Graph theory in action: evaluating planned highway tracks based on connectivity measures

Maintaining connectivity among local populations in a fragmented landscape is crucial for the survival of many species. For isolated habitat patches, stochastic fluctuations and reduced gene flow can lead to high risk of extinction. The connectivity of the landscape is especially crucial for the carabid species living in the fragmented forests of the Bereg plain (NE Hungary and W Ukraine) because a highway will be constructed through the plain. Our purpose is to (1) evaluate the impacts of three possible highway tracks, (2) suggest a solution that is realistic with less impact on connectivity than other plans and (3) discuss how to decrease the disadvantageous effects of each track. Our results, based on a network analysis of landscape graph of patches and ecological corridors, indicate that the intended highway could have deleterious consequences on forest-living carabids. Relatively simple actions, like the establishment of stepping stones, could compensate for the loss of habitat connectivity and promote the survival of carabids, or minor modifications in one possible track could diminish its adverse effects. While many other studies would be needed for a comprehensive assessment of the biotic impact of the highway, we provide an example on the usefulness of network analysis for land use management. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

ROS and NO production in compatible and incompatible tomato-<Emphasis Type="Italic">Meloidogyne incognita</Emphasis> interactions

Nitric oxide (NO) has been shown to be an essential regulatory molecule in plant response to pathogen infection in synergy with reactive oxygen species (ROS). At the present, nothing is known about the role of NO in disease resistance to nematode infection. We used a resistant tomato cultivar with different sensitivity to avirulent and virulent populations of the root-knot nematode Meloidogyne incognita to investigate the key components involved in oxidative and nitrosative metabolism. We analyzed the superoxide radical production, hydrogen peroxide content, and nitric oxide synthase (NOS)-like and nitrate reductase activities, as potential sources of NO. A rapid NO accumulation and ROS production were found at 12 h after infection in compatible and incompatible tomato-nematode interactions, whereas the amount of NO and ROS gave different results 24 and 48 h after infection amongst compatible and incompatible interactions. NOS-like arginine-dependent enzyme rather than nitrate reductase was the main source of NO production, and NOS-like activity increased substantially in the incompatible interaction. We can envisage a functional overlap of both NO and ROS in tomato defence response to nematode invasion, NO and H₂O₂ cooperating in triggering hypersensitive cell death. Therefore, NO and ROS are key molecules which may help to orchestrate events following nematode challenge, and which may influence the host cellular metabolism.     

Reaction of glucosinolate-myrosinase defence system in <Emphasis Type="Italic">Brassica</Emphasis> plants to pathogenicity factor of <Emphasis Type="Italic">Sclerotinia sclerotiorum</Emphasis>

The glucosinolate-myrosinase defence system, specific to Brassicales plants, produces toxic volatile compounds during mechanical injury or pathogen attack. The reaction of this system to oxalic acid, known as a pathogenicity factor of Sclerotinia sclerotiorum, is not fully understood. The hydrolysis of glucosinolates was studied at varying conditions in the presence of oxalic acid in the substrate. In a bioassay, colonies of the pathogen were exposed to volatiles from hydrated mustard powder used as a myrosinase and glucosinolate source. The glucosinolate-myrosinase (GSL-M) system was activated in the presence of oxalic acid at a concentration and pH similar to that expected in vivo. Volatile production was inhibited only when the pH fell to 3 or below. It is unlikely that oxalic acid plays a significant role in disarming the GSL-M system during infection of Brassica hosts.     

Integrating animal movement with habitat suitability for estimating dynamic migratory connectivity

Context

High-resolution animal movement data are becoming increasingly available, yet having a multitude of empirical trajectories alone does not allow us to easily predict animal movement. To answer ecological and evolutionary questions at a population level, quantitative estimates of a species’ potential to link patches or populations are of importance.

Objectives

We introduce an approach that combines movement-informed simulated trajectories with an environment-informed estimate of the trajectories’ plausibility to derive connectivity. Using the example of bar-headed geese we estimated migratory connectivity at a landscape level throughout the annual cycle in their native range.

Methods

We used tracking data of bar-headed geese to develop a multi-state movement model and to estimate temporally explicit habitat suitability within the species’ range. We simulated migratory movements between range fragments, and calculated a measure we called route viability. The results are compared to expectations derived from published literature.

Results

Simulated migrations matched empirical trajectories in key characteristics such as stopover duration. The viability of the simulated trajectories was similar to that of the empirical trajectories. We found that, overall, the migratory connectivity was higher within the breeding than in wintering areas, corroborating previous findings for this species.

Conclusions

We show how empirical tracking data and environmental information can be fused for meaningful predictions of animal movements throughout the year and even outside the spatial range of the available data. Beyond predicting migratory connectivity, our framework will prove useful for modelling ecological processes facilitated by animal movement, such as seed dispersal or disease ecology.

     

Effects of landscape urbanization on magpie occupancy dynamics in France

Responses of species to landscape modifications are generally documented through their distribution at a given time along an intensity gradient of land transformation. By focusing on patterns, we are limited to infer ecological processes occurring within a system and its response to environmental disturbances which can further change over time. Using diachronic datasets at the scale of France, we analyzed the spatial responses of the black-billed magpie, which has recently colonized cities, to landscape urbanization. This study applied recently developed statistical approaches incorporating detection uncertainty of the magpie, based on the capture-recapture statistical framework. We tested whether, and how, extinction and colonization mechanisms influenced variations of magpie occupancy from 2001 to 2005. In addition, we assessed the importance of the recent urbanization of the French countryside in determining population dynamics. Overall, our analysis proved that the proportion of urban areas and recent urbanization in France led to an increase in the probability of magpie occupancy. Unexpectedly, the species is concomitantly disappearing from the countryside, leading to a rapid change in the distribution of the species. This study stressed the importance of incorporating detection uncertainty in inference process about spatial dynamics. Overall, we show how useful it is to account for the dynamic evolution of the landscape in ecological studies.     

Incidence and etiology of postharvest fungal diseases of loquat fruit (<Emphasis Type="Italic">Eriobotrya japonica</Emphasis> (Thunb.) Lindl. cv. ‘Algerie’) in Alacant province (Spain)

‘Algerie’ is currently the most important loquat cultivar in Spain. The incidence and etiology of postharvest diseases affecting this cultivar were determined under local conditions. Latent and wound pathogens were evaluated for two consecutive seasons on commercially grown loquats from two orchards. Healthy loquats were either surface-disinfected or artificially wounded in the rind and placed in humid chambers at 20 °C for up to 5 weeks. Additionally, decay was assessed on commercially-handled loquats stored at 5 °C for up to 20 weeks. The most frequent disease was caused by Alternaria alternata, followed by Penicillium expansum. These two pathogens were present on fruit assessed for all types of infection. Moreover, decay caused by Botrytis cinerea was abundantly observed on both wounded and cold-stored fruit, while Colletotrichum gloeosporioides was frequently found on surface-disinfected fruit. Other pathogens that were observed causing latent infection to a lesser extent included Pestalotiopsis clavispora and Diplodia seriata. Common isolates were identified by macroscopic and microscopic morphology and/or DNA amplification and sequencing. Pathogenicity of selected isolates was demonstrated by fulfilling Koch’s postulates and disease development was assessed on artificially inoculated loquats stored at either 20 or 5 °C.     

Genetic characterization of <Emphasis Type="Italic">Pepino mosaic virus</Emphasis> isolates from Belgian greenhouse tomatoes reveals genetic recombination

Over a period of a few years, Pepino mosaic virus (PepMV) has become one of the most important viral diseases in tomato production worldwide. Infection by PepMV can cause a broad range of symptoms on tomato plants, often leading to significant financial losses. At present, five PepMV genotypes (EU, LP, CH2, US1 and US2) have been described, three of which (EU, LP and US2) have been reported in Europe. Thus far, no correlation has been found between different PepMV genotypes and the symptoms expressed in infected plants. In this paper, the genetic diversity of the PepMV population in Belgian greenhouses is studied and related to symptom development in tomato crops. A novel assay based on restriction fragment length polymorphism (RFLP) was developed to discriminate between the different PepMV genotypes. Both RFLP and sequence analysis revealed the occurrence of two genotypes, the EU genotype and the CH2 genotype, within tomato production in Belgium. Whereas no differences were observed in symptom expression between plants infected by one of the two genotypes, co-infection with both genotypes resulted in more severe PepMV symptoms. Furthermore, our study revealed that PepMV recombinants frequently occur in mixed infections under natural conditions. This may possibly result in the generation of viral variants with increased aggressiveness.     

Aloe ring spot,a new disease of aloe caused by <Emphasis Type="Italic">Haematonectria haematococca</Emphasis> (Berk. &; Broome) Samuels &; Nirenberg (anamorph: <Emphasis Type="Italic">Fusarium</Emphasis> sp.)

A ring spot disease of Aloe vera was found on leaves of potted seedlings of Aloe vera in Hachijojima and Chichijima Islands, Tokyo. From tissue of ring spot lesions, a fungus producing Fusarium-type conidia was consistently isolated. After 1 month, reddish perithecia of nectriaceous fungus had formed on the colonies of this isolate on PDA. These nectriaceous and Fusarium fungi were identified as Haematonectria haematococca and Fusarium sp., respectively. From a single ascospore isolation, the former was confirmed to be the teleomorph of the Fusarium sp. Typical ring spot lesions were reproduced by artificial inoculations using single ascospore and single conidium isolates. Inoculations of five species of genus Aloe revealed that they were highly susceptible except for A. arborescens. This is the first report of a disease on Aloe caused by H. haematococca (anamorph: Fusarium sp.) in Japan, and it was named aloe ring spot.     

Foliar application of the exogenous plant hormones at pre-blooming stage improves flowering and fruiting in cashew (<Emphasis Type="Italic">Anacardium occidentale</Emphasis> L.)

The problem of declining tree yield has led to an investigation into the effectiveness of foliar application of exogenous hormones to improve flowering, fruit set, and fruit retention in cashew. Five exogenous hormones, one Gibberellic Acid (GA₃) and four Auxins (IAA, IBA, NAA, and 2,4-D) at seven different rates of application (0 mg L⁻¹, 10 mg L⁻¹, 25 mg L⁻¹, 50 mg L⁻¹, 100 mg L⁻¹, 250 mg L⁻¹, and 500 mg L⁻¹) were tested on six yield-related components of the two Brazilian cashew genotypes. This trial was a factorial split-split-plot design with each treatment replicated five times within a tree and three replications (three trees) per genotype. Responses varied significantly between exogenous hormones, concentrations and genotypes. The cashew plants used showed hormone-specific and optimum concentration response patterns. Of the five exogenous hormones tested, GA₃ was most effective as its application at 50–100 mg L⁻¹ gave five-fold improvements in flowering (precocity and number of hermaphrodite flowers) and fruiting, and about 69% increase in fruit retention ability and 25% in nut size. Panicles treated with GA₃ also produced relatively bigger nuts compared to the untreated. Days to flowering was found to be hormone sensitive, while production of hermaphrodite flowers, fruit set, and nut development tended to be concentration specific. The GA₃ exhibited a broad concentration tolerance among the five exogenous hormones investigated. Our data showed that using GA₃ at 50 mg L⁻¹ will enhance flowering precocity, shorten flowering duration, increase production of hermaphrodite flowers and fruit set significantly, and resultant nuts develop optimally with high percentage retention. Thus, it suggests cashew yield could be increased by exogenous foliar application of GA₃ at 50–100 mg L⁻¹ at pre-blooming stage.