Apfeltriebsucht – Stand des Wissens aus Theorie und Praxis

Phytoplasmas give rise to big economic losses in all plant growing branches worldwide. Well known in Europe is the apple proliferation disease. In order to control this disorder, the use of certificated planting material is recommended and other methods, such as vector-management and eradication of infected plants are necessary. The use of resistant cultivars or rootstocks may also be considered.     

Predicting species-habitat relationships: does body size matter?

Context

Allometric scaling laws are foundational to structuring processes from cellular to ecosystem levels. The idea that allometric relationships underlie species characteristic selection scales, the spatial scales at which species respond to landscape features, has recently been investigated, however, supporting empirical evidence is scarce.

Objectives

Lack of pattern can be explained by inaccurate estimation, low power, confounding factors, or absence of a relationship. In this paper, we evaluate the relationship between body size and species characteristic selection scales after overcoming limitations of previous study designs.

Methods

We conducted 1328 avian point counts across the state of Nebraska using the robust sampling design to account for imperfect detection. We used Bayesian latent indicator scale selection with N-mixture models to estimate species’ characteristic selection scales of six habitat features for 86 species. We propagated the uncertainty associated with assigning characteristic scales to a model of the relationship between body size and characteristic spatial scales.

Results

Species characteristic scales varied across habitat predictors, and varied in the uncertainty associated with selecting single characteristic scales. After propagating uncertainty our results do not support a relationship between species’ body size and the spatial scales at which they respond to landscape features.

Conclusions

As species abundance integrates birth, death, immigration, and emigration processes, each of which are influenced by ecological processes manifesting at various scales, we question whether a general allometric relationship should be expected. Our results suggest that selection may act on responses to specific environmental features, rather than responses to spatial scale per se.

     

Intra‐cohort cannibalism in early life stages of pikeperch

Cannibalism has been described in 390 teleost fish species belonging to 104 families. In rearing conditions, intra‐cohort cannibalism is one of the major bottlenecks during the early life stages of pikeperch (Sander lucioperca). This study aims to describe precisely the occurrence and the onset of cannibalism of this species during the first two post‐hatching months. In a first step, the cannibalistic behaviour was analysed through observations in three experiments. In each experiment, the number of cannibalistic cases was similar. From 14 to 48 days post‐hatching (dph), more than 60 % of prey ingestions were realized by tail‐first, but after 48 dph, the number of prey ingestions by head‐first increased. In a second step, the behavioural sequence exhibited to attack and to capture a conspecific was analysed, taking into account the size ratio between the cannibal and its prey. The behavioural sequence to capture was always the same, similar to a predatory sequence and it seems that the cannibal chose its prey about 10 s before attacking. Moreover, prey choice by a cannibal was based more on the size ratio between the cannibal and its prey than the previous activity of the potential prey. These new results could lead to solutions to decrease cannibalism in pikeperch rearing.     

What can we learn by studying dead fish fry?

This study investigated the influence of temperature (4, 8 and 12°C) on development and survival of brown trout (Salmo trutta) fry. The three aims of this study were: (a) to propose a typology of malformations; (b) to compare malformation types between live and dead fry and (c) to establish relationships between temperature and malformation occurrences. It was found 20 single malformations and 39 combinations of two or more malformations. Comparison between dead and live fry at different development stages (hatching, emergence and first food intake) showed that malformations of yolk sac were predominant at hatching and then decreased, while malformations of skeleton or multiple malformations were higher thereafter. All dead fry, and only 14% of live fry were malformed. Dead fry were mainly characterized by yolk sac malformations and multiple malformations whatever the temperature. Live fry showed a higher rate of skeleton malformations at 12°C, and the different types of malformations were equally represented at two other temperatures (4 and 8°C). To conclude, it is suggested that some malformations (yolk sac at hatching, yolk sac associated with skeleton malformations at emergence and skeleton at first food intake or combinations of malformations at all stages)might be lethal as they were founding dead fry and that temperature influences differently the occurrence of malformations.     

Histological evaluation of the elimination of Artemia nauplii from larval rearing protocols on the digestive system ontogeny of shi drum (Umbrina cirrosa L.)

The influence of the absence of Artemia nauplii from larval diet protocols on growth and digestive system ontogeny was studied using histological techniques in the shi drum (Umbrina cirrosa). One group of larvae was reared using the standard intensive rearing protocol, which offers a combination of enriched rotifers (Brachionus plicatilis), Artemia spp. nauplii and artificial diet (Std-group). Another group was reared using the same protocol, but without the offering of Artemia nauplii (group No-Artemia). The ontogenesis of the digestive system from hatching to metamorphosis was a very rapid process, and there were no differences between the two feeding regimes in the temporal appearance of the various components of the digestive system. The first organised presence of the hepatic and pancreatic tissue appeared at 2–3 d after hatching (dah), suggesting that these organs function from a very early developmental stage. In the No-Artemia larvae between 13 and 29 dah there was a reduction in the height of enterocytes in the intestinal mucosa, a progressive flattening of the primary intestinal folds in the anterior and posterior intestine and a decrease in lipid stores in the liver, suggesting a period of relative starvation. However, by the end of the study at 41 dah, there were no significant differences in body length, intestinal morphology or liver lipid stores between larvae reared under the two feeding regimes. The study suggests that the diet may influence the maturation and/or function, but not the ontogeny of the digestive system. Furthermore, the rapid differentiation of the digestive system in shi drum and the prompt recovery of the No-Artemia larvae from the symptoms of starvation by 29 dah, indicate a plasticity during ontogenesis and the ability of larvae to adapt to artificial diets at very early developmental stages.     

Genomic comparison of virulent and non‐virulent Streptococcus agalactiae in fish

Streptococcus agalactiae infections in fish are predominantly caused by beta‐haemolytic strains of clonal complex (CC) 7, notably its namesake sequence type (ST) 7, or by non‐haemolytic strains of CC552, including the globally distributed ST260. In contrast, CC23, including its namesake ST23, has been associated with a wide homeothermic and poikilothermic host range, but never with fish. The aim of this study was to determine whether ST23 is virulent in fish and to identify genomic markers of fish adaptation of S. agalactiae. Intraperitoneal challenge of Nile tilapia, Oreochromis niloticus (Linnaeus), showed that ST260 is lethal at doses down to 10² cfu per fish, whereas ST23 does not cause disease at 10⁷ cfu per fish. Comparison of the genome sequence of ST260 and ST23 with those of strains derived from fish, cattle and humans revealed the presence of genomic elements that are unique to subpopulations of S. agalactiae that have the ability to infect fish (CC7 and CC552). These loci occurred in clusters exhibiting typical signatures of mobile genetic elements. PCR‐based screening of a collection of isolates from multiple host species confirmed the association of selected genes with fish‐derived strains. Several fish‐associated genes encode proteins that potentially provide fitness in the aquatic environment.     

Chitosanases from Family 46 of Glycoside Hydrolases: From Proteins to Phenotypes

Chitosanases, enzymes that catalyze the endo-hydrolysis of glycolytic links in chitosan, are the subject of numerous studies as biotechnological tools to generate low molecular weight chitosan (LMWC) or chitosan oligosaccharides (CHOS) from native, high molecular weight chitosan. Glycoside hydrolases belonging to family GH46 are among the best-studied chitosanases, with four crystallography-derived structures available and more than forty enzymes studied at the biochemical level. They were also subjected to numerous site-directed mutagenesis studies, unraveling the molecular mechanisms of hydrolysis. This review is focused on the taxonomic distribution of GH46 proteins, their multi-modular character, the structure-function relationships and their biological functions in the host organisms.     

Levels of domestication in fish: implications for the sustainable future of aquaculture

The agricultural world today is dominated by a few domesticated mammal species, that is, animals modified from their wild ancestors through selective breeding in captivity for traits beneficial to human usages. As a result, a clear dichotomy exists between wild (from hunting) and domesticated mammals (produced in farms) used for human consumption. Similar to agriculture, aquaculture is often viewed as the only solution that can provide more fish products given that harvesting wild stocks have reached an upper limit. Aquaculture is considerably younger than agriculture relying on natural sources to farm numerous species. To better describe the diverse strategies for fish production, we propose a new classification comprising five levels of ‘domestication’ with 1 being the least to 5 being the most domesticated. Our classification places 70% of the 250 farmed finfish species recorded in the 2009 FAO database into levels 1, 2 and 3 representing a transitory form of fish production dependent on the availability of the wild resource. In contrast, only a few species, or more accurately populations, can be considered truly domesticated, similar to cattle or sheep. Based on this classification, two scenarios for the future of aquaculture are discussed: either the industry focuses on few truly domesticated species, similar to the path taken by agriculture, but avoiding its negative impacts or aquaculture proceeds with inter‐specific diversification by focusing primarily on the domestication of native species.