Fitness, developmental instability, and the ontogeny of fluctuating asymmetry in Daphnia magna

Fluctuating asymmetry (FA) is the most commonly used measure of developmental instability. The relation between FA and individual fitness remains controversial, partly due to limited knowledge on the mechanisms behind variation in FA. To address this, we investigated the associations between FA, growth and reproduction as well as the ontogeny of FA in a clonal population of Daphnia magna . FA was not correlated with growth and reproduction, either at the between- or the within-individual level, in a high ( N  = 48 individuals) or in a low ( N  = 52 individuals) food-quantity regime. There were therefore no indications of functional effects of FA or of phenotypic trade-offs between developmental stability, growth and reproduction. Individual asymmetries varied randomly in sign and magnitude between subsequent molts ( N  = 19 individuals, 9–11 instars), but the levels of FA were generally lowest at intermediate ages. No feedback between right and left sides was detected. This suggests that FA only reflects the most recent growth history, that developmental instability may increase in old age, and that FA depends on processes operating on each side of the body independently. The results also suggest that FA differences within and among individual Daphnia are largely random, with limited biological significance.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 179–192.     

Modelling of underwater light in freshwater lakes using survival and failure time analysis

1. This study presents a new approach to modelling subsurface irradiance using concepts from survival and failure time analysis. The model applies a modified Weibull distribution function to predict downwelling irradiance. Data sets from forty-seven Norwegian sites show extremely high coefficients of determination, up to 99.99%, when analysed by the Weibull model.
2. The uncritical use of a single k _d value to model underwater light conditions is likely to result in poor estimates of received irradiance. This error may amount to several hundred per cent. The practice of force-fitting linear least-squares regressions to log-transformed irradiance data inevitably leads to highly biased estimates of the true fraction of incident irradiance entering the water.
3. Wave effects causing fluctuations of subsurface irradiance are modelled with synthetic data and compared with field observations. Fluctuations of surface elevation by waves produce skewed frequency distributions of the underwater light field. The result of these effects, which are to reduce the accuracy of estimated model parameters, can be largely eliminated by carefully designing field procedures used for the acquisition of subsurface light data.     

Dentistry as a prospective career choice in india

Career choice is a complex decision in a student''s life. The opportunity to participate in dental education in many countries, especially in the developing ones, is limited to a small percentage of the community. There is a wide range of options for students to choose as a career in general family, gender, personal interest; outcome expectancies can affect the decision in choosing it. Many studies showed that many individuals find themselves in occupations not really knowing why they made that particular decision. The changing nature of the dental workforce and the need to retain the services of future members has made it important to understand why current dental students have chosen dentistry as their career. However, the choice of dentistry becomes forceful at times by peer pressure, cultural thrust or inability to procure medicine. It is of interest to evaluate dentistry as a prospective career choice in India. The participants answered a questionnaire based online survey and the results were collected and analysed statistically. Analyses of data from the survey shows that majority (36.72%) of students had chosen dentistry as a career choice having missed entry or selection into medicine.     

Structural and mechanistic investigations on Salmonella typhimurium acetate kinase (AckA): identification of a putative ligand binding pocket at the dimeric interface

Background

A large number of studies have been carried out to obtain amino acid propensities for ??-helices and ??-sheets. The obtained propensities for ??-helices are consistent with each other, and the pair-wise correlation coefficient is frequently high. On the other hand, the ??-sheet propensities obtained by several studies differed significantly, indicating that the context significantly affects ??-sheet propensity.

Results

We calculated amino acid propensities for ??-helices and ??-sheets for 39 and 24 protein folds, respectively, and addressed whether they correlate with the fold. The propensities were also calculated for exposed and buried sites, respectively. Results showed that ??-helix propensities do not differ significantly by fold, but ??-sheet propensities are diverse and depend on the fold. The propensities calculated for exposed sites and buried sites are similar for ??-helix, but such is not the case for the ??-sheet propensities. We also found some fold dependence on amino acid frequency in ??-strands. Folds with a high Ser, Thr and Asn content at exposed sites in ??-strands tend to have a low Leu, Ile, Glu, Lys and Arg content (correlation coefficient = ?0.90) and to have flat ??-sheets. At buried sites in ??-strands, the content of Tyr, Trp, Gln and Ser correlates negatively with the content of Val, Ile and Leu (correlation coefficient = ?0.93). "All-??" proteins tend to have a higher content of Tyr, Trp, Gln and Ser, whereas "??/??" proteins tend to have a higher content of Val, Ile and Leu.

Conclusions

The ??-helix propensities are similar for all folds and for exposed and buried residues. However, ??-sheet propensities calculated for exposed residues differ from those for buried residues, indicating that the exposed-residue fraction is one of the major factors governing amino acid composition in ??-strands. Furthermore, the correlations we detected suggest that amino acid composition is related to folding properties such as the twist of a ??-strand or association between two ?? sheets.     

Effects of Hunting on Response Behaviors of Wild Reindeer

ABSTRACT Because wild reindeer (Rangifer tarandus) are hunted in southern Norway, reindeer may perceive all recreationists as threats. Potential adverse effects of hunting on reindeer behavior may be exacerbated by other forms of recreation because the number of skiers and hikers in areas inhabited by reindeer has also increased. The Norefjell-Reinsjøfjell wild reindeer area is used extensively for recreation and tourism. Reindeer hunting was introduced in the area in 1992, and harvest rate has been stable at about 38% of winter herd size. We recorded behavioral responses of reindeer to a person approaching directly on foot or skis during 1992 and again in 2002–2006. Compared to 1992, flight-initiation distance increased and fewer groups assessed the observer before taking flight during 2002–2006. In winter, when reindeer are usually comparably more vigilant than in other seasons, flight-initiation distance increased from only 60 m to 115 m and escape distance decreased from 400 m to 210 m. Neither alert distance, calf carcass weights (23.6 ± 0.7 [SE] kg to 22.4 ± 0.2 kg), nor reindeer herd size (661 ± 73 to 579 ± 15) changed during the 15 years of our study. Reindeer appeared to habituate to the observer because they initiated flight at shorter distances as the number of approaches on the same day increased. In Norefjell-Reinsjøfjell, encounters with a person on foot or skis did not result in behavioral responses likely to entail substantial energy costs for reindeer; therefore, hunting at current levels appears compatible with other recreational activities.     

The Simulium vernum group (Diptera: Simuliidae) in Europe: multiple character sets for assessing species status

The value of using characters from multiple sources – chromosomes, ecology, gene sequences, and morphology – to evaluate the species status of closely related black flies is demonstrated for three European members of the Simulium vernum group: Simulium crenobium (Knoz, 1961), Simulium juxtacrenobium Bass & Brockhouse, 1990, and Simulium vernum s.s. Macquart, 1826. Simulium juxtacrenobium is a chromosomally, molecularly, and morphologically distinct species that diverged from S. crenobium and S. vernum s.s. about 2 Mya. It is specialized for intermittent streams, is univoltine, and is recorded for the first time from northern Europe, based on collections from Finland and Sweden, representing a range extension of about 1800 km. In contrast, S. crenobium, although confirmed as a distinct species, differs from S. vernum s.s. by only a few larval and chromosomal characters, and by a breeding habitat restricted to mountain spring brooks. Whereas all four character sets independently support the specific distinctness of S. juxtacrenobium and S. vernum s.s., multiple character sets are required to establish the specific validity of S. crenobium.     

Temperature,predator–prey interaction strength and population stability

Warming could strongly stabilize or destabilize populations and food webs by changing the interaction strengths between predators and their prey. Predicting the consequences of warming requires understanding how temperature affects ingestion (energy gain) and metabolism (energy loss). Here, we studied the temperature dependence of metabolism and ingestion in laboratory experiments with terrestrial arthropods (beetles and spiders). From this data, we calculated ingestion efficiencies (ingestion/metabolism) and per capita interaction strengths in the short and long term. Additionally, we investigated if and how body mass changes these temperature dependencies. For both predator groups, warming increased metabolic rates substantially, whereas temperature effects on ingestion rates were weak. Accordingly, the ingestion efficiency (the ratio of ingestion to metabolism) decreased in all treatments. This result has two possible consequences: on the one hand, it suggests that warming of natural ecosystems could increase intrinsic population stability, meaning less fluctuations in population density; on the other hand, decreasing ingestion efficiencies may also lead to higher extinction risks because of starvation. Additionally, predicted long‐term per capita interaction strengths decreased with warming, which suggests an increase in perturbation stability of populations, i.e., a higher probability of returning to the same equilibrium density after a small perturbation. Together, these results suggest that warming has complex and potentially profound effects on predator–prey interactions and food‐web stability.     

Patterns of inbreeding depression in a population of Brassica cretica (Brassicaceae): evidence from family-level analyses

In this investigation, we have collected family-structured data from a partly self-compatible, outcrossing population of Brassica cretica to estimate and compare the effects of one-generation selfing on different types of characters. Inbreeding not only depressed characters that should be positively correlated with fitness irrespective of habitat, e.g. germinability, leaf number and inflorescence size, but also resulted in later flowering, smaller and more asymmetric flowers, and an increased production of basal branches. Population-level estimates of inbreeding depression were similar in magnitude to estimates reported in other wild plant species. There was a tendency for direct components of fitness to exhibit a stronger response to inbreeding than other characters, but only when the differences between selfed and outbred offspring were measured in standard deviation units. Family-level estimates of inbreeding depression were weakly correlated across characters. Given these and other observations, we hypothesize that the genetic basis of inbreeding depression varies across the life cycle and that changes in local inbreeding will lead to shifts in the mean phenotypes of B. cretica populations. However, judging from data on current levels of population divergence, quite large changes in inbreeding will be required to influence large-scale patterns of variation in this species.  © 2002 The Linnean Society of London. Biological Journal of the Linnean Society , 2002, 76 , 317–325.     

Population history and genetic structure of a circumpolar species: the arctic fox

The circumpolar arctic fox Alopex lagopus thrives in cold climates and has a high migration rate involving long-distance movements. Thus, it differs from many temperate taxa that were subjected to cyclical restriction in glacial refugia during the Ice Ages. We investigated population history and genetic structure through mitochondrial control region variation in 191 arctic foxes from throughout the arctic. Several haplotypes had a Holarctic distribution and no phylogeographical structure was found. Furthermore, there was no difference in haplotype diversity between populations inhabiting previously glaciated and unglaciated regions. This suggests current gene flow among the studied populations, with the exception of those in Iceland, which is surrounded by year-round open water. Arctic foxes have often been separated into two ecotypes: 'lemming' and 'coastal'. An analysis of molecular variance suggested particularly high gene flow among populations of the 'lemming' ecotype. This could be explained by their higher migration rate and reduced fitness in migrants between ecotypes. A mismatch analysis indicated a sudden expansion in population size around 118 000 BP, which coincides with the last interglacial. We propose that glacial cycles affected the arctic fox in a way opposite to their effect on temperate species, with interglacials leading to short-term isolation in northern refugia.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 79–89.