Effects Of Growth History Research Articles

The effect of cyclic variation of shear stress on non‐cohesive sediment stabilization by microbial biofilms: the role of ‘biofilm precursors’

AbstractBiofilm mediated intertidal sediments exhibit more complex erosional behaviour than abiotic systems. A major feature of intertidal systems is the exposure to repeated cycles of high and low shear created by tidal conditions and also less predictable episodic events, such as storms. There is very little information on how biofilm‐forming communities respond to these conditions. In this study, the effects of both single and repeated‐cycles of shear on the stability of newly developed bio‐sedimentary beds was examined. Cleaned sand, without any potential biostabilization, was used as the control. For the single‐cycle scenario, biofilms were incubated on a non‐cohesive sandy bed under prolonged low shear periods varying between 5 and 22 days, after which erosional stress was applied. No significant biostabilization was observed for the youngest bio‐sedimentary bed (after five days of low shear incubation). After 22 days, microbial communities were characterized by a firmly attached surface biofilm. To cause erosion, greater hydrodynamic stress (0.28 Pa) was required. The erosional behaviour of the underlying sand was also affected in that bedform ripples noted in the control system were no longer observed. Instead, a sudden ‘mass erosion’ took place (0.33 Pa). The one‐cycle scenario indicated that significant biostabilization of sand only occurred after a relative long calm period. Under repeated cycles of stress (five days of low stress followed by high stress event and re‐incubation, repeated for four cycles = 20 days), frequent cyclic disturbance did not degrade the system stability but enhanced biostabilization. The properties of the sub‐surface sediments were also affected where erosion rates were further inhibited. We hypothesize that organic material eroded from the bed acted as a ‘biofilm precursor’ supporting the development of new biofilm growth. A conceptual framework is presented to highlight the dynamics of bio‐sedimentary beds and the effects of growth history under repeated‐cycles. © 2019 John Wiley & Sons, Ltd.

Changing maturation reaction norms and the effects of growth history in Alaskan Chinook salmon

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 595:187-202 (2018) - DOI: https://doi.org/10.3354/meps12564 Changing maturation reaction norms and the effects of growth history in Alaskan Chinook salmon Jared E. Siegel1,*, Milo D. Adkison2, Megan V. McPhee2 1South Fork Research, Inc., 44842 SE 145th St., North Bend, WA 98045, USA 2College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 17101 Point Lena Loop Road, Juneau, AK 99801, USA *Corresponding author: derajlegeis@gmail.com ABSTRACT: We explored the nature of declines in size and age at maturity in 2 populations of Chinook salmon Oncorhynchus tshawytscha in western Alaska, USA, using multidimensional probabilistic maturation reaction norms (PMRNs) accounting for growth history. Individual growth histories informed by retrospective scale analysis were used to construct PMRNs and to describe the relative influence of different life-history periods on age at maturity. Similar results were found in both populations. Models accounting for growth history uniformly outperformed size-at-age models, suggesting the importance of growth history for the determination of maturation. The second year of marine growth was found to have a disproportionate influence on the age at maturity in both sexes. Males tended to grow more than females in length during the second year at sea, possibly as a consequence of females storing more energy in preparation for the high cost of female gonad development. Finally, we found that growth thresholds for maturation have shown a long-term decline in both sexes. This suggests that declines in the average age at maturity of western Alaskan Chinook salmon may have been caused in part by adaptation to environmental or fisheries-induced selection. KEY WORDS: Oncorhynchus tshawytschka · Size at age · PMRN · Age at maturity · Life history · Plasticity · Evolution · Retrospective scale analysis Full text in pdf format Supplementary material PreviousNextCite this article as: Siegel JE, Adkison MD, McPhee MV (2018) Changing maturation reaction norms and the effects of growth history in Alaskan Chinook salmon. Mar Ecol Prog Ser 595:187-202. https://doi.org/10.3354/meps12564 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 595. Online publication date: May 14, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Quantifying Variability in Growth and Thermal Inactivation Kinetics of Lactobacillus plantarum.

The presence and growth of spoilage organisms in food might affect the shelf life. In this study, the effects of experimental, reproduction, and strain variabilities were quantified with respect to growth and thermal inactivation using 20 Lactobacillus plantarum strains. Also, the effect of growth history on thermal resistance was quantified. The strain variability in μmax was similar (P > 0.05) to reproduction variability as a function of pH, aw, and temperature, while being around half of the reproduction variability (P < 0.05) as a function of undissociated lactic acid concentration [HLa]. The cardinal growth parameters were estimated for the L. plantarum strains, and the pHmin was between 3.2 and 3.5, the aw,min was between 0.936 and 0.953, the [HLamax], at pH 4.5, was between 29 and 38 mM, and the Tmin was between 3.4 and 8.3°C. The average D values ranged from 0.80 min to 19 min at 55°C, 0.22 to 3.9 min at 58°C, 3.1 to 45 s at 60°C, and 1.8 to 19 s at 63°C. In contrast to growth, the strain variability in thermal resistance was on average six times higher than the reproduction variability and more than ten times higher than the experimental variability. The strain variability was also 1.8 times higher (P < 0.05) than the effect of growth history. The combined effects of strain variability and growth history on D value explained all of the variability as found in the literature, although with bias. Based on an illustrative milk-processing chain, strain variability caused ∼2-log10 differences in growth between the most and least robust strains and >10-log10 differences after thermal treatment. Accurate control and realistic prediction of shelf life is complicated by the natural diversity among microbial strains, and limited information on microbiological variability is available for spoilage microorganisms. Therefore, the objectives of the present study were to quantify strain variability, reproduction (biological) variability, and experimental variability with respect to the growth and thermal inactivation kinetics of Lactobacillus plantarum and to quantify the variability in thermal resistance attributed to growth history. The quantitative knowledge obtained on experimental, reproduction, and strain variabilities can be used to improve experimental designs and to adequately select strains for challenge growth and inactivation tests. Moreover, the integration of strain variability in prediction of microbial growth and inactivation kinetics will result in more realistic predictions of L. plantarum dynamics along the food production chain.

Quantifying variability on thermal resistance of Listeria monocytogenes

Knowledge of the impact of strain variability and growth history on thermal resistance is needed to provide a realistic prediction and an adequate design of thermal treatments. In the present study, apart from quantifying strain variability on thermal resistance of Listeria monocytogenes, also biological variability and experimental variability were determined to prioritize their importance. Experimental variability was defined as the repeatability of parallel experimental replicates and biological variability was defined as the reproducibility of biologically independent reproductions. Furthermore, the effect of growth history was quantified. The thermal inactivation curves of 20 L. monocytogenes strains were fitted using the modified Weibull model, resulting in total 360 D-value estimates. The D-value ranged from 9 to 30min at 55°C; from 0.6 to 4min at 60°C; and from 0.08 to 0.6min at 65°C. The estimated z-values of all strains ranged from 4.4 to 5.7°C. The strain variability was ten times higher than the experimental variability and four times higher than the biological variability. Furthermore, the effect of growth history on thermal resistance variability was not significantly different from that of strain variability and was mainly determined by the growth phase.

Effects of Growth History and Exogenous Thyroxine on Size and Age at Metamorphosis in the ToadBufo americanus

By using food rations and thyroxine supplements, I manipulated the growth and differentiation of tadpoles of the toad Bufo americanus to test the hypothesis that the plasticity in metamorphic timing can be lost. A significant food effect indicated that tadpoles that grew rapidly during the middle period of the experiment metamorphosed earlier than slow-growing tadpoles. The changes in growth induced early and late in this experiment did not influence metamorphic timing. There was a significant thyroxine effect: all tadpoles treated with thyroxine metamorphosed early. All thyroxine-treated tadpoles metamorphosed at the same time, indicating that differentiation at the time of thyroxine supplementation was independent of growth rate. A food-by-thyroxine interaction provided evidence that the growth rate/differentiation antagonism may have been active at least during the middle of the experiment. This suggests that the growth rate/differentiation antagonism is decoupled or overridden during later stages of larval development. This result implies limits to metamorphic plasticity and is consistent with a fixed-rate model of amphibian metamorphosis.

Transient repression of β-galactosidase synthesis: Effect of growth history

Transient repression of β-galactosidase synthesis: Effect of growth history