Currents, landscape structure, and recruitment success along a passive–active dispersal gradient     

C. Ashton Drew  David B. Eggleston 《Landscape Ecology》2006,21(6):917-931

There exists a gradient in dispersal behavior from passive to active, which reflects organisms’ dependence upon currents vs. self-propelled movement. We asked: Do currents modify organism–landscape interactions to influence recruitment success along this dispersal gradient? Using a spatially-explicit cellular model, we simulated the recruitment success of three generalized dispersal strategies (walkers, swimmers, and drifters) through hierarchically structured benthic landscapes. We evaluated the relative recruitment success (recruited population size, overall area occupied, time to recruit) of the three dispersal strategies in similar landscapes, as well as the consequences of varying the total proportion of habitat suitable for recruitment, and the scale and pattern of habitat patchiness on recruitment success. In the presence of currents, swimmers and drifters generally recruited over larger areas and in less time than walkers. Differences among the dispersal strategies’ recruitment success were most pronounced when an intermediate number of good habitat cells (16–48% of landscape) were broadly dispersed across the landscape. Although recruitment success always increased with increasing proportion of good habitat, drifters were more sensitive, and swimmers less sensitive, to these landscape changes than walkers. We also found that organisms dispersing within currents typically responded non-linearly (logarithmically or exponentially) to increasing proportion of total good habitat, whereas walkers more often responded linearly.  相似文献   

Growth of native tree species planted in montane reforestation projects in the Colombian and Ecuadorian Andes differs among site and species     

Matthew C. Bare  Mark S. Ashton 《New Forests》2016,47(3):333-355

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Generation and Characterization of Embryonic Stem-Like Cell Lines Derived from In Vitro Fertilization Buffalo (Bubalus bubalis) Embryos     

B Huang  T Li  X-L Wang  T-S Xie  Y-Q Lu  FM da Silva  D-S Shi 《Reproduction in domestic animals》2010,45(1):122-128

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Influence of Superovulatory Protocols on In Vitro Production of Nellore (Bos indicus) Embryos     

FM Monteiro  MMG Ferreira  JR Potiens  BG Eberhardt  LA Trinca  CM Barros 《Reproduction in domestic animals》2010,45(5):860-864

There are indications in the literature that delaying the period between ovarian superestimulation and ovum pick up (OPU) would induce follicles to a condition of initial atresia, which could be beneficial to oocyte development. In this work, we compared three protocols for OPU and in vitro production (IVP) of embryos, in Nellore cattle. Nellore cows (n = 18) were randomly allocated in three groups: Group 1 (OPU), Group 2 [Follicle stimulating hormone (FSH) and OPU] and Group 3 (FSH deprivation and OPU). Three OPUs were performed, and the animals were switched to a different group each time (crossover), in such a way that at the end of the experiment all cows received the 3 protocols. At random stage of the oestrous cycle (D‐2), all follicles ≥ 6 mm were aspirated to induce a new follicular wave 2 days afterwards (D0). In Group 1, OPU was performed on D2 and oocytes were processed to IVP. In Group 2, starting on D0, cows were superstimulated (FSH, Folltropin^®, 30 mg administered daily, i.m., during three consecutive days, total dose = 180 mg), and 6 h after the last FSH dose, they received exogenous luteinizing hormone (LH) (12.5 mg, i.m., Lutropin^®, D3). The OPU was performed 6 h after LH administration, i.e. 12 h after the last dose of FSH. Animals in Group 3 received the same treatment as those in Group 2, except that LH was administered 42 h after the last dose of FSH, and OPU occurred 6 h later. Therefore, in this group, follicles were deprived of FSH at 48 h. Both cleavage and blastocyst rates were similar (p > 0.05, anova ) among oocytes from Groups 1, 2 and 3, respectively: 77.4% (144/185) and 42.70% (79/185); 75.54% (105/139) and 31.65% (44/139); 63.52% (101/159) and 33.33% (53/159). However, hatched blastocyst rate was higher (p < 0.01) in Group 1 (30.27%, 56/185) when compared with Group 2 (11.51%, 16/139) or 3 (15.72%, 25/159). It is concluded that, contrary to previous work on European breeds (Bos taurus), ovarian superstimulation associated with deprivation of FSH and OPU (Group 3) did not increase IVP of Nellore embryos (Bos indicus). On the contrary, the highest hatched blastocyst rates were observed in oocytes from non‐superstimulated cows.  相似文献   

Investigation of the effect of pamidronate disodium on the in vitro viability of osteosarcoma cells from dogs   总被引：4，自引：0，他引：4  

Ashton JA  Farese JP  Milner RJ  Lee-Ambrose LM  van Gilder JM 《American journal of veterinary research》2005,66(5):885-891

OBJECTIVE: To determine the effect of pamidronate disodium on the in vitro viability of osteosarcoma cells and non-neoplastic cells from dogs. SAMPLE POPULATION: 3 osteosarcoma and 1 fibroblast cell lines derived from dogs. PROCEDURE: Cell counts and cell viability assays were performed in cultures of osteosarcoma cells (POS, HMPOS, and COS31 cell lines) and fibroblasts after 24, 48, and 72 hours of incubation with pamidronate at concentrations of 0.001 to 1000 microM or with no drug (control treatment). Percentage viability was determined in cell samples for each concentration of pamidronate and each incubation time. A DNA fragmentation analysis was performed to assess bisphosphonate-induced apoptosis. RESULTS: Osteosarcoma cell viability decreased significantly in a concentration- and time-dependent manner at pamidronate concentrations ranging from 100 to 1000 microM, most consistently after 48 and 72 hours' exposure. In treated osteosarcoma cells, the lowest percentage cell viability was 34% (detected after 72 hours' exposure to 1000 microM pamidronate). Conversely, 72 hours' exposure to 1000 microM pamidronate did not significantly reduce fibroblast viability (the lowest percentage viability was 76%). After 72 hours of exposure, pamidronate did not cause DNA fragmentation in POS or HMPOS cells. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that pamidronate may have the potential to inhibit osteosarcoma growth in dogs, possibly through a nonapoptotic mechanism. The clinical relevance of these in vitro findings remains to be determined, but administration of pamidronate may potentially be indicated as an adjuvant treatment in chemotherapeutic protocols used in dogs.  相似文献   

Amphidial structure of ivermectin-resistant and susceptible laboratory and field strains of Haemonchus contortus   总被引：3，自引：0，他引：3  

Freeman AS  Nghiem C  Li J  Ashton FT  Guerrero J  Shoop WL  Schad GA 《Veterinary parasitology》2003,110(3-4):217-226

The development of anthelmintic resistance by nematode parasites is a growing problem for veterinarians, pet owners, and producers. The intensive use of the macrocyclic lactones for the treatment of a variety of parasitic diseases has hastened the development of resistance to this family of parasiticides. As a result, resistance to ivermectin, moxidectin, nemadectin, and doramectin by Haemonchus contortus has been documented throughout the world.

Sensory neurons located in the cephalic end of nematodes are in close contact with the external environment. Through these neurons, important chemical and thermal cues are gathered by the parasite. Examination of serial electron micrographs of ivermectin-susceptible and ivermectin-resistant H. contortus allows for comparison of neuronal structure, arrangement of neurons within the amphidial channel, and distance of the tip of the dendritic processes to the amphidial pore. The latter of these characteristics provides a useful means by which to compare the association between the neurons and the external environment of the worm.

Comparison of parental laboratory strains of ivermectin-susceptible strains of H. contortus with related selected, ivermectin-resistant strains and with a wild-type ivermectin-susceptible field strain of H. contortus from Louisiana reveal that the ivermectin-resistant worms examined have markedly shorter sensory cilia than their ivermectin-susceptible parental counterparts. Additionally, the amphidial neurons of ivermectin-resistant worms are characterized by generalized degeneration and loss of detail, whereas other neurons outside of the channels, such as the labial and cephalic neurons, are normal in structure. These findings raise a number of questions regarding the relationship between amphidial structure and ivermectin resistance as well as the role of amphids as a means of entry for ivermectin. While shortened amphidial sensilla are associated with ivermectin resistance, it remains unclear if such a structural modification facilitates survival of nematodes exposed to macrocyclic lactones.  相似文献   

Long-term effect on the equine eye of an intravitreal device used for sustained release of cyclosporine A   总被引：4，自引：1，他引：3  

Gilger BC  Malok E  Stewart T  Ashton P  Smith T  Jaffe GJ  Allen JB 《Veterinary ophthalmology》2000,3(2-3):105-110

OBJECTIVE: To determine the long-term toxicity of an intravitreal device releasing continuous cyclosporinee A (CsA) in normal eyes of horses by evaluating clinical signs, electroretinography, and histopathology. Animals Studied Ten adult horses with normal ophthalmic examinations were used in this study Procedure(s) Four horses had one eye implanted with a CsA device, and six horses had the right eye implanted with a CsA-containing device (10 eyes with CsA in total) and the left eye (six eyes in total) with the device without drug (control). The implants were placed in the vitreous of the eyes through a sclerotomy 1 cm posterior to the limbus in the dorso-temporal quadrant of the eye. Scotopic electroretinograms were performed prior to implantation and at 1 week, and at 1, 3, 6, 9, and 12 months postimplantation. Two of the unilaterally implanted horses were euthanized at 1 weeks postimplantation, and two at 6 weeks postimplantation. Two of the bilaterally implanted horses were euthanized at 6 months, two at 9 months, and two at 12 months postimplantation. At euthanasia, the eyes were removed, aqueous and vitreous humor aspirated, and tissues fixed in 10% buffered formalin and processed for histopathology. CsA concentrations were measured by high pressure liquid chromatography in the aqueous and vitreous humors, and in peripheral blood. RESULTS: The devices were tolerated well in 14 of 16 eyes. There was minimal postoperative inflammation in most eyes, with a normal appearance within 7 days. In two eyes implanted with the CsA device, severe inflammation resulted in phthisis bulbi by 28 days. One of these eyes exhibited suspected bacterial endophthalmitis, and one had a sterile endophthalmitis and cataract presumably from trauma to the lens during implantation. In the other 14 eyes, no change was observed in the scotopic electroretinograms (ERG) from preoperative results, and no significant differences between the right (CsA) and left (control device) eyes were observed. CsA levels in the aqueous and vitreous humor, and peripheral blood were below the detection limit of the HPLC. Histologic findings revealed only a mild lymphoplasmacytic cellular infiltrate in the ciliary body and pars plana near the implantation site. CONCLUSIONS: The CsA devices were well tolerated with no long-term complications from the implants themselves. However, complications may occur from inadvertent implantation trauma or contamination during surgery. The long-term safety of the device may make it useful for delivery of CsA in the control of equine recurrent uveitis.  相似文献   

The Selaginella genome identifies genetic changes associated with the evolution of vascular plants     

Banks JA  Nishiyama T  Hasebe M  Bowman JL  Gribskov M  dePamphilis C  Albert VA  Aono N  Aoyama T  Ambrose BA  Ashton NW  Axtell MJ  Barker E  Barker MS  Bennetzen JL  Bonawitz ND  Chapple C  Cheng C  Correa LG  Dacre M  DeBarry J  Dreyer I  Elias M  Engstrom EM  Estelle M  Feng L  Finet C  Floyd SK  Frommer WB  Fujita T  Gramzow L  Gutensohn M  Harholt J  Hattori M  Heyl A  Hirai T  Hiwatashi Y  Ishikawa M  Iwata M  Karol KG  Koehler B  Kolukisaoglu U  Kubo M  Kurata T  Lalonde S  Li K  Li Y  Litt A  Lyons E  Manning G  Maruyama T  Michael TP 《Science (New York, N.Y.)》2011,332(6032):960-963

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Growth,feeding and thyroxine‐related responses of hybrid striped (sunshine) bass (Morone chrysops ♀ X M. saxatilis ♂) fed de‐oiled carinata (Brassica carinata) meal     

Tom Kasiga  Ashton L. Fey  Mark A. Berhow  Timothy J. Bruce  Michael L. Brown 《Aquaculture Nutrition》2020,26(1):109-122

De‐oiled (<10 g/kg oil) carinata (Brassica carinata) meal is high (>400 g/kg) in protein, but its use in fish diets will likely be limited mainly by glucosinolates (GLS), sinapine and crude fibre. Two feeding experiments were conducted to determine the response of hybrid striped bass (Morone chrysops ♀ X M. saxatilis ♂, HSB) to inclusion of cold‐pressed carinata meal (CPCM) in diets. Cook extrusion reduced an average of 44% and 57% of GLS and sinapine concentrations in diets, respectively. In experiment 1, diets containing 0.71–2.71 μmoles of GLS and 0.034–0.181 mg of sinapine/g did not significantly (p > .05) reduce feed consumption, utilization or growth, resulting in similar concentrations of thyroxines and consequently no effect on deiodinase enzymes. In experiment 2, there was a significantly reduced (p < .05) feed consumption in fish fed diets containing 5.58–9.52 μmoles of GLS and 0.54–0.75 mg of sinapine/g, resulting in HSB exhibiting lethargic swimming and feeding behaviours, and consequently poor feed utilization and growth. Cook extrusion reduced about half of GLS and sinapine, and HSB tolerated ≤2.71 μmoles of GLS and ≤0.31 mg of sinapine/g of diet without affecting feed consumption and utilization, growth and thyroid metabolism.  相似文献   

A STUDY OF THE POSSIBLE ROLE OF CHELATION IN THE OCCURRENCE OF HYPOMAGNESAEMIA IN SHEEP     

W. M. Ashton  K. B. Sinclair 《Grass and Forage Science》1965,20(2):118-122

Wethers fitted with permanent rumen cannulae were used in a study of the effect of various doses of ammonium salts and E. D.T. A. (ethylene-diamine-tetra-acetic acid, disodium salt) on the pH of rumen digesta and the levels of serum calcium and magnesium. Doses of up to 200 g ammonium acetate had little effect on the pH of rumen contents or on serum Mg levels, but appeared to produce a fall in serum Ca. Ammonium carbonate, however, when given alone or with E. D.T. A., caused a marked increase in the pH of rumen fluid and a temporary fall in the serum Ca level. When given singly, neither ammonium carbonate nor E. D.T. A. significantly affected the levels of serum Mg which were, however, reduced when these compounds were given together, possibly because the increased pH of rumen contents produced by the ammonium carbonate was conducive to chelation of Mg by the E. D.T. A. High levels of ammonia may occur in rumen liquor after the ingestion of young nitrogen-rich herbage, and it is suggested that chelation of dietary Mg by such compounds as amino acids and peptides, which abound in young herbage, may be a factor concerned in the low 'availability' of this form of Mg.  相似文献