Alien Invasive Slider Turtle in Unpredicted Habitat: A Matter of Niche Shift or of Predictors Studied?

BACKGROUND: Species Distribution Models (SDMs) aim on the characterization of a species' ecological niche and project it into geographic space. The result is a map of the species' potential distribution, which is, for instance, helpful to predict the capability of alien invasive species. With regard to alien invasive species, recently several authors observed a mismatch between potential distributions of native and invasive ranges derived from SDMs and, as an explanation, ecological niche shift during biological invasion has been suggested. We studied the physiologically well known Slider turtle from North America which today is widely distributed over the globe and address the issue of ecological niche shift versus choice of ecological predictors used for model building, i.e., by deriving SDMs using multiple sets of climatic predictor. PRINCIPAL FINDINGS: In one SDM, predictors were used aiming to mirror the physiological limits of the Slider turtle. It was compared to numerous other models based on various sets of ecological predictors or predictors aiming at comprehensiveness. The SDM focusing on the study species' physiological limits depicts the target species' worldwide potential distribution better than any of the other approaches. CONCLUSION: These results suggest that a natural history-driven understanding is crucial in developing statistical models of ecological niches (as SDMs) while "comprehensive" or "standard" sets of ecological predictors may be of limited use

Endophytes vs tree pathogens and pests: can they be used as biological control agents to improve tree health?

Like all other plants, trees are vulnerable to attack by a multitude of pests and pathogens. Current control measures for many of these diseases are limited and relatively ineffective. Several methods, including the use of conventional synthetic agro-chemicals, are employed to reduce the impact of pests and diseases. However, because of mounting concerns about adverse effects on the environment and a variety of economic reasons, this limited management of tree diseases by chemical methods is losing ground. The use of biological control, as a more environmentally friendly alternative, is becoming increasingly popular in plant protection. This can include the deployment of soil inoculants and foliar sprays, but the increased knowledge of microbial ecology in the phytosphere, in particular phylloplane microbes and endophytes, has stimulated new thinking for biocontrol approaches. Endophytes are microbes that live within plant tissues. As such, they hold potential as biocontrol agents against plant diseases because they are able to colonize the same ecological niche favoured by many invading pathogens. However, the development and exploitation of endophytes as biocontrol agents will have to overcome numerous challenges. The optimization and improvement of strategies employed in endophyte research can contribute towards discovering effective and competent biocontrol agents. The impact of environment and plant genotype on selecting potentially beneficial and exploitable endophytes for biocontrol is poorly understood. How endophytes synergise or antagonise one another is also an important factor. This review focusses on recent research addressing the biocontrol of plant diseases and pests using endophytic fungi and bacteria, alongside the challenges and limitations encountered and how these can be overcome. We frame this review in the context of tree pests and diseases, since trees are arguably the most difficult plant species to study, work on and manage, yet they represent one of the most important organisms on Earth

Endophytes vs tree pathogens and pests: can they be used as biological control agents to improve tree health?

Like all other plants, trees are vulnerable to attack by a multitude of pests and pathogens. Current control measures for many of these diseases are limited and relatively ineffective. Several methods, including the use of conventional synthetic agro-chemicals, are employed to reduce the impact of pests and diseases. However, because of mounting concerns about adverse effects on the environment and a variety of economic reasons, this limited management of tree diseases by chemical methods is losing ground. The use of biological control, as a more environmentally friendly alternative, is becoming increasingly popular in plant protection. This can include the deployment of soil inoculants and foliar sprays, but the increased knowledge of microbial ecology in the phytosphere, in particular phylloplane microbes and endophytes, has stimulated new thinking for biocontrol approaches. Endophytes are microbes that live within plant tissues. As such, they hold potential as biocontrol agents against plant diseases because they are able to colonize the same ecological niche favoured by many invading pathogens. However, the development and exploitation of endophytes as biocontrol agents will have to overcome numerous challenges. The optimization and improvement of strategies employed in endophyte research can contribute towards discovering effective and competent biocontrol agents. The impact of environment and plant genotype on selecting potentially beneficial and exploitable endophytes for biocontrol is poorly understood. How endophytes synergise or antagonise one another is also an important factor. This review focusses on recent research addressing the biocontrol of plant diseases and pests using endophytic fungi and bacteria, alongside the challenges and limitations encountered and how these can be overcome. We frame this review in the context of tree pests and diseases, since trees are arguably the most difficult plant species to study, work on and manage, yet they represent one of the most important organisms on Earth

Organogenesis of the harderian gland: A comparative survey

Although research interest in the Harderian gland (HG) has increased during the last few years, only a small amount of information exists about its organogenesis. In mouse the HG appears in the posterior part of eye region, in the form of nonluminated tubules between the sixteenth and eighteenth days of gestation. At birth it is still not differentiated histologically. In birds the HG originates from the conjunctival epithelium at a late embryonic stage. In the English sparrow, Passer domesticus (incubation period of about 13 days), it appears between the seventh and the eighth days of incubation. In the chick embryo (incubation period of about 21 days) it originates between the eleventh and the twelfth days. Among reptiles the lizard Podarcis s. sicula has proved to be a useful model to clarify the embryological origin of the orbital glands since it possesses the anterior lacrimal gland contiguous to the HG in the medial corner of the orbit. The anlage of the orbital glands appears on about the twenty-second day of development (incubation period of about 43 days) in the form of a short tubule projecting from the conjunctival epithelium, at the time of development of the nictitating membrane. At this stage the mesenchymal cells surrounding the glandular blastema form a well-defined sac, later occupied by the orbital glands. From this stage until hatching the growth of the glandular blastema continues with the formation of acini which move posteriorly into the preformed mesenchymal sac. At the thirty-sixth day of development the more lateral acini differentiate into the HG. Only at the forty-first day do the more medial acini differentiate into the anterior lacrimal gland. At hatching the HG is fully differentiated. In anuran amphibia the primordium of the HG appears during the metamorphosis at the time of development of the nictitating membrane

MORPHOLOGICAL OBSERVATIONS ON PANCREATIC-ISLET BLOOD-VESSELS IN LOW-DOSE STREPTOZOCIN-TREATED MICE

The aim of this study was to observe modifications occurring within the blood vessels of pancreatic islets in low-dose streptozocin (STZ)-treated mice. Forty-two male C57 BL/6J mice were given 40 mg STZ on 5 consecutive days and killed 6 or 10 d after the first STZ injection. Immunocytochemistry revealed a dense accumulation of cells carrying the 7D10 epitope, related to macrophage inhibitor factor, arranged around the 'vascular pole' of the islets on d 6, and a small number of positive cells within the islets on d 10. Many Ia positive cells (equivalent to MHC class II antigen positive elements) were also found at the periphery of the islet. Ultrastructural observations showed the presence of monocytes within almost all the capillary vessels encircling the islets and entering them at the 'vascular pole' (d 6). On d 10 capillary lumina no longer contained marginating monocytes but activated macrophages were seen in the islet parenchyma

Morphological changes in frog mast cells induced by nerve stimulation in vivo

We investigated at both histochemical and ultrastructural levels the effects of unilateral electrical stimulation in vivo of the frog hypoglossal nerve on the mast cells (MCs) within the nerve fascicles and among the axon terminals. The right ventral root of the hypoglossal nerve in different experiments was stimulated respectively for 1, 3, 5, 10 min with over-threshold stimuli (10 Hz; 2 ms duration). The stimulations at 3, 5 and 10 min caused a progressive degranulation and histochemical and ultrastructural changes of the MCs at the stimulated side. The morphological changes consisted of the loss of Alcian Blue secretory content and of a progressive release of safranin + secretory granules, depending upon duration of stimulation. The ultrastructural study showed that granules are discharged whole into the microenvironment or may release their content through exocytosis. A functional relationship between nerve and MCs is also suggested by the close anatomical association between MCs and pre-terminal axons observed following 10 min of hypoglossal stimulation. No changes in MC morphology occurred after 1 min of electrical stimulation. The results suggest that active cholinergic fibres can modulate MC secretion. © 2001 Elsevier Science Ireland Ltd. All rights reserved

ORGANOGENESIS OF THE HARDERIAN-GLAND IN RANA-ESCULENTA AND BUFO-VIRIDIS

The Harderian gland of Rana esculenta and Bufo viridis originates from an ingrowing of the conjunctival epithelium at the medial corner of the orbit, at stage 28 of Witschi’s standard tables. This primordium organizes into acini at stage 29-30 in Rana esculenta and at stage 30 in Bufo viridis. Afterwards, the glandular cells lengthen and the diameters of the acinar lumina become narrower. Forty days after climax, the Harderian gland reaches adult morphology. The onset of the secretory activity at climax is marked by the appearance of «blue nuclei» in a significant number of glandular cells (10?). This unusual staining of the nuclei, which stain orange with the Mallory trichrome method, has been correlated with an increased rate of RNA synthesis. The secretory granules of the glandular cells are only PAS-positive at stage 29-31 but become also Alcian-positive at metamorphic climax (stage 33), indicating the presence at the latter stage of sulphated mucopolysaccharides, as it has been described in the adult gland of both Rana esculenta and Buio viridis. © 1990 Taylor & Francis Group, LLC

THE IMMUNOSUPPRESSANT FK506 INHIBITS THE DAMAGE TO MOUSE PANCREATIC-ISLETS INDUCED BY LOW-DOSE STREPTOZOCIN

Diabetes mellitus was induced in 40 male C57BL6 mice by injection of a low dose of streptozocin (45 mg/kg body weight) on 5 consecutive days. Twenty four of the mice were immunosuppressed by administration of 1.5 mg FK506/kg body weight daily for 10, 15, 18 and 24 days. Administration of FK506 almost completely inhibited the streptozocin-induced islet damage, and consequently glycaemia remained normal. In FK506-treated animals any inflammatory infiltrate was very sparse and was limited to the vascular pole of the islets. Immunocytochemical results demonstrated that infiltrating cells were Ia-immunoreactive, but were not activated. Ultrastructural observations confirmed the absence of B cell necrosis and degranulation in FK506-treated mice; the few infiltrating elements encountered did not contain phagocytic vesicles or show other signs of activation. © 1994 Springer-Verlag

ORGANOGENESIS OF THE ORBITAL GLANDS IN THE LIZARD PODARCIS-S-SICULA - A HISTOLOGICAL, HISTOCHEMICAL AND ULTRASTRUCTURAL-STUDY

The orbital glands of the lizard Podarcis s. sicula are represented by the anterior and posterior lacrimal glands and the Harderian gland. The anlage of the Harderian gland appears on about the 22nd day of development in the form of a short tubule projecting from the conjunctival epithelium. This event is coincident with the appearance of the nictitating membrane. At this stage the mesenchymal cells surrounding the glandular blastema proliferate at a high rate and form a definite sac, later occupied by both the Harderian gland and the anterior lacrimal glands. At the 26th day of development, the glandular blastema forms acini at its distal end. The prospective glandular cells are not yet differentiated histologically. At the 36th day of development, differentiated serous glandular cells become visible. At the 41st day of development, the acini fill up the preformed mesenchymal sac. Only at this stage does the most medial part of the gland differentiate into mucous-secreting anterior lacrimal gland. At the same time, a small primordium of the posterior lacrimal gland can be seen in the posterior commissure of the eye. The appearance of junctional complexes between epithelial cells and mesenchymal cells in the early developmental stages supports the role of the mesenchyme in the differentiation of the glandular cells. Since the glandular anlage differentiates laterally into Harderian gland and medially into anterior lacrimal gland, spatial and temporal differences seem to exist in the inductive process. Furthermore, a concentration gradient of the inductive substance(s) may be envisaged, since an intermediate zone is present between the Harderian gland and the anterior lacrimal gland, consisting of mixed glandular cells containing both mucous and serous secretory granules. © 1995 Springer-Verlag