Age‐related increases in human lymphocyte DNA damage: is there a role of aerobic fitness?

Oxidative stress has been advanced as one of the major causes of damage to DNA and other macromolecules. Although physical exercise may also increase oxidative stress, an important role has been recognized for regular exercise in improving the overall functionality of the body, as indicated by an increase in maximal aerobic uptake (O_2max), and in resistance to cell damage. The aims of this study were 1) to evaluate the association between DNA damage in human lymphocytes and age and 2) to evaluate the association between DNA damage in human lymphocytes and O_2max. The sample was composed of 36 healthy and nonsmoking males, aged from 20 to 84 years. O_2max was evaluated through the Bruce protocol with direct measurement of oxygen consumption. The comet assay was used to evaluate the DNA damage, strand breaks and formamidopyrimidine DNA glycosylase (FPG)‐sensitive sites. We found a positive correlation of age with DNA strand breaks but not with FPG‐sensitive sites. O_2max was significantly inversely related with DNA strand breaks, but this relation disappeared when adjusted for age. A significantly positive relation between O_2max and FPG‐sensitive sites was verified. In conclusion, our results showed that younger subjects have lower DNA strand breaks and higher O_2max compared with older subjects and FPG‐sensitive sites are positively related with O_2max, probably as transient damage due to the acute effects of daily physical activity. Copyright © 2013 John Wiley & Sons, Ltd.     

Intraspecific variation in parasites- what is a strain?

The use of molecular techniques in parasitology has revealed a startling degree of diversity within species of parasite. These discoveries have emphasized the need for parasitologists to define and describe accurately the organisms with which they work. Andrew Thompson and Alan Lymbery propose that parasite strains be described by a combination of genetic and biological characteristics since reliance on the genotype alone may confer significance on a feature of little biological relevance.     

Uncommon mechanism of egg incubation in the endemic Southern hermit crab Loxopagurus loxochelis: how is this phenomenon related to egg production?

The aim of the present work was to characterize the egg production of Loxopagurus loxochelis. A total of 71 ovigerous females were obtained, 28% of which were simultaneously incubating eggs at different developmental stages. This phenomenon can be the result of incomplete fertilization, or may represent a rapid gonadal cycle by this species in this area, which is, to our understanding, the best explanation of this phenomenon. Egg volume decreased 25.6% during the incubation period. The reproductive output based on dry and wet weight was 6.8 and 19.3%, respectively. Water was the prevailing component of the eggs, representing 86.0% of the total weight at initial stage, increasing to 95.1% at the final stage. Ash content increased at the same time as a decrease in the organic content occurred, indicating the consumption of yolk and absorption of salts from the water medium. In conclusion, we hypothesized that this population has the capacity to copulate and deposit another brood even before the release of the larvae from the previous one, intensifying the reproductive effort of these hermit crabs as a strategy of adaptation in a region considered the northern limit of the geographical distribution of this species.     

Is death-feigning adaptive? Heritable variation in fitness difference of death-feigning behaviour.

The adaptation of death-feigning (thanatosis), a subject that has been overlooked in evolutionary biology, was inferred in a model prey-and-predator system. We studied phenotypic variation among individuals, fitness differences, and the inheritance of death-feigning behaviour in the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). Two-way artificial selections for the duration of death-feigning, over 10 generations, showed a clear direct response in the trait and a correlated response in the frequency of death-feigning, thus indicating variation and inheritance of death-feigning behaviour. A comparison of the two selected strains with divergent frequencies of death-feigning showed a significant difference in the fitness for survival when a model predator, a female Adanson jumper spider, Hasarius adansoni Audouin (Araneomophae: Salticidae), was presented to the beetles. The frequency of predation was lower among beetles from strains selected for long-duration than among those for short-duration death-feigning. The results indicate the possibility of the evolution of death-feigning under natural selection.     

Is cardiorespiratory fitness related to quality of life in survivors of breast cancer?

The purpose of this study was to investigate whether indices of cardiorespiratory fitness are related to quality of life (QOL) in women survivors of breast cancer. Using the European Organization for Research and Treatment of Cancer QLQ-30 questionnaire, we assessed the QOL of 16 participants (age, 50 +/- 9 years; body mass, 66.6 +/- 9.6 kg). All participants performed incremental cycle ergometer exercise to determine several indices of cardiorespiratory fitness (e.g., peak oxygen uptake [.V(O2)peak, in L.min(-1), ml.kg(-1).min(-1)]), peak power output (PPO, in W), PPO/ body mass (W.kg(-1), peak heart rate (HRpeak, b.min(-1), peak ventilation (VEpeak), and .V(O2) and heart rate (HR) at the ventilatory (VT) and respiratory compensation (RCT) thresholds. Relationships between QOL and variables were assessed using Spearman rank-difference correlation tests. A significant inverse relationship (p < 0.05) was found for QOL scores and values for age (years) and body mass (kg) ( = -0.53), %HRpeak@VT ( = -0.59) and %VEpeak@VT ( = -0.61). A significant positive relationship (p < 0.05) was found for QOL and PPO/body mass ( = 0.59) and HRpeak ( = 0.78), .V(O2)@RCT (ml.kg(-1.min(-1) ( = 0.51), power output (PO, expressed as either W or W.kg(-1) at RCT, and HR at RCT ( = 0.54). No other significant relationship was found between QOL and variables obtained from the tests. In conclusion, these findings highlight possible relationships between cardiorespiratory fitness and well-being in survivors of breast cancer. From a practical point of view, our data emphasize the need for this population to engage in programmed cardiorespiratory exercise training, mainly designed to improve VT and RCT. The improvement of both submaximal indices can have a beneficial effect on QOL.     

Stress and fitness in parthenogens: is dormancy a key feature for bdelloid rotifers?

Background

Bdelloid rotifers are the most common and abundant group of animals that reproduce by ameiotic parthenogenesis, only. They are common in temporally ephemeral habitats, and it is unclear if they dwell in unstable habitats because are excluded from better conditions by stronger competitors, or because they need unstable conditions for their success. We tested the hypothesis that bdelloids 'require' stressful conditions for their persistence by comparing fitness-related traits of stressed (desiccated, D) and unstressed (hydrated, H) lines of two species, Adineta ricciae and Macrotrachela quadricornifera.

Results

For both bdelloid species, fecundity was significantly lower in H than in parallel D line. Fitness components decreased with time progressively in the H line but not in the D line. Recovery rates of D lines were recorded after every desiccation and did not reveal any trend in time, suggesting that no selection was operating.

Conclusion

Stress in the form of reiterated desiccations seemed to help both bdelloid species to keep fitness stable; in contrast under stable conditions, like permanent hydration, these bdelloid species had poorer performances. Bdelloids, although aquatic animals, are not only efficient in tolerating desiccation, but seem somehow dependent on anhydrobiosis, a circumstance that might represent a key event in their life cycle. If this is true, life in unpredictable habitats should not be seen as the result of competitive exclusion from 'easier' habitats, but a requirement for long-term survival of these parthenogenetic animals.

     

How precise is egg discrimination in weaverbirds?

The village weaverbird, Ploceus cucullatus, lays eggs of an extremely broad range of appearance between individuals. This variation is thought to have evolved as a counteradaptation to brood parasitism by the diederik cuckooChrysococcyx caprius . The primary objective of our study was to characterize the relationship between egg appearance and egg rejection in the African village weaverbird. We test predictions of three hypotheses in a study in The Gambia, West Africa: (1) interindividual egg variability permits individuals to discriminate between own and foreign eggs by rejecting eggs in proportion to the difference in appearance from their own; (2) village weavers remember the appearance of their own eggs and do not require a discordancy within their clutch, nor even the presence of one of their own eggs, in order to distinguish a foreign egg as such; and (3) colour and speckling contain the signature information by which village weavers can distinguish their eggs from foreign ones; whereas shape and mass, being less reliable, do not. We analysed rejection behaviour according to egg appearance differences by logistic regression. Results supported all three hypotheses. We estimated the predictive efficacy of our model, the amount of explained variation and the relative contribution of various egg appearance factors to discrimination by the host. These results are consistent with the hypothesis that interindividual egg variation in this species facilitates offspring recognition and is a counteradaptation to either interspecific or intraspecific brood parasitism. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Green algae in Lake Tanganyika: is morphological variation a response to seasonal changes?

In the framework of a planktological and ecological study in Lake Tanganyika, East Africa (CLIMLAKE, 2001–2005), variations of cell abundance and size were observed in a green alga, Eremosphaera tanganyikae, at two study sites, one in the north basin of the lake (off Kigoma, Tanzania) and the other in the south basin (off Mpulungu, Zambia). Whereas most green algae developed better in the rainy season and in the northern part of the lake, Eremosphaera developed better in the southern basin, in the dry season. It also exhibited large variations in cell abundance and cell size, with maxima in the middle of the dry season, which may be related to increased phosphorus availability. Moreover, increase in cell size (up to 80 μm in length), without notable change in S/V ratio, may provide the alga with resistance to grazing by copepods, which reach maximal abundance during the dry season.     

Facultative primary sex ratio variation: a lack of evidence in birds?

The facultative control of primary sex ratio by breeding birds has become a major focus in evolutionary biology in recent years. A combination of well-developed theoretical literature and rapid publication of empirical results has created considerable confusion, with controversial claims for both extreme control of primary sex ratio versus no control around inherent random variability. We present a robust and quantitative summary of published empirical literature to assess clearly the body of evidence for female birds to control sex assignment in their offspring. Our meta-analytical approach reveals that published studies do not exhibit any variability beyond that which could be expected owing to sampling error. Therefore, we conclude that facultative control of offspring sex is not a characteristic biological phenomenon in breeding birds.     

Logic of experiments in ecology: is pseudoreplication a pseudoissue?

Hurlbert divides experimental ecologist into ‘those who do not see any need for dispersion (of replicated treatments and controls), and those who do recognize its importance and take whatever measures are necessary to achieve a good dose of it’. Experimental ecologists could also be divided into those who do not see any problems with sacrificing spatial and temporal scales in order to obtain replication, and those who understand that appropriate scale must always have priority over replication. If an experiment is conducted in a spatial or temporal scale, where the predictions of contesting hypotheses are convergent or ambiguous, no amount of technical impeccability can make the work instructive. Conversely, replication can always be obtained afterwards, by conducting more experiments with basically similar design in different areas and by using meta‐analysis. This approach even reduces the sampling bias obtained if resources are allocated to a small number of well‐replicated experiments. For a strict advocate of the hypothetico‐deductive method, replication is unnecessary even as a matter of principle, unless the predicted response is so weak that random background noise is a plausible excuse for a discrepancy between predictions and results. By definition, a prediction is an ‘all‐statement’, referring to all systems within a well‐defined category. What applies to all must apply to any. Hence, choosing two systems and assigning them randomly to a treatment and a control is normally an adequate design for a deductive experiment. The strength of such experiments depends on the firmness of the predictions and their a priori probability of corroboration. Replication is but one of many ways of reducing this probability. Whether the experiment is replicated or not, inferential statistics should always be used, to enable the reader to judge how well the apparent patterns in samples reflect real patterns in statistical populations. The concept ‘pseudoreplication’ amounts to entirely unwarranted stigmatization of a reasonable way to test predictions referring to large‐scale systems.     

Egg quality in fish: what makes a good egg?

Factors affecting egg quality are determined by the intrinsic properties of the egg itself and the environment in which the egg is fertilized and subsequently incubated. Egg quality in fish is very variable. Some of the factors affecting egg quality in fish are known, but many (probably most) are unknown. Components that do affect egg quality include the endocrine status of the female during the growth of the oocyte in the ovary, the diet of the broodfish, the complement of nutrients deposited into the oocyte, and the physiochemical conditions of the water in which the eggs are subsequently incubated. In captive broodfish, the husbandry practices to which fish are subjected are probably a major contributory factor affecting egg quality. Our knowledge of the genetic influences on egg quality is very limited indeed. We know that parental genes strongly influence both fecundity and egg quality, but almost nothing is known about gene expression and/or mRNA translation in fish oocytes/embryos. This is surprising because the products synthesized in ovoand the mechanisms controlling their expression are likely to play a central role in determining egg quality. The genetic mechanisms underpinning oocyte and embryo growth and development are a priority for research     

Heterozygosity at a single locus explains a large proportion of variation in two fitness‐related traits in great tits: a general or a local effect?

In natural populations, mating between relatives can have important fitness consequences due to the negative effects of reduced heterozygosity. Parental level of inbreeding or heterozygosity has been also found to influence the performance of offspring, via direct and indirect parental effects that are independent of the progeny own level of genetic diversity. In this study, we first analysed the effects of parental heterozygosity and relatedness (i.e. an estimate of offspring genetic diversity) on four traits related to offspring viability in great tits (Parus major) using 15 microsatellite markers. Second, we tested whether significant heterozygosity–fitness correlations (HFCs) were due to ‘local’ (i.e. linkage to genes influencing fitness) and/or ‘general’ (genome‐wide heterozygosity) effects. We found a significant negative relationship between parental genetic relatedness and hatching success, and maternal heterozygosity was positively associated with offspring body size. The characteristics of the studied populations (recent admixture, polygynous matings) together with the fact that we found evidence for identity disequilibrium across our set of neutral markers suggest that HFCs may have resulted from genome‐wide inbreeding depression. However, one locus (Ase18) had disproportionately large effects on the observed HFCs: heterozygosity at this locus had significant positive effects on hatching success and offspring size. It suggests that this marker may lie near to a functional locus under selection (i.e. a local effect) or, alternatively, heterozygosity at this locus might be correlated to heterozygosity across the genome due to the extensive ID found in our populations (i.e. a general effect). Collectively, our results lend support to both the general and local effect hypotheses and reinforce the view that HFCs lie on a continuum from inbreeding depression to those strictly due to linkage between marker loci and genes under selection.     

Natural variation in phosphorylation of photosystem II proteins in Arabidopsis thaliana: is it caused by genetic variation in the STN kinases?

Reversible phosphorylation of photosystem II (PSII) proteins is an important regulatory mechanism that can protect plants from changes in ambient light intensity and quality. We hypothesized that there is natural variation in this process in Arabidopsis (Arabidopsis thaliana), and that this results from genetic variation in the STN7 and STN8 kinase genes. To test this, Arabidopsis accessions of diverse geographical origins were exposed to two light regimes, and the levels of phospho-D1 and phospho-light harvesting complex II (LHCII) proteins were quantified by western blotting with anti-phosphothreonine antibodies. Accessions were classified as having high, moderate or low phosphorylation relative to Col-0. This variation could not be explained by the abundance of the substrates in thylakoid membranes. In genotypes with atrazine-resistant forms of the D1 protein, low D1 and LHCII protein phosphorylation was observed, which may be due to low PSII efficiency, resulting in reduced activation of the STN kinases. In the remaining genotypes, phospho-D1 levels correlated with STN8 protein abundance in high-light conditions. In growth light, D1 and LHCII phosphorylation correlated with longitude and in the case of LHCII phosphorylation also with temperature variability. This suggests a possible role of natural variation in PSII protein phosphorylation in the adaptation of Arabidopsis to diverse environments.     

Bergmann and converse bergmann latitudinal clines in arthropods: two ends of a continuum?

Two seemingly opposite evolutionary patterns of clinal variationin body size and associated life history traits exist in nature.According to Bergmann's rule, body size increases with latitude,a temperature effect. According to the converse Bergmann rule,body size decreases with latitude, a season length effect. Athird pattern causally related to the latter is countergradientvariation, whereby populations of a given species compensateseasonal limitations at higher latitudes by evolving fastergrowth and larger body sizes compared to their low latitudeconspecifics. We discuss these patterns and argue that theyare not mutually exclusive because they are driven by differentenvironmental causes and proximate mechanisms; they thereforecan act in conjunction, resulting in any intermediate pattern.Alternatively, Bergmann and converse Bergmann clines can beinterpreted as over- and undercompensating countergradient variation,respectively. We illustrate this with data for the wide-spreadyellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae),which in Europe shows a Bergmann cline for size and a converseBergmann cline (i.e., countergradient variation) for developmenttime. A literature review of the available evidence on arthropodlatitudinal clines further shows a patterned continuum of responses.Converse Bergmann clines due to end-of-season time limitationsare more common in larger species with longer development times.Our study thus provides a synthesis to the controversy aboutthe importance of Bergmann's rule and the converse Bergmannrule in nature.     

Selection in modular organisms: is intraclonal variation in macroalgae evolutionarily important?

Theoretical and practical difficulties occur when defining the units of selection in modular organisms that grow by iteration of repeated parts (modules). Modules may become physically autonomous through fragmentation and may vary because of genetic variation arising in somatic cell lineages. Since cells destined for gamete production are not sequestered in early development, heritable variation and selection among asexual progeny are possible. We used the branching red macroalgae Delisea pulchra and Asparagopsis armata to test whether modules fulfill three fundamental criteria for units of selection: that they replicate, that they display heritable variation, and that selective agents distinguish among the variants. We detected significant phenotypic variation among modules for fitness-related traits (growth, secondary metabolite concentrations, and rates of tissue loss to herbivory) in each species and significant heritability estimates for secondary metabolite production and tissue loss to herbivory in D. pulchra. Variation in growth rate among A. armata modules was largely phenotypic with small but important estimates of genetic variation. Our results indicate that selection may indeed act on phenotypic variation among modules within individuals and that this process may effect evolutionary change within asexual lineages given sufficient genetic variation in the traits examined.     

Palm distribution patterns in Amazonian rainforests: What is the role of topographic variation?

Question: Are soil properties and topographic variation related with palm (Arecaceae) species composition and distribution patterns? If so, are species distribution patterns consistent across sites? Location: 100–200 m a.s.l, non‐inundated Amazonian rainforest, NE Peru. Methods: One 0.65‐ha line transect divided into 5 m by 5 m subunits was inventoried for all palm individuals at each site. Soil samples were collected, and topography was measured. Results: A total of 56 palm taxa were recorded. Floristic similarity among transects clearly corresponded with similarity in soil cation content when species abundances were taken into account, but less so when only presence‐absence data were used. Taxon‐wise distribution analyses were done for the 37 most abundant palm taxa. Quite a few of these taxa proved not to be randomly distributed along the transects, but instead were clearly more abundant in some topographic positions than in others. However, the consistency of the distribution patterns across study sites proved to be rather low, and many of the palm taxa showed different distribution patterns at different sites. Conclusions: The ambiguity in distribution patterns across study sites may partly be due to the complexity of topography as a measure of ecological conditions, and the probability that it is related to the variation in different environmental variables at different sites.     

Temporal variation in bird assemblages: How representative is a one‐year snapshot?

Abstract Bird assemblages generally are no longer regarded as stable entities, but rather as fluctuating in response to many factors. Australia's highly variable climate is likely to result in a high degree of dynamism in its bird assemblages, yet few studies have investigated variation on an inter‐annual temporal scale. We compared 2 year‐long samples of the bird assemblages of a series of highly fragmented buloke Allocasuarina luehmannii (Casuarinaceae) woodland remnants in south‐eastern Australia, the first sample taken in 1994–95 and the second in 2001–02. Bird densities were almost three times higher in the second period than in the first. Mean species richness also was significantly higher. Species richness of each individual site was unrelated between the 2 years. Minimum species turnover was 63% and was higher, on average, for migratory and nomadic than for sedentary species. Therefore, site‐level bird assemblage composition was markedly different between the two survey periods and, on average, the assemblage composition of each site bore greater resemblance to those of other sites in the same year than to that of the same site in the other survey period. Most species changed substantially in their distribution among remnants between the two periods. The change in distribution of most species did not differ significantly from that expected if the species had redistributed at random among the sites. This suggests that although the remnant vegetation of the area is highly fragmented with minimal interpatch connectivity, bird movements among remnants are relatively frequent. Inter‐annual variability in Australian bird assemblages may be higher than is commonly recognized. In such dynamic systems, we must be cautious when extrapolating from the findings of short‐term studies to longer temporal scales, especially in relation to conservation management. A greater understanding of the processes driving distributional patterns is likely to enable better predictions of species’ responses to habitat change.     

Mosquito transgenesis: what is the fitness cost?

The generation of transgenic mosquitoes with a minimal fitness load is a prerequisite for the success of strategies for controlling mosquito-borne diseases using transgenic insects. It is important to assemble as much information as possible on this subject because realistic estimates of transgene fitness costs are essential for modeling and planning release strategies. Transgenic mosquitoes must have minimal fitness costs, because such costs would reduce the effectiveness of the genetic drive mechanisms that are used to introduce the transgenes into field mosquito populations. Several factors affect fitness of transgenic mosquitoes, including the potential negative effect of transgene products and insertional mutagenesis. Studies to assess fitness of transgenic mosquitoes in the field (as opposed to the laboratory) are still needed.     

Seasonal variation in the effect of cache pilferage on cache and body mass regulation in Carolina chickadees: what are the trade-offs?

Current dynamic optimization models predict that animals shouldrespond to cache pilferage by decreasing the probability ofcaching food and by increasing internal fat storage to compensatefor a reduction in cache size. We tested these predictions underlaboratory conditions with variable food access (four 15-minintervals/day). Carolina chickadees (Poecile carolinensis) weresubjected to two environments: under pilferage conditions, one-quarterof their cached seeds were stolen every 0.5 h, and under no-pilferageconditions, seeds were left in place. Half the birds startedwith pilferage conditions and were then switched to the no-pilferagecondition; the other half started with no pilferage and werethen switched to pilferage conditions. The experiment was conductedover the course of a year to test for seasonal variation inthe response to seed pilferage. The birds responded to seedpilferage by taking more seeds from a feeder, suggesting thatthey monitored cache availability. Alternatively, the birdsmay have taken additional seeds from the feeder in responseto increased hunger caused by a loss of cached food. Contraryto our prediction, birds cached a higher percentage of seedsfrom the feeder when cached seeds were pilfered than when cacheswere left in place. Treatment order also affected caching behaviorfor all but the summer birds: chickadees initially subjectedto pilferage stored a higher proportion of seeds than thoseinitially subjected to no pilferage. Caching percentages inthe summer were unaffected by cache pilferage. Caching rates(number cached/day) also followed the same trends: rates werehigher when seeds were pilfered than when seeds were not pilfered,and there was a treatment-order effect for all but the summerbirds. Variation in body mass also failed to match predictedtrends. All birds exhibited a monotonic increase in mass asthe experiments proceeded, irrespective of treatment order.Controlling for this monotonic increase in mass, an analysisof residual variation in body mass indicated that birds gainedless weight when seeds were pilfered than when seeds were leftin place. Finally, birds tested in the fall and spring wereheavier than those tested in the summer. These results failto support the relationship between cache maintenance and bodymass regulation predicted by current models of energy regulation.We discuss the applicability of three hypotheses for the observedtrends.