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11.
Examination of the reproductive morphology of the adelphoparasitic red alga Gardneriella tuberifera Kylin reveals that this monotypic genus is correctly placed in the family Solieriaceae (Gigartinales), to which its host Agardhiella gaudichaudii (Montagne) Silva et Papenfuss also belongs. Gardneriella is multiaxial, nonprocarpic and has an inwardly directed, three-celled carpogonial branch. The large, reniform uninucleate auxiliary cell is distinct prior to and after fertilization. It is diploidized by an unbranched, multicellular connecting filament which lacks pit connections. One or two connecting filaments arise from each fertilized carpogonium. From the diploidized auxiliary cell, the gonimoblast initial is cut off obliquely toward the interior of the thallus. The cells of the gonimoblast fuse with adjacent unpigmented vegetative cells of Gardneriella and pigmented cells of the host. These cells become incorporated into the developing cystocarp and, from those of Gardneriella, additional short chains of gonimoblast cells arise. The mature cystocarp is placentate, radiately lobed, and lacks a surrounding involucre. Carposporangia are borne in short chains and the unpigmented carpospores are released upon the dissolution of outer vegetative cells. No ostiole is present. Gardneriella appears to be most closely related to the placentate solieriacean genera Agardhiella, Sarcodiotheca, and Meristiella and therefore this genus should be placed in the tribe recently erected for these taxa, the Agardhielleae. 相似文献
12.
Diatom systematics depends almost entirely upon structure of the silica shell. It is not known to what extent the taxonomic species, as defined by shell structure, corresponds to the genetic species—i.e., to the reproductively isolated population. As an approach to this problem, we report here a comparison of enzymes by electrophoresis. We have examined the genetic constitution of a number of clones of (presumably) the same species for each of 2 closely related, centric diatom species: Thalassiosira pseudonana Hasle and Heimdal and T. fluviatilis Hustedt. The 4 clones of T. fluviatilis form a distinct group, clearly separated from all the T. pseudonana clones. Within T. pseudonana, 4 estuarine clones and one reef clone form a group that is distinctly different from 4 oceanic clones. A single clone of T. pseudonana from the Continental Slope waters is intermediate between these 2 groups and probably shares genes with both groups, indicating that the 2 T. pseudonana groups are not genetically isolated. We conclude that i) within groups, isolates are closely related even though they originated from different continents; and, ii) T. pseudonana is subdivided into ecological races. 相似文献
13.
Two species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolates of Gonium pectorale Mueller can interbreed while isolates of Pandorina morum Bory behave quite differently. More than 20 sexually isolated subpopulations occur within this species; these have been termed “syngens” (sensu Sonneborn). Because prezygotic barriers to mating cause intersyngen pairings to fail, breeding analyses cannot be used to estimate genetic relatedness among the syngens of P. morum. DNA comparisons provide an alternative method of assessing genetic relatedness. We compared the nucleotide sequence of the internal transcribed spacer (ITS) region of the nuclear ribosomal repeat among clones of P. morum and of G. pectorale. Members of syngens of P. morum with distribution restricted to one small geographical area show great similarity. Likewise, members of any syngen of worldwide distribution show near uniformity, even those from different continents. However, the ITS sequence of each syngen differs from that of other syngens. In contrast, G. pectorale, which has an ITS region that is remarkably uniform throughout the world, appears to consist of a single syngen within North America and Europe by mating tests. The molecular data are in complete conformity with previous syngen assignment. Because the latter is based on mating affinity, with two complementary mating types per syngen, the evolution of new mating type pairs appears to be the basis of microevolution in these algae. We infer that either P. morum is a more ancient species than G. pectorale or that P. morum has a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the past. 相似文献
14.
15.
Janet C. Steven Ingrid A. Anderson Edmund D. Brodie Lynda F. Delph 《Ecology and evolution》2020,10(1):569-578
Genetic covariance between two traits generates correlated responses to selection, and may either enhance or constrain adaptation. Silene latifolia exhibits potentially constraining genetic covariance between specific leaf area (SLA) and flower number in males. Flower number is likely to increase via fecundity selection but the correlated increase in SLA increases mortality, and SLA is under selection to decrease in dry habitats. We selected on trait combinations in two selection lines for four generations to test whether genetic covariance could be reduced without significantly altering trait means. In one selection line, the genetic covariance changed sign and eigenstructure changed significantly, while in the other selection line eigenstructure remained similar to the control line. Changes in genetic variance–covariance structure are therefore possible without the introduction of new alleles, and the responses we observed suggest that founder effects and changes in frequency of alleles of major effect may be acting to produce the changes. 相似文献
16.
Detecting trends in tree growth: not so simple 总被引:1,自引:0,他引:1
17.
Shawnita Sealy-Jefferson Brenda W. Gillespie Allison E. Aiello Mary N. Haan Lewis B. Morgenstern Lynda D. Lisabeth 《PloS one》2013,8(6)
Background
Persistent pathogens have been proposed as risk factors for stroke; however, the evidence remains inconclusive. Mexican Americans have an increased risk of stroke especially at younger ages, as well as a higher prevalence of infections caused by several persistent pathogens.Methodology/Principal
Findings Using data from the Sacramento Area Latino Study on Aging (n = 1621), the authors used discrete-time regression to examine associations between stroke risk and (1) immunoglobulin G antibody levels to Helicobacter pylori (H. pylori), Cytomegalovirus, Varicella Zoster Virus, Toxoplasma gondii and Herpes simplex virus 1, and (2) concurrent exposure to several pathogens (pathogen burden), defined as: (a) summed sero-positivity, (b) number of pathogens eliciting high antibody levels, and (c) average antibody level. Models were adjusted for socio-demographics and stroke risk factors. Antibody levels to H. pylori predicted incident stroke in fully adjusted models (Odds Ratio: 1.58; 95% Confidence Interval: 1.09, 2.28). No significant associations were found between stroke risk and antibody levels to the other four pathogens. No associations were found for pathogen burden and incident stroke in fully adjusted models.Conclusions/Significance
Our results suggest that exposure to H. pylori may be a stroke risk factor in Mexican Americans and may contribute to ethnic differences in stroke risk given the increased prevalence of exposure to H. pylori in this population. Future studies are needed to confirm this association. 相似文献18.
T. J. Sego Matthew Prideaux Jane Sterner Brian Paul McCarthy Ping Li Lynda F. Bonewald Burcin Ekser Andres Tovar Lester Jeshua Smith 《Biotechnology and bioengineering》2020,117(3):798-815
Natural tissues are incorporated with vasculature, which is further integrated with a cardiovascular system responsible for driving perfusion of nutrient-rich oxygenated blood through the vasculature to support cell metabolism within most cell-dense tissues. Since scaffold-free biofabricated tissues being developed into clinical implants, research models, and pharmaceutical testing platforms should similarly exhibit perfused tissue-like structures, we generated a generalizable biofabrication method resulting in self-supporting perfused (SSuPer) tissue constructs incorporated with perfusible microchannels and integrated with the modular FABRICA perfusion bioreactor. As proof of concept, we perfused an MLO-A5 osteoblast-based SSuPer tissue in the FABRICA. Although our resulting SSuPer tissue replicated vascularization and perfusion observed in situ, supported its own weight, and stained positively for mineral using Von Kossa staining, our in vitro results indicated that computational fluid dynamics (CFD) should be used to drive future construct design and flow application before further tissue biofabrication and perfusion. We built a CFD model of the SSuPer tissue integrated in the FABRICA and analyzed flow characteristics (net force, pressure distribution, shear stress, and oxygen distribution) through five SSuPer tissue microchannel patterns in two flow directions and at increasing flow rates. Important flow parameters include flow direction, fully developed flow, and tissue microchannel diameters matched and aligned with bioreactor flow channels. We observed that the SSuPer tissue platform is capable of providing direct perfusion to tissue constructs and proper culture conditions (oxygenation, with controllable shear and flow rates), indicating that our approach can be used to biofabricate tissue representing primary tissues and that we can model the system in silico. 相似文献
19.
Marzia Scortegagna Chelsea Ruller Surya K. De Elisa Barile Stan Krajewski Pedro Aza‐Blanc Roy Williams Anthony B. Pinkerton Michael Jackson Lynda Chin Maurizio Pellecchia Marcus Bosenberg Ze'ev A. Ronai 《Pigment cell & melanoma research》2013,26(1):136-142
To date, there are no effective therapies for tumors bearing NRAS mutations, which are present in 15–20% of human melanomas. Here we extend our earlier studies where we demonstrated that the small molecule BI‐69A11 inhibits the growth of melanoma cell lines. Gene expression analysis revealed the induction of interferon‐ and cell death‐related genes that were associated with responsiveness of melanoma cell lines to BI‐69A11. Strikingly, the administration of BI‐69A11 inhibited melanoma development in genetically modified mice bearing an inducible form of activated Nras and a deletion of the Ink4a gene (Nras(Q61K)::Ink4a?/?). Biweekly administration of BI‐69A11 starting at 10 weeks or as late as 24 weeks after the induction of mutant Nras expression inhibited melanoma development (100 and 36%, respectively). BI‐69A11 treatment did not inhibit the development of histiocytic sarcomas, which constitute about 50% of the tumors in this model. BI‐69A11‐resistant Nras(Q61K)::Ink4a?/? tumors exhibited increased CD45 expression, reflective of immune cell infiltration and upregulation of gene networks associated with the cytoskeleton, DNA damage response, and small molecule transport. The ability to attenuate the development of NRAS mutant melanomas supports further development of BI‐69A11 for clinical assessment. 相似文献
20.
Clay Trauernicht Brett P. Murphy Lynda D. Prior Michael J. Lawes David M. J. S. Bowman 《Ecosystems》2016,19(5):896-909
Woody plant demographics provide important insight into ecosystem state-shifts in response to changing fire regimes. In Australian tropical savannas, the switch from patchy landscape burning by Aborigines to unmanaged wildfires within the past century has been implicated in biodiversity declines including the fire-sensitive conifer, Callitris intratropica. C. intratropica commonly forms small, closed-canopy groves that exclude fire and allow recruitment of conspecifics and other fire-sensitive woody plants. C. intratropica groves provide a useful indicator of heterogeneity and fire regime change, but the mechanisms driving the species’ persistence and decline remain poorly understood. We examined the hypothesis that C. intratropica population stability depends upon a regime of frequent, low-intensity fires maintained by Aboriginal management. We combined integral projection models of C. intratropica population behaviour with an environmental state change matrix to examine how vital rates, grove dynamics and the frequency of high- and low-intensity fires contribute to population stability. Closed-canopy C. intratropica groves contributed disproportionately to population growth by promoting recruitment, whereas singleton trees accounted for a larger proportion of adult mortality. Our patch-based population model predicted population declines under current fire frequencies and that the recruitment of new groves plays a critical role in the species’ persistence. Our results also indicated that reducing fire intensity, a key outcome of Aboriginal burning, leads to C. intratropica population persistence even at high fire frequencies. These findings provide insight into the relationship between ecosystem composition and human–fire interactions and the role of fire management in sustaining the mosaics that comprise ‘natural’ systems. 相似文献