Naturalization and invasion of alien plants: concepts and definitions

Abstract.  Much confusion exists in the English-language literature on plant invasions concerning the terms 'naturalized' and 'invasive' and their associated concepts. Several authors have used these terms in proposing schemes for conceptualizing the sequence of events from introduction to invasion, but often imprecisely, erroneously or in contradictory ways. This greatly complicates the formulation of robust generalizations in invasion ecology.
Based on an extensive and critical survey of the literature we defined a minimum set of key terms related to a graphic scheme which conceptualizes the naturalization/invasion process. Introduction means that the plant (or its propagule) has been transported by humans across a major geographical barrier. Naturalization starts when abiotic and biotic barriers to survival are surmounted and when various barriers to regular reproduction are overcome. Invasion further requires that introduced plants produce reproductive offspring in areas distant from sites of introduction (approximate scales: > 100 m over < 50 years for taxa spreading by seeds and other propagules; > 6 m/3 years for taxa spreading by roots, rhizomes, stolons or creeping stems). Taxa that can cope with the abiotic environment and biota in the general area may invade disturbed, seminatural communities. Invasion of successionally mature, undisturbed communities usually requires that the alien taxon overcomes a different category of barriers.
We propose that the term 'invasive' should be used without any inference to environmental or economic impact. Terms like 'pests' and 'weeds' are suitable labels for the 50–80% of invaders that have harmful effects. About 10% of invasive plants that change the character, condition, form, or nature of ecosystems over substantial areas may be termed 'transformers'.     

Towards a Case Definition for Devil Facial Tumour Disease: What Is It?

In the mid 1990s an emerging disease characterised by the development of proliferative lesions around the face of Tasmanian devils (Sarcophilus harrisii) was observed. A multi-disciplinary approach was adopted to define the condition. Histopathological and transmission electron microscopic examination combined with immunohistochemistry help define Devil Facial Tumour Disease (DFTD) as a neoplastic condition of cells of neuroendocrine origin. Cytogenetic analysis of neoplastic tissue revealed it to be markedly different from normal devil tissue and having a consistent karyotype across all tumours examined. Combined with evidence for Major histocompatability (MHC) gene analysis there is significant evidence to confirm the tumour is a transmissible neoplasm.     

Lack of response to all-trans retinoic acid supplementation in adult dogs following left pneumonectomy.

We showed previously that removing 55-58% of the lung by right pneumonectomy (R-PNX) in adult dogs triggers compensatory growth of the remaining lung, but removing 42-45% of the lung by left PNX (L-PNX) does not. We also showed that, following R-PNX, supplemental all-trans retinoic acid (RA) selectively enhances alveolar capillary endothelial cell volume (Yan X, Bellotto DJ, Foster DJ, Johnson RL, Jr., Hagler HH, Estrera AS, and Hsia CC. J Appl Physiol 96: 1080-1089, 2004). We hypothesized that RA supplementation might enhance compensation following L-PNX and tested this hypothesis by administering RA (2 mg.kg(-1).day(-1), 4 days/wk) or placebo orally to litter-matched adult foxhounds for 4 mo following L-PNX. Resting lung function was measured under anesthesia. Air and tissue volumes of the remaining lung were assessed by high-resolution computed tomography scan and by detailed postmortem morphometric analysis of the fixed lung. There was no significant difference in resting lung function, lung volume, alveolar structure, or septal ultrastructure between RA and placebo treatment groups. We conclude that RA supplementation does not induce post-PNX compensatory lung growth in the absence of existing cellular growth activities initiated by other primary signals.     

Female Goldeneye Ducks (Bucephala clangula) Do Not Discriminate among Male Precopulatory Display Patterns

Female goldeneyes remain motionless on the surface of the water while single males circle them performing a series of highly stereotyped displays. After performing between eight and 90 of these displays the male either copulates or attempts to copulate with the female. However, females allow only 58% of males to mount them, while rejecting 42%. We have examined 804 of these precopulatory sequences containing 11,841 actions in an effort to determine why females find some display sequences of males unsuitable, while others are accepted. Males have an extraordinarily varied sequence of actions, and sequence variation leading to successful and unsuccessful copulation attempts was similar. Most surprising was the tendency of males to eliminate one of the five actions, whether in successful or unsuccessful attempts. As unlikely as we think it might be as the result of natural selection, the only statistically significant difference we found between successful and unsuccessful attempts was the reduction in the frequency of expression of one or more of the behaviors in successful attempts. These observations, coupled with the large variation seen in most sequences, suggest that there is not a correct sequence, or even a correct set of actions leading to copulation. The male must, however, perform goldeneye species-specific precopulatory behavior as performed by adult males, although it apparently can be performed in a wide variety of patterns.     

Cry2 Is Critical for Circadian Regulation of Myogenic Differentiation by Bclaf1-Mediated mRNA Stabilization of Cyclin D1 and Tmem176b

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Rapid,efficient production of homozygous transgenic tobacco plants withagrobacterium tumefaciens: A seed-to-seed protocol

An optimized complete protocol was developed forAgrobacterium tumefaciens-mediated transformation of tobacco (Nicotiana tabacum L. cultivar SR1), producing T₁ flowering plants homozygous for the inserted T-DNA as verified by kanamycin resistance in T₂ seedlings in 6 to 7 months from the time of cocultivation withAgrobacterium. Previous protocols require up to 9 to 12 months to obtain similar results. Procedures unique and important to this protocol include; a modified “whole-leaf” transformation coupled with a long duration of cocultivation, resulting in high rates of transformation, high levels of kanamycin in selection media resulting in few escapes, and extensive rooting of regenerants prior to a greenhouse hardening procedure. Once in the greenhouse, primary regenerants were maintained in small containers with long day photoperiod and high light levels, greatly shortening the time to seed set. Flowers from primary transformants were bagged to allow self pollination, and seed capsules harvested and dried prior to normal maturation on the plant. T₁ and T₂ seeds were plated and selected on kanamycin media by an improved seed plating technique which eliminates the need for the placement of individual seeds, saving time and improving selection homogeneity. Using this protocol, over 130 independent tobacco lines from six separate gene constructs have been generated in a very short time period. Of these 130, nearly 60 percent segregated 3∶1 for kanamycin resistance: susceptibility, indicating single transgene insertion events.     

Mechanosensitivity below Ground: Touch-Sensitive Smell-Producing Roots in the Shy Plant Mimosa pudica

The roots of the shy plant Mimosa pudica emit a cocktail of small organic and inorganic sulfur compounds and reactive intermediates into the environment, including SO₂, methanesulfinic acid, pyruvic acid, lactic acid, ethanesulfinic acid, propanesulfenic acid, 2-aminothiophenol, S-propyl propane 1-thiosulfinate, phenothiazine, and thioformaldehyde, an elusive and highly unstable compound that, to our knowledge, has never before been reported to be emitted by a plant. When soil around the roots is dislodged or when seedling roots are touched, an odor is detected. The perceived odor corresponds to the emission of higher amounts of propanesulfenic acid, 2-aminothiophenol, S-propyl propane 1-thiosulfinate, and phenothiazine. The mechanosensitivity response is selective. Whereas touching the roots with soil or human skin resulted in odor detection, agitating the roots with other materials such as glass did not induce a similar response. Light and electron microscopy studies of the roots revealed the presence of microscopic sac-like root protuberances. Elemental analysis of these projections by energy-dispersive x-ray spectroscopy revealed them to contain higher levels of K⁺ and Cl⁻ compared with the surrounding tissue. Exposing the protuberances to stimuli that caused odor emission resulted in reductions in the levels of K⁺ and Cl⁻ in the touched area. The mechanistic implications of the variety of sulfur compounds observed vis-à-vis the pathways for their formation are discussed.Plant roots are known to exude a diversity of both small and macromolecular chemicals that mediate antimicrobial, antiquorum sensing, allelopathic, and other effects (De-la-Peña et al., 2012). However, the machinery associated with the synthesis and extrusion of these compounds is not well understood. One of the most intriguing but least studied of these is the emission of volatile and reactive organosulfur compounds such as the foul and toxic gas carbonyl sulfide (COS) and volatile carbon disulfide (CS₂). Both are reportedly released by numerous plants and are proposed to make a significant contribution to the environmental sulfur burden (Haines et al., 1989). As a case in point, the Central American rainforest plant Stryphnodendron exelsum (Mimosaceae) is a sufficiently strong sulfur emitter that its location in the forest can be determined by odor (Haines et al., 1989). Furthermore, 40 taxa from nine genera within the subfamily Mimosoideae revealed that 29 taxa from six genera produced CS₂ and 19 of the 40 taxa produced COS (Piluk et al., 2001). It has been proposed that the COS and CS₂ are derived from a putative Cys lyase-mediated cleavage of djenkolic acid, an amino acid previously isolated from the plant (Piluk et al., 1998), but this has not been confirmed.We used Mimosa pudica (Leguminosae), a perennial shrub endemic to Brazil but now pantropical in its distribution (Howard, 1988), as a model to begin investigations of how this and related plants emit these highly reactive and corrosive compounds without themselves incurring tissue damage. Its various colloquial names, such as sensitive plant, touch-me-not, shy plant, and humble plant, among many others (Holm, 1977), derive from its seismonastic movements: in response to touch, water, shaking, wind, or warming, its leaves quickly close, slowly opening after an average of about 10 min (Song et al., 2014). It also displays nyctinasty, with its leaves closing or “sleeping” with the onset of darkness. These curious characteristics coupled with its small size have made the plant a convenient and popular attraction in schools, greenhouses, and other learning environments, where it is used to illustrate seismonasty.Our studies show that by using direct analysis in real time high-resolution mass spectrometry (DART-HRMS; Cody et al., 2005), it is possible to detect the compounds emitted by plant roots in situ. Using this method, it was revealed that both M. pudica plants germinated aseptically on agar and those germinated in soil emitted a variety of small molecules into the atmosphere at levels that were not detectable by human subjects. However, an odor detectable by humans could be sensed when the plant root was disturbed, with odor emission being dependent on the nature of the stimulus. Analysis of the chemical contributors to the odor revealed that, although the array of compounds observed to be produced by the roots was the same both before and after stimulation, emission of a subset of organosulfur compounds was increased when the roots were stimulated. Light and scanning electron microscope imaging studies revealed the presence of sac-like protuberances dotted along M. pudica seedling root shafts that collapsed when the roots were exposed to stimuli that elicited odor emission. The detection by energy-dispersive x-ray spectroscopy (EDS) of relatively high levels of K⁺ and Cl⁻ prior to root stimulation, on the one hand, and reductions in the levels of these species, on the other hand, implicate the involvement of these ions in the observed mechanostimulatory behavior.