Effects of an exotic invasive macrophyte (tropical signalgrass) on native plant community composition,species richness and functional diversity

1. The issue of freshwater species being threatened by invasion has become central in conservation biology because inland waters exhibit the highest species richness per unit area, but apparently have the highest extinctions rates on the planet. 2. In this article, we evaluated the effects of an exotic, invasive aquatic grass (Urochloa subquadripara– tropical signalgrass) on the diversity and assemblage composition of native macrophytes in four Neotropical water bodies (two reservoirs and two lakes). Species cover was assessed in quadrats, and plant biomass was measured in further quadrats, located in sites where tropical signalgrass dominated (D quadrats) and sites where it was not dominant or entirely absent (ND quadrats). The effects of tropical signalgrass on macrophyte species richness, Shannon diversity and number of macrophyte life forms (a surrogate of functional richness) were assessed through regressions, and composition was assessed with a DCA. The effects of tropical signalgrass biomass on the likelihood of occurrence of specific macrophyte life forms were assessed through logistic regression. 3. Tropical signalgrass had a negative effect on macrophyte richness and Shannon and functional diversity, and also influenced assemblage composition. Emergent, rooted with floating stems and rooted submersed species were negatively affected by tropical signalgrass, while the occurrence of free‐floating species was positively affected. 4. Our results suggest that competition with emergent species and reduction of underwater radiation, which reduces the number of submersed species, counteract facilitation of free‐floating species, contributing to a decrease in plant diversity. In addition, homogenisation of plant assemblages shows that tropical signalgrass reduces the beta diversity in the macrophyte community. 5. Although our results were obtained at fine spatial scales, they are cause for concern because macrophytes are an important part of freshwater diversity.     

Changes in sperm tail development associated with Y chromosome meiotic drive leading to an excess of males in the medfly Ceratitis capitata (Diptera: Tephritidae)

The Mediterranean fruit fly Ceratitis capitata (Wied.) normally produces the sexes in equal ratio but strains carrying the Y chromosome meiotic drive MP (male‐producing) factor show an excess of males. This is associated with a loss of sperm, and abnormal sperm structure in terms of multiple axonemes, atypical numbers of mitochondrial derivatives, and sometimes an incorrect initial orientation of paracrystalline bodies to the axoneme. Sperms are bundled together within spermatocysts, and those with depleted content and abnormalities occur in the same MP testes as normal spermatocysts. The maximum number of sperms per cyst in control strains was 256, each with a single axoneme originating from a single centriole (kinetosome). The maximum per cyst in MP strains was also 256 but MP cysts contained up to 300 axonemes, providing evidence of multiplication of centrioles. The structural changes in MP sperm are discussed in relation to similar abnormalities reported in the mosquito Aedes aegypti inheriting the Y chromosome meiotic drive haplotype MD. The evolutionary significance of this phenomenon is considered. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 351–359.     

Personality disorder: a new global perspective

Personality disorder is now being accepted as an important condition in mainstream psychiatry across the world. Although it often remains unrecognized in ordinary practice, research studies have shown it is common, creates considerable morbidity, is associated with high costs to services and to society, and interferes, usually negatively, with progress in the treatment of other mental disorders. We now have evidence that personality disorder, as currently classified, affects around 6% of the world population, and the differences between countries show no consistent variation. We are also getting increasing evidence that some treatments, mainly psychological, are of value in this group of disorders. What is now needed is a new classification that is of greater value to clinicians, and the WPA Section on Personality Disorders is currently undertaking this task.     

Translocation of 32P between interacting mycelia of a wood-decomposing fungus and ectomycorrhizal fungi in microcosm systems

Interactions between saprotrophic and ectomycorrhizal fungi have been largely ignored, although their mycelia often share the same microsites. The mycelial systems show general similarity to each other and, although the enzymatic potential of the saprotrophic fungi is generally considered to be higher, the importance of organic nutrient sources to ectomycorrhizal fungi is now widely accepted. In the experiments described here, nutritional interactions involving transfer of elements from one mycelium to the other have been monitored dynamically using radioactive tracers and a non-destructive electronic autoradiography system. Microcosms were used in which mycelial systems of the ectomycorrhizal fungi Suillus variegatus and Paxillus involutus , extending from Pinus sylvestris host plants, were confronted with mycelia of the saprotroph Hypholoma fasciculare extending from wood blocks. The fungi showed a clear morphological confrontation response. The mycorrhizal mycelium often formed dense patches over the Hypholoma mycelia. Up to 25% of the ³²P present in the Hypholoma mycelium was captured by the mycorrhizal fungi and translocated to the plant host within 30 d. The transfer of ³²P to the saprotroph from labelled mycorrhizal mycelium was one to two orders of magnitude lower. The significance of this transfer as a 'short cut' in nutrient cycling is discussed.     

Fitness consequences of potential assortative mating inside and outside a hybrid zone in Chorthippus parallelus (Orthoptera: Acrididae): implications for reinforcement and sexual selection theory

We have examined the fitness consequences of random and potentially non-random matings within two populations taken from inside, and two from outside a hybrid zone in Chorthippus parallelus. When given the opportunity to mate non-randomly, females from all populations laid egg pods more quickly than females obliged to mate at random. A range of fitness parameters measured on the offspring did not show increased fitness following potential non-random mating for any population. However, in non-hybrid populations, the sons of non-randomly mated females had about twice the mating success of the sons of those females forced to mate at random, suggesting the existence of heritable variation for male reproductive success. Hybrid dysfunction did not occur amongst the offspring of randomly mated hybrid females, demonstrating that the lack of dysfunction within these populations is not due to the evolution of assortative mating within them.     

REPLICATED TRIANGLE TESTS: EFFECT OF FEED-BACK AND PRODUCT COMPARISON ON PERFORMANCE

The feed-back procedure consists of informing assessors of the quality of their response (correct or incorrect) after each triangle test. This procedure showed a contrasted effect according to assessors'detection abilities. A decrease in performance was observed for assessors who had low detection abilities whereas a slight increase was observed for assessors who had higher detection abilities. When the feed-back procedure is followed by a comparison by tasting of the two products, the increase in performance from the beginning to the end of the session is larger than that of both feed-back and control (no information) groups. We suggest that information inference from previous tests, which allows assessors to perform better at subsequent tests, is facilitated by the presence of a double information (feed-back and product comparison). This effect might be due to an attentional process allowing assessors to focus their attention on the difference between the two products. An attempt was made to model learning effect by variation of attentional weights.     

Within-island geographic variation of the dangerous Taiwanese snake, Trimeresurus stejnegeri, in relation to ecology

Multivariate analysis shows that geographic variation occurs in the scalation and body proportions of the dangerously venomous snake Tritneresurus stejnegeri , within the island of Taiwan. Canonical correlation analysis reveals a high correlation between constellations of morphological characters and ecological factors. Numerical hypothesis testing, using partial Mantel tests, provides evidence of a causal relationship with ecology. Head shape was found to be primarily associated with mean annual temperature and altitude, and head scalation with the annual range of temperature. Body scalation was found to be influenced by altitude, mean annual temperature and mean annual rainfall. Tail length is primarily associated with the range of temperature and rainfall and secondarily with the mean annual temperature and altitude. Geographic proximity was found to be less important in the explanation of the observed geographic pattern than some ecological factors, supporting the hypothesis of an ecogenetic origin of morphological variation.     

Fine Structure Observations of Phagotrophic Activity By Plasmodia of Physarum Polycephalum

ABSTRACT. Scanning electron microscopic observations of feeding plasmodia show three characteristic features: 1) extension of multilobed pseudopodia protruding from the leading edge of the plasmodium as it advances onto the surface of a food particle, 2) confluence of the lobes to form a sheath-like pseudopodium attached to the surface of the food particle, and 3) protrusion of small nodules with thin lamellar projections from the leading edge of the plasmodium. Sections through freeze-dried preparations of the feeding plasmodium exhibit a highly convoluted under surface in contact with loosened starch grains that appear to be released by extracellular digestion. the cytoplasm, viewed by transmission electron microscopy, contains branched, internally penetrating canals (ca. 2 μm wide) enclosing engulfed starch grains. Starch grains in the deeper part of the canals are more electron dense and appear to be digested. Micropseudopodia (70-80 nm dia.), projecting from the surface of the canals, protrude toward and into the ingested starch grains. Digestive marker enzyme (acid phosphatase) activity was detected cytochemically in food particles penetrated by micropseu-dopodia indicating a digestive role for these structures not reported previously.