Optimal resting-growth strategies of microbial populations in fluctuating environments

Bacteria spend most of their lifetime in non-growing states which allow them to survive extended periods of stress and starvation. When environments improve, they must quickly resume growth to maximize their share of limited nutrients. Cells with higher stress resistance often survive longer stress durations at the cost of needing more time to resume growth, a strong disadvantage in competitive environments. Here we analyze the basis of optimal strategies that microorganisms can use to cope with this tradeoff. We explicitly show that the prototypical inverse relation between stress resistance and growth rate can explain much of the different types of behavior observed in stressed microbial populations. Using analytical mathematical methods, we determine the environmental parameters that decide whether cells should remain vegetative upon stress exposure, downregulate their metabolism to an intermediate optimum level, or become dormant. We find that cell-cell variability, or intercellular noise, is consistently beneficial in the presence of extreme environmental fluctuations, and that it provides an efficient population-level mechanism for adaption in a deteriorating environment. Our results reveal key novel aspects of responsive phenotype switching and its role as an adaptive strategy in changing environments

Optimal Resting-Growth Strategies of Microbial Populations in Fluctuating Environments

Bacteria spend most of their lifetime in non-growing states which allow them to survive extended periods of stress and starvation. When environments improve, they must quickly resume growth to maximize their share of limited nutrients. Cells with higher stress resistance often survive longer stress durations at the cost of needing more time to resume growth, a strong disadvantage in competitive environments. Here we analyze the basis of optimal strategies that microorganisms can use to cope with this tradeoff. We explicitly show that the prototypical inverse relation between stress resistance and growth rate can explain much of the different types of behavior observed in stressed microbial populations. Using analytical mathematical methods, we determine the environmental parameters that decide whether cells should remain vegetative upon stress exposure, downregulate their metabolism to an intermediate optimum level, or become dormant. We find that cell-cell variability, or intercellular noise, is consistently beneficial in the presence of extreme environmental fluctuations, and that it provides an efficient population-level mechanism for adaption in a deteriorating environment. Our results reveal key novel aspects of responsive phenotype switching and its role as an adaptive strategy in changing environments

A Tractable Experimental Model for Study of Human and Animal Scabies

Scabies, a neglected parasitic disease caused by the microscopic mite Sarcoptes scabiei, is a major driving force behind bacterial skin infections in tropical settings. Aboriginal and Torres Strait Islander peoples are nearly twenty times more likely to die from acute rheumatic fever and rheumatic heart disease than individuals from the wider Australian community. These conditions are caused by bacterial pathogens such as Group A streptococci, which have been linked to underlying scabies infestations. Community based initiatives to reduce scabies and associated disease have expanded, but have been threatened in recent years by emerging drug resistance. Critical biological questions surrounding scabies remain unanswered due to a lack of biomedical research. This has been due in part to a lack of either a suitable animal model or an in vitro culture system for scabies mites. The pig/mite model reported here will be a much needed resource for parasite material and will facilitate in vivo studies on host immune responses to scabies, including relations to associated bacterial pathogenesis, and more detailed studies of molecular evolution and host adaptation. It represents the missing tool to extrapolate emerging molecular data into an in vivo setting and may well allow the development of clinical interventions

Genetics of Microenvironmental Sensitivity of Body Weight in Rainbow Trout (Oncorhynchus mykiss) Selected for Improved Growth

Microenvironmental sensitivity of a genotype refers to the ability to buffer against non-specific environmental factors, and it can be quantified by the amount of residual variation in a trait expressed by the genotype’s offspring within a (macro)environment. Due to the high degree of polymorphism in behavioral, growth and life-history traits, both farmed and wild salmonids are highly susceptible to microenvironmental variation, yet the heritable basis of this characteristic remains unknown. We estimated the genetic (co)variance of body weight and its residual variation in 2-year-old rainbow trout (Oncorhynchus mykiss) using a multigenerational data of 45,900 individuals from the Finnish national breeding programme. We also tested whether or not microenvironmental sensitivity has been changed as a correlated genetic response when genetic improvement for growth has been practiced over five generations. The animal model analysis revealed the presence of genetic heterogeneity both in body weight and its residual variation. Heritability of residual variation was remarkably lower (0.02) than that for body weight (0.35). However, genetic coefficient of variation was notable in both body weight (14%) and its residual variation (37%), suggesting a substantial potential for selection responses in both traits. Furthermore, a significant negative genetic correlation (−0.16) was found between body weight and its residual variation, i.e., rapidly growing genotypes are also more tolerant to perturbations in microenvironment. The genetic trends showed that fish growth was successfully increased by selective breeding (an average of 6% per generation), whereas no genetic change occurred in residual variation during the same period. The results imply that genetic improvement for body weight does not cause a concomitant increase in microenvironmental sensitivity. For commercial production, however, there may be high potential to simultaneously improve weight gain and increase its uniformity if both criteria are included in a selection index

Morphological variation in the specialist Dupont’s Lark Chersophilus duponti: geographical clines vs. local ecological determinants

Intraspecific geographic variation in morphology is common in animals along geographic or climatic clines. Local ecological factors are likely to act simultaneously at smaller spatial scales, but have hardly been contrasted with wide-ranging predictors. We tested here whether the morphological variation of Dupont’s Larks (Chersophilus duponti) responded to ecological parameters at two different spatial scales. First, we investigated the effects of geographic and climatic gradients over its breeding range. Second, we focussed at a smaller spatial scale on a fragmented population and tested additionally several fine-grained ecological factors related to key components in the species’ habitat. Contrary to Bergmann’s rule, wing length and cranium size decreased with rainfall and increased with aridity and maximum temperature at the large scale, so birds tend to be larger at lower latitudes. At the same time, wing and tarsus length increased at high elevations where minimum temperatures are lower, providing some support to Bergmann’s rule. At the small spatial scale we failed to detect any relationship between body size and positional or climatic variables, nor did food availability, intra- and inter-specific competition and predation pressure produce any significant effect on morphology. Nevertheless, cranium size and wing length differed between habitats as measured by soil and vegetation types, and wing length decreased with patch size. This later result could be explained in the context of strong habitat fragmentation if larger individuals have a higher propensity of dispersing or a higher probability of surviving dispersal events. Our study indicates that several geographic and environmental sources may occur simultaneously at different spatial scales. Further, even at the same scale, intraspecific morphological variation may show contrasting patterns for climatic, latitudinal, and elevational gradients that make their interpretation difficult in the context of ecogeographical rules. The effects elicited by aridity, habitat loss, and fragmentation on body size should be considered in future studies of global change, as they may have serious consequences for the distribution, abundance, and ultimately the persistence of birds in arid environments.Peer Reviewe

Population Thinking and Evolutionary Economic Analysis: Exploring Marshall's Fable of the Trees

It is increasingly recognised that population thinking is a basic characteristic of evolutionary economics. By taking its starting point in what is here called Marshall's fable of the trees, the paper demonstrates that there are several forms of population thinking. The most basic form is intra-population thinking for single populations, and this thinking easily extends to structured populations, where selection takes place at several levels. But there is also a need of applying inter-population thinking to the co-evolution of populations and intra-to-inter population thinking to the emergence of new populations. To transform these forms of population thinking into evolutionary analyses, there is a need of simple analytical tools. The paper emphasises a simple and basic tool for population thinking 'Price' equation. This little known equation provides a surprisingly powerful tool for the partitioning of overall evolutionary change into a selection effect and what may be called an innovation effect. This partitioning serves as a means of accounting for evolution and as a starting point for the explanation of evolution. The applications of Price's equation cover relatively short-term evolutionary change within individual industries as well as the study of more complexly structured populations of firms. It also, to some extent, helps to understand the effects of co-evolution between populations and the emergence of new populations.Population thinking; Alfred Marshall; statistical analysis of economic evolution; Price'