Benign Laboratory Conditions Research Articles

Wolbachia-infected pharaoh ant colonies have higher egg production, metabolic rate and worker survival.

Wolbachia is a widespread maternally transmitted endosymbiotic bacteria with diverse phenotypic effects on its insect hosts, ranging from parasitic to mutualistic. Wolbachia commonly infects social insects, where it faces unique challenges associated with its host's caste-based reproductive division of labor and colony living. Here, we dissect the benefits and costs of Wolbachia infection on life-history traits of the invasive pharaoh ant, Monomorium pharaonis, which are relatively short lived and show natural variation in Wolbachia infection status between colonies. We quantified the effects of Wolbachia infection on the lifespan of queen and worker castes, the egg-laying rate of queens across queen lifespan, and the metabolic rates of whole colonies and colony members. Infected queens laid more eggs than uninfected queens but had similar metabolic rates and lifespans. Interestingly, infected workers outlived uninfected workers. At the colony level, infected colonies were more productive as a consequence of increased queen egg-laying rates and worker longevity, and infected colonies had higher metabolic rates during peak colony productivity. While some effects of infection, such as elevated colony-level metabolic rates, may be detrimental in more stressful natural conditions, we did not find any costs of infection under relatively benign laboratory conditions. Overall, our study emphasizes that Wolbachia infection can have beneficial effects on ant colony growth and worker survival in at least some environments.

Dietary restriction extends lifespan across different temperatures in the fly

Abstract Dietary restriction (DR) has been consistently shown to extend lifespan across a range of taxa. However, it has recently been reported that DR does not extend lifespan at certain, namely lower, temperatures in flies (Drosophila melanogaster). Similar to the interpretation of other findings that appear to question DR's universality, this finding has been interpreted as suggesting that lifespan extension in response to DR is an artefact of benign laboratory conditions. We re‐test this hypothesis, now using a strain that shows robust lifespan extension at 25°C (across three prior experiments), and using a range of five diets across two temperatures, 18°C and 21°C. We found the DR longevity response to be robust, extending lifespan irrespective of temperature. We measured fecundity as a positive control for the DR phenotype, and found, as predicted, that DR reduces egg laying. We suggest differences in experimental setup, genetic lines used and variation in the diet‐lifespan reaction norm are responsible for this discrepancy. In addition, starting with a strain and conditions that show a lifespan extension by DR, as we do here, and then changing environment and/or genotype promises a more robust test of DR modulating factors. In conclusion, it will be important for results that question DR as a phenotype to not be overinterpreted readily, as with a substantially larger sample size and a larger range of diets we were unable to replicate this prior work. Read the free Plain Language Summary for this article on the Journal blog.

Dietary restriction fails to extend life in stressful environments

Abstract Moderate dietary restriction often prolongs life in laboratory animals, and this response has been interpreted as an adaptive strategy that promotes survival during famine. However, dietary restriction can also increase frailty, and it therefore remains unclear whether restricted diets prolong life under stressful conditions like those experienced by wild animals. We manipulated adult dietary protein of Drosophila melanogaster across a gradient of ambient temperature, and examined effects on survival. To test for trade‐offs, we also quantified reproduction, and performance of F1, F2 and F3 descendants. We found that protein restriction increased longevity of one or both sexes at benign ambient temperatures (25°C and 27°C), but failed to extend longevity of flies maintained in cold (21°C and 23°C) or hot (29°C) conditions. Instead, in females, protein restriction resulted in strongly elevated mortality at cold temperatures. Protein restriction also generally reduced reproductive performance, and did not consistently enhance performance of F1, F2 or F3 descendants. Taken together, our results challenge the long‐held idea that extended longevity of diet‐restricted laboratory animals represents an adaptive survival strategy in natural populations. Our findings suggest instead that this response is an artefact of benign laboratory conditions, and that DR‐induced life extension might not be achieved in the more stressful conditions experienced in the wild. Read the free Plain Language Summary for this article on the Journal blog.

Recycling copper and gold from e-waste by a two-stage leaching and solvent extraction process

The recycling of metals such as gold and copper from discarded end-of-life electronic waste (e-waste or WEEE) is an important aspect to the development of environmentally benign manufacturing processes that exhibit circularity in materials flow. Global e-waste production is increasing at a 3–5% rate, so it is concerning that only 30% is recycled using regulated processes. We present here a new hydrometallurgical route for the technically feasible recycling of copper and gold from waste printed circuit boards (WPCBs) of mobile phones. This process comprises the liberation of the metallic fractions from downsized WPCBs, a two-stage acid leaching process to provide a bulk separation of copper and gold from the other metals present, and subsequent purification of the copper and gold-containing solutions by solvent extraction using highly selective phenolic oxime and amide extractants, respectively. Complete dissolution of the base metals was seen using 3 M nitric acid at 30 °C and the selective separation of copper from this leach liquor was achieved by solvent extraction using ACORGA M5640 dissolved in kerosene. The residues from base-metal leaching were treated with a mixture of 3 M sulfuric acid and 3 M sodium bromide at 70 °C, resulting in greater than 95% gold dissolution. The selective separation of gold from this precious metal leachate was achieved by solvent extraction using 0.1 M tertiary amide extractant dissolved in toluene. This process delivers complete copper and gold recycling from WPCBs under relatively benign laboratory conditions and represents a proof of concept for liberating valuable and critical metals back into active service from end-of-life electronic devices.

Testing evolutionary explanations for the lifespan benefit of dietary restriction in fruit flies ( Drosophila melanogaster )

Dietary restriction (DR), limiting calories or specific nutrients without malnutrition, extends lifespan across diverse taxa. Traditionally, this lifespan extension has been explained as a result of diet‐mediated changes in the trade‐off between lifespan and reproduction, with survival favored when resources are scarce. However, a recently proposed alternative suggests that the selective benefit of the response to DR is the maintenance of reproduction. This hypothesis predicts that lifespan extension is a side effect of benign laboratory conditions, and DR individuals would be frailer and unable to deal with additional stressors, and thus lifespan extension should disappear under more stressful conditions. We tested this by rearing outbred female fruit flies (Drosophila melanogaster) on 10 different protein:carbohydrate diets. Flies were either infected with a bacterial pathogen (Pseudomonas entomophila), injured with a sterile pinprick, or unstressed. We monitored lifespan, fecundity, and measures of aging. DR extended lifespan and reduced reproduction irrespective of injury and infection. Infected flies on lower protein diets had particularly poor survival. Exposure to infection and injury did not substantially alter the relationship between diet and aging patterns. These results do not provide support for lifespan extension under DR being a side effect of benign laboratory conditions.

Synthesis and Absolute Stereochemical Reassignment of Mukanadin F: A Study of Isomerization of Bromopyrrole Alkaloids with Implications on Marine Natural Product Isolation

Synthesis of both enantiomers of mukanadin F was achieved by using a seven step synthesis. Comparison of the optical rotation data of synthetic samples to that reported for the isolated natural product determined that the absolute configuration of the natural product is 9S and not the reported 9R. Further studies established that the reported low magnitude of optical rotation in the isolated sample is due to compounds of this type undergoing isomerization and racemization under benign laboratory conditions. Additionally the synthetic methods developed were applied to synthesize mukanadins B and D.

Sequential exposure to low levels of pesticides and temperature stress increase toxicological sensitivity of crustaceans

Frequent pesticide-related impacts on ecosystems at concentrations considered environmentally safe indicate that the current risk assessment framework for registration of pesticides is not protective enough. Causes may include difficulties in assessing the effects of sequential pesticide pulses and their interaction with environmental stressors. By contrast to such realistic scenarios, risk assessment for registration of pesticides is typically based on tests of a single exposure period under benign laboratory conditions. Here, we investigated the toxicological sensitivity of Gammarus pulex, an ecologically relevant crustacean, from uncontaminated control streams and pesticide-contaminated agricultural streams by exposing them to pesticide contamination in the laboratory. Individuals from contaminated streams were 2.7-fold more sensitive to pesticide exposure than individuals from the reference streams. We revealed that this increase in sensitivity was the result of a synergistic interaction of sequential pesticide exposure and temperature stress. Such multiple stressor scenarios are typical for agricultural streams. We conclude that the interactive effects of sequential toxicant exposure and additional environmental stressors need to be considered in a realistic risk assessment framework.

Does it Pay to Care?: Exploring the Costs and Benefits of Parental Care in the Hibiscus Harlequin BugTectocoris diophthalmus(Heteroptera: Scutelleridae)

AbstractKnowledge of the selective pressures favouring parental care can inform our understanding of the evolutionary origins and transitions of sociality in insects. Here, we report upon investigations designed to estimate the costs and benefits of parental care in the egg‐guarding hibiscus harlequin bugTectocoris diophthalmus(Heteroptera:Scutelleridae). We found that the presence of a guarding female had no effect on hatching success under benign laboratory conditions. In the wild, however, guarding decreased the likelihood of total clutch failure, and produced a fourfold greater egg‐hatching rate relative to unguarded clutches. Females guarded against generalist invertebrate egg predators, including conspecific nymphs, but were ineffective against hymenopteran egg parasitoids. Females continued to feed during the guarding period and exhibited no signs of weight loss or increased mortality due to this behaviour. We did not observe the production of subsequent clutches in any experimental females; therefore, the lifetime fecundity costs of providing parental care inT. diophthalmusremain indeterminate. Overall, maternal egg guarding appears to function as a relatively low cost–low benefit strategy that increases hatching success by protecting against predation – but not parasitism.

Differential evolution of asexual and sexual females in a benign culture environment.

Here we report one of the first investigations of evolvability of lifespan and reproduction in metazoans, examining both extrinsic and intrinsic factors. We tested effects on senescence of an environmental variable (simulated lake hydroperiod, the length of time an aquatic habitat is inundated), female reproductive physiology (asexual females that reproduce by ameiosis, versus sexual females reproducing by meiosis), and time in a benign culture environment (minimal, if any, external mortality factors). To do this we established chemostat cultures of the rotifer Brachionus plicatilis s.s., and maintained the cultures for 385 d. Hydroperiod alone or in interaction with the effects of time in the benign environment (season) or reproductive physiology had no significant effect on the net reproductive rate, generation time, or rate of aging. Yet combining animals from both ephemeral and permanent hydroperiods revealed a 26% increase in asexual female lifespan across seasons (23% decrease in the rate of aging) and a 56% increase in asexual fecundity, suggesting that maintenance in benign laboratory conditions leads to slower aging. The relative stasis of traits for sexual females implies an impact of reproductive physiology on evolvability. In addition we found a positive correlation between fecundity and lifespan, suggesting an absence of trade-offs in life history traits in the benign laboratory environment.

The offspring size/fecundity trade-off and female fitness in the Atlantic molly (Poecilia mexicana, Poeciliidae)

Across a variety of taxa, large offspring have been demonstrated to have a fitness advantage over smaller offspring of the same species. However, producing large offspring often comes at the cost of having to produce fewer young, and the payoff (and thus, evolutionary outcome) of this trade-off is expected to vary between environments. Atlantic mollies (Poecilia mexicana: Poeciliidae, Teleostei), inhabiting a sulfidic cave and various non-sulfidic surface habitats in Tabasco (Mexico), are reproductively isolated and evolved divergent female life-history traits: females of the cave ecotype produce considerably fewer, but larger offspring. Stressful (sulfidic) environments may favor the production of larger offspring, as they are better able to cope with chemical stressors. It remains to be determined though if increased offspring survival outweighs the fitness cost of producing fewer but larger offspring even under benign laboratory conditions. We tested 30-day newborn survival of offspring from wild-caught P. mexicana females from diverging populations in a low-density, no predation, no cannibalism, and ad-libitum-food, benign laboratory environment. Survival rates were highly skewed towards larger cave molly offspring; however, surface molly females still had a higher fitness than cave molly females in terms of higher total numbers of surviving offspring. Our study provides evidence for an innate fitness advantage of larger cave molly offspring. Furthermore, the observed differences in life-history strategies could promote further divergence and reproductive isolation among these ecotypes of P. mexicana, because cave molly females immigrating into the adjacent surface habitats would most likely be selected against.

The life-history impact and implications of multiple parasites for bumble bee queens

Most studies of the consequences of parasitism on fitness have examined single host–parasite systems. However, parasitological studies show that most hosts are constantly challenged by a complex parasite community. Thus, neither the response of hosts to individual parasite species nor the individual impact of these parasite species is likely to be as unconstrained as studies of single host–parasite systems might suggest. In this study, the parasite community structure in spring queens of the common European bumble bee, Bombus pratorum, was assessed. By capturing queens and allowing them to rear colonies in the laboratory, the relative impact of different parasite species on fitness across the annual host life-cycle could be examined. Of 160 queens, 67% were parasitised by one or more members of a five-species parasite community. The impact of parasites varied from being highly virulent to undetectable under benign laboratory conditions. The majority of multi-parasite infections involved a high impact parasite, which resulted in the removal of associated parasites from the host population. This study shows that, whilst multiple infections occur within individual hosts, most parasites act individually on their hosts. However, multiple parasite species in the host population may constrain the host population’s ability to adapt to single parasite species.

Patterns and fitness consequences of intraclutch variation in egg provisioning in tropical Australian frogs

Intraclutch variation in offspring size should evolve when offspring encounter unpredictable environmental conditions. This form of bet-hedging should maximise the lifetime reproductive success of individuals that engage it. We documented the numbers of eggs and means and variances of yolk volume in 15 frog species that occur in tropical savanna woodland. We experimentally determined the effects of initial yolk volume on larval growth patterns in four species. Intraclutch variation in yolk volume occurred to some degree in all species surveyed. Some species had very low, others had very high, intraclutch variation in yolk volume, but all species in which some clutches were highly variable also produced clutches with low variability. Species that occur in areas where the offspring environment is likely to be unpredictable had elevated levels of intraclutch variation in egg provisioning. There was no trade-off between egg size and number in any species surveyed. Under benign laboratory conditions, tadpoles from eggs with larger yolk volumes hatched at larger sizes, and these size differences persisted through a substantial proportion of the larval stage. This indicates that intraclutch variation in egg size has major offspring and thus parental fitness consequences, and is therefore a functional selection variable. This study provides evidence in support of models which predict that intraclutch variation in offspring provisioning can evolve in organisms that reproduce in unpredictable habitats.

The importance of ice cover for energy turnover in juvenile Atlantic salmon

Summary Under benign laboratory tank conditions we compared food consumption and metabolism of Atlantic salmon (Salmo salar) juveniles exposed to simulated ice cover (darkness) with fish in natural short, 6 h light, day length (without ice). Three different populations along an ice‐cover gradient were tested (59°N−70°N). Resting metabolism was on average 30% lower under simulated ice cover (6·6 J g−1 day−1) than under natural day length (9·4 J g−1 day−1), and the response was similar for all populations. Northern salmon grew equally well in dark and light conditions, whereas the southern grew significantly poorer in the dark. Fish from all populations fed more under natural day length than in the dark and the northern population had higher consumption than the southern. The relative high growth of fish from the northern population in the dark compared to the southern populations was due partly to higher consumption and partly to higher growth efficiency. Fish from the southern populations had negative growth efficiency in the dark. We also studied the importance of ice cover under more hostile conditions in stream channels using the northern population only. Juveniles held in channels with simulated ice cover lost less energy (20 J g−1 day−1) than those held in channels with transparent cover (26 J g−1 day−1). This difference in energy loss was due partly (50%) to higher food consumption under simulated ice (4·5 and 1·6 J g−1, respectively) and partly (30%) to light‐induced differences in resting metabolic rate. In conclusion, both experiments showed lower metabolic costs in darkness under simulated ice cover than without ice. Under benign laboratory conditions the response to light (ice cover) varied among populations and only the northern population were able to attain positive growth in the dark. Under semi‐natural conditions the lack of ice cover induced strong negative effects on the energy budget. Because energetic deficiencies are assumed to be an important cause of winter mortality, our study indicates that ice break‐ups or removal following climatic change may affect winter survival significantly, particularly in northern populations.

Estimating genetic correlations in natural populations

Information on the genetic correlation between traits provides fundamental insight into the constraints on the evolutionary process. Estimates of such correlations are conventionally obtained by raising individuals of known relatedness in artificial environments. However, many species are not readily amenable to controlled breeding programmes, and considerable uncertainty exists over the extent to which estimates derived under benign laboratory conditions reflect the properties of populations in natural settings. Here, non-invasive methods that allow the estimation of genetic correlations from phenotypic measurements derived from individuals of unknown relatedness are introduced. Like the conventional approach, these methods demand large sample sizes in order to yield reasonably precise estimates, and special precautions need to be taken to eliminate bias from shared environmental effects. Provided the sample consists of at least 20% or so relatives, informative estimates of the genetic correlation are obtainable with sample sizes of several hundred individuals, particularly if supplemental information on relatedness is available from polymorphic molecular markers.

Effect of Environment on the Magnitude of Inbreeding Depression in Seed Germination in a Partially Self-Fertile Perennial Herb (Blandfordia grandiflora, Liliaceae)

Inbreeding depression, the decreased fitness of progeny derived from self-fertilization compared to outcrossing, is affected by the environmental conditions in which it is examined, often being greater in adverse environments than in benign environments. We germinated selfed and outcrossed seeds from the same Blandfordia grandiflora plants and estimated inbreeding depression in germination under benign laboratory conditions and adverse field conditions. In both environments, more outcrossed seeds germinated than did selfed seeds. In the laboratory, only 7.7% more outcrossed seeds germinated than did selfed seeds (98.4% ± 0.6 vs. 90.7% ± 3.9), whereas in the field the difference was 22.1% (92.5% ± 1.9 vs. 70.4% ± 5.0). The decrease in germination between the laboratory and field was only 5.9% for outcrossed seeds, but was 20.8% for selfed seeds. Germination of selfed seeds was more variable than of outcrossed seeds in both environments (coefficients of variation, selfed seeds vs. outcrossed seeds: laboratory, 13.6% vs. 1.9%; field, 22.5% vs. 6.5%). Germination success varied significantly among maternal plants, except for outcrossed seeds in the laboratory. In the laboratory, 60% of plants expressed inbreeding depression, whereas in the field all plants expressed inbreeding depression. The magnitude of inbreeding depression was significantly greater in the field than in the laboratory (0.242 ± 0.156 vs. 0.078 ± 0.130). Inbreeding depression of individual plants was positively related between the two environments (r = 0.69). The greater inbreeding depression in the field indicated that selfed seeds were unable to cope with the physiological demands that were imposed by the more adverse field environment.

Segmental Intelligibility and Speech Interference Thresholds of High-Quality Synthetic Speech in Presence of Noise

Technological advancement in the area of synthetic speech has made it increasingly difficult to distinguish quality of speech based solely on intelligibility scores obtained in benign laboratory conditions. Intelligibility scores obtained for natural speech and a high-quality text-to-speech system (DECtalk) are not substantially different. This study examined the perceived intelligibility and speech interference thresholds of DECtalk male and female voices and compared them with data obtained for natural speech. Results revealed that decreasing signal-to-noise levels had more deleterious effects on the perception of DECtalk male and female voices than on the perception of natural speech. Analysis of pattern of phoneme errors revealed that similar general patterns of errors tended to occur in DECtalk and in natural speech. The speech interference test did not demonstrate any significant difference between the DECtalk male and female voices. These results were supported by the absence of a significant difference between DECtalk male and female voices during intelligibility testing at different signal-to-noise ratios.