Does cyclicity of growth rate in rainbow trout exist?

Ninety rainbow trout Oncorhynchus mykiss were reared in three tanks ( n= 30), and their growth rate was monitored for 25 weeks. During the experiment, fish were fed ad libitum , and kept under simulated natural photoperiod and constant temperature (14 ± 1°C). Throughout the experiment, water quality (pH, O₂, N-NH₃, N-NH₄, NO₂) was considered optimum. Two growth rate periods were observed on the population: first an acclimation period (weeks 1–5), followed by a period of general decrease in growth rate (weeks 5–25). This trend was modelled with a third-order polynomial function. The autocorrelation analysis of the fluctuations revealed a cyclicity of the growth rate with a 4–5-week period. This cyclicity was independent of the tanks and of the growth rate trend type (long- v . short-term acclimation period). However, at the individual level, trends as well as short-term fluctuations were heterogeneous and no clear cyclicity could be detected. The biological relevance of the population growth rate cyclicity and the apparent absence of similar individual fluctuations are discussed.     

Does individual variation in stress responses and agonistic behavior reflect divergent stress coping strategies in juvenile rainbow trout?

Individual rainbow trout were transferred to visual isolation in experimental aquaria. As a measure of the speed of acclimation, individual food intake was quantified during the first 6 d following transfer. Following acclimation, aggression was quantified by subjecting the fish to three resident-intruder tests, with 30 d of recovery between the tests. Moreover, between the resident-intruder tests (i.e., two times) the fish were exposed to an unfamiliar environment and their cortisol response was measured. The results of this study show that individuals of juvenile rainbow trout differ distinctly in their response to changes in their environment, and that this diversity in behavior is reflected by consistent behavioral traits displayed by individual fish. These traits have proven to be consistent not only over time but also across situations, revealing two distinct behavioral profiles, in the same manner as shown in studies on proactive and reactive mammals. Our results also show that the reactivity of the hypothalamic-pituitary-interrenal (HPI) axis, when exposed to a stressor, is a consistent physiological trait in juvenile rainbow trout. We found that difference in HPI axis reactivity is linked to the different behavioral profiles. However, HPI axis reactivity could not be linked directly to the singular behavioral traits measured. In other words, we did not find that the consistent behavioral traits shown by the fish were associated with a difference in HPI axis reactivity in the same manner as the reactivity of the hypothalamic-pituitary-adrenocortical axis does in mammals. Taken together, our results show that stress coping strategies akin to what has been described as reactive and proactive stress coping in mammals appear to exist in juvenile rainbow trout.     

Plasticity of boldness in rainbow trout,Oncorhynchus mykiss: do hunger and predation influence risk-taking behaviour?

Boldness, a measure of an individual's propensity for taking risks, is an important determinant of fitness but is not necessarily a fixed trait. Dependent upon an individual's state, and given certain contexts or challenges, individuals may be able to alter their inclination to be bold or shy in response. Furthermore, the degree to which individuals can modulate their behaviour has been linked with physiological responses to stress. Here we attempted to determine whether bold and shy rainbow trout, Oncorhynchus mykiss, can exhibit behavioural plasticity in response to changes in state (nutritional availability) and context (predation threat). Individual trout were initially assessed for boldness using a standard novel object paradigm; subsequently, each day for one week fish experienced either predictable, unpredictable, or no simulated predator threat in combination with a high (2% body weight) or low (0.15%) food ration, before being reassessed for boldness. Bold trout were generally more plastic, altering levels of neophobia and activity relevant to the challenge, whereas shy trout were more fixed and remained shy. Increased predation risk generally resulted in an increase in the expression of three candidate genes linked to boldness, appetite regulation and physiological stress responses - ependymin, corticotrophin releasing factor and GABA(A) - but did not produce a significant increase in plasma cortisol. The results suggest a divergence in the ability of bold and shy trout to alter their behavioural profiles in response to internal and exogenous factors, and have important implications for our understanding of the maintenance of different behavioural phenotypes in natural populations.     

Treatment of columnaris disease of rainbow trout: low pH and salt as possible tools?

The impact of salt and low pH on columnaris disease of fish was studied. Survival of Flavobacterium columnare after exposure to either 4% NaCl (pH 7.2) or pH 5.0, pH 4.86 or pH 4.6 for 15 min or 1 h was studied in vitro. All conditions significantly reduced the numbers of viable bacterial cells. The effects of salt (4 and 2%) and acidic baths (pH 4.6) were studied in 2 experiments in vivo with rainbow trout Oncorhynchus mykiss infected with F. columnare. Both salt and acidic baths failed to prevent fish mortality; the overall mortality reached 100% in all groups. However, according to survival analysis, the mortality rate was lower in fish treated with 4% salt baths compared to a control group. The buffering capacity of fish skin mucus against low water pH was also studied. Fish skin mucus was an efficient buffer against decreased water pH and the pH of the skin could be remarkably higher than that of the mucus. This may explain the failure of bath treatments to prevent mortality providing that attached F. columnare are located below the mucus surface. We suggest, however, that salt and acidic bath treatments can be used to disinfect water containing F. columnare cells shed by infected fish and thus prevent the transmission of the disease.     

Does predator abundance influence species diversity of equilibrium macroinvertebrate assemblages in spring fens?

1. Predation may significantly control number and density of coexisting species. The effects of predation on species diversity have traditionally been tested in experiments and theoretical models of simple trophic systems. In complex natural ecosystems, however, disentangling multiple sources of variation is difficult. In groundwater-fed environments, a significant effect of predation can be expected due to the relatively stable environmental conditions; however, it has never been properly examined.
2. We analysed species diversity and total abundance of macroinvertebrate assemblages in 48 Western Carpathian spring fens, separately for whole sites and mesohabitat/season, and partitioned the effects of predation intensity from those of environmental variables in robust models using a bootstrapping technique. We verified our results by accounting for taxa resistant to predation.
3. The assumption that predation-mediated coexistence of species is the main mechanism responsible for the relatively species-rich assemblages in the Western Carpathian spring fens was not supported. However, predation may significantly influence abundance of non-predatory species and, under some conditions, it may contribute to explaining patterns in species diversity.
4. The effect of predation did not differ between the mesohabitats with different stability. However, we found higher environmental control in spring and a stronger effect of predators in autumn, which suggests that different mechanisms influence fen assemblages in different seasons.
5. Our study provides a new robust approach how to test the effect of predation on natural macroinvertebrate assemblages. The importance of predation was lower than expected in equilibrium assemblages but it may vary in time.

     

Does RU486 modify hormonal responses to handling stressor and cortisol treatment in fed and fasted rainbow trout?

This study examines the effect of the steroid analogue, RU486, on the physiological responses of fed and chronically fasted rainbow trout to an acute handling stressor. This potent ligand of the glucocorticoid receptor was administered as a slow-release implant either alone, or in combination with cortisol. There were temporal changes in plasma cortisol concentrations following administration of cortisol implants in both fed and fasted trout. By day 14, plasma cortisol levels in fed fish were similar in all treatment groups, but in fasted fish, the effect of cortisol administration on plasma cortisol concentrations was still evident; RU486 administered with cortisol, did not affect this response. Cortisol administration also elicited a small, but significant increase in plasma GH concentrations in fed rainbow trout and in plasma glucose concentrations in fasted animals. RU486-treatment prevented these responses. Conversely, whereas RU486 alone had no effect on hepatic 5'-monodeiodinase activity, when administered with cortisol it enhanced the marked suppressive effect of cortisol evident in both fed and fasted groups, suggesting that it may exert an interactive effect with cortisol on this process. Stressor-related changes in plasma cortisol, glucose, GH and thyroid hormone concentrations were evident in both fed and fasted groups; however, there was no evidence of a suppressive effect of RU486 treatment on any of the measured plasma parameters. Although RU486 did not prevent the stressor-related changes, the post-stressor cortisol profiles in RU-treated trout were extremely erratic compared with the oil-treated controls. This implies a disturbance of the normal interactions of the components of the hypothalamus-pituitary-interrenal tissue axis.     

Does predation by the introduced rainbow trout cascade down to detritus and algae in a forested small stream in Patagonia?

Cascade effects of an exotic predator, the rainbow trout (Oncorhynchus mykiss), on periphyton and leaf litter were analysed in a headwater, forested stream of Andean Patagonia (Argentina). We conducted seasonal field sampling and two field experiments measuring leaf litter mass, periphyton biomass and macroinvertebrate biomass in relation to the presence and absence of rainbow trout. In the field survey, the presence of trout influenced resource mass: leaf litter (60% decrease in summer, P = 0.024) and periphyton (tenfold increase in chlorophyll a, P < 0.001) were affected, which were mediated by a decrease in the biomass of shredders (95% decrease in summer, P < 0.001) and scrapers (90% decrease, P < 0.001). There was an effect on leaf litter biomass only in the summer, whereas fish presence reduced periphyton biomass all year except in the winter. In the field experiments, we observed that leaf litter breakdown and periphyton development were effectively controlled by consumers in the absence of fish. In contrast, the presence of fish caused a release of herbivory and detritivory resulting in a significant increase in periphyton biomass (100% increase, P < 0.001) and a decrease in leaf litter decay (40% decrease, P < 0.001). Our results suggest that in low order streams and in the presence of visual predators, trophic cascades may operate both on detritus and algae, but with different timing.     

Does neonatal androgen modulate uptake and retention of 3H-estradiol in gonadotrophs and lactotrophs?

Summary Castrated adult male and female and androgenized female rats (AS rats) were injected i.v. with ³H-estradiol (E₂). Nuclear uptake and retention of the ³H-steroid was examined in pituitary luteinizing hormone (LH) and prolactin (PRL) cells by the combined techniques of autoradiography and immunocytochemistry. About 80% of PRL cells were found to concentrate the radioactive steroid compound in all experimental groups, while 89%, 82% and 68% of LH cells were found to be labeled in AS rats, normal female and male rats, respectively. This suggests that there are subpopulations of LH or PRL cells that contain no or, if any, small numbers of E₂ receptor. Statistical analysis revealed that PRL cells take up more radioactivity than LH cells in male rats, while there is no significant difference between female and AS rats. Variations in E₂ uptake (coefficient of variation) was higher in LH cells than in PRL cells in male rats and in AS rats. In females, on the contrary, coefficient of variation was larger in PRL cells. Thus the characteristics of nuclear uptake and retention of estradiol in LH and PRL cells appear to be modulated in part by neonatal androgen since the pattern found in AS rats is different than that found in normal male and female rats.     

Does climate influence assemblages of anurans and lizards in a coastal area of north-eastern Brazil?

Environmental factors influence diverse assemblage features such as species abundances, richness, and nestedness. Amphibians and reptiles play important roles in terrestrial ecosystems, but there is still a lack of information about the assemblages of these animals in many regions. In this study, we aimed to understand how environmental factors influence the anurans and lizards assemblages from São Gonçalo do Amarante, Ceará, Brazil. Herpetofauna samplings were performed monthly in São Gonçalo do Amarante from January 2008 to May 2009, excluding April 2008. We sampled animals (anurans and lizards) using pitfall traps and active searches. The abundance and richness of lizards were positively related to temperature and negatively related to precipitation. Anuran assemblage was not influenced by precipitation, but its abundance was negatively influenced by temperature. Temperature generated a nested pattern in the lizard assemblage, but precipitation did not produce this pattern in anurans. Finally, our results reinforce the importance of environmental factors, mainly temperature, in structuring assemblages of anurans and lizards.     

Does circadian and seasonal variation in occurrence of acute aortic dissection influence in-hospital outcomes?

The risk of acute aortic dissection (AAD) exhibits chronobiological variations with peak onset in the morning and in winter. However, it is not known whether the time of day or season of the year of the AAD affects clinical outcomes. We studied 1,032 patients enrolled in the International Registry of Acute Aortic Dissection from January 1997 to December 2001. For circadian and seasonal analysis, the time and date of symptom onset were available for 741 and 1,007 patients, respectively, and were grouped into four 6 h periods (morning, afternoon, evening, and night) and four seasons (winter, spring, summer, and autumn). The χ² test for goodness of fit was used to evaluate non-uniformity of the time of day and time of year for critical in-hospital clinical events, including death. While highest incidence of AAD occurred in the morning and winter, clinical events (including mortality) were similar during the four different periods of the 24 h (χ²=1.9, p=0.60) and seasonal (χ²=1.2, p=0.75) periods.     

Background level of risk and the survival of predator-naive prey: can neophobia compensate for predator naivety in juvenile coral reef fishes?

Neophobia—the generalized fear response to novel stimuli—provides the first potential strategy that predator-naive prey may use to survive initial predator encounters. This phenotype appears to be highly plastic and present in individuals experiencing high-risk environments, but rarer in those experiencing low-risk environments. Despite the appeal of this strategy as a ‘solution’ for prey naivety, we lack evidence that this strategy provides any fitness benefit to prey. Here, we compare the relative effect of environmental risk (high versus low) and predator-recognition training (predator-naive versus predator-experienced individuals) on the survival of juvenile fish in the wild. We found that juveniles raised in high-risk conditions survived better than those raised in low-risk conditions, providing the first empirical evidence that environmental risk, in the absence of any predator-specific information, affects the way naive prey survive in a novel environment. Both risk level and experience affected survival; however, the two factors did not interact, indicating that the information provided by both factors did not interfere or enhance each other. From a mechanistic viewpoint, this indicates that the combination of the two factors may increase the intensity, and hence efficacy, of prey evasion strategies, or that both factors provide qualitatively separate benefits that would result in an additive survival success.     

Worker brain development and colony organization in ants: Does division of labor influence neuroplasticity?

Brain compartment size allometries may adaptively reflect cognitive needs associated with behavioral development and ecology. Ants provide an informative system to study the relationship of neural architecture and development because worker tasks and sensory inputs may change with age. Additionally, tasks may be divided among morphologically and behaviorally differentiated worker groups (subcastes), reducing repertoire size through specialization and aligning brain structure with task‐specific cognitive requirements. We hypothesized that division of labor may decrease developmental neuroplasticity in workers due to the apparently limited behavioral flexibility associated with task specialization. To test this hypothesis, we compared macroscopic and cellular neuroanatomy in two ant sister clades with striking contrasts in worker morphological differentiation and colony‐level social organization: Oecophylla smaragdina , a socially complex species with large colonies and behaviorally distinct dimorphic workers, and Formica subsericea , a socially basic species with small colonies containing monomorphic workers. We quantified volumes of functionally distinct brain compartments in newly eclosed and mature workers and measured the effects of visual experience on synaptic complex (microglomeruli) organization in the mushroom bodies—regions of higher‐order sensory integration—to determine the extent of experience‐dependent neuroplasticity. We demonstrate that, contrary to our hypothesis, O. smaragdina workers have significant age‐related volume increases and synaptic reorganization in the mushroom bodies, whereas F. subsericea workers have reduced age‐related neuroplasticity. We also found no visual experience‐dependent synaptic reorganization in either species. Our findings thus suggest that changes in the mushroom body with age are associated with division of labor, and therefore social complexity, in ants. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1072–1085, 2017     

Does storage time in LN2 influence survival and pregnancy outcome of vitrified rabbit embryos?

Vitrification is one of the most widely used techniques for embryo cryopreservation. The aim of this work was to study the effect of storage time in liquid nitrogen on vitrified rabbit embryos. A total of 1467 vitrified rabbit embryos were transferred into 174 females. The embryos had been maintained in liquid nitrogen during 3 different periods, A) < 1 year (98 transfers, 827 embryos); B) 2-5 years (44 transfers, 360 embryos) and C) > 15 years (32 transfers, 280 embryos). A generalized linear model was used to determine the effect of period on pregnancy and birth rates. A Bayesian approach was applied to analyze the survival rate of the vitrified embryos. In all analyses the number of transferred embryos was included as covariate. It was observed that neither the period of storage nor the number of transferred embryos affected pregnancy rate, and all periods presented similar pregnancy rates (0.85 ± 0.04; 0.86 ± 0.05; 0.78 ± 0.07 for A, B and C). Fertility at birth was affected by the number of transferred embryos, but non-significant differences between periods were detected (0.77 ± 0.04, 0.75 ± 0.07; 0.69 ± 0.08 for A, B and C). Also, the posterior means (highest posterior density intervals at 95%) of embryo survival at birth from pregnant females were similar between the different periods (47 [41 53]; 47 [38 56]; 42 [31 54]; for A, B and C). Results obtained in the present experiment point out that vitrified embryos could be stored in liquid nitrogen during at least fifteen years, achieving good pregnancy rate, fertility and survival at birth.     

Does the timing of attainment of maturity influence sexual size dimorphism and adult sex ratio in turtles?

The attainment of sexual maturity has been shown to affect measures of sexual size dimorphism (SSD) and adult sex ratios in several groups of vertebrates. Using data for turtles, we tested the model that sex ratios are expected to be male‐biased when females are larger than males and female‐biased when males are larger than females because of the relationship of each with the attainment of maturity. Our model is based on the premise that the earlier‐maturing sex remains smaller, on average throughout life, and predominates numerically unless the sexes are strongly affected by differential mortality, differential emigration, and immigration, or biased primary sex ratios. Based on data for 24 species in seven families, SSD and sex ratios were significantly negatively correlated for most analyses, even after the effect of phylogenetic bias was removed. The analyses provide support for the model that SSD and adult sex ratios are correlated in turtles as a result of simultaneous correlation of each with sexual differences in attainment of maturity (bimaturism). Environmental sex determination provides a possible mechanism for the phenomenon in turtles and some other organisms. © 2014 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 142–149.     

Nestmate recognition in sweat bees (Lasioglossum zephyrum): Does an individual recognize its own odour or only odours of its nestmates?

We investigated the olfactory mechanism by which guard bees of Lasioglossum zephyrum decide whether to admit conspecifics to their nests. First we set up colonies of young bees, consisting of sisters from a single family or a mixture of bees from two distinct families. These bees were then introduced into colonies other than their own. Our experimental evidence shows that guards learn the odours of their nestmates, then accept or reject other bees on the basis of the similarity of the latters' odours to those of the guards' nestmates. Guards act as though they do not use their own odour as a reference for nestmate recognition. This recognition mechanism enables individuals with different odours to live together; it may also enhance the operation of kin selection by providing a more complete basis for discriminating relatives from non-relatives. No evidence was found that nestmates acquire one another's odours. Such lack of odour transfer may be characteristic of early stages in the evolution of recognition mechanisms.     

Does the badge of status influence parental care and investment in house sparrows? An experimental test

Theory predicts that traits which signal parental quality might evolve in males of species with biparental care. In avian species, male ornaments may be the most likely candidates for such signals. Male house sparrows (Passer domesticus) possess a black throat patch often referred to as a “badge” or a “badge of status”. By assuming a trade-off between male attractiveness (reflected in male ornaments) and parental care under the differential allocation hypothesis, we predicted that badge size would be negatively correlated with male parental investment. An experiment in which the badge was enlarged in one group and unchanged in a control group was conducted. Our manipulation was predicted to affect female as well as male parental investment. However, we found that eight variables associated with parental investment—the start date for breeding, clutch size, male and female incubation time, male and female food provisioning rate, and average chick weight and the number of fledglings—barely differed between treatments. Also, little evidence for correlations between natural variation in badge size and any of these eight variables was found. Instead, the start date for breeding and the number of fledglings were significantly correlated with both male and female age, while clutch size increased with female age. Female condition was a positive predictor of clutch size and number of fledglings. Female tarsus length, unexpectedly, is related to both male and female incubation time. Badge size was also positively correlated with male age. However, parental age (male or female) was not related to parental care. We conclude that badge size does not signal parental quality, but that the ages of both sexes and the condition of the female play significant roles in the reproductive performance of this species.     

Does troop size of wild Japanese macaques influence birth rate and infant mortality in the absence of predators?

For the wild Japanese macaques of Yakushima and Kinkazan Islands, we analyzed the relationship between the troop size or the number of adult females of each troop, infant/adult female ratio (IFR; crude birth rate), and infant mortality (IM) in habitats with no predators. In Yakushima, IFR was positively correlated to troop size and the number of adult females. In Kinkazan, however, IFR tended to decrease with the number of adult females. This difference may be due to the difference in troop size; i.e. in Yakushima, where troop size was small, IFR may increase with that of troop size, because a relatively larger troop is likely to the advantage in intertroop competition. In Kinkazan, where troop size was large, however, IFR is likely to decrease with troop size, because intratroop competition may increase. Thus, the present data roughly supportWrangham's model of the social structure of female-bonded primates, and suggests that there is an optimal troop size for birth rate (BR). On the other hand, there was no clear correlation between IM and the troop size or number of adult females of each troop.     

Does interspecific hybridization influence evolutionary rates? An experimental study of laboratory adaptation in hybrids between Drosophila serrata and Drosophila birchii.

The low initial fitness of progeny from interspecific crosses in animals and the rarity of interspecific hybridization in natural environments have led to a debate about the evolutionary importance of this phenomenon. Here we directly assess the effects of hybridization between Drosophila serrata and Drosophila birchii on evolutionary rates. We looked at the effects on laboratory adaptation over 30 generations in two laboratory environments, one of which involved nutrition and temperature stress. Laboratory adaptation occurred over time in both environments as reflected by a marked change in viability. However, whilst hybrid lines at no stage performed poorly relative to parental lines, their rate of adaptation never exceeded that of the parentals. Thus, there was no evidence that hybridization increased evolutionary rates. Instead, hybrid lines converged phenotypically with one of the parental species.     

Does BMI predict the early spatial variation and intensity of Covid-19 in developing countries? Evidence from India

This paper studies BMI as a correlate of the early spatial distribution and intensity of Covid-19 across the districts of India and finds that conditional on a range of individual, household and regional characteristics, adult BMI significantly predicts the likelihood that the district is a hotspot, the natural log of the confirmed number of cases, the case fatality rate, and the propensity that the district is a red zone. Controlling for air-pollution, rainfall, temperature, demographic factors that measure population density, the proportion of the elderly, and health infrastructure including per capita health spending and the proportion of respiratory cases, does not diminish the predictive power of BMI in influencing the spatial incidence and spread of the virus. The association between adult BMI and measures of spatial outcomes is especially pronounced among educated populations in urban settings, and impervious to conditioning on differences in testing rates across states. We find that among women, BMI proxies for a range of comorbidities (hemoglobin, high blood pressure and high glucose levels) that affects the severity of the virus while among men, these health indicators are also important, as is exposure to risk of contracting the virus as measured by work propensities. We conduct sensitivity checks and control for differences that may arise due to variations in timing of onset. Our results provide a readily available health marker that may be used to identify and protect especially at-risk populations in developing countries like India.