Niche-based modelling as a tool for predicting the risk of alien plant invasions at a global scale

Predicting the probability of successful establishment of plant species by matching climatic variables has considerable potential for incorporation in early warning systems for the management of biological invasions. We select South Africa as a model source area of invasions worldwide because it is an important exporter of plant species to other parts of the world because of the huge international demand for indigenous flora from this biodiversity hotspot. We first mapped the five ecoregions that occur both in South Africa and other parts of the world, but the very coarse definition of the ecoregions led to unreliable results in terms of predicting invasible areas. We then determined the bioclimatic features of South Africa's major terrestrial biomes and projected the potential distribution of analogous areas throughout the world. This approach is much more powerful, but depends strongly on how particular biomes are defined in donor countries. Finally, we developed bioclimatic niche models for 96 plant taxa (species and subspecies) endemic to South Africa and invasive elsewhere, and projected these globally after successfully evaluating model projections specifically for three well‐known invasive species (Carpobrotus edulis, Senecio glastifolius, Vellereophyton dealbatum) in different target areas. Cumulative probabilities of climatic suitability show that high‐risk regions are spatially limited globally but that these closely match hotspots of plant biodiversity. These probabilities are significantly correlated with the number of recorded invasive species from South Africa in natural areas, emphasizing the pivotal role of climate in defining invasion potential. Accounting for potential transfer vectors (trade and tourism) significantly adds to the explanatory power of climate suitability as an index of invasibility. The close match that we found between the climatic component of the ecological habitat suitability and the current pattern of occurrence of South Africa alien species in other parts of the world is encouraging. If species' distribution data in the donor country are available, climatic niche modelling offers a powerful tool for efficient and unbiased first‐step screening. Given that eradication of an established invasive species is extremely difficult and expensive, areas identified as potential new sites should be monitored and quarantine measures should be adopted.     

Sequential Analysis of the Organogenesis of Lucerne (Medicago sativa) Root Nodules Using Symbiotically-Defective Mutants of Rhizobium meliloti

Legume root-nodules are differentiated organs composed of peripheral tissue containing vascular bundles, and a central tissue in which are located the nitrogen-fixing bacteroids. The morphogenesis of these eukaryotic organs is induced by a prokaryotic organism, Rhizobium , which is amenable to genetic analysis. Inoculation of lucerne seedlings with leucine-requiring (Leu⁻) mutants of R. meliloti resulted in the formation of ineffective nodules. In these nodules, bacteria were not released from the infection threads into the host cytoplasm. When urea was provided as a nitrogen source to compensate for the defect in nitrogen fixation, the nodules became anatomically similar to those of effective nodules induced by the wild-type strain. The fact that these nodules were induced by bacteria which remained sequestered in infection threads indicates that nodule morphogenesis can be triggered from a distance. We hypothesize the existence of a bacterial nodule organogenesis-inducing principle (NOIP) which can cross the plant cell wall and plasmalemma.
In nitrogen-fixing nodules the central tissue exhibited a ploidy gradient, while in ineffective Leu⁻ nodules it was found to be monosomatic. The initiation of nodule formation is therefore independent of polyploidy. Supplying the defective plant-bacterial system with l -leucine or one of its precursors, α-ketoisovalerate or α-ketoisocaproate, caused the release of rhizobia into the plant cytoplasm and a restoration of nitrogen fixation. In the central tissue infected cells were polyploid and enlarged, and uninfected cells remained small and contained small nuclei. Therefore induction of differentiation of the central tissue requires the presence of bacteria in the cytoplasm. We hypothesize the role of a bacterial central tissue differentiation inducing principle (CTDIP) which cannot pass from cell to cell.     

GROWTH AND DEMOGRAPHY OF POPULATIONS OF BIOMPHALARIA PFEIFFERI (GASTROPODA, PLANORBIDAE) IN THE LABORATORY

The growth and demography of the freshwater snail Biomphalariapfeifferi, an intermediate host of the parasitic worm Schistosomamansoni in Eastern Zaire, were investigated in the laboratoryunder two conditions of crowding. Both individual and populationgrowth were depressed by crowding. Crowding reduced growth rateand all the variables and parameters related to reproduction(fecundity, instantaneous birth rate, net reproduction rate),but did not affect maximum size, survivorship, instantaneousdeath rate and life expectancy. The mechanism involved in theseeffects is likely to be exploitation competition for especiallyprofitable food items such as diatoms. (Received 10 November 1986;     

Adipokinetic hormone of the true armyworm, Pseudaletia unipuncta: immunohistochemistry, amino acid analysis, quantification and bioassay

Abstract A cluster of five to seven AKH-like immunoreactive cells lie in each lobe of the paired corpora cardiaca of the true armyworm, Pseudaletia unipuncta. These cells form a mesh work of immunoreactive processes within the corpora cardiaca, and immunoreactive tracts projecting posteriorly over the aorta.
Reversed-phase high performance liquid chromatography of extracts of the corpora cardiaca of P.unipuncta revealed a single large U.V. absorbent peak with a retention time identical to synthetic Manduca- AKH. Amino acid analysis of the contents of this peak yielded a composition identical to that of synthetic Manduca-AKH which was analysed in a parallel manner. Furthermore the material within the peak possessed adipokinetic activity when bioassayed in day 2 adult male P. unipuncta. The corpora cardiaca of similar individuals were found to contain approximately 17.6ng (17.6pmol) of Manduca-AKH equivalents per pair.
Injection of Manduca-AKH into 2-day-old adult male P.unipuncta resulted in a dose-dependent elevation in haemolymph lipid levels with a maximum level of 80–90μmg/μl obtained with 5–10 ng of Manduca-AKH. Continuous flight also elevated haemolymph lipid levels in day 4 adult males with a significant elevation evident in the first samples taken after 15 min of flight and lipid levels plateauing at approximately 100 μg/μl by about 60 min of flight.     

A comparative study of sex pheromone reception in the Hadeninae (Lepidoptera: Noctuidae)

Abstract A comparative study of the olfactory responses to pheromone compounds was performed in twenty-four species of Hadeninae. Electroantennograms (EAG) were recorded on male moths in response to thirty compounds and the response profiles of each species were analysed by factorial correspondence analysis. A limited number of molecules were found active and the most effective stimuli were Z9 tetradecenes and Z11 hexadecenes. The species of the Mythimna genus were most sensitive to aldehydes. Tholera decimalis did not respond to any of the molecules tested. The species belonging to the Mamestra and the Orthosia genera responded to a variety of molecules and no simple correlation was found between the genus and the EAG sensibility. Pheromone reception is discussed in relation to the taxonomy and the evolution of olfactory communication in Hadeninae.     

Adulthood and phylogenetic analysis in gastropods: character recognition and coding in shells of Lavigeria (Cerithioidea, Thiaridae) from Lake Tanganyika

In the study of gastropod shell morphology, determination of comparable ontogenetic stages is crucial, because all the states that various shell features go through during ontogeny are preserved on the shell. The protoconch/teleoconch transition and marks of episodic growth are among the few ways of defining discrete, comparable, growth stages. In gastropods with determinate growth the attainment of adulthood may provide additional shell markers permitting comparison among individuals and taxa. Adulthood is reflected in shell morphology in ways as diverse as shell deposition covering all the previous whorls and radically changing the shape of the shell through to slight changes in the trajectory of the suture. While the very prominent adulthood‐related changes of shell morphology have been used as systematic characters, the more moderate changes have not been studied in detail and their potential systematic value has been ignored. In this paper we give a detailed account of adult modifications of the shell appearing with cessation of growth. Our study group comprises eight closely related species of Lavigeria from Lake Tanganyika. We show that the ways adulthood is manifested are quite diverse. We describe eight characters of the aperture, the suture and the sculptural ornamentation. Character occurrence varies greatly among species. We show that characters appear in suites and that in many cases their appearance is connected to size. We use size as a proxy for adulthood and test whether character occurrence alone or its connection to size can help resolve species relationships. In both cases our characters confirm the monophyly of our ingroup and yield cladograms with various degrees of resolution of ingroup relationships. The coding method that yields the greater character congruence is the one that takes into consideration the connection between appearance of a character and size. This study demonstrates that ontogenetically correlated character transformations may nevertheless be phylogenetically independent. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 223?240.