( 2008 ) showed that the distribution of Elliptio complanata (Unionidae) in Canadian Shield lakes is constrained by physical forces. Here we test Cyr's model in a very different group of mussels (Hyriidae), in different types of lakes (warm monomictic lakes) that cover a wider range of sizes and morphologies.
  2. We use data on the depth distribution of Echyridella menziesii along 38 depth transects in 11 warm monomictic lakes located in New Zealand to test three hypotheses: (1) wave‐mixed depth and bottom slope are good predictors of the depth of maximum mussel density, (2) thermocline depth does not limit the distribution of mussels in warm monomictic lakes, and (3) the lower boundary of mussel distribution is determined by the mud deposition boundary.
  3. Mussels in New Zealand lakes reach their maximum density within the epilimnion, at increasing depths with increasing lake size and increasing site exposure. The only exceptions were found in large lakes or parts of large lakes with shallow bathymetric slopes, where high mussel densities were found in relatively shallow waters. Mussel density peaks are found much deeper in the volcanic New Zealand lakes than in (glacial) Canadian Shield lakes, a discrepancy we hypothesise could be due to lower sediment stability along the steep slopes of volcanic lakes.
  4. Mussels appear to have a very broad range of depth distribution in these warm monomictic lakes. The deepest samples collected in deep oligotrophic lakes (down to 12–30 m) all contained mussels, often in substantial numbers (up to 2–186 mussels/m2), and can only offer a minimal estimate of the lower boundary of their distribution. However, the distribution of mussels in highly productive lakes is limited by hypolimnetic anoxia, and therefore by position of the thermocline.
  5. Echyridella menziesii are found in a wide range of substrates. Mussels were found below the mud deposition boundary in many lakes, suggesting that the presence of fine flocculent organic sediments does not prevent them from living in deep areas.
  6. The distribution of E. menziesii in warm monomictic lakes appears to be governed by relatively simple physical processes. This supports findings for a very different group of mussels in Canadian Shield lakes and suggests that general models could be developed to predict the distribution of mussels in lakes.
  相似文献   

14.
    
Freshwater turtle hatchlings primarily use visual cues for orientation while dispersing from nests; however, hatchlings rapidly develop a relationship between a sun or geomagnetic compass and a dispersal target that allows them to maintain an established direction of movement when target habitats are not visible. We examined dispersal patterns of hatchling snapping turtles (Chelydra serpentina) and Blanding's turtles (Emydoidea blandingii) dispersing in large arenas in a mowed field and in dense corn. The dispersal of three categories of hatchlings were examined: (1) naïve individuals (no previous dispersal experience), (2) arena‐experienced (limited dispersal experience in arenas in natural habitat), and (3) natural‐experienced hatchling Blanding's turtles (captured after extensive experience dispersing W in natural habitats toward wetlands). Experienced hatchlings were assigned to treatments consisting of having a magnet or a non‐magnetic aluminum sham or nothing glued to their anterior carapace before release in the corn arena. Dispersal patterns of naïve hatchlings of both species were strongly directional in the field arena with visible target horizons and primarily random in the corn arena where typical target horizons were blocked. When released in corn, dispersal patterns were similar for arena‐experienced hatchlings with magnets or shams attached and differed from their prior dispersal headings in the field arena as naïve hatchlings. Natural‐experienced hatchling Blanding's turtles with and without magnets were able to accurately maintain their prior headings to the WNW while dispersing in the field or corn arenas (i.e., the presence of a magnet did not disrupt their ability to maintain their prior heading). Based on the assumption that no other type of compass exists in hatchlings, we conclude that they were not using a geomagnetic compass, but by default were using sun compass orientation to maintain dispersal headings in dense corn where no typical target habitats were visible.  相似文献   

15.
    
  1. Freshwater mussel populations have declined, in part, from changes in host communities. However, it is unknown if fish from adjacent catchments could be used to augment mussel populations in the Great Lakes inland rivers, and if so, whether this association would be impacted by known genetic structure in mussels and fish.
  2. This study tested how host fish origin (i.e. catchment) impacts the transformation of the endangered unionid Epioblasma triquetra from larval into juvenile life stages while concurrently considering potentially genetically distinct populations of mussels and hosts.
  3. We quantitatively determined if Percina caprodes and Percina maculata from the Lake Michigan, Erie and Huron basins are laboratory‐successful hosts for E. triquetra. Experiments were performed in autumn and spring to document any seasonal effects on transformation.
  4. Percina caprodes was reconfirmed to be a successful host for E. triquetra, and for the first time, P. maculata was also determined to be a successful host in the Great Lakes region. Results suggest no differences in juvenile transformation with allopatric and sympatric fish and mussel pairings based on Great Lakes basin origin; therefore, transformation success may not parallel differences in genetic structure. In addition, results suggest seasonal differences in the developmental stages of E. triquetra juveniles.
  5. Knowing the most efficient strategy to optimise juvenile transformations can make reintroductions, augmentation and overall conservation efforts of E. triquetra successful. These data will help in developing recovery strategies for E. triquetra in the Laurentian Great Lakes by understanding variation in host use and nuances in this host–parasite relationship.
  相似文献   

16.
    
A study of nematodes associated with the large larch bark beetle Ips cembrae (Heer 1836) was carried out at three locations in the Czech Republic. The proportion of beetles infested by endoparasitic nematodes (representatives of genera Contortylenchus, Parasitylenchus, Cryptaphelenchus and Parasitorhabditis) ranged from 29.9 to 50.9%. Significant differences were determined in nematode infestation levels among locations, generations and sampling methods. No differences were found in infestation rates between males and females. The percentage of bark beetles with phoretic nematodes ranged from 18 to 42.9%. Phoretic nematodes directly found under elytra, on wings and between body segments of the bark beetles belong to the genus Micoletzkya. However, adults and juveniles of other two phoretic species Laimaphelenchus penardi and Bursaphelenchus sp. were found in the gallery frass of I. cembrae. Infestation by phoretic nematodes positively correlated with the presence of mites under elytra.  相似文献   

17.
Mimicry is one of the best examples of coevolution. For a mimetic system to function, the mimic has to equal its model. Due to this close dependence, mimetic systems promise deep insights into modes and means of evolution. Mimicry is known to occur in many taxa across different groups of organisms. However, while a plethora of mimetic systems exist, cross‐phyla convergences have only rarely been reported in shelled gastropods. Our literature survey brought to light several mimetic systems including gastropods (as model or mimic), all of them in either a marine or a terrestrial setting. We here report on the first potential case of mimicry involving freshwater snails. We found larval cases of European Helicopsyche caddisfly to closely resemble Valvata gastropod shells in shape and size. In particular, stunning is the detailed similarity of features in these trichopteran cases to those characteristic for snail shells, for example, apex, aperture and umbilicus, hinting at a strong selection pressure to be involved. We discuss this unique case of mimicry that might hold unparalleled insight in mimetic relationships, taking into account alternative environmental factors and potential predatory dupes, in particular birds that might have successively caused the evolution of coiled cases in helicopsychid trichopterans.  相似文献   

18.
    
Cyanobacterial blooms are found in many freshwater ecosystems around the world, but the effect of environmental factors on their growth and the proportion of species still require more investigation. In this study, the physiological responses of bloom‐forming cyanobacteria M icrocystis aeruginosa FACHB912, M icrocystis flos‐aquae FACHB1028 and P seudanabaena sp. FACHB1282 to iron deficiency were investigated. Their specific growth rates were found to decrease as the available iron concentration decreased. At low available iron concentrations of 1 × 10?7 M (pFe 21.3) and 5 × 10?8 M (pFe 21.6), M . aeruginosa had the lowest specific growth rate among three studied species. The cell sizes of M . flos‐aquae and Pseudanabaena sp. were significantly smaller under the lowest iron concentration. The chlorophyll a content of the three species decreased at the lowest iron concentration. The maximal relative electron transport rate, photosynthetic efficiency, and light‐saturation parameter of M . aeruginosa were lower than the other two cyanobacteria at pFe 21.3. Therefore, M . aeruginosa was the least able to adapt to iron deficiency. Under iron deficiency, the functional absorption cross‐section of PSII and electron transport rate on the acceptor side of PSII decreased in M . aeruginosa, while the connectivity factor between individual photosynthetic units increased in M . flos‐aquae, and the electron transport rate on the acceptor side of PSII and between PSII and PSI decreased in P seudanabaena sp. The ability to store iron was highest in M . flos‐aquae, followed by P seudanabaena sp. and M . aeruginosa. Thus, these results provide necessary information for detecting the role of iron in the succession of cyanobacterial species in Lake Taihu, the third largest freshwater lake in China, because all three species were isolated from this lake.  相似文献   

19.
    
Mongolia's salmonids are suffering extensive population declines; thus, more comprehensive fisheries management and conservation strategies are required. To assist with their development, a better understanding of the genetic structure and diversity of these threatened species would allow a more targeted approach for preserving genetic variation and ultimately improve long‐term species recoveries. It is hypothesized that the unfragmented river basins that have persisted across Mongolia provide unobstructed connectivity for resident salmonid species. Thus, genetic structure is expected to be primarily segregated between major river basins. We tested this hypothesis by investigating the population structure for three salmonid genera (Hucho, Brachymystax and Thymallus) using different genetic markers to identify evolutionarily significant units (ESUs) and priority rivers to focus conservation efforts. Fish were assigned to separate ESUs when the combined evidence of mitochondrial and nuclear data indicated genetic isolation. Hucho taimen exhibited a dichotomous population structure forming two ESUs, with five priority rivers. Within the Brachymystax genus, there were three B. lenokESUs and one B. tumensisESU, along with six priority rivers. While B. tumensiswas confirmed to display divergent mtDNA haplotypes, haplotype sharing between these two congeneric species was also identified. For T. baicalensis,only a single ESU was assigned, with five priority rivers identified plus Lake Hovsgol. Additionally, we confirmed that T. nigrescens from Lake Hovsgol is a synonym of T. baicalensis. Across all species, the most prominent pattern was strong differentiation among major river basins with low differentiation and weak patterns of isolation by distance within river basins, which corroborated our hypothesis of high within‐basin connectivity across Mongolia. This new genetic information provides authorities the opportunity to distribute resources for management between ESUs while assigning additional protection for the more genetically valuable salmonid rivers so that the greatest adaptive potential within each species can be preserved.  相似文献   

20.
    
The characterization of a complete mitogenome is widely used in genomics studies for systematics and evolutionary research. However, the sequences and structural motifs contained within the mitogenome of Testudines taxa have rarely been examined. The present study decodes the first complete mitochondrial genome of the Indian Tent Turtle, Pangshura tentoria (16,657 bp) by using next‐generation sequencing. This denovo assembly encodes 37 genes: 13 protein‐coding genes (PCGs), 22 transfer RNA (tRNAs), two ribosomal RNA, and one control region (CR). Most of the genes were encoded on majority strand, except for one PCG (NADH dehydrogenase subunit 6) and eight tRNAs. Most of the PCGs were started with an ATG initiation codon, except for Cytochrome oxidase subunit 1 with “GTG” and NADH dehydrogenase subunit 5 with “ATA.” The termination codons, “TAA” and “AGA” were observed in two subunits of NADH dehydrogenase gene. The relative synonymous codon usage analysis revealed the maximum abundance of alanine, isoleucine, leucine, and threonine. The nonsynonymous/synonymous ratios were <1 in all PCGs, which indicates strong negative selection among all Geoemydid species. The study also found the typical cloverleaf secondary structure in most of the tRNA genes, except for serine with the lack of the conventional DHU arm. The comparative study of Geoemydid mitogenomes revealed the occurrence of tandem repeats was frequent in the 3′ end of CR. Further, two copies of a unique tandem repeat “TTCTCTTT” were identified in P. tentoria. The Bayesian and maximum‐likelihood phylogenetic trees using concatenation of 13 PCGs revealed the close relationships of P. tentoria with Batagur trivittata in the studied dataset. All the Geoemydid species showed distinct clustering with high bootstrap support congruent with previous evolutionary hypotheses. We suggest that the generations of more mitogenomes of Geoemydid species are required, to improve our understanding of their in‐depth phylogenetic and evolutionary relationships.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号