Effects of multiple fires on tree invasion in montane grasslands

There is circumstantial evidence that grasslands on the Bunya Mountains were once maintained by Aboriginal burning, and with lack of fire under European management are being colonised by trees. To assess the efficacy of burning for maintaining grasslands, 119 fires were lit between 1996 and 2006. The total area of unburnt grasslands decreased by 27%, while grasslands burnt at least once decreased by 1%. The density of invading trees was recorded from fixed plots on 23 grasslands burnt between one and six times. Cassinia was virtually eliminated and the density of the Rainforest species guild slowly but continually declined. Acacia irrorata exhibited a humped response, with initial increases resulting from vegetative resprouting and gradual decline with persistent burning. Phyllodinous Acacia and Woodland trees were the least fire sensitive guilds, having stable or increased density with repeated burning. Multi-factor regression modelling detected no significant relationships between changes in woody plant density and the interval between fires, fire intensity, the initial density of large trees, an index of soil moisture, or the cumulative number of fires for any species guild. The survivorship of both Cassinia and Rainforest guilds was significantly lower with summer burning than winter burning, but a seasonal effect of burning was not evident for other guilds. The findings suggest that regardless of fire conditions, frequent burning will reduce the number of adult trees, maintain resprouts in an immature state, facilitate further fire and reduce the rate of grassland loss. Woodland species are especially resilient to fire, and burning to maintain grassy ecosystems will be most successful where the main colonisers are rainforest species and burning is conducted in summer. The findings suggest that the montane grasslands of the Bunya Mountains were maintained by anthropogenic burning and active fire management will prolong their existence.     

Protocol: Streamline cloning of genes into binary vectors in Agrobacterium via the Gateway® TOPO vector system

Background

Freezing tolerance is an important factor in the geographical distribution of plants and strongly influences crop yield. Many plants increase their freezing tolerance during exposure to low, nonfreezing temperatures in a process termed cold acclimation. There is considerable natural variation in the cold acclimation capacity of Arabidopsis that has been used to study the molecular basis of this trait. Accurate methods for the quantitation of freezing damage in leaves that include spatial information about the distribution of damage and the possibility to screen large populations of plants are necessary, but currently not available. In addition, currently used standard methods such as electrolyte leakage assays are very laborious and therefore not easily applicable for large-scale screening purposes.

Results

We have performed freezing experiments with the Arabidopsis accessions C24 and Tenela, which differ strongly in their freezing tolerance, both before and after cold acclimation. Freezing tolerance of detached leaves was investigated using the well established electrolyte leakage assay as a reference. Chlorophyll fluorescence imaging was used as an alternative method that provides spatial resolution of freezing damage over the leaf area. With both methods, LT₅₀ values (i.e. temperature where 50% damage occurred) could be derived as quantitative measures of leaf freezing tolerance. Both methods revealed the expected differences between acclimated and nonacclimated plants and between the two accessions and LT₅₀ values were tightly correlated. However, electrolyte leakage assays consistently yielded higher LT₅₀ values than chlorophyll fluorescence imaging. This was to a large part due to the incubation of leaves for electrolyte leakage measurements in distilled water, which apparently led to secondary damage, while this pre-incubation was not necessary for the chlorophyll fluorescence measurements.

Conclusion

Chlorophyll fluorescence imaging is an alternative method to accurately determine the freezing tolerance of leaves. It is quick and inexpensive and the system could potentially be used for large scale screening, allowing new approaches to elucidate the molecular basis of plant freezing tolerance.     

Effect of Geotrichum candidum protein substitution in pelleted fish feed on the growth of rainbow trout (Salmo gairdneri Rich.) and on utilization of the diet

Three experiments were conducted with rainbow trout to determine if Geotrichum candidum GC single cell protein could replace 100, 75 or 50% of fish meal in a pelleted diet. When the fish meal was completely replaced by GC the fish growth was retarded after 3 weeks of the experiment. With the larger fish (individual weight 47–54 g) in the short trial there were significant differences between fish fed the control diet (fish meal) and those fed the 75% substitution of GC diet. The most remarkable differences in fish growth appeared in a 42-day trial with small fish (5 g individual weight) when fish groups fed diets with 0.50 and 75% replacement gave significantly different results (P < 0.05), being 93,9, 46.6 and 34.2% gain, with feed coefficients of 1.49, 2.77 and 3.67, respectively. With large fish fed diets with 0,50 and 75% GC replacement, apparent digestibility of protein was 64.7, 68.2 and 37.5%, but fat digestibility was 79.5, 91.1 and 81.0%, respectively. No significant differences in amounts of free plasma amino acid (PAA) were found between rainbow trout fed diets with 0 or 50% substitution, but there was a marked decrease in PAA in the group fed the diet with 75% GC substitution. Analysis of chosen heavy metals was made on diets, fish and faeces, and Cu in particular was found not to be accumulated in the fish body.     

Spatial and temporal patterns of vertical distribution for three planktivorous fishes in Lake Washington

Abstract – We sampled three limnetic fish species: juvenile sockeye salmon (Oncorhynchus nerka), three‐spine stickleback (Gasterosteus aculeatus) and longfin smelt (Spirinchus thaleichthys) in Lake Washington to quantify species‐specific patterns of diel vertical migration (DVM). Catch‐per‐unit‐effort data analysed from 15 years of midwater trawling documented seasonal and diel differences in vertical distributions for each species. These results were consistent with the hypothesis that the patterns of DVM in Lake Washington were affected by life history, size and morphology. Sockeye salmon showed clear DVM in spring but essentially no DVM in fall, remaining in deep water, whereas three‐spine sticklebacks were prevalent at the surface at night in both seasons. In fall, distribution patterns may be explained by differences in thermal performance (e.g., sticklebacks favouring warm water), but the patterns were also consistent with inter‐specific differences in predation risk. Younger sockeye salmon and longfin smelt were present in greater proportions higher in the water column during dusk and night periods than older conspecifics. Compared with sockeye salmon, the greater use by three‐spine sticklebacks of surface waters throughout the diel cycle during weak thermal stratification in spring was consistent with the hypothesis that sticklebacks’ armour reduces predation risk, but use of this warmer, metabolically beneficial stratum may also have promoted growth. This study illustrates variation in the vertical distribution of three sympatric planktivores and offers broader implications for the DVM phenomenon and applied lake ecology.     

Waste potato dumps as sources of insects contaminated with soft rot coliform bacteria in relation to re-contamination of pathogen-free potato stocks

Summary Insects belonging to 12 genera in the Order Diptera, found at two large waste potato dumps in Scotland. were contaminated with soft rot coliform bacteria. In 1973, 5.7% and 3.2% and in 1974, 4.8% and 4.1% of the insects caught at each site yielded these organisms. The bacteria were identified mainly asErwinia carotovora var.carotovora, though some isolates wereErwinia carotovora var.atroseptica. Isolations from potato dump waste showed that at the time when fly activity was greatest the majority of soft rot coliforms in the waste wereE. carotovora var.carotovora, despite the fact that tubers originally forming the dumps were almost certainly infected mostly withE. carotovora var.atroseptica. Contaminated insects could readily transmit soft rot coliforms to damaged areas on the aerial parts of potato plants. It is suggested that potato stocks freed from these organisms by the stem cutting procedure could become re-contaminated by insects that disperse from potato dumps.

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Zusammenfassung Zw?lf Arten von Insekten der Gattung Diptera, periodisch gesammelt auf zwei grossen Kartoffelabfallhaufen in Schottland, waren mit koliformen Nassf?ulebakterien kontaminiert (Tab. 2, 3, 5 und 6). Nur zwei der Arten galten vorher als m?gliche Ubertr?ger dieser Organismen. 1973 waren 4,6% der an den beiden Orten w?hrend der Saison gesammelten Insekten mit diesen Organismen behaftet, 1974 waren es 4,5%. Nicht weniger als 9,6% der Insekten waren bei einigen F?ngen im Jahre 1973 und 14,7% im Jahre 1974 Tr?ger von Nassf?uleErwinia sp. Die Fruchtfliegen (Parascaptomyza sp. undDrosophila spp.) waren 1973 die am h?ufigsten kontaminierten Insekten (Tab. 2 und 3). Diese Gruppe von Insekten war auch 1974 meistens kontaminiert, aber am h?ufigsten wurden die Bakterien vonScatophaga spp. undDelia spp. (Tab. 5 und 6) isoliert. Sowohl 1973 als auch 1974 wurdeErwinia carotovora var.carotovora (in der FolgeE. carotovora genannt) h?ufiger von den Insekten isoliert alsErwinia carotovora var.atroseptica (in der FolgeE. atroseptica genannt) (Tab. 1 und 4), obwohl die Knollen. die ursprünglich den Abfallhaufen ausmachten, fast sicher meistens mitE. atroseptica infiziert waren. Das Verh?ltnis vonE. carotovora zuE. atroseptica, isoliert von Insekten beider Haufen, war 1973 9,5∶1 (13,5∶1 und 5,5∶1 je Abfallhaufen) und 1974 3,8∶1 (2,7∶1 und 6,8∶1 für die beiden Orte).E. atroseptica wurde 1973 nur früh in der Vegetationszeit (vor dem 30. Juli) von den Insekten isoliert (Tab. 1), 1974 nur früh (vor dem 30. Juli) oder sp?t in der Vegetationszeit (nach dem 10. Oktober) (Tab. 4).E. carotovora dagegen konnte in beiden Jahren über die ganze Vegatationszeit isoliert werden (Tab. 1 und 4). Die Wiedergewinnung vonE. atroseptica von Insekten war mit dem Vorhandensein von frisch abgelagerten faulen Knollen zur Zeit. wenn die Insekten gesammelt werden. verbunden. EinzigE. carotovora wurde von Insekten isoliert. die zu einer Zeit gesammelt wurden, wenn auf den Abfallhaufen nur?lteres verfaulendes Material vorhanden war. Isolationen von faulenden Ueberresten, die 1975 dem Abfallhaufen entnommen wurden (Tab. 7), zeigten, dass sowohlE. carotovora als auchE. atroseptica in der Regel das ganze Jahr vorhanden waren.E. atroseptica herrschte früh im Jahr (Januar bis Juni) vor und an einem Ort auch sp?t in der Zeit der Musterentnahme (Oktober bis Dezember).E. carotovora war von Juni bis Oktober der am meisten isolierte Organismus. Das Vorherrschen vonErwinia carotovora var.atroseptica war mit dem Vorhandensein von frisch weggeworfenen Kartoffelknollen früh und sp?t in der Zeit der Musterentnahme verbunden.E. carotovora schien in den faulenden Knollen l?nger zu überleben und war der am meisten isolierte Organismus aus ?lterem verwesendem Material. Die Verh?ltniswerte vonE. carotovora zuE. atroseptica. isoliert von Insekten. waren h?her alsjene, die für das verfaulende Material aus den Abfallhaufen gefunden wurden. Es ist anzunehmen, dass die Insekten selbst einen selektiven Einfluss zu Gunsten vonE. carotovora ausüben. Von einem der Abfallhaufen gesammelten Insekten übertrugen im GlashausE. carotovora sogleich auf verletzte Kartoffelstengel. Man nimmt an, dass Kartoffelbest?nde. die mit Hilfe des Stengelschnittes von koliformen Nassf?uleerregern befreit wurden, durch Insekten, die von Kartoffelabfallhaufen kommen, wieder verseucht werden k?nnen.

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Résumé 12 genres d'insectes appartenant à l'ordre des Diptères, capturés périodiquement en Ecosse. sur deux grands tas de déchets de pommes de terre se sont révélés être contaminés par des bactéries coliformes. agents de la pourriture molle (tableaux 2, 3, 5 et 6). Auparavant, seuls 2 genres avaient été cités comme vecteurs possibles de ces microorganismes. En 1973, 4.6% des insectes capturés aux 2 endroits, et en cours de saison. portaient ces parasites de la pomme de terre. En 1974. 4,5% étaient également contaminés. Pour l'ensemble de ces captures. il y a eu 9.6% des insectes en 1973. et 14.7% en 1974 qui portaientErwinia sp. Les mouches des fruits (Parascaptomyza etDrosophila spp.) ont été le plus fréquemment contaminés en 1973 (tableaux 2 et 3). Ce groupe d'insectes était également atteint en 1974. mais les bactéries on été plus fréquemment isolées à partir deScatophaga spp. etDélia spp. (tableaux 5 et 6). En 1973 et 1974.Erwinia carotovora var.carotovora (dans la suiteE. carotovora) a été plus fréquemment isolé de ces insectes qu'Erwinia carotovora var.atroseptica (dans la suiteE. atroseptica) (tableaux 1 et 4) bien que les tubercules constituant à l'origine les tas de déchets étaient certainement plus infestés parE. atroseptica. Le rapport entreE. carotovora etE. atroseptica pour les isolements sur insectes provenant des deux endroits a été 9,5/1 (respectivement 13.5/1 et 5.5/1 pour chacun des tas de déchets) en 1973 et 3,8/1 (2,7/1 et 6,8/1) en 1974.E. atroseptica n'a été isolé que t?t dans l'année (avant le 30 juillet) en 1973 (tableau 1) et 1974 (tableau 4) elle l'a été précocement (avant le 30 juillet) ou tardivement (après le 10 octobre).E. carotovora, par contre, l'a été durant toute la saison pendant les deux années (tableuaux 1 et 4) l'isolement d'E. atroseptica est lié au moment de la capture des insectes, à la présence de tubercules nouvellement pourris lors de la mise en tas. Par contreE. carotovora a été isolé à partir des insectes capturés sur les tas où il n'y avait que du matériel présentant des pourritures plus agées. En 1975, des isolements effectués sur les tas de déchets ont montré qu'E. carotovora etE. atroseptica étaient habituellement présents toute l'année (tableau 7).E. atroseptica était prédominante en début de saison (de janvier à juin). II n'y a eu qu'un seul cas où on l'a observé plus tardivement durant la période d'échantillonage (octobre à décembre).E. carotovora a été le principal organisme isolé de juin à octobre. La prédominance d'E. atroseptica était associée à la présence de tubercules nouvellement entreposés précocement et tardivement durant la période d'échantillonage.E. carotovora semblait subsister plus longuement dans les tubercules pourris et était le principal organisme isolé à partir de matériel altéré le plus agé. Les rapportsE. carotovora surE. atroseptica obtenus à partir des isolements effectués sur insectes ont été plus élévés que ceux trouvés à partir du matériel pourri en provenance des tas. Les auteurs suggèrent que les insectes euxmêmes peuvent exercer une action sélective en faveur d'E. carotovora. Les insectes collectés à partir d'un des tas peuvent transmettre facilementE. carotovora aux pommes de terre se trouvant en serre et dont les tiges sont endommagées. Les auteurs suggèrent que les lots de pommes de terre indemnes de bactéries coliformes grace au procédé de bouturage peuvent être à nouveau recontaminé à partir des tas de déchets de pommes de terre et par l'intermédiaire des insectes.

     

Associations between canine juvenile weight gain and coxofemoral joint laxity at 16 weeks of age

OBJECTIVE: Evaluation of the relationship between canine weight gain from 6 to 15 weeks of age and passive coxofemoral joint (CFJ) laxity at 16 weeks of age. STUDY DESIGN: Longitudinal cohort study. ANIMALS: Full- or half-sibling hounds (n = 56). METHODS: Hounds were weighed weekly from 6 to 15 weeks of age. Individual average daily gain (ADG) was calculated for each week (weekly) and for the study (overall). PennHIP distraction index (DI) was determined for each CFJ at 16 weeks. Mixed effects linear models were evaluated for associations of DI (highest and mean) with 15-week weight and ADGs (actual or normalized). Left and right DIs were compared with a Student's paired t-test. Significance was set at P<.05. Trends were considered at P<.10. RESULTS: Mean (+/-SD) 16-week DI score and 15-week weight was 0.67 +/- 0.16 and 12.5 +/- 1.8 kg, respectively. Within animal left and right DIs were not significantly different. There were no significant associations between DI and any of the weight gains evaluated. There was a trend for a negative relationship between normalized 14-week ADG and DI in one statistical model. CONCLUSIONS: Weight gain from 6 to 15 weeks of age was unrelated to 16-week PennHIP DI in a homogenous canine population with moderate-to-severe CFJ joint laxity. CLINICAL RELEVANCE: Based on our results, ad libitum feeding between 6 and 15 weeks of age does not appear to have an adverse impact on joint laxity at 16 weeks of age as measured by the PennHIP DI.     

In vivo evaluation of intra-articular protection in a novel model of canine cranial cruciate ligament mid-substance elongation injury

OBJECTIVES: To evaluate the effects of intra-articular protection (IAP) on the canine cranial cruciate ligament (CrCL) and stifle in a CrCL midsubstance elongation injury model. STUDY DESIGN: Experimental longitudinal cohort study. ANIMALS: Skeletally mature female mixed breed hounds (n=12; mean+/-SEM weight, 25.6+/-0.7 kg). METHODS: After CrCL elongation in 1 stifle of each dog, IAP was applied in 6 joints. In vivo assessment included radiographs, cranial-caudal joint translation, gait analysis, and synovial fluid levels of 3B3(-) (proteoglycan epitope) and C2C (collagen II neoepitope) up to 12 weeks after surgery. Joint translation and rotation were quantified at necropsy. CrCL midsubstance length was determined before and after elongation and at necropsy. CrCLs were subjectively assessed with light microscopy. Comparisons were made between stifles containing elongated CrCLs with and without IAP and unoperated controls. RESULTS: Four weeks after surgery, ground reaction forces were significantly decreased in operated limbs. Absolute C2C levels were significantly elevated in operated stifles 4 weeks post-surgery. C2C and 3B3(-) levels normalized to total protein were significantly elevated in IAP+ stifles 8 weeks after surgery. Protected CrCLs appeared to have decreased granulation tissue and better collagen fiber alignment. CONCLUSIONS: IAP has negligible effects on the canine stifle based on the response variables evaluated in this 12-week study. Protection of elongated CrCLs may promote reduced, organized scar formation. CLINICAL RELEVANCE: These results support the healing capacity of the canine CrCL midsubstance following elongation injury and IAP application to potentially reduce cicatrix formation in elongated CrCLs.